Electronic Circuitry & ComponentsCompiled by Chad Mairn

Contents

1 Electronic circuit 11.1 Analog circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Digital circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Mixed-signal circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.5 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Electronic component 42.1 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2 Active components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.1 Semiconductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2.2 Display technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.2.3 Vacuum tubes (valves) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.2.4 Discharge devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.2.5 Power sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.3 Passive components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3.1 Resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3.2 Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3.3 Magnetic (inductive) devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3.4 Memristor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3.5 Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3.6 Transducers, sensors, detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3.7 Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3.8 Assemblies, modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.3.9 Prototyping aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.4 Electromechanical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.4.1 Piezoelectric devices, crystals, resonators . . . . . . . . . . . . . . . . . . . . . . . . . . 92.4.2 Terminals and connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.4.3 Cable assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.4.4 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.4.5 Protection devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.4.6 Mechanical accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.4.7 Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

i

ii CONTENTS

2.4.8 Obsolete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.5 Standard symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.6 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 Resistor 123.1 Electronic symbols and notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2 Theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.2.1 Ohm’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2.2 Series and parallel resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.2.3 Power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3 Nonideal properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.4 Fixed resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.4.1 Lead arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.4.2 Carbon composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.4.3 Carbon pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.4.4 Carbon film . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.4.5 Printed carbon resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.4.6 Thick and thin film . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.4.7 Metal film . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.4.8 Metal oxide film . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.4.9 Wire wound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.4.10 Foil resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.4.11 Ammeter shunts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.4.12 Grid resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.4.13 Special varieties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.5 Variable resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.5.1 Adjustable resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.5.2 Potentiometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.5.3 Resistance decade boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.5.4 Special devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.6 Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.7 Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.7.1 Production resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.7.2 Resistance standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.8 Resistor marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.8.1 Preferred values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.8.2 SMT resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.8.3 Industrial type designation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.9 Electrical and thermal noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.10 Failure modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213.11 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

CONTENTS iii

3.12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.13 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4 Transistor 244.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.2 Importance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.3 Simplified operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4.3.1 Transistor as a switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.3.2 Transistor as an amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.4 Comparison with vacuum tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.4.1 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274.4.2 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.5 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.5.1 Bipolar junction transistor (BJT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.5.2 Field-effect transistor (FET) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294.5.3 Usage of bipolar and field-effect transistors . . . . . . . . . . . . . . . . . . . . . . . . . . 294.5.4 Other transistor types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.6 Part numbering standards / specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.6.1 Japanese Industrial Standard (JIS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.6.2 European Electronic Component Manufacturers Association (EECA) . . . . . . . . . . . . 314.6.3 Joint Electron Devices Engineering Council (JEDEC) . . . . . . . . . . . . . . . . . . . . 314.6.4 Proprietary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.6.5 Naming problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.7 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324.7.1 Semiconductor material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324.7.2 Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.8 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.9 Directory of external websites with datasheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.11 Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.12 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5 Capacitor 365.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375.2 Theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385.2.2 Hydraulic analogy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385.2.3 Energy of electric field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.2.4 Current–voltage relation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.2.5 DC circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.2.6 AC circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.2.7 Laplace circuit analysis (s-domain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

iv CONTENTS

5.2.8 Parallel-plate model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405.2.9 Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.3 Non-ideal behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.3.1 Breakdown voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.3.2 Equivalent circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.3.3 Q factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.3.4 Ripple current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.3.5 Capacitance instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435.3.6 Current and voltage reversal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445.3.7 Dielectric absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445.3.8 Leakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445.3.9 Electrolytic failure from disuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.4 Capacitor types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445.4.1 Dielectric materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455.4.2 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5.5 Capacitor markings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465.5.1 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5.6 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475.6.1 Energy storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475.6.2 Pulsed power and weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475.6.3 Power conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475.6.4 Suppression and coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485.6.5 Motor starters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495.6.6 Signal processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495.6.7 Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495.6.8 Oscillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5.7 Hazards and safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505.8 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515.10 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515.11 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6 Inductor 536.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

6.1.1 Constitutive equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536.1.2 Lenz’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546.1.3 Ideal and real inductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

6.2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546.3 Inductor construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556.4 Types of inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

6.4.1 Air core inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566.4.2 Ferromagnetic core inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

CONTENTS v

6.4.3 Variable inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596.5 Circuit theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

6.5.1 Reactance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 606.5.2 Laplace circuit analysis (s-domain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616.5.3 Inductor networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616.5.4 Stored energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

6.6 Q factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616.7 Inductance formulas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626.8 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626.9 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 636.11 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

7 Diode 647.1 Main functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647.2 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

7.2.1 Vacuum tube diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657.2.2 Solid-state diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667.2.3 Etymology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

7.3 Thermionic diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667.4 Semiconductor diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

7.4.1 Electronic symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677.4.2 Point-contact diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677.4.3 Junction diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677.4.4 Current–voltage characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687.4.5 Shockley diode equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697.4.6 Small-signal behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697.4.7 Reverse-recovery effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

7.5 Types of semiconductor diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707.6 Numbering and coding schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

7.6.1 EIA/JEDEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737.6.2 JIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737.6.3 Pro Electron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

7.7 Related devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737.8 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

7.8.1 Radio demodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747.8.2 Power conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747.8.3 Over-voltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747.8.4 Logic gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747.8.5 Ionizing radiation detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747.8.6 Temperature measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757.8.7 Current steering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

vi CONTENTS

7.8.8 Waveform Clipper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757.8.9 Clamper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

7.9 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757.10 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757.11 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757.12 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

8 Wire 778.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778.2 Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788.3 Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788.4 Finishing, jacketing, and insulating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798.5 Forms of wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

8.5.1 Solid wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798.5.2 Stranded wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798.5.3 Braided wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808.5.4 Number of strands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

8.6 Varieties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808.7 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818.8 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818.10 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

9 Printed circuit board 829.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829.2 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

9.2.1 PCB CAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839.2.2 Panelization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839.2.3 Copper patterning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839.2.4 Subtractive, additive and semi-additive processes . . . . . . . . . . . . . . . . . . . . . . . 849.2.5 Chemical etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849.2.6 Inner layer automated optical inspection (AOI) . . . . . . . . . . . . . . . . . . . . . . . . 859.2.7 Lamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859.2.8 Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859.2.9 Plating and coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869.2.10 Solder resist application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869.2.11 Legend printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869.2.12 Bare-board test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869.2.13 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879.2.14 Protection and packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

9.3 PCB characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889.3.1 Through-hole technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

CONTENTS vii

9.3.2 Surface-mount technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889.3.3 Circuit properties of the PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899.3.4 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

9.4 Multiwire boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909.5 Cordwood construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909.6 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909.7 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 929.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 929.9 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

10 Electric current 9510.1 Symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9510.2 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

10.2.1 Reference direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9610.3 Ohm’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9610.4 AC and DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

10.4.1 Direct current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9610.4.2 Alternating current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

10.5 Occurrences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9710.6 Current measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9710.7 Resistive heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9710.8 Electromagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

10.8.1 Electromagnet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9710.8.2 Radio waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

10.9 Conduction mechanisms in various media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9810.9.1 Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9810.9.2 Electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9810.9.3 Gases and plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9910.9.4 Vacuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9910.9.5 Superconductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9910.9.6 Semiconductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

10.10Current density and Ohm’s law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10010.11Drift speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10010.12See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10110.13References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10110.14External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

11 Integrated circuit 10211.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10311.2 Invention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10311.3 Generations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

11.3.1 SSI, MSI and LSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

viii CONTENTS

11.3.2 VLSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10411.3.3 ULSI, WSI, SOC and 3D-IC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

11.4 Advances in integrated circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10511.5 Computer assisted design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10511.6 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10511.7 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

11.7.1 Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10611.7.2 Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10811.7.3 Chip labeling and manufacture date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

11.8 Intellectual property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10811.9 Other developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10911.10Silicon labelling and graffiti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10911.11ICs and IC families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10911.12See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10911.13References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11011.14Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11111.15External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

12 Breadboard 11312.1 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

12.1.1 Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11312.2 Solderless breadboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

12.2.1 Typical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11412.2.2 Bus and terminal strips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11412.2.3 Jump wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11512.2.4 Inside a breadboard: construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11512.2.5 Advanced solderless breadboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11512.2.6 High frequencies and dead bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11612.2.7 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

12.3 Gallery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11612.4 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11612.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11712.6 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

13 Perfboard 11813.1 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

14 Stripboard 12014.1 Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12014.2 Hole spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12014.3 Board dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12014.4 Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

CONTENTS ix

14.5 Comparison with other systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12114.5.1 Wire wrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12114.5.2 Breadboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

14.6 Prototype boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12114.6.1 TriPad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12114.6.2 Perf+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12114.6.3 Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

14.7 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12214.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

15 Analogue electronics 12315.1 Analogue signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12315.2 Inherent noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12315.3 Analogue vs digital electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

15.3.1 Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12415.3.2 Precision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12415.3.3 Design difficulty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

15.4 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12415.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

16 Digital electronics 12516.1 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12516.2 Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12616.3 Design issues in digital circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12616.4 Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

16.4.1 Structure of digital systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12716.4.2 Automated design tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12916.4.3 Design for testability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12916.4.4 Trade-offs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13016.4.5 Logic families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

16.5 Recent developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13116.6 See also . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13116.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13116.8 External links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13216.9 Text and image sources, contributors, and licenses . . . . . . . . . . . . . . . . . . . . . . . . . . 133

16.9.1 Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13316.9.2 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14016.9.3 Content license . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

Chapter 1

Electronic circuit

The die from an Intel 8742, an 8-bit microcontroller that includesa CPU, 128 bytes of RAM, 2048 bytes of EPROM, and I/O “data”on current chip.

A circuit built on a printed circuit board (PCB).

An electronic circuit is composed of individualelectronic components, such as resistors, transistors,capacitors, inductors and diodes, connected by conduc-tive wires or traces through which electric current canflow. The combination of components and wires al-lows various simple and complex operations to be per-formed: signals can be amplified, computations can beperformed, and data can be moved from one place toanother.[1] Circuits can be constructed of discrete com-

ponents connected by individual pieces of wire, but to-day it is much more common to create interconnectionsby photolithographic techniques on a laminated substrate(a printed circuit board or PCB) and solder the compo-nents to these interconnections to create a finished circuit.In an integrated circuit or IC, the components and inter-connections are formed on the same substrate, typically asemiconductor such as silicon or (less commonly) galliumarsenide.[2]

Breadboards, perfboards, and stripboards are commonfor testing new designs. They allow the designer to makequick changes to the circuit during development.An electronic circuit can usually be categorized as ananalog circuit, a digital circuit, or a mixed-signal circuit(a combination of analog circuits and digital circuits).

1.1 Analog circuits

Main article: Analog electronicsAnalog electronic circuits are those in which current or

A circuit diagram representing an analog circuit, in this case asimple amplifier

voltage may vary continuously with time to correspondto the information being represented. Analog circuitry isconstructed from two fundamental building blocks: seriesand parallel circuits. In a series circuit, the same cur-rent passes through a series of components. A string of

1

2 CHAPTER 1. ELECTRONIC CIRCUIT

Christmas lights is a good example of a series circuit: ifone goes out, they all do. In a parallel circuit, all the com-ponents are connected to the same voltage, and the cur-rent divides between the various components accordingto their resistance.

A simple schematic showing wires, a resistor, and a battery

The basic components of analog circuits are wires, re-sistors, capacitors, inductors, diodes, and transistors. (In2012 it was demonstrated that memristors can be addedto the list of available components.) Analog circuits arevery commonly represented in schematic diagrams, inwhich wires are shown as lines, and each componenthas a unique symbol. Analog circuit analysis employsKirchhoff’s circuit laws: all the currents at a node (a placewhere wires meet), and the voltage around a closed loopof wires is 0. Wires are usually treated as ideal zero-voltage interconnections; any resistance or reactance iscaptured by explicitly adding a parasitic element, such asa discrete resistor or inductor. Active components such astransistors are often treated as controlled current or volt-age sources: for example, a field-effect transistor can bemodeled as a current source from the source to the drain,with the current controlled by the gate-source voltage.When the circuit size is comparable to a wavelength of therelevant signal frequency, a more sophisticated approachmust be used. Wires are treated as transmission lines,with (hopefully) constant characteristic impedance, andthe impedances at the start and end determine transmit-ted and reflected waves on the line. Such considerationstypically become important for circuit boards at frequen-cies above a GHz; integrated circuits are smaller and canbe treated as lumped elements for frequencies less than10 10GHz or so.An alternative model is to take independent powersources and induction as basic electronic units; this al-lows modeling frequency dependent negative resistors,gyrators, negative impedance converters, and dependentsources as secondary electronic components

1.2 Digital circuits

Main article: Digital electronics

In digital electronic circuits, electric signals take on dis-crete values, to represent logical and numeric values.[3]These values represent the information that is being pro-cessed. In the vast majority of cases, binary encoding isused: one voltage (typically the more positive value) rep-resents a binary '1' and another voltage (usually a valuenear the ground potential, 0 V) represents a binary '0'.Digital circuits make extensive use of transistors, inter-connected to create logic gates that provide the func-tions of Boolean logic: AND, NAND, OR, NOR, XORand all possible combinations thereof. Transistors inter-connected so as to provide positive feedback are usedas latches and flip flops, circuits that have two or moremetastable states, and remain in one of these states un-til changed by an external input. Digital circuits there-fore can provide both logic and memory, enabling themto perform arbitrary computational functions. (Mem-ory based on flip-flops is known as static random-accessmemory (SRAM). Memory based on the storage ofcharge in a capacitor, dynamic random-access memory(DRAM) is also widely used.)The design process for digital circuits is fundamentallydifferent from the process for analog circuits. Each logicgate regenerates the binary signal, so the designer neednot account for distortion, gain control, offset voltages,and other concerns faced in an analog design. As a conse-quence, extremely complex digital circuits, with billionsof logic elements integrated on a single silicon chip, canbe fabricated at low cost. Such digital integrated circuitsare ubiquitous in modern electronic devices, such as cal-culators, mobile phone handsets, and computers. As dig-ital circuits become more complex, issues of time delay,logic races, power dissipation, non-ideal switching, on-chip and inter-chip loading, and leakage currents, becomelimitations to the density, speed and performance.Digital circuitry is used to create general purpose comput-ing chips, such as microprocessors, and custom-designedlogic circuits, known as application-specific integratedcircuit (ASICs). Field-programmable gate arrays (FP-GAs), chips with logic circuitry whose configuration canbe modified after fabrication, are also widely used in pro-totyping and development.

1.3 Mixed-signal circuits

Main article: mixed-signal integrated circuit

Mixed-signal or hybrid circuits contain elements ofboth analog and digital circuits. Examples includecomparators, timers, phase-locked loops, analog-to-digital converters, and digital-to-analog converters. Most

1.5. EXTERNAL LINKS 3

modern radio and communications circuitry uses mixedsignal circuits. For example, in a receiver, analog cir-cuitry is used to amplify and frequency-convert signals sothat they reach a suitable state to be converted into dig-ital values, after which further signal processing can beperformed in the digital domain.

1.4 References[1] Charles Alexander and Matthew Sadiku (2004). “Funda-

mentals of Electric Circuits”. McGraw-Hill.

[2] Richard Jaeger (1997). “Microelectronic Circuit Design”.McGraw-Hill.

[3] John Hayes (1993). “Introduction to Digital Logic De-sign”. Addison Wesley.

1.5 External links• Electronic Circuit Theory

Chapter 2

Electronic component

Various electronic components

An electronic component is any basic discrete deviceor physical entity in an electronic system used to affectelectrons or their associated fields. Electronic compo-nents are mostly industrial products, available in a sin-gular form and are not to be confused with electrical el-ements, which are conceptual abstractions representingidealized electronic components.Electronic components have two or more electricalterminals (or leads) aside from antennas which may onlyhave one terminal. These leads connect to create anelectronic circuit with a particular function (for examplean amplifier, radio receiver, or oscillator). Basic elec-tronic components may be packaged discretely, as ar-rays or networks of like components, or integrated insideof packages such as semiconductor integrated circuits,hybrid integrated circuits, or thick film devices. The fol-lowing list of electronic components focuses on the dis-crete version of these components, treating such packagesas components in their own right.

2.1 Classification

Components can be classified as passive, active, or elec-tromechanic. The strict physics definition treats pas-sive components as ones that cannot supply energy them-selves, whereas a battery would be seen as an active com-ponent since it truly acts as a source of energy.However, electronic engineers who perform circuit anal-

ysis use a more restrictive definition of passivity. Whenonly concerned with the energy of signals, it is conve-nient to ignore the so-called DC circuit and pretend thatthe power supplying components such as transistors orintegrated circuits is absent (as if each such componenthad its own battery built in), though it may in reality besupplied by the DC circuit. Then, the analysis only con-cerns the AC circuit, an abstraction that ignores DC volt-ages and currents (and the power associated with them)present in the real-life circuit. This fiction, for instance,lets us view an oscillator as “producing energy” eventhough in reality the oscillator consumes even more en-ergy from a DC power supply, which we have chosen toignore. Under that restriction, we define the terms as usedin circuit analysis as:

• Active components rely on a source of energy (usu-ally from the DC circuit, which we have chosen toignore) and usually can inject power into a circuit,though this is not part of the definition.[1] Activecomponents include amplifying components such astransistors, triode vacuum tubes (valves), and tunneldiodes.

• Passive components can't introduce net energy intothe circuit. They also can't rely on a source of power,except for what is available from the (AC) circuitthey are connected to. As a consequence they can'tamplify (increase the power of a signal), althoughthey may increase a voltage or current (such as isdone by a transformer or resonant circuit). Passivecomponents include two-terminal components suchas resistors, capacitors, inductors, and transformers.

• Electromechanical components can carry outelectrical operations by using moving parts or by us-ing electrical connections

Most passive components with more than two terminalscan be described in terms of two-port parameters that sat-isfy the principle of reciprocity—though there are rareexceptions.[2] In contrast, active components (with morethan two terminals) generally lack that property.

4

2.2. ACTIVE COMPONENTS 5

2.2 Active components

2.2.1 Semiconductors

Diodes

Various types of Light-emitting diode

Conduct electricity easily in one direction, among morespecific behaviors.

• Diode, Rectifier, Bridge rectifier

• Schottky diode, hot carrier diode – super fast diodewith lower forward voltage drop

• Zener diode – Passes current in reverse direction toprovide a constant voltage reference

• Transient voltage suppression diode (TVS), Unipo-lar or Bipolar – used to absorb high-voltage spikes

• Varactor, Tuning diode, Varicap, Variable capaci-tance diode – A diode whose AC capacitance variesaccording to the DC voltage applied.

• Light-emitting diode (LED) – A diode that emitslight

• Photodiode – Passes current in proportion to inci-dent light

• Avalanche photodiode Photodiode with inter-nal gain

• Solar Cell, photovoltaic cell, PV array orpanel, produces power from light

• DIAC (Diode for Alternating Current), TriggerDiode, SIDAC) – Often used to trigger an SCR

• Constant-current diode

• Peltier cooler – A semiconductor heat pump

Transistors

Transistors were considered the invention of the twenti-eth century that changed electronic circuits forever. Atransistor is a semiconductor device used to amplify andswitch electronic signals and electrical power.

• Transistors

• Bipolar junction transistor (BJT, or simply“transistor”) – NPN or PNP• Photo transistor – Amplified photodetec-tor

• Darlington transistor – NPN or PNP• Photo Darlington – Amplified photode-tector

• Sziklai pair (Compound transistor, comple-mentary Darlington)

• Field-effect transistor (FET)

• JFET (Junction Field-Effect Transistor) – N-CHANNEL or P-CHANNEL

• MOSFET (Metal Oxide Semiconductor FET)– N-CHANNEL or P-CHANNEL

• MESFET (MEtal Semiconductor FET)• HEMT (High electron mobility transistor)

• Thyristors

• Silicon-controlled rectifier (SCR) – Passescurrent only after triggered by a sufficient con-trol voltage on its gate

• TRIAC (TRIode for Alternating Current) –Bidirectional SCR

• Unijunction transistor (UJT)• Programmable Unijunction transistor (PUT)• SIT (Static induction transistor)• SITh (Static induction thyristor)

• Composite transistors

• IGBT (Insulated-gate bipolar transistor)

Integrated circuits

• Digital

• Analog

• Hall effect sensor –senses a magnetic field• Current sensor – Senses a current through it

Optoelectronic devices

• Optoelectronics

• Opto-Isolator, Opto-Coupler, Photo-Coupler– Photodiode, BJT, JFET, SCR, TRIAC,Zero-crossing TRIAC, Open collector IC,CMOS IC, Solid state relay (SSR)

• Opto switch, Opto interrupter, Optical switch,Optical interrupter, Photo switch, Photo inter-rupter

• LED display – Seven-segment display,Sixteen-segment display, Dot-matrix display

6 CHAPTER 2. ELECTRONIC COMPONENT

2.2.2 Display technologies

Current:

• Filament lamp (indicator lamp)

• Vacuum fluorescent display (VFD) (preformedcharacters, 7 segment, starburst)

• Cathode ray tube (CRT) (dot matrix scan, radialscan (e.g. radar), arbitrary scan (e.g. oscilloscope))(monochrome & colour)

• LCD (preformed characters, dot matrix) (passive,TFT) (monochrome, colour)

• Neon (individual, 7 segment display)

• LED (individual, 7 segment display, starburst dis-play, dot matrix)

• Flap indicator (numeric, preprinted messages)

• Plasma display (dot matrix)

Obsolete:

• Filament lamp 7 segment display (aka 'minitron')

• Nixie Tube

• Dekatron (aka glow transfer tube)

• Magic eye tube indicator

• Penetron (a 2 colour see-through CRT)

2.2.3 Vacuum tubes (valves)

A vacuum tube is based on current conduction through avacuum (see Vacuum tube).

• Diode or rectifier tube

Amplifying tubes

• Triode

• Tetrode

• Pentode

• Hexode

• Pentagrid

• Octode

• Microwave tubes

• Klystron• Magnetron

• Traveling-wave tube

Optical detectors or emitters

• Phototube or Photodiode – tube equivalent of semi-conductor photodiode

• Photomultiplier tube – Phototube with internal gain

• Cathode ray tube (CRT) or television picture tube

• Vacuum fluorescent display (VFD) – Modern non-raster sort of small CRT display

• Magic eye tube – Small CRT display used as a tuningmeter (obsolete)

• X-ray tube – Produces x-rays

2.2.4 Discharge devices

• Gas discharge tube

Obsolete:

• Mercury arc rectifier

• Voltage regulator tube

• Nixie tube

• Thyratron

• Ignitron

2.2.5 Power sources

Sources of electrical power:

• Battery – acid- or alkali-based power supply

• Fuel cell – an electrochemical generator

• Power supply – usually a mains hook-up

• Photo voltaic device – generates electricity fromlight

• Thermo electric generator – generates electricityfrom temperature gradients

• Electrical generator – an electromechanical powersource

• Piezoelectric pressure - creates electricity from me-chanical strain

• Van de Graaff generator - Van de Graaff generatoror essentially creating voltage from friction

2.3. PASSIVE COMPONENTS 7

SMD resistors on a backside of a PCB

2.3 Passive components

2.3.1 Resistors

Pass current in proportion to voltage (Ohm’s law) and op-pose current.

• Resistor – fixed value

• Power resistor – larger to safely dissipate heatgenerated

• SIP or DIP resistor network – array of resistorsin one package

• Variable resistor

• Rheostat – two-terminal variable resistor (of-ten for high power)

• Potentiometer – three-terminal variable resis-tor (variable voltage divider)

• Trim pot – Small potentiometer, usually for in-ternal adjustments

• Thermistor – thermally sensitive resistorwhose prime function is to exhibit a large, pre-dictable and precise change in electrical re-sistance when subjected to a correspondingchange in body temperature.[3]

• Humistor – humidity-varied resistor• Photoresistor• Memristor• Varistor, Voltage Dependent Resistor, MOV– Passes current when excessive voltage ispresent

• Resistance wire, Nichrome wire – wire of high-resistance material, often used as a heating element

• Heater – heating element

2.3.2 Capacitors

Some different capacitors for electronic equipment

Capacitors store and release electrical charge. They areused for filtering power supply lines, tuning resonant cir-cuits, and for blocking DC voltages while passing AC sig-nals, among numerous other uses.

• Capacitor

• Integrated capacitors• MIS capacitor• Trench capacitor

• Fixed capacitors• Ceramic capacitor• Film capacitor• Electrolytic capacitor

• Aluminum electrolytic capacitor• Tantalum electrolytic capacitor• Niobium electrolytic capacitor• Polymer capacitor, OS-CON

• Supercapacitor (Electric double-layer ca-pacitor)• Nanoionic supercapacitor• Lithium-ion capacitor

• Mica capacitor• Vacuum capacitor

• Variable capacitor – adjustable capacitance

8 CHAPTER 2. ELECTRONIC COMPONENT

• Tuning capacitor – variable capacitor fortuning a radio, oscillator, or tuned circuit

• Trim capacitor– small variable capacitoris usually for slight internal adjustmentsmade with a small screw driver turnedinto the right position.

• Vacuum variable capacitor• Capacitors for special applications

• Power capacitor• Safety capacitor• Filter capacitor• Light-emitting capacitor• Motor capacitor• Photoflash capacitor• Reservoir capacitor

• Capacitor network (array)

• Varicap diode – AC capacitance varies according tothe DC voltage applied

2.3.3 Magnetic (inductive) devices

Electrical components that use magnetism in the storageand release of electrical charge through current:

• Inductor, coil, choke

• Variable inductor

• Saturable Inductor

• Transformer

• Magnetic amplifier (toroid)

• ferrite impedances, beads

• Motor / Generator

• Solenoid

• Loudspeaker and microphone

2.3.4 Memristor

Electrical components that pass charge in proportion tomagnetism or magnetic flux, and have the ability to retaina previous resistive state, hence the name ofMemory plusResistor.

• Memristor

2.3.5 Networks

Components that use more than one type of passive com-ponent:

• RC network – forms an RC circuit, used in snubbers

• LC Network – forms an LC circuit, used in tunabletransformers and RFI filters.

2.3.6 Transducers, sensors, detectors

1. Transducers generate physical effects when drivenby an electrical signal, or vice versa.

2. Sensors (detectors) are transducers that react to en-vironmental conditions by changing their electricalproperties or generating an electrical signal.

3. The transducers listed here are single electroniccomponents (as opposed to complete assemblies),and are passive (see Semiconductors and Tubes foractive ones). Only the most common ones are listedhere.

• Audio (see also piezoelectric devices)

• Loudspeaker – Magnetic or piezoelectric de-vice to generate full audio

• Buzzer – Magnetic or piezoelectric sounder togenerate tones

• Position, motion

• Linear variable differential transformer(LVDT) – Magnetic – detects linear position

• Rotary encoder, Shaft Encoder – Optical,magnetic, resistive or switches – detects abso-lute or relative angle or rotational speed

• Inclinometer – Capacitive – detects angle withrespect to gravity

• Motion sensor, Vibration sensor• Flow meter – detects flow in liquid or gas

• Force, torque

• Strain gauge – Piezoelectric or resistive – de-tects squeezing, stretching, twisting

• Accelerometer – Piezoelectric – detects accel-eration, gravity

• Thermal

• Thermocouple, thermopile –Wires that gener-ate a voltage proportional to delta temperature

• Thermistor – Resistor whose resistancechanges with temperature, up PTC or downNTC

2.4. ELECTROMECHANICAL 9

• Resistance Temperature Detector (RTD) –Wire whose resistance changes with temper-ature

• Bolometer – Device for measuring the powerof incident electromagnetic radiation

• Thermal cutoff – Switch that is opened orclosed when a set temperature is exceeded

• Magnetic field (see also Hall Effect in semiconduc-tors)

• Magnetometer, Gauss meter

• Humidity

• Hygrometer

• Electromagnetic, light

• Photo resistor – Light dependent resistor(LDR)

2.3.7 Antennas

Antennas transmit or receive radio waves

• Elemental dipole

• Yagi

• Phased array

• Loop antenna

• Parabolic dish

• Log-periodic dipole array

• Biconical

• Feedhorn

2.3.8 Assemblies, modules

Multiple electronic components assembled in a devicethat is in itself used as a component

• Oscillator

• Display devices

• Liquid crystal display (LCD)• Digital voltmeters

• Filter

2.3.9 Prototyping aids

• Wire-wrap

• Breadboard

2.4 Electromechanical

2 crystalline type oscillators

2.4.1 Piezoelectric devices, crystals, res-onators

Passive components that use piezoelectric effect:

• Components that use the effect to generate or filterhigh frequencies

• Crystal – a ceramic crystal used to generateprecise frequencies (See the Modules class be-low for complete oscillators)

• Ceramic resonator – Is a ceramic crystal usedto generate semi-precise frequencies

• Ceramic filter – Is a ceramic crystal used tofilter a band of frequencies such as in radio re-ceivers

• surface acoustic wave (SAW) filters

• Components that use the effect as mechanicaltransducers.

• Ultrasonicmotor – Electricmotor that uses thepiezoelectric effects

• For piezo buzzers and microphones, see theTransducer class below

2.4.2 Terminals and connectors

Devices to make electrical connection

• Terminal

• Connector

• Socket• Screw terminal, Terminal Blocks• Pin header

10 CHAPTER 2. ELECTRONIC COMPONENT

2.4.3 Cable assemblies

Cables with connectors or terminals at their ends

• Power cord

• Patch cord

• Test lead

2 different tactile switches

2.4.4 Switches

Components that can pass current (“closed”) or break theflow of current (“open”):

• Switch – Manually operated switch.

• Electrical description: SPST, SPDT, DPST,DPDT, NPNT (general)

• Technology: slide switches, toggle switches,rocker switches, rotary switches, pushbuttonswitches

• Keypad – Array of pushbutton switches

• DIP switch – Small array of switches for internalconfiguration settings

• Footswitch – Foot-operated switch

• Knife switch – Switch with unenclosed conductors

• Micro switch – Mechanically activated switch withsnap action

• Limit switch – Mechanically activated switch tosense limit of motion

• Mercury switch – Switch sensing tilt

• Centrifugal switch – Switch sensing centrifugal forcedue to rate of rotation

• Relay – Electrically operated switch (mechanical,also see Solid State Relay below)

• Reed switch – Magnetically activated switch

• Thermostat – Thermally activated switch

• Humidistat – Humidity activated switch

• Circuit breaker – Switch opened in response to ex-cessive current: a resettable fuse

2.4.5 Protection devices

Passive components that protect circuits from excessivecurrents or voltages:

• Fuse – over-current protection, one time use

• Circuit breaker – resettable fuse in the form of a me-chanical switch

• Resettable fuse or PolySwitch – circuit breaker ac-tion using solid state device

• Ground-fault protection or residual-current device –circuit breaker sensitive to mains currents passing toground

• Metal oxide varistor (MOV), surge absorber, TVS –Over-voltage protection.

• Inrush current limiter – protection against initialInrush current

• Gas discharge tube – protection against high voltagesurges

• Spark gap – electrodes with a gap to arc over at ahigh voltage

• Lightning arrester – spark gap used to protect againstlightning strikes

2.4.6 Mechanical accessories

• Enclosure (electrical)

• Heat sink

• Fan

2.4.7 Other

• Printed circuit boards

• Lamp

• Waveguide

• Memristor

2.7. REFERENCES 11

2.4.8 Obsolete

• Carbon amplifier (see Carbon microphones used asamplifiers)

• Carbon arc (negative resistance device)

• Dynamo (historic rf generator)

• Coherer

2.5 Standard symbols

Main article: Electronic symbol

On a circuit diagram, electronic devices are representedby conventional symbols. Reference designators are ap-plied to the symbols to identify the component.

2.6 See also• Circuit design

• Circuit diagram

• Counterfeit electronic components

• Electrical element

• Electronic mixer

• Electronic components’ Datasheets

• IEEE 315-1975

2.7 References[1] For instance, a computer could be contained inside a black

box with two external terminals. It might do various cal-culations and signal its results by varying its resistance, butalways consuming power as a resistance does. Neverthe-less, it’s an active component, since it relies on a powersource to operate.

[2] Nonreciprocal passive devices include the gyrator (thoughas a truly passive component, this exists more in theo-retical terms, and is usually implemented using an activecircuit)—and the circulator, which is used at microwaveand optical frequencies

[3] What is a Thermistor. U.S. Sensor Corp.

Chapter 3

Resistor

Axial-lead resistors on tape. The component is cut from the tapeduring assembly and the part is inserted into the board.

A resistor is a passive two-terminal electrical componentthat implements electrical resistance as a circuit element.Resistors act to reduce current flow, and, at the same time,act to lower voltage levels within circuits. In electroniccircuits resistors are used to limit current flow, to adjustsignal levels, bias active elements, terminate transmissionlines among other uses. High-power resistors that can dis-sipate many watts of electrical power as heat may be usedas part of motor controls, in power distribution systems,or as test loads for generators. Fixed resistors have resis-tances that only change slightly with temperature, time oroperating voltage. Variable resistors can be used to ad-just circuit elements (such as a volume control or a lampdimmer), or as sensing devices for heat, light, humidity,force, or chemical activity.Resistors are common elements of electrical networksand electronic circuits and are ubiquitous in electronicequipment. Practical resistors as discrete componentscan be composed of various compounds and forms. Re-sistors are also implemented within integrated circuits.The electrical function of a resistor is specified by itsresistance: common commercial resistors are manufac-tured over a range of more than nine orders of magni-tude. The nominal value of the resistance will fall withina manufacturing tolerance.

3.1 Electronic symbols and nota-tion

Main article: Electronic symbol

Two typical schematic diagram symbols are as follows;

• (a) resistor, (b) rheostat (variable resistor), and (c)potentiometer

• IEC resistor symbol

The notation to state a resistor’s value in a circuit diagramvaries, too. The European notation BS 1852 avoids usinga decimal separator, and replaces the decimal separatorwith the SI prefix symbol for the particular value. For ex-ample, 8k2 in a circuit diagram indicates a resistor valueof 8.2 kΩ. Additional zeros imply tighter tolerance, forexample 15M0. When the value can be expressed with-out the need for an SI prefix, an 'R' is used instead of thedecimal separator. For example, 1R2 indicates 1.2 Ω,and 18R indicates 18 Ω. The use of a SI prefix symbol orthe letter 'R' circumvents the problem that decimal sep-arators tend to 'disappear' when photocopying a printedcircuit diagram.

3.2 Theory of operation

3.2.1 Ohm’s law

Main article: Ohm’s law

The behavior of an ideal resistor is dictated by the rela-tionship specified by Ohm’s law:

V = I ·R.

Ohm’s law states that the voltage (V) across a resistor isproportional to the current (I), where the constant of pro-portionality is the resistance (R). For example, if a 300ohm resistor is attached across the terminals of a 12 volt

12

3.2. THEORY OF OPERATION 13

Hairin pipe

Large RSame flow

Higherpressure

Lowerpressure

Small R

The hydraulic analogy compares electric current flowing throughcircuits to water flowing through pipes. When a pipe (left) isfilled with hair (right), it takes a larger pressure to achieve thesame flow of water. Pushing electric current through a large re-sistance is like pushing water through a pipe clogged with hair:It requires a larger push (voltage drop) to drive the same flow(electric current).[1]

battery, then a current of 12 / 300 = 0.04 amperes flowsthrough that resistor.Practical resistors also have some inductance andcapacitance which will also affect the relation betweenvoltage and current in alternating current circuits.The ohm (symbol: Ω) is the SI unit of electrical resis-tance, named after Georg Simon Ohm. An ohm is equiv-alent to a volt per ampere. Since resistors are specifiedand manufactured over a very large range of values, thederived units of milliohm (1 mΩ = 10−3 Ω), kilohm (1kΩ = 103 Ω), and megohm (1 MΩ = 106 Ω) are also incommon usage.

3.2.2 Series and parallel resistors

Main article: Series and parallel circuits

The total resistance of resistors connected in series is thesum of their individual resistance values.

R2R1 Rn

Req = R1 +R2 + · · ·+Rn.

The total resistance of resistors connected in parallel isthe reciprocal of the sum of the reciprocals of the indi-vidual resistors.

R2R1 Rn

1Req

= 1R1

+ 1R2

+ · · ·+ 1Rn

.

So, for example, a 10 ohm resistor connected in paral-lel with a 5 ohm resistor and a 15 ohm resistor will pro-duce the inverse of 1/10+1/5+1/15 ohms of resistance,or 1/(.1+.2+.067)=2.725 ohms.A resistor network that is a combination of parallel andseries connections can be broken up into smaller partsthat are either one or the other. Some complex networksof resistors cannot be resolved in this manner, requiringmore sophisticated circuit analysis. Generally, the Y-Δtransform, or matrix methods can be used to solve suchproblems.[2][3][4]

3.2.3 Power dissipation

At any instant of time, the power P (watts) consumed bya resistor of resistance R (ohms) is calculated as: P =I2R = IV = V 2

R where V (volts) is the voltage acrossthe resistor and I (amps) is the current flowing throughit. Using Ohm’s law, the two other forms can be de-rived. This power is converted into heat which must bedissipated by the resistor’s package before its temperaturerises excessively.Resistors are rated according to their maximum powerdissipation. Most discrete resistors in solid-state elec-tronic systems absorb much less than a watt of electri-cal power and require no attention to their power rating.Such resistors in their discrete form, including most ofthe packages detailed below, are typically rated as 1/10,1/8, or 1/4 watt.

An aluminium-housed power resistor rated for 50 W when heat-sinked

Resistors required to dissipate substantial amounts ofpower, particularly used in power supplies, power con-

14 CHAPTER 3. RESISTOR

version circuits, and power amplifiers, are generally re-ferred to as power resistors; this designation is loosely ap-plied to resistors with power ratings of 1 watt or greater.Power resistors are physically larger and may not use thepreferred values, color codes, and external packages de-scribed below.If the average power dissipated by a resistor is more thanits power rating, damage to the resistor may occur, per-manently altering its resistance; this is distinct from thereversible change in resistance due to its temperature co-efficient when it warms. Excessive power dissipation mayraise the temperature of the resistor to a point where it canburn the circuit board or adjacent components, or evencause a fire. There are flameproof resistors that fail (opencircuit) before they overheat dangerously.Since poor air circulation, high altitude, or high operatingtemperatures may occur, resistors may be specified withhigher rated dissipation than will be experienced in ser-vice.All resistors have a maximum voltage rating; this maylimit the power dissipation for higher resistance values.

3.3 Nonideal properties

Practical resistors have a series inductance and a smallparallel capacitance; these specifications can be importantin high-frequency applications. In a low-noise amplifieror pre-amp, the noise characteristics of a resistor may bean issue.The temperature coefficient of the resistance may also beof concern in some precision applications.The unwanted inductance, excess noise, and tempera-ture coefficient are mainly dependent on the technologyused in manufacturing the resistor. They are not normallyspecified individually for a particular family of resistorsmanufactured using a particular technology.[5] A familyof discrete resistors is also characterized according to itsform factor, that is, the size of the device and the positionof its leads (or terminals) which is relevant in the practicalmanufacturing of circuits using them.Practical resistors are also specified as having a maximumpower rating which must exceed the anticipated powerdissipation of that resistor in a particular circuit: this ismainly of concern in power electronics applications. Re-sistors with higher power ratings are physically larger andmay require heat sinks. In a high-voltage circuit, attentionmust sometimes be paid to the rated maximum workingvoltage of the resistor. While there is no minimum work-ing voltage for a given resistor, failure to account for aresistor’s maximum rating may cause the resistor to in-cinerate when current is run through it.

3.4 Fixed resistor

A single in line (SIL) resistor package with 8 individual, 47 ohmresistors. One end of each resistor is connected to a separate pinand the other ends are all connected together to the remaining(common) pin – pin 1, at the end identified by the white dot.

3.4.1 Lead arrangements

Resistors with wire leads for through-hole mounting

Through-hole components typically have “leads” (pro-nounced to rhyme with “reeds”) leaving the body “axi-ally,” that is, on a line parallel with the part’s longest axis.Others have leads coming off their body “radially” in-stead. Other components may be SMT (surface mounttechnology), while high power resistors may have one oftheir leads designed into the heat sink.

3.4.2 Carbon composition

Carbon composition resistors consist of a solid cylindri-cal resistive element with embedded wire leads or metalend caps to which the lead wires are attached. The bodyof the resistor is protected with paint or plastic. Early20th-century carbon composition resistors had uninsu-lated bodies; the leadwires were wrapped around the endsof the resistance element rod and soldered. The com-pleted resistor was painted for color-coding of its value.The resistive element is made from a mixture of finelyground (powdered) carbon and an insulating material(usually ceramic). A resin holds the mixture together.

3.4. FIXED RESISTOR 15

Three carbon composition resistors in a 1960s valve (vacuumtube) radio

The resistance is determined by the ratio of the fill ma-terial (the powdered ceramic) to the carbon. Higherconcentrations of carbon— a good conductor— resultin lower resistance. Carbon composition resistors werecommonly used in the 1960s and earlier, but are notso popular for general use now as other types have bet-ter specifications, such as tolerance, voltage dependence,and stress (carbon composition resistors will change valuewhen stressed with over-voltages). Moreover, if internalmoisture content (from exposure for some length of timeto a humid environment) is significant, soldering heat willcreate a non-reversible change in resistance value. Car-bon composition resistors have poor stability with timeand were consequently factory sorted to, at best, only 5%tolerance.[6] These resistors, however, if never subjectedto overvoltage nor overheating were remarkably reliableconsidering the component’s size.[7]

Carbon composition resistors are still available, but com-paratively quite costly. Values ranged from fractions ofan ohm to 22 megohms. Due to their high price, these re-sistors are no longer used in most applications. However,they are used in power supplies and welding controls.[7]

3.4.3 Carbon pile

A carbon pile resistor is made of a stack of carbon diskscompressed between two metal contact plates. Adjustingthe clamping pressure changes the resistance between theplates. These resistors are used when an adjustable loadis required, for example in testing automotive batteries orradio transmitters. A carbon pile resistor can also be usedas a speed control for small motors in household appli-ances (sewing machines, hand-held mixers) with ratingsup to a few hundred watts.[8] A carbon pile resistor canbe incorporated in automatic voltage regulators for gen-erators, where the carbon pile controls the field currentto maintain relatively constant voltage.[9] The principle isalso applied in the carbon microphone.

Carbon film resistor with exposed carbon spiral (Tesla TR-212 1kΩ)

3.4.4 Carbon film

A carbon film is deposited on an insulating substrate,and a helix is cut in it to create a long, narrow resis-tive path. Varying shapes, coupled with the resistivityof amorphous carbon (ranging from 500 to 800 μΩ m),can provide a wide range of resistance values. Comparedto carbon composition they feature low noise, becauseof the precise distribution of the pure graphite withoutbinding.[10] Carbon film resistors feature a power ratingrange of 0.125 W to 5 W at 70 °C. Resistances availablerange from 1 ohm to 10 megohm. The carbon film resis-tor has an operating temperature range of −55 °C to 155°C. It has 200 to 600 volts maximum working voltagerange. Special carbon film resistors are used in applica-tions requiring high pulse stability.[7]

3.4.5 Printed carbon resistor

A carbon resistor printed directly onto the SMD pads on a PCB.Inside a 1989 vintage Psion II Organiser

Carbon composition resistors can be printed directly ontoprinted circuit board (PCB) substrates as part of the PCBmanufacturing process. Although this technique is morecommon on hybrid PCB modules, it can also be used onstandard fibreglass PCBs. Tolerances are typically quitelarge, and can be in the order of 30%. A typical applica-tion would be non-critical pull-up resistors.

3.4.6 Thick and thin film

Thick film resistors became popular during the 1970s,and most SMD (surface mount device) resistors today are

16 CHAPTER 3. RESISTOR

Laser Trimmed Precision Thin Film Resistor Network fromFluke, used in the Keithley DMM7510 multimeter. Ceramicbacked with glass hermetic seal cover.

of this type. The resistive element of thick films is 1000times thicker than thin films,[11] but the principal differ-ence is how the film is applied to the cylinder (axial resis-tors) or the surface (SMD resistors).Thin film resistors are made by sputtering (a method ofvacuum deposition) the resistive material onto an insulat-ing substrate. The film is then etched in a similar mannerto the old (subtractive) process for making printed cir-cuit boards; that is, the surface is coated with a photo-sensitive material, then covered by a pattern film, irradi-ated with ultraviolet light, and then the exposed photo-sensitive coating is developed, and underlying thin film isetched away.Thick film resistors are manufactured using screen andstencil printing processes.[7]

Because the time during which the sputtering is per-formed can be controlled, the thickness of the thin filmcan be accurately controlled. The type of material isalso usually different consisting of one or more ceramic(cermet) conductors such as tantalum nitride (TaN),ruthenium oxide (RuO2), lead oxide (PbO), bismuth ruthenate (Bi2Ru2O7), nickel chromium (NiCr), or bismuth iridate (Bi2Ir2O7).The resistance of both thin and thick film resistors af-ter manufacture is not highly accurate; they are usuallytrimmed to an accurate value by abrasive or laser trim-ming. Thin film resistors are usually specified with toler-ances of 0.1, 0.2, 0.5, or 1%, and with temperature co-efficients of 5 to 25 ppm/K. They also have much lowernoise levels, on the level of 10–100 times less than thickfilm resistors.Thick film resistors may use the same conductive ceram-ics, but they are mixed with sintered (powdered) glassand a carrier liquid so that the composite can be screen-printed. This composite of glass and conductive ceramic(cermet)material is then fused (baked) in an oven at about

850 °C.Thick film resistors, when first manufactured, had toler-ances of 5%, but standard tolerances have improved to2% or 1% in the last few decades. Temperature coef-ficients of thick film resistors are high, typically ±200 or±250 ppm/K; a 40 kelvin (70 °F) temperature change canchange the resistance by 1%.Thin film resistors are usually far more expensive thanthick film resistors. For example, SMD thin film resis-tors, with 0.5% tolerances, and with 25 ppm/K tempera-ture coefficients, when bought in full size reel quantities,are about twice the cost of 1%, 250 ppm/K thick filmresistors.

3.4.7 Metal film

A common type of axial-leaded resistor today is themetal-film resistor. Metal Electrode Leadless Face(MELF) resistors often use the same technology, andare also cylindrically shaped but are designed for surfacemounting. Note that other types of resistors (e.g., carboncomposition) are also available in MELF packages.Metal film resistors are usually coated with nickelchromium (NiCr), but might be coated with any of thecermet materials listed above for thin film resistors. Un-like thin film resistors, the material may be applied usingdifferent techniques than sputtering (though this is one ofthe techniques). Also, unlike thin-film resistors, the resis-tance value is determined by cutting a helix through thecoating rather than by etching. (This is similar to the waycarbon resistors are made.) The result is a reasonable tol-erance (0.5%, 1%, or 2%) and a temperature coefficientthat is generally between 50 and 100 ppm/K.[12] Metalfilm resistors possess good noise characteristics and lownon-linearity due to a low voltage coefficient. Also bene-ficial are their tight tolerance, low temperature coefficientand long-term stability.[7]

3.4.8 Metal oxide film

Metal-oxide film resistors are made of metal oxides suchas tin oxide. This results in a higher operating tempera-ture and greater stability/reliability than Metal film. Theyare used in applications with high endurance demands.

3.4.9 Wire wound

Wirewound resistors are commonly made by winding ametal wire, usually nichrome, around a ceramic, plastic,or fiberglass core. The ends of the wire are soldered orwelded to two caps or rings, attached to the ends of thecore. The assembly is protected with a layer of paint,molded plastic, or an enamel coating baked at high tem-perature. These resistors are designed to withstand un-usually high temperatures of up to 450 °C.[7] Wire leads

3.4. FIXED RESISTOR 17

High-power wire wound resistors used for dynamic braking onan electric railway car. Such resistors may dissipate many kilo-watts for an extended length of time.

Types of windings in wire resistors:1. common2. bifilar3. common on a thin former4. Ayrton-Perry

in low power wirewound resistors are usually between 0.6and 0.8 mm in diameter and tinned for ease of solder-ing. For higher power wirewound resistors, either a ce-ramic outer case or an aluminum outer case on top ofan insulating layer is used – if the outer case is ceramic,such resistors are sometimes described as “cement” resis-tors, though they do not actually contain any traditionalcement. The aluminum-cased types are designed to beattached to a heat sink to dissipate the heat; the ratedpower is dependent on being used with a suitable heatsink, e.g., a 50 W power rated resistor will overheat at afraction of the power dissipation if not used with a heatsink. Large wirewound resistors may be rated for 1,000watts or more.Because wirewound resistors are coils they have more un-desirable inductance than other types of resistor, althoughwinding the wire in sections with alternately reversed di-rection can minimize inductance. Other techniques em-ploy bifilar winding, or a flat thin former (to reduce cross-section area of the coil). For themost demanding circuits,resistors with Ayrton-Perry winding are used.Applications of wirewound resistors are similar to thoseof composition resistors with the exception of the high

frequency. The high frequency response of wirewoundresistors is substantially worse than that of a compositionresistor.[7]

3.4.10 Foil resistor

The primary resistance element of a foil resistor is a spe-cial alloy foil several micrometers thick. Since their in-troduction in the 1960s, foil resistors have had the bestprecision and stability of any resistor available. One ofthe important parameters influencing stability is the tem-perature coefficient of resistance (TCR). The TCR of foilresistors is extremely low, and has been further improvedover the years. One range of ultra-precision foil resistorsoffers a TCR of 0.14 ppm/°C, tolerance ±0.005%, long-term stability (1 year) 25 ppm, (3 years) 50 ppm (furtherimproved 5-fold by hermetic sealing), stability under load(2000 hours) 0.03%, thermal EMF 0.1 μV/°C, noise −42dB, voltage coefficient 0.1 ppm/V, inductance 0.08 μH,capacitance 0.5 pF.[13]

3.4.11 Ammeter shunts

An ammeter shunt is a special type of current-sensingresistor, having four terminals and a value in milliohmsor even micro-ohms. Current-measuring instruments, bythemselves, can usually accept only limited currents. Tomeasure high currents, the current passes through theshunt across which the voltage drop is measured and in-terpreted as current. A typical shunt consists of two solidmetal blocks, sometimes brass, mounted on an insulat-ing base. Between the blocks, and soldered or brazed tothem, are one or more strips of low temperature coef-ficient of resistance (TCR) manganin alloy. Large boltsthreaded into the blocks make the current connections,while much smaller screws provide volt meter connec-tions. Shunts are rated by full-scale current, and oftenhave a voltage drop of 50 mV at rated current. Such me-ters are adapted to the shunt full current rating by usingan appropriately marked dial face; no change need to bemade to the other parts of the meter.

3.4.12 Grid resistor

In heavy-duty industrial high-current applications, a gridresistor is a large convection-cooled lattice of stampedmetal alloy strips connected in rows between two elec-trodes. Such industrial grade resistors can be as largeas a refrigerator; some designs can handle over 500 am-peres of current, with a range of resistances extendinglower than 0.04 ohms. They are used in applications suchas dynamic braking and load banking for locomotivesand trams, neutral grounding for industrial AC distribu-tion, control loads for cranes and heavy equipment, loadtesting of generators and harmonic filtering for electricsubstations.[14][15]

18 CHAPTER 3. RESISTOR

The term grid resistor is sometimes used to describe aresistor of any type connected to the control grid of avacuum tube. This is not a resistor technology; it is anelectronic circuit topology.

3.4.13 Special varieties

• Cermet

• Phenolic

• Tantalum

• Water resistor

3.5 Variable resistors

3.5.1 Adjustable resistors

A resistor may have one or more fixed tapping points sothat the resistance can be changed bymoving the connect-ing wires to different terminals. Some wirewound powerresistors have a tapping point that can slide along the re-sistance element, allowing a larger or smaller part of theresistance to be used.Where continuous adjustment of the resistance value dur-ing operation of equipment is required, the sliding resis-tance tap can be connected to a knob accessible to an op-erator. Such a device is called a rheostat and has twoterminals.

3.5.2 Potentiometers

Main article: Potentiometer

A potentiometer or pot is a three-terminal resistor with acontinuously adjustable tapping point controlled by rota-tion of a shaft or knob or by a linear slider. It is calleda potentiometer because it can be connected as an ad-justable voltage divider to provide a variable potential atthe terminal connected to the tapping point. A volumecontrol for an audio device is a common use of a poten-tiometer.Accurate, high-resolution panel-mounted potentiometershave resistance elements typically wirewound on a heli-cal mandrel, although some include a conductive-plasticresistance coating over the wire to improve resolution.These typically offer ten turns of their shafts to covertheir full range. They are usually set with dials that in-clude a simple turns counter and a graduated dial. Elec-tronic analog computers used them in quantity for settingcoefficients, and delayed-sweep oscilloscopes of recentdecades included one on their panels.

3.5.3 Resistance decade boxes

Resistance decade box “KURBELWIDERSTAND”, made in for-mer East Germany.

A resistance decade box or resistor substitution box isa unit containing resistors of many values, with one ormore mechanical switches which allow any one of vari-ous discrete resistances offered by the box to be dialedin. Usually the resistance is accurate to high precision,ranging from laboratory/calibration grade accuracy of 20parts per million, to field grade at 1%. Inexpensive boxeswith lesser accuracy are also available. All types offer aconvenient way of selecting and quickly changing a resis-tance in laboratory, experimental and development workwithout needing to attach resistors one by one, or evenstock each value. The range of resistance provided, themaximum resolution, and the accuracy characterize thebox. For example, one box offers resistances from 0 to100 megohms, maximum resolution 0.1 ohm, accuracy0.1%.[16]

3.5.4 Special devices

There are various devices whose resistance changes withvarious quantities. The resistance of NTC thermistorsexhibit a strong negative temperature coefficient, mak-ing them useful for measuring temperatures. Since theirresistance can be large until they are allowed to heat updue to the passage of current, they are also commonlyused to prevent excessive current surges when equipmentis powered on. Similarly, the resistance of a humistorvaries with humidity. One sort of photodetector, thephotoresistor, has a resistance which varies with illumi-nation.The strain gauge, invented by Edward E. Simmons andArthur C. Ruge in 1938, is a type of resistor that changesvalue with applied strain. A single resistor may be used,or a pair (half bridge), or four resistors connected in aWheatstone bridge configuration. The strain resistor isbonded with adhesive to an object that will be subjectedto mechanical strain. With the strain gauge and a filter,

3.8. RESISTOR MARKING 19

amplifier, and analog/digital converter, the strain on anobject can be measured.A related but more recent invention uses a Quantum Tun-nelling Composite to sense mechanical stress. It passes acurrent whose magnitude can vary by a factor of 1012 inresponse to changes in applied pressure.

3.6 Measurement

The value of a resistor can be measured with anohmmeter, which may be one function of a multimeter.Usually, probes on the ends of test leads connect to theresistor. A simple ohmmeter may apply a voltage froma battery across the unknown resistor (with an internalresistor of a known value in series) producing a currentwhich drives a meter movement. The current, in ac-cordance with Ohm’s law, is inversely proportional tothe sum of the internal resistance and the resistor beingtested, resulting in an analog meter scale which is verynon-linear, calibrated from infinity to 0 ohms. A digitalmultimeter, using active electronics, may instead pass aspecified current through the test resistance. The voltagegenerated across the test resistance in that case is linearlyproportional to its resistance, which is measured and dis-played. In either case the low-resistance ranges of themeter pass much more current through the test leads thando high-resistance ranges, in order for the voltages presentto be at reasonable levels (generally below 10 volts) butstill measurable.Measuring low-value resistors, such as fractional-ohm re-sistors, with acceptable accuracy requires four-terminalconnections. One pair of terminals applies a known, cal-ibrated current to the resistor, while the other pair sensesthe voltage drop across the resistor. Some laboratoryquality ohmmeters, especially milliohmmeters, and evensome of the better digital multimeters sense using fourinput terminals for this purpose, which may be used withspecial test leads. Each of the two so-called Kelvin clipshas a pair of jaws insulated from each other. One side ofeach clip applies the measuring current, while the otherconnections are only to sense the voltage drop. The re-sistance is again calculated using Ohm’s Law as the mea-sured voltage divided by the applied current.

3.7 Standards

3.7.1 Production resistors

Resistor characteristics are quantified and reported usingvarious national standards. In the US, MIL-STD-202[17]contains the relevant test methods to which other stan-dards refer.There are various standards specifying properties of re-sistors for use in equipment:

• BS 1852

• EIA-RS-279

• MIL-PRF-26

• MIL-PRF-39007 (Fixed Power, established reliabil-ity)

• MIL-PRF-55342 (Surface-mount thick and thinfilm)

• MIL-PRF-914

• MIL-R-11 STANDARD CANCELED

• MIL-R-39017 (Fixed, General Purpose, Estab-lished Reliability)

• MIL-PRF-32159 (zero ohm jumpers)

• UL 1412 (fusing and temperature limited resistors)[18]

There are other United States military procurement MIL-R- standards.

3.7.2 Resistance standards

The primary standard for resistance, the “mercury ohm”was initially defined in 1884 in as a column of mercury106.3 cm long and 1 square millimeter in cross-section,at 0 degrees Celsius. Difficulties in precisely measuringthe physical constants to replicate this standard result invariations of as much as 30 ppm. From 1900 the mer-cury ohm was replaced with a precision machined plateof manganin.[19] Since 1990 the international resistancestandard has been based on the quantized Hall effect dis-covered by Klaus von Klitzing, for which he won the No-bel Prize in Physics in 1985.[20]

Resistors of extremely high precision are manufacturedfor calibration and laboratory use. They may have fourterminals, using one pair to carry an operating current andthe other pair to measure the voltage drop; this eliminateserrors caused by voltage drops across the lead resistances,because no charge flows through voltage sensing leads. Itis important in small value resistors (100–0.0001 ohm)where lead resistance is significant or even comparablewith respect to resistance standard value.[21]

3.8 Resistor marking

Main article: Electronic color code

Most axial resistors use a pattern of colored stripes to in-dicate resistance, which also indicate tolerance, and mayalso be extended to show temperature coefficient and reli-ability class. Cases are usually tan, brown, blue, or green,

20 CHAPTER 3. RESISTOR

though other colors are occasionally found such as darkred or dark gray. The power rating is not usually markedand is deduced from the size.The color bands of the carbon resistors can be three, four,five or, six bands. The first two bands represent first twodigits to measure their value in ohms. The third band ofa three- or four-banded resistor represents multiplier; afourth band denotes tolerance (which if absent, denotes±20%). For five and six color-banded resistors, the thirdband is a third digit, fourth band multiplier and fifth istolerance. The sixth band represents temperature co-efficient in a six-banded resistor.Surface-mount resistors are marked numerically, if theyare big enough to permit marking; more-recent smallsizes are impractical to mark.Early 20th century resistors, essentially uninsulated, weredipped in paint to cover their entire body for color-coding. A second color of paint was applied to one endof the element, and a color dot (or band) in the middleprovided the third digit. The rule was “body, tip, dot”,providing two significant digits for value and the deci-mal multiplier, in that sequence. Default tolerance was±20%. Closer-tolerance resistors had silver (±10%) orgold-colored (±5%) paint on the other end.

3.8.1 Preferred values

See also: Preferred number § E series

Early resistors were made in more or less arbitrary roundnumbers; a series might have 100, 125, 150, 200, 300,etc. Resistors as manufactured are subject to a certainpercentage tolerance, and it makes sense to manufacturevalues that correlate with the tolerance, so that the ac-tual value of a resistor overlaps slightly with its neigh-bors. Wider spacing leaves gaps; narrower spacing in-creases manufacturing and inventory costs to provide re-sistors that are more or less interchangeable.A logical scheme is to produce resistors in a range ofvalues which increase in a geometric progression, so thateach value is greater than its predecessor by a fixed multi-plier or percentage, chosen to match the tolerance of therange. For example, for a tolerance of ±20% it makessense to have each resistor about 1.5 times its predeces-sor, covering a decade in 6 values. In practice the factorused is 1.4678, giving values of 1.47, 2.15, 3.16, 4.64,6.81, 10 for the 1–10-decade (a decade is a range in-creasing by a factor of 10; 0.1–1 and 10–100 are otherexamples); these are rounded in practice to 1.5, 2.2, 3.3,4.7, 6.8, 10; followed, by 15, 22, 33, … and precededby … 0.47, 0.68, 1. This scheme has been adopted asthe E6 series of the IEC 60063 preferred number values.There are also E12, E24, E48, E96 and E192 series forcomponents of progressively finer resolution, with 12, 24,96, and 192 different values within each decade. The ac-

tual values used are in the IEC 60063 lists of preferrednumbers.A resistor of 100 ohms ±20%would be expected to have avalue between 80 and 120 ohms; its E6 neighbors are 68(54–82) and 150 (120–180) ohms. A sensible spacing,E6 is used for ±20% components; E12 for ±10%; E24for ±5%; E48 for ±2%, E96 for ±1%; E192 for ±0.5% orbetter. Resistors are manufactured in values from a fewmilliohms to about a gigaohm in IEC60063 ranges ap-propriate for their tolerance. Manufacturers may sort re-sistors into tolerance-classes based on measurement. Ac-cordingly a selection of 100 ohms resistors with a toler-ance of ±10%, might not lie just around 100 ohm (but nomore than 10% off) as one would expect (a bell-curve),but rather be in two groups – either between 5 to 10% toohigh or 5 to 10% too low (but not closer to 100 ohm thanthat) because any resistors the factory had measured asbeing less than 5% off would have been marked and soldas resistors with only ±5% tolerance or better. When de-signing a circuit, this may become a consideration.Earlier power wirewound resistors, such as brownvitreous-enameled types, however, were made with a dif-ferent system of preferred values, such as some of thosementioned in the first sentence of this section.

3.8.2 SMT resistors

This image shows four surface-mount resistors (the componentat the upper left is a capacitor) including two zero-ohm resistors.Zero-ohm links are often used instead of wire links, so that theycan be inserted by a resistor-inserting machine. Their resistanceis non-zero but negligible.

Surface mounted resistors are printed with numericalvalues in a code related to that used on axial resistors.Standard-tolerance surface-mount technology (SMT) re-sistors are marked with a three-digit code, in which thefirst two digits are the first two significant digits of thevalue and the third digit is the power of ten (the numberof zeroes). For example:

3.10. FAILURE MODES 21

Resistances less than 100 ohms are written: 100, 220,470. The final zero represents ten to the power zero,which is 1. For example:Sometimes these values are marked as 10 or 22 to preventa mistake.Resistances less than 10 ohms have 'R' to indicate the po-sition of the decimal point (radix point). For example:Precision resistors are marked with a four-digit code, inwhich the first three digits are the significant figures andthe fourth is the power of ten. For example:000 and 0000 sometimes appear as values on surface-mount zero-ohm links, since these have (approximately)zero resistance.More recent surface-mount resistors are too small, phys-ically, to permit practical markings to be applied.

3.8.3 Industrial type designation

Format: [two letters]<space>[resistance value (threedigit)]<nospace>[tolerance code(numerical – one digit)][22]

3.9 Electrical and thermal noise

Main article: Noise (electronics)

In amplifying faint signals, it is often necessary to mini-mize electronic noise, particularly in the first stage of am-plification. As a dissipative element, even an ideal resistorwill naturally produce a randomly fluctuating voltage or“noise” across its terminals. This Johnson–Nyquist noiseis a fundamental noise source which depends only uponthe temperature and resistance of the resistor, and is pre-dicted by the fluctuation–dissipation theorem. Using alarger value of resistance produces a larger voltage noise,whereas with a smaller value of resistance there will bemore current noise, at a given temperature.The thermal noise of a practical resistor may also belarger than the theoretical prediction and that increase istypically frequency-dependent. Excess noise of a practi-cal resistor is observed only when current flows through it.This is specified in unit of μV/V/decade – μV of noise pervolt applied across the resistor per decade of frequency.The μV/V/decade value is frequently given in dB so thata resistor with a noise index of 0 dB will exhibit 1 μV(rms) of excess noise for each volt across the resistor ineach frequency decade. Excess noise is thus an exampleof 1/f noise. Thick-film and carbon composition resistorsgenerate more excess noise than other types at low fre-quencies. Wire-wound and thin-film resistors are oftenused for their better noise characteristics. Carbon com-position resistors can exhibit a noise index of 0 dB while

bulk metal foil resistors may have a noise index of −40dB, usually making the excess noise of metal foil resistorsinsignificant.[23] Thin film surface mount resistors typi-cally have lower noise and better thermal stability thanthick film surface mount resistors. Excess noise is alsosize-dependent: in general excess noise is reduced as thephysical size of a resistor is increased (or multiple resis-tors are used in parallel), as the independently fluctuatingresistances of smaller components will tend to averageout.While not an example of “noise” per se, a resistor may actas a thermocouple, producing a small DC voltage differ-ential across it due to the thermoelectric effect if its endsare at different temperatures. This induced DC voltagecan degrade the precision of instrumentation amplifiersin particular. Such voltages appear in the junctions of theresistor leads with the circuit board and with the resistorbody. Common metal film resistors show such an effectat a magnitude of about 20 µV/°C. Some carbon compo-sition resistors can exhibit thermoelectric offsets as highas 400 µV/°C, whereas specially constructed resistors canreduce this number to 0.05 µV/°C. In applications wherethe thermoelectric effect may become important, care hasto be taken to mount the resistors horizontally to avoidtemperature gradients and to mind the air flow over theboard.[24]

3.10 Failure modes

The failure rate of resistors in a properly designed circuitis low compared to other electronic components such assemiconductors and electrolytic capacitors. Damage toresistors most often occurs due to overheating when theaverage power delivered to it (as computed above) greatlyexceeds its ability to dissipate heat (specified by the resis-tor’s power rating). This may be due to a fault external tothe circuit, but is frequently caused by the failure of an-other component (such as a transistor that shorts out) inthe circuit connected to the resistor. Operating a resistortoo close to its power rating can limit the resistor’s lifes-pan or cause a significant change in its resistance. A safedesign generally uses overrated resistors in power appli-cations to avoid this danger.Low-power thin-film resistors can be damaged by long-term high-voltage stress, even below maximum specifiedvoltage and below maximum power rating. This is oftenthe case for the startup resistors feeding the SMPS inte-grated circuit.When overheated, carbon-film resistors may decrease orincrease in resistance.[25] Carbon film and compositionresistors can fail (open circuit) if running close to theirmaximum dissipation. This is also possible but less likelywith metal film and wirewound resistors.There can also be failure of resistors due to mechanicalstress and adverse environmental factors including hu-

22 CHAPTER 3. RESISTOR

midity. If not enclosed, wirewound resistors can corrode.Surface mount resistors have been known to fail due tothe ingress of sulfur into the internal makeup of the re-sistor. This sulfur chemically reacts with the silver layerto produce non-conductive silver sulfide. The resistor’simpedance goes to infinity. Sulfur resistant and anti-corrosive resistors are sold into automotive, industrial,and military applications. ASTM B809 is an industrystandard that tests a part’s susceptibility to sulfur.An alternative failure mode can be encountered wherelarge value resistors are used (hundreds of kilohms andhigher). Resistors are not only specified with a maximumpower dissipation, but also for a maximum voltage drop.Exceeding this voltage will cause the resistor to degradeslowly reducing in resistance. The voltage dropped acrosslarge value resistors can be exceeded before the powerdissipation reaches its limiting value. Since themaximumvoltage specified for commonly encountered resistors is afew hundred volts, this is a problem only in applicationswhere these voltages are encountered.Variable resistors can also degrade in a different man-ner, typically involving poor contact between the wiperand the body of the resistance. This may be due to dirtor corrosion and is typically perceived as “crackling” asthe contact resistance fluctuates; this is especially noticedas the device is adjusted. This is similar to cracklingcaused by poor contact in switches, and like switches,potentiometers are to some extent self-cleaning: runningthe wiper across the resistance may improve the contact.Potentiometers which are seldom adjusted, especially indirty or harsh environments, are most likely to developthis problem. When self-cleaning of the contact is in-sufficient, improvement can usually be obtained throughthe use of contact cleaner (also known as “tuner cleaner”)spray. The crackling noise associated with turning theshaft of a dirty potentiometer in an audio circuit (such asthe volume control) is greatly accentuated when an unde-sired DC voltage is present, often indicating the failure ofa DC blocking capacitor in the circuit.

3.11 See also

• thermistor

• piezoresistor

• Circuit design

• Dummy load

• Electrical impedance

• Iron-hydrogen resistor

• Shot noise

• Trimmer (electronics)

3.12 References[1] Douglas Wilhelm Harder. “Resistors: A Motor with a

Constant Force (Force Source)". Department of Electri-cal and Computer Engineering, University of Waterloo.Retrieved 9 November 2014.

[2] Farago, PS, An Introduction to Linear Network Analysis,pp. 18–21, The English Universities Press Ltd, 1961.

[3] F Y Wu (2004). “Theory of resistor networks: Thetwo-point resistance”. Journal of Physics A: Mathemat-ical and General 37 (26): 6653. doi:10.1088/0305-4470/37/26/004.

[4] Fa Yueh Wu; Chen Ning Yang (15 March 2009). ExactlySolved Models: A Journey in Statistical Mechanics : Se-lected Papers with Commentaries (1963–2008). WorldScientific. pp. 489–. ISBN 978-981-281-388-6. Re-trieved 14 May 2012.

[5] A family of resistors may also be characterized accordingto its critical resistance. Applying a constant voltage acrossresistors in that family below the critical resistance willexceed the maximum power rating first; resistances largerthan the critical resistance will fail first from exceedingthe maximum voltage rating. See Wendy Middleton; MacE. Van Valkenburg (2002). Reference data for engineers:radio, electronics, computer, and communications (9 ed.).Newnes. pp. 5–10. ISBN 0-7506-7291-9.

[6] James H. Harter, Paul Y. Lin, Essentials of electric circuits,pp. 96–97, Reston Publishing Company, 1982 ISBN 0-8359-1767-3.

[7] Vishay Beyschlag Basics of Linear Fixed Resistors Appli-cation Note, Document Number 28771, 2008.

[8] C. G. Morris (ed) Academic Press Dictionary of Scienceand Technology, Gulf Professional Publishing, 1992 ISBN0122004000, page 360

[9] Principles of automotive vehicles United States. Dept. ofthe Army, 1985 page 13-13

[10] “Carbon Film Resistor”. The Resistorguide. Retrieved 10March 2013.

[11] “Thick Film and Thin Film” (PDF). Digi-Key (SEI). Re-trieved 23 July 2011.

[12] Kenneth A. Kuhn. “Measuring the Temperature Coeffi-cient of a Resistor” (PDF). Retrieved 2010-03-18.

[13] “Alpha Electronics Corp. Metal Foil Resistors”. Alpha-elec.co.jp. Retrieved 2008-09-22.

[14] Milwaukee Resistor Corporation. ''Grid Resistors: HighPower/High Current''. Milwaukeeresistor.com. Retrievedon 2012-05-14.

[15] Avtron Loadbank. ''Grid Resistors’'. Avtron.com. Re-trieved on 2012-05-14.

[16] “Decade Box – Resistance Decade Boxes”. Ietlabs.com.Retrieved 2008-09-22.

3.13. EXTERNAL LINKS 23

[17] “Test method standard: electronic and electrical compo-nent parts” (PDF). Department of Defense.

[18] http://ulstandardsinfonet.ul.com/scopes/scopes.asp?fn=1412.html

[19] Stability of Double-Walled Manganin Resistors.NIST.gov

[20] Klaus von Klitzing The Quantized Hall Effect. Nobel lec-ture, December 9, 1985. nobelprize.org

[21] “Standard Resistance Unit Type 4737B”. Tinsley.co.uk.Retrieved 2008-09-22.

[22] A. K. Maini Electronics and Communications Simplified,9th ed., Khanna Publications (India)

[23] Audio Noise Reduction Through the Use of Bulk Metal FoilResistors – “Hear the Difference” (PDF)., Application noteAN0003, Vishay Intertechnology Inc, 12 July 2005.

[24] Walt Jung. “Chapter 7 – Hardware and HousekeepingTechniques” (PDF). Op Amp Applications Handbook. p.7.11. ISBN 0-7506-7844-5.

[25] “Electronic components – resistors”. Inspector’s Techni-cal Guide. US Food and Drug Administration. 1978-01-16. Archived from the original on 2008-04-03. Retrieved2008-06-11.

3.13 External links• 4-terminal resistors – How ultra-precise resistorswork

• Beginner’s guide to potentiometers, including de-scription of different tapers

• Color Coded Resistance Calculator – archived withWayBack Machine

• Resistor Types – Does It Matter?

• Standard Resistors & Capacitor Values That Indus-try Manufactures

• Ask The Applications Engineer – Difference be-tween types of resistors

• Resistors and their uses

• Thick film resistors and heaters

Chapter 4

Transistor

For other uses, see Transistor (disambiguation).A transistor is a semiconductor device used to amplify

Assorted discrete transistors. Packages in order from top to bot-tom: TO-3, TO-126, TO-92, SOT-23

and switch electronic signals and electrical power. It iscomposed of semiconductor material with at least threeterminals for connection to an external circuit. A voltageor current applied to one pair of the transistor’s terminalschanges the current through another pair of terminals.Because the controlled (output) power can be higher thanthe controlling (input) power, a transistor can amplify asignal. Today, some transistors are packaged individu-ally, but many more are found embedded in integratedcircuits.The transistor is the fundamental building block of mod-ern electronic devices, and is ubiquitous in modern elec-tronic systems. Following its development in 1947by American physicists John Bardeen, Walter Brattain,and William Shockley, the transistor revolutionized the

field of electronics, and paved the way for smaller andcheaper radios, calculators, and computers, among otherthings. The transistor is on the list of IEEE milestones inelectronics,[1] and the inventors were jointly awarded the1956 Nobel Prize in Physics for their achievement.[2]

4.1 History

Main article: History of the transistorThe thermionic triode, a vacuum tube invented in 1907

A replica of the first working transistor.

enabled amplified radio technology and long-distancetelephony. The triode, however, was a fragile device thatconsumed a lot of power. Physicist Julius Edgar Lilien-feld filed a patent for a field-effect transistor (FET) inCanada in 1925, which was intended to be a solid-statereplacement for the triode.[3][4] Lilienfeld also filed iden-tical patents in the United States in 1926[5] and 1928.[6][7]However, Lilienfeld did not publish any research articlesabout his devices nor did his patents cite any specific ex-amples of a working prototype. Because the productionof high-quality semiconductor materials was still decadesaway, Lilienfeld’s solid-state amplifier ideas would nothave found practical use in the 1920s and 1930s, even ifsuch a device had been built.[8] In 1934, German inventor

24

4.2. IMPORTANCE 25

Oskar Heil patented a similar device.[9]

John Bardeen, William Shockley and Walter Brattain at BellLabs, 1948.

From November 17, 1947 to December 23, 1947, JohnBardeen and Walter Brattain at AT&T's Bell Labs in theUnited States, performed experiments and observed thatwhen two gold point contacts were applied to a crys-tal of germanium, a signal was produced with the out-put power greater than the input.[10] Solid State PhysicsGroup leader William Shockley saw the potential in this,and over the next few months worked to greatly expandthe knowledge of semiconductors. The term transis-tor was coined by John R. Pierce as a contraction ofthe term transresistance.[11][12][13] According to LillianHoddeson and Vicki Daitch, authors of a biography ofJohn Bardeen, Shockley had proposed that Bell Labs’ firstpatent for a transistor should be based on the field-effectand that he be named as the inventor. Having unearthedLilienfeld’s patents that went into obscurity years ear-lier, lawyers at Bell Labs advised against Shockley’s pro-posal because the idea of a field-effect transistor that usedan electric field as a “grid” was not new. Instead, whatBardeen, Brattain, and Shockley invented in 1947 wasthe first point-contact transistor.[8] In acknowledgementof this accomplishment, Shockley, Bardeen, and Brattainwere jointly awarded the 1956Nobel Prize in Physics “fortheir researches on semiconductors and their discovery ofthe transistor effect.”[14]

In 1948, the point-contact transistor was independentlyinvented by German physicists Herbert Mataré andHeinrich Welker while working at the Compagnie desFreins et Signaux, a Westinghouse subsidiary locatedin Paris. Mataré had previous experience in develop-ing crystal rectifiers from silicon and germanium in theGerman radar effort during World War II. Using thisknowledge, he began researching the phenomenon of"interference" in 1947. By June 1948, witnessing cur-rents flowing through point-contacts, Mataré producedconsistent results using samples of germanium producedby Welker, similar to what Bardeen and Brattain had ac-complished earlier in December 1947. Realizing that

Bell Labs’ scientists had already invented the transistorbefore them, the company rushed to get its “transistron”into production for amplified use in France’s telephonenetwork.[15]

Philco surface-barrier transistor developed and produced in1953

The first high-frequency transistor was the surface-barriergermanium transistor developed by Philco in 1953, ca-pable of operating up to 60 MHz.[16] These were madeby etching depressions into an N-type germanium basefrom both sides with jets of Indium(III) sulfate until itwas a few ten-thousandths of an inch thick. Indium elec-troplated into the depressions formed the collector andemitter.[17][18] The first all-transistor car radio, which wasproduced in 1955 byChrysler and Philco, used these tran-sistors in its circuitry and also they were the first suitablefor high-speed computers.[19][20][21][22]

The first working silicon transistor was developed at BellLabs on January 26, 1954 by Morris Tanenbaum. Thefirst commercial silicon transistor was produced by TexasInstruments in 1954. This was the work of Gordon Teal,an expert in growing crystals of high purity, who had pre-viously worked at Bell Labs. [23][24][25] The first MOStransistor actually built was by Kahng and Atalla at BellLabs in 1960.[26]

4.2 Importance

The transistor is the key active component in practicallyall modern electronics. Many consider it to be one of thegreatest inventions of the 20th century.[27] Its importancein today’s society rests on its ability to be mass-producedusing a highly automated process (semiconductor devicefabrication) that achieves astonishingly low per-transistor

26 CHAPTER 4. TRANSISTOR

A Darlington transistor opened up so the actual transistor chip(the small square) can be seen inside. A Darlington transistoris effectively two transistors on the same chip. One transistor ismuch larger than the other, but both are large in comparison totransistors in large-scale integration because this particular ex-ample is intended for power applications.

costs. The invention of the first transistor at Bell Labs wasnamed an IEEE Milestone in 2009.[28]

Although several companies each produce over a billionindividually packaged (known as discrete) transistors ev-ery year,[29] the vast majority of transistors are now pro-duced in integrated circuits (often shortened to IC, mi-crochips or simply chips), along with diodes, resistors,capacitors and other electronic components, to producecomplete electronic circuits. A logic gate consists of upto about twenty transistors whereas an advanced micro-processor, as of 2009, can use as many as 3 billion transis-tors (MOSFETs).[30] “About 60 million transistors werebuilt in 2002 ... for [each] man, woman, and child onEarth.”[31]

The transistor’s low cost, flexibility, and reliability havemade it a ubiquitous device. Transistorized mechatroniccircuits have replaced electromechanical devices in con-trolling appliances and machinery. It is often easier andcheaper to use a standard microcontroller and write acomputer program to carry out a control function thanto design an equivalent mechanical control function.

4.3 Simplified operation

The essential usefulness of a transistor comes from itsability to use a small signal applied between one pair of itsterminals to control a much larger signal at another pairof terminals. This property is called gain. It can producea stronger output signal, a voltage or current, that is pro-portional to a weaker input signal; that is, it can act asan amplifier. Alternatively, the transistor can be used toturn current on or off in a circuit as an electrically con-trolled switch, where the amount of current is determinedby other circuit elements.There are two types of transistors, which have slight dif-

base

collector

emitter

VOUT

VIN

VCC

A simple circuit diagram to show the labels of a n–p–n bipolartransistor.

ferences in how they are used in a circuit. A bipolar tran-sistor has terminals labeled base, collector, and emitter.A small current at the base terminal (that is, flowing be-tween the base and the emitter) can control or switch amuch larger current between the collector and emitter ter-minals. For a field-effect transistor, the terminals are la-beled gate, source, and drain, and a voltage at the gatecan control a current between source and drain.The image to the right represents a typical bipolar tran-sistor in a circuit. Charge will flow between emitter andcollector terminals depending on the current in the base.Because internally the base and emitter connections be-have like a semiconductor diode, a voltage drop developsbetween base and emitter while the base current exists.The amount of this voltage depends on the material thetransistor is made from, and is referred to as VBE.

4.3.1 Transistor as a switch

+ 6 V

1 k

IBE

ICE

BJT used as an electronic switch, in grounded-emitter configura-tion.

4.4. COMPARISON WITH VACUUM TUBES 27

Transistors are commonly used as electronic switches,both for high-power applications such as switched-modepower supplies and for low-power applications such aslogic gates.In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the base voltage rises, the emitterand collector currents rise exponentially. The collectorvoltage drops because of reduced resistance from collec-tor to emitter. If the voltage difference between the col-lector and emitter were zero (or near zero), the collectorcurrent would be limited only by the load resistance (lightbulb) and the supply voltage. This is called saturation be-cause current is flowing from collector to emitter freely.When saturated, the switch is said to be on.[32]

Providing sufficient base drive current is a key problem inthe use of bipolar transistors as switches. The transistorprovides current gain, allowing a relatively large currentin the collector to be switched by a much smaller cur-rent into the base terminal. The ratio of these currentsvaries depending on the type of transistor, and even for aparticular type, varies depending on the collector current.In the example light-switch circuit shown, the resistor ischosen to provide enough base current to ensure the tran-sistor will be saturated.In any switching circuit, values of input voltage would bechosen such that the output is either completely off,[33] orcompletely on. The transistor is acting as a switch, andthis type of operation is common in digital circuits whereonly “on” and “off” values are relevant.

4.3.2 Transistor as an amplifier

B C

E

V

V

V R

R

R

R

C

C

C

+

in

out C

E

1

2

in

out

E

Amplifier circuit, common-emitter configuration with a voltage-divider bias circuit.

The common-emitter amplifier is designed so that a smallchange in voltage (V ᵢ ) changes the small current throughthe base of the transistor; the transistor’s current amplifi-cation combined with the properties of the circuit meanthat small swings in V ᵢ produce large changes in Vₒᵤ .Various configurations of single transistor amplifier arepossible, with some providing current gain, some voltagegain, and some both.Frommobile phones to televisions, vast numbers of prod-ucts include amplifiers for sound reproduction, radiotransmission, and signal processing. The first discrete-transistor audio amplifiers barely supplied a few hun-dred milliwatts, but power and audio fidelity graduallyincreased as better transistors became available and am-plifier architecture evolved.Modern transistor audio amplifiers of up to a few hundredwatts are common and relatively inexpensive.

4.4 Comparison with vacuumtubes

Prior to the development of transistors, vacuum (elec-tron) tubes (or in the UK “thermionic valves” or just“valves”) were the main active components in electronicequipment.

4.4.1 Advantages

The key advantages that have allowed transistors to re-place their vacuum tube predecessors in most applica-tions are

• No power consumption by a cathode heater; thecharacteristic orange glow of vacuum tubes is dueto a simple electrical heating element, much like alight bulb filament.

• Small size and minimal weight, allowing the devel-opment of miniaturized electronic devices.

• Low operating voltages compatible with batteries ofonly a few cells.

• No warm-up period for cathode heaters required af-ter power application.

• Lower power dissipation and generally greater en-ergy efficiency.

• Higher reliability and greater physical ruggedness.

• Extremely long life. Some transistorized deviceshave been in service for more than 50 years.

• Complementary devices available, facilitating thedesign of complementary-symmetry circuits, some-thing not possible with vacuum tubes.

28 CHAPTER 4. TRANSISTOR

• Greatly reduced sensitivity to mechanical shockand vibration, thus reducing the problem ofmicrophonics in sensitive applications, such as au-dio.

4.4.2 Limitations

• Silicon transistors can age and fail.[34]

• High-power, high-frequency operation, such as thatused in over-the-air television broadcasting, is betterachieved in vacuum tubes due to improved electronmobility in a vacuum.

• Solid-state devices are more vulnerable toelectrostatic discharge in handling and opera-tion

• A vacuum tubemomentarily overloaded will just geta little hotter; solid-state devices have less mass toabsorb the heat due to overloads, in proportion totheir rating

• Sensitivity to radiation and cosmic rays (specialradiation-hardened chips are used for spacecraft de-vices).

• Vacuum tubes create a distortion, the so-called tubesound, which some people find to be more tolerableto the ear.[35]

4.5 Types

BJT and JFET symbolsJFET and IGFET symbols

Transistors are categorized by

• Semiconductor material (date first used): themetalloids germanium (1947) and silicon (1954)—in amorphous, polycrystalline and monocrystallineform; the compounds gallium arsenide (1966) andsilicon carbide (1997), the alloy silicon-germanium(1989), the allotrope of carbon graphene (researchongoing since 2004), etc.—see Semiconductor ma-terial

• Structure: BJT, JFET, IGFET (MOSFET),insulated-gate bipolar transistor, “other types”

• Electrical polarity (positive and negative): n–p–n,p–n–p (BJTs); n-channel, p-channel (FETs)

• Maximum power rating: low, medium, high

• Maximum operating frequency: low, medium, high,radio (RF), microwave frequency (the maximum ef-fective frequency of a transistor is denoted by the

term fT , an abbreviation for transition frequency—the frequency of transition is the frequency at whichthe transistor yields unity gain)

• Application: switch, general purpose, audio, highvoltage, super-beta, matched pair

• Physical packaging: through-hole metal, through-hole plastic, surface mount, ball grid array, powermodules—see Packaging

• Amplification factor h ₑ, βF (transistor beta)[36] org (transconductance).

Thus, a particular transistor may be described as silicon,surface-mount, BJT, n–p–n, low-power, high-frequencyswitch.

4.5.1 Bipolar junction transistor (BJT)

Main article: Bipolar junction transistor

Bipolar transistors are so named because they conduct byusing both majority and minority carriers. The bipolarjunction transistor, the first type of transistor to be mass-produced, is a combination of two junction diodes, andis formed of either a thin layer of p-type semiconduc-tor sandwiched between two n-type semiconductors (ann–p–n transistor), or a thin layer of n-type semiconduc-tor sandwiched between two p-type semiconductors (ap–n–p transistor). This construction produces two p–njunctions: a base–emitter junction and a base–collectorjunction, separated by a thin region of semiconductorknown as the base region (two junction diodes wired to-gether without sharing an intervening semiconducting re-gion will not make a transistor).BJTs have three terminals, corresponding to the threelayers of semiconductor—an emitter, a base, and a col-lector. They are useful in amplifiers because the cur-rents at the emitter and collector are controllable by arelatively small base current.”[37] In an n–p–n transistoroperating in the active region, the emitter–base junctionis forward biased (electrons and holes recombine at thejunction), and electrons are injected into the base re-gion. Because the base is narrow, most of these elec-trons will diffuse into the reverse-biased (electrons andholes are formed at, and move away from the junction)base–collector junction and be swept into the collector;perhaps one-hundredth of the electrons will recombinein the base, which is the dominant mechanism in the basecurrent. By controlling the number of electrons that canleave the base, the number of electrons entering the col-lector can be controlled.[37] Collector current is approx-imately β (common-emitter current gain) times the basecurrent. It is typically greater than 100 for small-signaltransistors but can be smaller in transistors designed forhigh-power applications.

4.5. TYPES 29

Unlike the field-effect transistor (see below), the BJT is alow–input-impedance device. Also, as the base–emittervoltage (Vbe) is increased the base–emitter current andhence the collector–emitter current (Ice) increase expo-nentially according to the Shockley diode model and theEbers-Moll model. Because of this exponential relation-ship, the BJT has a higher transconductance than the FET.Bipolar transistors can be made to conduct by exposureto light, because absorption of photons in the base regiongenerates a photocurrent that acts as a base current; thecollector current is approximately β times the photocur-rent. Devices designed for this purpose have a transparentwindow in the package and are called phototransistors.

4.5.2 Field-effect transistor (FET)

Main articles: Field-effect transistor, MOSFET andJFET

The field-effect transistor, sometimes called a unipolartransistor, uses either electrons (in n-channel FET) orholes (in p-channel FET) for conduction. The four termi-nals of the FET are named source, gate, drain, and body(substrate). On most FETs, the body is connected to thesource inside the package, and this will be assumed forthe following description.In a FET, the drain-to-source current flows via a conduct-ing channel that connects the source region to the drain re-gion. The conductivity is varied by the electric field thatis produced when a voltage is applied between the gateand source terminals; hence the current flowing betweenthe drain and source is controlled by the voltage appliedbetween the gate and source. As the gate–source volt-age (Vgs) is increased, the drain–source current (Ids) in-creases exponentially forVgs below threshold, and then ata roughly quadratic rate ( Ids ∝ (Vgs−VT )

2 ) (whereVTis the threshold voltage at which drain current begins)[38]in the "space-charge-limited" region above threshold. Aquadratic behavior is not observed in modern devices, forexample, at the 65 nm technology node.[39]

For low noise at narrow bandwidth the higher input resis-tance of the FET is advantageous.FETs are divided into two families: junction FET (JFET)and insulated gate FET (IGFET). The IGFET is morecommonly known as a metal–oxide–semiconductor FET(MOSFET), reflecting its original construction from lay-ers of metal (the gate), oxide (the insulation), and semi-conductor. Unlike IGFETs, the JFET gate forms a p–ndiode with the channel which lies between the source anddrain. Functionally, this makes the n-channel JFET thesolid-state equivalent of the vacuum tube triode which,similarly, forms a diode between its grid and cathode.Also, both devices operate in the depletion mode, theyboth have a high input impedance, and they both conductcurrent under the control of an input voltage.

Metal–semiconductor FETs (MESFETs) are JFETs inwhich the reverse biased p–n junction is replaced by ametal–semiconductor junction. These, and the HEMTs(high-electron-mobility transistors, or HFETs), in whicha two-dimensional electron gas with very high carrier mo-bility is used for charge transport, are especially suitablefor use at very high frequencies (microwave frequencies;several GHz).FETs are further divided into depletion-mode andenhancement-mode types, depending on whether thechannel is turned on or off with zero gate-to-source volt-age. For enhancement mode, the channel is off at zerobias, and a gate potential can “enhance” the conduction.For the depletion mode, the channel is on at zero bias, anda gate potential (of the opposite polarity) can “deplete”the channel, reducing conduction. For either mode, amore positive gate voltage corresponds to a higher currentfor n-channel devices and a lower current for p-channeldevices. Nearly all JFETs are depletion-mode becausethe diode junctions would forward bias and conduct ifthey were enhancement-mode devices; most IGFETs areenhancement-mode types.

4.5.3 Usage of bipolar and field-effecttransistors

The bipolar junction transistor (BJT) was the most com-monly used transistor in the 1960s and 70s. Even afterMOSFETs became widely available, the BJT remainedthe transistor of choice for many analog circuits such asamplifiers because of their greater linearity and ease ofmanufacture. In integrated circuits, the desirable prop-erties of MOSFETs allowed them to capture nearly allmarket share for digital circuits. Discrete MOSFETs canbe applied in transistor applications, including analog cir-cuits, voltage regulators, amplifiers, power transmittersand motor drivers.

4.5.4 Other transistor types

For early bipolar transistors, see Bipolar junction tran-sistor#Bipolar transistors.

• Bipolar junction transistor

• Heterojunction bipolar transistor, up to sev-eral hundred GHz, common in modern ultra-fast and RF circuits

• Schottky transistor• Avalanche transistor• Darlington transistors are two BJTs connectedtogether to provide a high current gain equalto the product of the current gains of the twotransistors.

30 CHAPTER 4. TRANSISTOR

Transistor symbol drawn on Portuguese pavement in theUniversity of Aveiro.

• Insulated-gate bipolar transistors (IGBTs) usea medium-power IGFET, similarly connectedto a power BJT, to give a high inputimpedance. Power diodes are often connectedbetween certain terminals depending on spe-cific use. IGBTs are particularly suitable forheavy-duty industrial applications. The AseaBrown Boveri (ABB) 5SNA2400E170100 il-lustrates just how far power semiconduc-tor technology has advanced.[40] Intended forthree-phase power supplies, this device housesthree n–p–n IGBTs in a case measuring 38 by140 by 190 mm and weighing 1.5 kg. EachIGBT is rated at 1,700 volts and can handle2,400 amperes.

• Photo transistor• Multiple-emitter transistor, used in transistor–transistor logic

• Multiple-base transistor, used to amplify very-low-level signals in noisy environments such asthe pickup of a record player or radio frontends. Effectively, it is a very large numberof transistors in parallel where, at the output,the signal is added constructively, but randomnoise is added only stochastically.[41]

• Field-effect transistor

• Carbon nanotube field-effect transistor (CN-FET), where the channel material is replacedby a carbon nanotube.

• JFET, where the gate is insulated by a reverse-biased p–n junction

• MESFET, similar to JFET with a Schottkyjunction instead of a p–n junction• High-electron-mobility transistor(HEMT, HFET, MODFET)

• MOSFET, where the gate is insulated by ashallow layer of insulator

• Inverted-T field-effect transistor (ITFET)• FinFET, source/drain region shapes fins on thesilicon surface.

• FREDFET, fast-reverse epitaxial diode field-effect transistor

• Thin-film transistor, in LCDs.• Organic field-effect transistor (OFET), inwhich the semiconductor is an organic com-pound

• Ballistic transistor• Floating-gate transistor, for non-volatile stor-age.

• FETs used to sense environment• Ion-sensitive field effect transistor (IF-SET), to measure ion concentrations insolution.

• EOSFET, electrolyte-oxide-semiconductor field-effect transistor(Neurochip)

• DNAFET, deoxyribonucleic acid field-effect transistor

• Tunnel field-effect transistor. TFETs switch bymodulating quantum tunnelling through a barrier.

• Diffusion transistor, formed by diffusing dopantsinto semiconductor substrate; can be both BJT andFET

• Unijunction transistors can be used as simple pulsegenerators. They comprise a main body of either P-type or N-type semiconductor with ohmic contactsat each end (terminals Base1 and Base2). A junctionwith the opposite semiconductor type is formed ata point along the length of the body for the thirdterminal (Emitter).

• Single-electron transistors (SET) consist of a gate is-land between two tunneling junctions. The tunnel-ing current is controlled by a voltage applied to thegate through a capacitor.[42]

• Nanofluidic transistor, controls the movementof ions through sub-microscopic, water-filledchannels.[43]

• Multigate devices

• Tetrode transistor• Pentode transistor• Trigate transistors (Prototype by Intel)• Dual-gate FETs have a single channel withtwo gates in cascode; a configuration opti-mized for high-frequency amplifiers, mixers,and oscillators.

4.6. PART NUMBERING STANDARDS / SPECIFICATIONS 31

• Junctionless nanowire transistor (JNT), uses a sim-ple nanowire of silicon surrounded by an electricallyisolated “wedding ring” that acts to gate the flow ofelectrons through the wire.

• Vacuum-channel transistor: In 2012, NASA and theNational Nanofab Center in South Korea were re-ported to have built a prototype vacuum-channeltransistor in only 150 nanometers in size, can bemanufactured cheaply using standard silicon semi-conductor processing, can operate at high speedseven in hostile environments, and could consumejust as much power as a standard transistor.[44]

• Organic electrochemical transistor

4.6 Part numbering standards /specifications

The types of some transistors can be parsed from the partnumber. There are three major semiconductor namingstandards; in each the alphanumeric prefix provides cluesto type of the device.

4.6.1 Japanese Industrial Standard (JIS)

The JIS-C-7012 specification for transistor part numbersstarts with “2S”,[45] e.g. 2SD965, but sometimes the “2S”prefix is not marked on the package – a 2SD965 mightonly be marked “D965"; a 2SC1815 might be listed bya supplier as simply “C1815”. This series sometimes hassuffixes (such as “R”, “O”, “BL”... standing for “Red”,“Orange”, “Blue” etc.) to denote variants, such as tighterhFE (gain) groupings.

4.6.2 European Electronic ComponentManufacturers Association (EECA)

The Pro Electron standard, the European ElectronicComponent Manufacturers Association part numberingscheme, begins with two letters: the first gives the semi-conductor type (A for germanium, B for silicon, and Cfor materials like GaAs); the second letter denotes theintended use (A for diode, C for general-purpose tran-sistor, etc.). A 3-digit sequence number (or one letterthen 2 digits, for industrial types) follows. With early de-vices this indicated the case type. Suffixes may be used,with a letter (e.g. “C” often means high hFE, such as in:BC549C[46]) or other codes may follow to show gain (e.g.BC327-25) or voltage rating (e.g. BUK854-800A[47]).The more common prefixes are:

4.6.3 Joint Electron Devices EngineeringCouncil (JEDEC)

The JEDEC EIA370 transistor device numbers usuallystart with “2N”, indicating a three-terminal device (dual-gate field-effect transistors are four-terminal devices, sobegin with 3N), then a 2, 3 or 4-digit sequential num-ber with no significance as to device properties (althoughearly devices with low numbers tend to be germanium).For example 2N3055 is a silicon n–p–n power transistor,2N1301 is a p–n–p germanium switching transistor. Aletter suffix (such as “A”) is sometimes used to indicate anewer variant, but rarely gain groupings.

4.6.4 Proprietary

Manufacturers of devices may have their own proprietarynumbering system, for example CK722. Since devicesare second-sourced, a manufacturer’s prefix (like “MPF”in MPF102, which originally would denote a MotorolaFET) now is an unreliable indicator of who made thedevice. Some proprietary naming schemes adopt partsof other naming schemes, for example a PN2222A is a(possibly Fairchild Semiconductor) 2N2222A in a plas-tic case (but a PN108 is a plastic version of a BC108, nota 2N108, while the PN100 is unrelated to other xx100devices).Military part numbers sometimes are assigned their owncodes, such as the British Military CV Naming System.Manufacturers buying large numbers of similar parts mayhave them supplied with “house numbers”, identifyinga particular purchasing specification and not necessar-ily a device with a standardized registered number. Forexample, an HP part 1854,0053 is a (JEDEC) 2N2218transistor[48][49] which is also assigned the CV number:CV7763[50]

4.6.5 Naming problems

With so many independent naming schemes, and the ab-breviation of part numbers when printed on the devices,ambiguity sometimes occurs. For example two differentdevices may be marked “J176” (one the J176 low-powerJunction FET, the other the higher-powered MOSFET2SJ176).As older “through-hole” transistors are given surface-mount packaged counterparts, they tend to be assignedmany different part numbers because manufacturers havetheir own systems to cope with the variety in pinout ar-rangements and options for dual or matched n–p–n+p–n–p devices in one pack. So even when the original device(such as a 2N3904) may have been assigned by a stan-dards authority, and well known by engineers over theyears, the new versions are far from standardized in theirnaming.

32 CHAPTER 4. TRANSISTOR

4.7 Construction

4.7.1 Semiconductor material

The first BJTs were made from germanium (Ge). Silicon(Si) types currently predominate but certain advancedmicrowave and high-performance versions now employthe compound semiconductor material gallium arsenide(GaAs) and the semiconductor alloy silicon germanium(SiGe). Single element semiconductor material (Ge andSi) is described as elemental.Rough parameters for the most common semiconductormaterials used to make transistors are given in the table tothe right; these parameters will vary with increase in tem-perature, electric field, impurity level, strain, and sundryother factors.The junction forward voltage is the voltage applied to theemitter–base junction of a BJT in order to make the baseconduct a specified current. The current increases ex-ponentially as the junction forward voltage is increased.The values given in the table are typical for a current of1 mA (the same values apply to semiconductor diodes).The lower the junction forward voltage the better, as thismeans that less power is required to “drive” the transis-tor. The junction forward voltage for a given current de-creases with increase in temperature. For a typical siliconjunction the change is −2.1 mV/°C.[51] In some circuitsspecial compensating elements (sensistors) must be usedto compensate for such changes.The density of mobile carriers in the channel of a MOS-FET is a function of the electric field forming the chan-nel and of various other phenomena such as the impuritylevel in the channel. Some impurities, called dopants, areintroduced deliberately in making a MOSFET, to controlthe MOSFET electrical behavior.The electron mobility and hole mobility columns show theaverage speed that electrons and holes diffuse through thesemiconductor material with an electric field of 1 volt permeter applied across the material. In general, the higherthe electron mobility the faster the transistor can operate.The table indicates that Ge is a better material than Si inthis respect. However, Ge has four major shortcomingscompared to silicon and gallium arsenide:

• Its maximum temperature is limited;

• it has relatively high leakage current;

• it cannot withstand high voltages;

• it is less suitable for fabricating integrated circuits.

Because the electron mobility is higher than the hole mo-bility for all semiconductor materials, a given bipolar n–p–n transistor tends to be swifter than an equivalent p–n–p transistor. GaAs has the highest electron mobility ofthe three semiconductors. It is for this reason that GaAs

is used in high-frequency applications. A relatively re-cent FET development, the high-electron-mobility tran-sistor (HEMT), has a heterostructure (junction betweendifferent semiconductor materials) of aluminium gal-lium arsenide (AlGaAs)-gallium arsenide (GaAs) whichhas twice the electron mobility of a GaAs-metal barrierjunction. Because of their high speed and low noise,HEMTs are used in satellite receivers working at frequen-cies around 12 GHz. HEMTs based on gallium nitrideand aluminium gallium nitride (AlGaN/GaN HEMTs)provide a still higher electron mobility and are being de-veloped for various applications.Max. junction temperature values represent a crosssection taken from various manufacturers’ data sheets.This temperature should not be exceeded or the transistormay be damaged.Al–Si junction refers to the high-speed (aluminum–silicon) metal–semiconductor barrier diode, commonlyknown as a Schottky diode. This is included in the ta-ble because some silicon power IGFETs have a parasiticreverse Schottky diode formed between the source anddrain as part of the fabrication process. This diode canbe a nuisance, but sometimes it is used in the circuit.

4.7.2 Packaging

See also: Semiconductor package and Chip carrierDiscrete transistors are individually packaged transis-

Assorted discrete transistors

tors. Transistors come in many different semiconductorpackages (see image). The two main categories arethrough-hole (or leaded), and surface-mount, also knownas surface-mount device (SMD). The ball grid array(BGA) is the latest surface-mount package (currently onlyfor large integrated circuits). It has solder “balls” on theunderside in place of leads. Because they are smaller andhave shorter interconnections, SMDs have better high-frequency characteristics but lower power rating.Transistor packages are made of glass, metal, ceramic, orplastic. The package often dictates the power rating andfrequency characteristics. Power transistors have largerpackages that can be clamped to heat sinks for enhancedcooling. Additionally, most power transistors have thecollector or drain physically connected to the metal en-

4.10. REFERENCES 33

closure. At the other extreme, some surface-mount mi-crowave transistors are as small as grains of sand.Often a given transistor type is available in several pack-ages. Transistor packages are mainly standardized, butthe assignment of a transistor’s functions to the terminalsis not: other transistor types can assign other functionsto the package’s terminals. Even for the same transis-tor type the terminal assignment can vary (normally indi-cated by a suffix letter to the part number, q.e. BC212Land BC212K).Nowadays most transistors come in a wide range of SMTpackages, in comparison the list of available through-holepackages is relatively small, here is a short list of themost common through-hole transistors packages in alpha-betical order: ATV, E-line, MRT, HRT, SC-43, SC-72,TO-3, TO-18, TO-39, TO-92, TO-126, TO220, TO247,TO251, TO262, ZTX851

Flexible transistors

Researchers have made several kinds of flexible tran-sistors, including organic field-effect transistors.[52][53][54]Flexible transistors are useful in some kinds of flexibledisplays and other flexible electronics.

4.8 See also• Band gap

• Digital electronics

• Moore’s law

• Semiconductor device modeling

• Transistor count

• Transistor model

• Transresistance

• Very-large-scale integration

4.9 Directory of external websiteswith datasheets

• 2N3904/2N3906, BC182/BC212 andBC546/BC556: Ubiquitous, BJT, general-purpose,low-power, complementary pairs. They have plasticcases and cost roughly ten cents U.S. in smallquantities, making them popular with hobbyists.

• AF107: Germanium, 0.5 watt, 250 MHz p–n–pBJT.

• BFP183: Low-power, 8 GHz microwave n–p–nBJT.

• LM394: “supermatch pair”, with two n–p–n BJTson a single substrate.

• 2N2219A/2N2905A: BJT, general purpose,medium power, complementary pair. With metalcases they are rated at about one watt.

• 2N3055/MJ2955: For years, the n–p–n 2N3055 hasbeen the “standard” power transistor. Its comple-ment, the p–n–p MJ2955 arrived later. These 1MHz, 15 A, 60 V, 115 W BJTs are used in audio-power amplifiers, power supplies, and control.

• 2SC3281/2SA1302: Made by Toshiba, these BJTshave low-distortion characteristics and are used inhigh-power audio amplifiers. They have been widelycounterfeited .

• BU508: n–p–n, 1500 V power BJT. Designed fortelevision horizontal deflection, its high voltage ca-pability also makes it suitable for use in ignition sys-tems.

• MJ11012/MJ11015: 30 A, 120 V, 200 W, highpower Darlington complementary pair BJTs. Usedin audio amplifiers, control, and power switching.

• 2N5457/2N5460: JFET (depletion mode), generalpurpose, low power, complementary pair.

• BSP296/BSP171: IGFET (enhancement mode),medium power, near complementary pair. Used forlogic level conversion and driving power transistorsin amplifiers.

• IRF3710/IRF5210: IGFET (enhancement mode),40 A, 100 V, 200 W, near complementary pair.For high-power amplifiers and power switches, es-pecially in automobiles.

4.10 References[1] "Milestones:Invention of the First Transistor at Bell Tele-

phone Laboratories, Inc., 1947”. IEEE Global HistoryNetwork. IEEE. Retrieved 7 December 2014.

[2] “TheNobel Prize in Physics 1956”. Nobelprize.org. NobelMedia AB. Retrieved 7 December 2014.

[3] Vardalas, John, Twists and Turns in the Development ofthe Transistor IEEE-USA Today’s Engineer, May 2003.

[4] Lilienfeld, Julius Edgar, “Method and apparatus for con-trolling electric current” U.S. Patent 1,745,175 January28, 1930 (filed in Canada 1925-10-22, in US 1926-10-08).

[5] “Method And Apparatus For Controlling Electric Cur-rents”. United States Patent and Trademark Office.

[6] “Amplifier For Electric Currents”. United States Patentand Trademark Office.

34 CHAPTER 4. TRANSISTOR

[7] “Device For Controlling Electric Current”. United StatesPatent and Trademark Office.

[8] “Twists and Turns in the Development of the Transistor”.Institute of Electrical and Electronics Engineers, Inc.

[9] Heil, Oskar, “Improvements in or relating to electricalamplifiers and other control arrangements and devices”,Patent No. GB439457, European Patent Office, filed inGreat Britain 1934-03-02, published December 6, 1935(originally filed in Germany 1934-03-02).

[10] “November 17 – December 23, 1947: Invention of theFirst Transistor”. American Physical Society.

[11] Bell Laboratories (1983). S. Millman, ed. A History ofEngineering and Science in the Bell System, Physical Sci-ence (1925-1980). AT&T Bell Laboratories. p. 102.

[12] David Bodanis (2005). Electric Universe. Crown Publish-ers, New York. ISBN 0-7394-5670-9.

[13] “transistor”. American Heritage Dictionary (3rd ed.).Boston: Houghton Mifflin. 1992.

[14] “The Nobel Prize in Physics 1956”.

[15] “1948 - The European Transistor Invention”. ComputerHistory Museum.

[16] W.E. Bradley (December 1953). “The Surface-BarrierTransistor: Part I-Principles of the Surface-Barrier Tran-sistor”. Proceedings of the IRE 41 (12): 1702–1706.doi:10.1109/JRPROC.1953.274351.

[17] Wall Street Journal, December 4, 1953, page 4, Article“Philco Claims Its Transistor Outperforms Others Now InUse”

[18] Electronics magazine, January 1954, Article “Electro-plated Transistors Announced”

[19] Wall Street Journal, “Chrysler Promises Car Radio WithTransistors Instead of Tubes in '56”, April 28, 1955, page1

[20] Los Angeles Times, May 8, 1955, page A20, Article:“Chrysler Announces New Transistor Radio”

[21] Philco TechRep Division Bulletin, May–June 1955, Vol-ume 5 Number 3, page 28

[22] Saul Rosen (Jun 1991). PHILCO: Some Recollectionsof the PHILCO TRANSAC S-2000 (Computer ScienceTechnical Reports / Purdue e-Pubs) (CSD-TR-91-051).Purdue University. Here: page 2

[23] IEEE Spectrum, The Lost History of the Transis-tor, Author: Michael Riordan, May 2004, pp 48-49| url=http://spectrum.ieee.org/biomedical/devices/the-lost-history-of-the-transistor

[24] J. Chelikowski, “Introduction: Silicon in all its Forms”,Silicon: evolution and future of a technology (Editors: P.Siffert, E. F. Krimmel), p.1, Springer, 2004 ISBN 3-540-40546-1.

[25] Grant McFarland, Microprocessor design: a practicalguide from design planning to manufacturing, p.10,McGraw-Hill Professional, 2006 ISBN 0-07-145951-0.

[26] W. Heywang, K. H. Zaininger, “Silicon: The Semi-conductor Material”, Silicon: evolution and future of atechnology (Editors: P. Siffert, E. F. Krimmel), p.36,Springer, 2004 ISBN 3-540-40546-1.

[27] RobertW. Price (2004). Roadmap to Entrepreneurial Suc-cess. AMACOMDivAmericanMgmtAssn. p. 42. ISBN978-0-8144-7190-6.

[28] "Milestones:Invention of the First Transistor at Bell Tele-phone Laboratories, Inc., 1947”. IEEE Global HistoryNetwork. IEEE. Retrieved August 3, 2011.

[29] FETs/MOSFETs: Smaller apps push up surface-mountsupply

[30] "ATI and Nvidia face off.” October 7, 2009. Retrieved onFebruary 2, 2011.

[31] Jim Turley. “The Two Percent Solution” 2002.

[32] Kaplan, Daniel (2003). Hands-On Electronics. NewYork:Cambridge University Press. pp. 47–54, 60–61. ISBN978-0-511-07668-8.

[33] apart from a small value due to leakage currents

[34] John Keane and Chris H. Kim, “Transistor Aging,” IEEESpectrum (web feature), April 25, 2011.

[35] van der Veen, M. (2005). “Universal system and outputtransformer for valve amplifiers” (PDF). 118th AES Con-vention, Barcelona, Spain.

[36] “Transistor Example”. 071003 bcae1.com

[37] Streetman, Ben (1992). Solid State Electronic Devices.Englewood Cliffs, NJ: Prentice-Hall. pp. 301–305. ISBN0-13-822023-9.

[38] Horowitz, Paul; Winfield Hill (1989). The Art of Electron-ics (2nd ed.). Cambridge University Press. p. 115. ISBN0-521-37095-7.

[39] W. M. C. Sansen (2006). Analog design essentials. NewYork ; Berlin: Springer. p. §0152, p. 28. ISBN 0-387-25746-2.

[40] “IGBT Module 5SNA 2400E170100” (PDF). RetrievedJune 30, 2012.

[41] Zhong Yuan Chang, Willy M. C. Sansen, Low-NoiseWide-Band Amplifiers in Bipolar and CMOS Technologies,page 31, Springer, 1991 ISBN 0792390962.

[42] “Single Electron Transistors”. Snow.stanford.edu. Re-trieved June 30, 2012.

[43] Sanders, Robert (June 28, 2005). “Nanofluidic transistor,the basis of future chemical processors”. Berkeley.edu.Retrieved June 30, 2012.

[44] The return of the vacuum tube?

[45] “Clive TEC Transistors Japanese Industrial Standards”.Clivetec.0catch.com. Retrieved June 30, 2012.

[46] “Datasheet for BC549, with A,B and C gain groupings”(PDF). Retrieved June 30, 2012.

4.12. EXTERNAL LINKS 35

[47] “Datasheet for BUK854-800A (800volt IGBT)" (PDF).Retrieved June 30, 2012.

[48] “Richard Freeman’s HP Part numbers Crossreference”.Hpmuseum.org. Retrieved June 30, 2012.

[49] Transistor–Diode Cross Reference – H.P. Part Numbersto JEDEC (pdf)

[50] “CVDevice Cross-reference byAndy Lake”. Qsl.net. Re-trieved June 30, 2012.

[51] A.S. Sedra and K.C. Smith (2004). Microelectronic cir-cuits (Fifth ed.). New York: Oxford University Press. pp.397 and Figure 5.17. ISBN 0-19-514251-9.

[52] Jhonathan P. Rojas, Galo A. Torres Sevilla, and Muham-mad M. Hussain. “Can We Build a Truly High Perfor-mance Computer Which is Flexible and Transparent?".

[53] Kan Zhang, Jung-Hun Seo1, Weidong Zhou and Zhen-qiang Ma. “Fast flexible electronics using transferrablesilicon nanomembranes”. 2012.

[54] Lisa Zyga. “Carbon nanotube transistors could lead to in-expensive, flexible electronics”. 2011.

4.11 Further reading• Amos SW&JamesMR (1999). Principles of Tran-sistor Circuits. Butterworth-Heinemann. ISBN 0-7506-4427-3.

• Bacon, W. Stevenson (1968). “The Transistor’s20th Anniversary: How Germanium And A Bit ofWire Changed The World”. Bonnier Corp.: Popu-lar Science, retrieved from Google Books 2009-03-22 (Bonnier Corporation) 192 (6): 80–84. ISSN0161-7370.

• Horowitz, Paul & Hill, Winfield (1989). The Art ofElectronics. Cambridge University Press. ISBN 0-521-37095-7.

• Riordan, Michael & Hoddeson, Lillian (1998).Crystal Fire. W.W Norton & Company Limited.ISBN 0-393-31851-6. The invention of the transis-tor & the birth of the information age

• Warnes, Lionel (1998). Analogue and Digital Elec-tronics. Macmillan Press Ltd. ISBN 0-333-65820-5.

• “Herbert F. Mataré, An Inventor of the Transistorhas his moment”. The New York Times. February24, 2003.

• Michael Riordan (2005). “How Europe Missedthe Transistor”. IEEE Spectrum 42 (11): 52–57.doi:10.1109/MSPEC.2005.1526906.

• C. D. Renmore (1980). Silicon Chips and You.ISBN 0-8253-0022-3.

• Wiley-IEEE Press. Complete Guide to Semiconduc-tor Devices, 2nd Edition.

4.12 External links• The CK722Museum. Website devoted to the “classic”hobbyist germanium transistor

• The Transistor Educational content from Nobel-prize.org

• BBC: Building the digital age photo history of tran-sistors

• The Bell Systems Memorial on Transistors

• IEEE Global History Network, The Transistor andPortable Electronics. All about the history of tran-sistors and integrated circuits.

• Transistorized. Historical and technical informationfrom the Public Broadcasting Service

• This Month in Physics History: November 17 to De-cember 23, 1947: Invention of the First Transistor.From the American Physical Society

• 50 Years of the Transistor. From Science Friday, De-cember 12, 1997

Pinouts

• Common transistor pinouts

Datasheets

• Charts showing many characteristics and links tomost datasheets for 2N, 2SA, 2SB. 2SC, 2SD, 2SH-K, and other numbers.

• Discrete Databook (Historical 1978), NationalSemiconductor (now Texas Instruments)

• Discrete Databook (Historical 1982), SGS (nowSTMicroelectronics)

• Small-Signal Transistor Databook (Historical1984), Motorola

• Discrete Databook (Historical 1985), Fairchild

Chapter 5

Capacitor

This article is about the electronic component. For thephysical phenomenon, see capacitance. For an overviewof various kinds of capacitors, see types of capacitor.“Capacitive” redirects here. For the term used when re-ferring to touchscreens, see capacitive sensing.

A capacitor (originally known as a condenser) is a

Miniature low-voltage capacitors (next to a cm ruler)

A typical electrolytic capacitor

passive two-terminal electrical component used to storeenergy electrostatically in an electric field. The forms ofpractical capacitors vary widely, but all contain at leasttwo electrical conductors (plates) separated by a dielectric(i.e. insulator). The conductors can be thin films, foils

4 electrolytic capacitors of different voltages and capacitance

Solid electrolyte, resin-dipped 10 μF 35 V tantalum capacitors.The + sign indicates the positive lead.

or sintered beads of metal or conductive electrolyte, etc.The nonconducting dielectric acts to increase the capaci-tor’s charge capacity. A dielectric can be glass, ceramic,plastic film, air, vacuum, paper, mica, oxide layer etc.Capacitors are widely used as parts of electrical circuitsin many common electrical devices. Unlike a resistor, anideal capacitor does not dissipate energy. Instead, a ca-pacitor stores energy in the form of an electrostatic fieldbetween its plates.When there is a potential difference across the conductors(e.g., when a capacitor is attached across a battery), an

36

5.2. THEORY OF OPERATION 37

electric field develops across the dielectric, causing posi-tive charge +Q to collect on one plate and negative charge−Q to collect on the other plate. If a battery has beenattached to a capacitor for a sufficient amount of time,no current can flow through the capacitor. However, ifa time-varying voltage is applied across the leads of thecapacitor, a displacement current can flow.An ideal capacitor is characterized by a single constantvalue for its capacitance. Capacitance is expressed as theratio of the electric charge Q on each conductor to thepotential difference V between them. The SI unit of ca-pacitance is the farad (F), which is equal to one coulombper volt (1 C/V). Typical capacitance values range fromabout 1 pF (10−12 F) to about 1 mF (10−3 F).The capacitance is greater when there is a narrower sepa-ration between conductors and when the conductors havea larger surface area. In practice, the dielectric betweenthe plates passes a small amount of leakage current andalso has an electric field strength limit, known as thebreakdown voltage. The conductors and leads introducean undesired inductance and resistance.Capacitors are widely used in electronic circuits forblocking direct current while allowing alternating currentto pass. In analog filter networks, they smooth the outputof power supplies. In resonant circuits they tune radiosto particular frequencies. In electric power transmissionsystems, they stabilize voltage and power flow.[1]

5.1 History

In October 1745, Ewald Georg von Kleist of Pomerania,Germany, found that charge could be stored by connect-ing a high-voltage electrostatic generator by a wire to avolume of water in a hand-held glass jar.[2] Von Kleist’shand and the water acted as conductors, and the jar as adielectric (although details of the mechanism were incor-rectly identified at the time). Von Kleist found that touch-ing the wire resulted in a powerful spark, much morepainful than that obtained from an electrostatic machine.The following year, the Dutch physicist Pieter van Muss-chenbroek invented a similar capacitor, which was namedthe Leyden jar, after the University of Leiden where heworked.[3] He also was impressed by the power of theshock he received, writing, “I would not take a secondshock for the kingdom of France.”[4]

Daniel Gralath was the first to combine several jars inparallel into a “battery” to increase the charge storage ca-pacity. Benjamin Franklin investigated the Leyden jarand came to the conclusion that the charge was stored onthe glass, not in the water as others had assumed. He alsoadopted the term “battery”,[5][6] (denoting the increasingof power with a row of similar units as in a battery of can-non), subsequently applied to clusters of electrochemicalcells.[7] Leyden jars were later made by coating the insideand outside of jars with metal foil, leaving a space at the

Battery of four Leyden jars in Museum Boerhaave, Leiden, theNetherlands

mouth to prevent arcing between the foils. The earliestunit of capacitance was the jar, equivalent to about 1.11nanofarads.[8]

Leyden jars ormore powerful devices employing flat glassplates alternating with foil conductors were used exclu-sively up until about 1900, when the invention of wireless(radio) created a demand for standard capacitors, andthe steady move to higher frequencies required capacitorswith lower inductance. More compact constructionmeth-ods began to be used, such as a flexible dielectric sheet(like oiled paper) sandwiched between sheets of metalfoil, rolled or folded into a small package.Early capacitors were also known as condensers, a termthat is still occasionally used today, particularly in highpower applications, like automotive systems. The termwas first used for this purpose by Alessandro Volta in1782, with reference to the device’s ability to store ahigher density of electric charge than a normal isolatedconductor.[9]

5.2 Theory of operation

Main article: Capacitance

38 CHAPTER 5. CAPACITOR

Plate separation d

Electricfield E

Charge+Q -Q

Platearea A

- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +- + - +

dielectric

Charge separation in a parallel-plate capacitor causes an internalelectric field. A dielectric (orange) reduces the field and increasesthe capacitance.

A simple demonstration of a parallel-plate capacitor

5.2.1 Overview

A capacitor consists of two conductors separated by anon-conductive region.[10] The non-conductive region iscalled the dielectric. In simpler terms, the dielectric isjust an electrical insulator. Examples of dielectric mediaare glass, air, paper, vacuum, and even a semiconductordepletion region chemically identical to the conductors.A capacitor is assumed to be self-contained and isolated,with no net electric charge and no influence from any ex-ternal electric field. The conductors thus hold equal andopposite charges on their facing surfaces,[11] and the di-electric develops an electric field. In SI units, a capaci-tance of one farad means that one coulomb of charge oneach conductor causes a voltage of one volt across thedevice.[12]

An ideal capacitor is wholly characterized by a constantcapacitance C, defined as the ratio of charge ±Q on eachconductor to the voltage V between them:[10]

C =Q

V

Because the conductors (or plates) are close together, theopposite charges on the conductors attract one anotherdue to their electric fields, allowing the capacitor to storemore charge for a given voltage than if the conductorswere separated, giving the capacitor a large capacitance.Sometimes charge build-up affects the capacitor mechan-ically, causing its capacitance to vary. In this case, capac-itance is defined in terms of incremental changes:

C =dQdV

5.2.2 Hydraulic analogy

In the hydraulic analogy, a capacitor is analogous to a rub-ber membrane sealed inside a pipe. This animation illustratesa membrane being repeatedly stretched and un-stretched by theflow of water, which is analogous to a capacitor being repeatedlycharged and discharged by the flow of charge.

In the hydraulic analogy, charge carriers flowing througha wire are analogous to water flowing through a pipe. Acapacitor is like a rubber membrane sealed inside a pipe.Water molecules cannot pass through the membrane, butsome water can move by stretching the membrane. Theanalogy clarifies a few aspects of capacitors:

• The current alters the charge on a capacitor, just asthe flow of water changes the position of the mem-brane. More specifically, the effect of an electriccurrent is to increase the charge of one plate of thecapacitor, and decrease the charge of the other plateby an equal amount. This is just as when waterflow moves the rubber membrane, it increases theamount of water on one side of the membrane, anddecreases the amount of water on the other side.

• The more a capacitor is charged, the larger its voltagedrop; i.e., the more it “pushes back” against thecharging current. This is analogous to the factthat the more a membrane is stretched, the more itpushes back on the water.

• Charge can flow “through” a capacitor even thoughno individual electron can get from one side to the

5.2. THEORY OF OPERATION 39

other. This is analogous to the fact that water canflow through the pipe even though no water moleculecan pass through the rubber membrane. Of course,the flow cannot continue in the same direction for-ever; the capacitor will experience dielectric break-down, and analogously the membrane will eventu-ally break.

• The capacitance describes how much charge canbe stored on one plate of a capacitor for a given“push” (voltage drop). A very stretchy, flexiblemembrane corresponds to a higher capacitance thana stiff membrane.

• A charged-up capacitor is storing potential energy,analogously to a stretched membrane.

5.2.3 Energy of electric field

Work must be done by an external influence to “move”charge between the conductors in a capacitor. When theexternal influence is removed, the charge separation per-sists in the electric field and energy is stored to be releasedwhen the charge is allowed to return to its equilibriumposition. The work done in establishing the electric field,and hence the amount of energy stored, is[13]

W =

∫ Q

0

V (q)dq =

∫ Q

0

q

Cdq =

1

2

Q2

C=

1

2CV 2 =

1

2V Q

Here Q is the charge stored in the capacitor, V is the volt-age across the capacitor, and C is the capacitance.In the case of a fluctuating voltage V(t), the stored energyalso fluctuates and hence power must flow into or out ofthe capacitor. This power can be found by taking the timederivative of the stored energy:

P =dWdt =

ddt

(1

2CV 2

)= CV (t)

dVdt

5.2.4 Current–voltage relation

The current I(t) through any component in an electric cir-cuit is defined as the rate of flow of a charge Q(t) passingthrough it, but actual charges—electrons—cannot passthrough the dielectric layer of a capacitor. Rather, oneelectron accumulates on the negative plate for each onethat leaves the positive plate, resulting in an electron de-pletion and consequent positive charge on one electrodethat is equal and opposite to the accumulated negativecharge on the other. Thus the charge on the electrodesis equal to the integral of the current as well as propor-tional to the voltage, as discussed above. As with anyantiderivative, a constant of integration is added to repre-sent the initial voltage V(t0). This is the integral form ofthe capacitor equation:[14]

V (t) =Q(t)

C=

1

C

∫ t

t0

I(τ)dτ + V (t0)

Taking the derivative of this and multiplying by C yieldsthe derivative form:[15]

I(t) =dQ(t)

dt = CdV (t)

dtThe dual of the capacitor is the inductor, which stores en-ergy in a magnetic field rather than an electric field. Itscurrent-voltage relation is obtained by exchanging currentand voltage in the capacitor equations and replacing Cwith the inductance L.

5.2.5 DC circuits

See also: RC circuitA series circuit containing only a resistor, a capacitor, a

V

R

C0VC

A simple resistor-capacitor circuit demonstrates charging of a ca-pacitor.

switch and a constant DC source of voltage V0 is knownas a charging circuit.[16] If the capacitor is initially un-charged while the switch is open, and the switch is closedat t0, it follows from Kirchhoff’s voltage law that

V0 = vresistor(t) + vcapacitor(t) = i(t)R+1

C

∫ t

t0

i(τ)dτ

Taking the derivative and multiplying by C, gives a first-order differential equation:

RCdi(t)dt + i(t) = 0

At t = 0, the voltage across the capacitor is zero and thevoltage across the resistor isV0. The initial current is thenI(0) =V0/R. With this assumption, solving the differentialequation yields

I(t) =V0

Re−

tτ0

V (t) = V0

(1− e−

tτ0

)

40 CHAPTER 5. CAPACITOR

where τ0 = RC is the time constant of the system. As thecapacitor reaches equilibriumwith the source voltage, thevoltages across the resistor and the current through the en-tire circuit decay exponentially. The case of discharging acharged capacitor likewise demonstrates exponential de-cay, but with the initial capacitor voltage replacing V0

and the final voltage being zero.

5.2.6 AC circuits

See also: reactance (electronics) and electrical impedance§ Deriving the device-specific impedances

Impedance, the vector sum of reactance and resistance,describes the phase difference and the ratio of amplitudesbetween sinusoidally varying voltage and sinusoidallyvarying current at a given frequency. Fourier analysisallows any signal to be constructed from a spectrum offrequencies, whence the circuit’s reaction to the variousfrequencies may be found. The reactance and impedanceof a capacitor are respectively

X = − 1

ωC= − 1

2πfC

Z =1

jωC= − j

ωC= − j

2πfC

where j is the imaginary unit and ω is the angular fre-quency of the sinusoidal signal. The −j phase indicatesthat the AC voltage V = ZI lags the AC current by 90°:the positive current phase corresponds to increasing volt-age as the capacitor charges; zero current corresponds toinstantaneous constant voltage, etc.Impedance decreases with increasing capacitance and in-creasing frequency. This implies that a higher-frequencysignal or a larger capacitor results in a lower voltage am-plitude per current amplitude—an AC “short circuit” orAC coupling. Conversely, for very low frequencies, thereactance will be high, so that a capacitor is nearly anopen circuit in AC analysis—those frequencies have been“filtered out”.Capacitors are different from resistors and inductors inthat the impedance is inversely proportional to the defin-ing characteristic; i.e., capacitance.A capacitor connected to a sinusoidal voltage source willcause a displacement current to flow through it. In thecase that the voltage source is V0cos(ωt), the displace-ment current can be expressed as:

I = CdV

dt= −ωCV0 sin(ωt)

At sin(ωt) = −1, the capacitor has a maximum (or peak)current whereby I0 = ωCV0. The ratio of peak voltage topeak current is due to capacitive reactance (denoted XC).

XC = V0I0

= V0ωCV0

= 1ωC

XC approaches zero as ω approaches infinity. If XCapproaches 0, the capacitor resembles a short wire thatstrongly passes current at high frequencies. XC ap-proaches infinity as ω approaches zero. If XC approachesinfinity, the capacitor resembles an open circuit thatpoorly passes low frequencies.The current of the capacitor may be expressed in theform of cosines to better compare with the voltage of thesource:

I = −I0sin(ωt) = I0cos(ωt+ 90◦)

In this situation, the current is out of phase with the volt-age by +π/2 radians or +90 degrees (i.e., the current willlead the voltage by 90°).

5.2.7 Laplace circuit analysis (s-domain)

When using the Laplace transform in circuit analysis, theimpedance of an ideal capacitor with no initial charge isrepresented in the s domain by:

Z(s) =1

sC

where

• C is the capacitance, and

• s is the complex frequency.

5.2.8 Parallel-plate model

Conductive plates

Dielectric

dA

Dielectric is placed between two conducting plates, each of areaA and with a separation of d

The simplest capacitor consists of two parallel conduc-tive plates separated by a dielectric (such as air) with

5.2. THEORY OF OPERATION 41

permittivity ε . The model may also be used to makequalitative predictions for other device geometries. Theplates are considered to extend uniformly over an area Aand a charge density ±ρ = ±Q/A exists on their surface.Assuming that the width of the plates is much greater thantheir separation d, the electric field near the centre of thedevice will be uniform with the magnitude E = ρ/ε. Thevoltage is defined as the line integral of the electric fieldbetween the plates

V =

∫ d

0

E dz =

∫ d

0

ρ

εdz =

ρd

ε=

Qd

εA

Solving this for C = Q/V reveals that capacitance in-creases with area of the plates, and decreases as separa-tion between plates increases.

C =εA

d

The capacitance is therefore greatest in devices madefrom materials with a high permittivity, large plate area,and small distance between plates.A parallel plate capacitor can only store a finite amountof energy before dielectric breakdown occurs. The ca-pacitor’s dielectric material has a dielectric strength Uwhich sets the capacitor’s breakdown voltage at V = V= U d. The maximum energy that the capacitor can storeis therefore

E =1

2CV 2 =

1

2

εA

d(Udd)

2 =1

2εAdU2

d

We see that the maximum energy is a function of di-electric volume, permittivity, and dielectric strength perdistance. So increasing the plate area while decreasingthe separation between the plates while maintaining thesame volume has no change on the amount of energy thecapacitor can store. Care must be taken when increas-ing the plate separation so that the above assumption ofthe distance between plates being much smaller than thearea of the plates is still valid for these equations to beaccurate. In addition, these equations assume that theelectric field is entirely concentrated in the dielectric be-tween the plates. In reality there are fringing fields out-side the dielectric, for example between the sides of thecapacitor plates, which will increase the effective capac-itance of the capacitor. This could be seen as a form ofparasitic capacitance. For some simple capacitor geome-tries this additional capacitance term can be calculatedanalytically.[17] It becomes negligibly small when the ra-tio of plate area to separation is large.

5.2.9 Networks

See also: Series and parallel circuits

C2C1 Cn

Several capacitors in parallel

For capacitors in parallel Capacitors in a parallel con-figuration each have the same applied voltage. Theircapacitances add up. Charge is apportioned amongthem by size. Using the schematic diagram to visu-alize parallel plates, it is apparent that each capacitorcontributes to the total surface area.

Ceq = C1 + C2 + · · ·+ Cn

For capacitors in series

C2C1 Cn

Several capacitors in series

Connected in series, the schematic diagram re-veals that the separation distance, not the platearea, adds up. The capacitors each store instan-taneous charge build-up equal to that of everyother capacitor in the series. The total voltagedifference from end to end is apportioned toeach capacitor according to the inverse of itscapacitance. The entire series acts as a capac-itor smaller than any of its components.

1

Ceq=

1

C1+

1

C2+ · · ·+ 1

Cn

Capacitors are combined in series to achievea higher working voltage, for example forsmoothing a high voltage power supply. Thevoltage ratings, which are based on plate sep-aration, add up, if capacitance and leakagecurrents for each capacitor are identical. Insuch an application, on occasion, series strings

42 CHAPTER 5. CAPACITOR

are connected in parallel, forming a matrix.The goal is to maximize the energy storage ofthe network without overloading any capaci-tor. For high-energy storage with capacitors inseries, some safety considerations must be ap-plied to ensure one capacitor failing and leak-ing current will not apply too much voltage tothe other series capacitors.

Series connection is also sometimes usedto adapt polarized electrolytic capacitors forbipolar AC use. See electrolytic capaci-tor#Designing for reverse bias.

Voltage distribution in parallel-to-series networks.To model the distribution of voltages from a singlecharged capacitor (A) connected in parallel to achain of capacitors in series (Bn) :

(volts)Aeq = A

(1− 1

n+ 1

)(volts)B1..n =

A

n

(1− 1

n+ 1

)A−B = 0

Note: This is only correct if all capacitancevalues are equal.

The power transferred in this arrangement is:

P =1

R· 1

n+ 1Avolts (Afarads +Bfarads)

5.3 Non-ideal behavior

Capacitors deviate from the ideal capacitor equation in anumber of ways. Some of these, such as leakage currentand parasitic effects are linear, or can be assumed to belinear, and can be dealt with by adding virtual compo-nents to the equivalent circuit of the capacitor. The usualmethods of network analysis can then be applied. In othercases, such as with breakdown voltage, the effect is non-linear and normal (i.e., linear) network analysis cannot beused, the effect must be dealt with separately. There is yetanother group, which may be linear but invalidate the as-sumption in the analysis that capacitance is a constant.Such an example is temperature dependence. Finally,combined parasitic effects such as inherent inductance,resistance, or dielectric losses can exhibit non-uniformbehavior at variable frequencies of operation.

5.3.1 Breakdown voltage

Main article: Breakdown voltage

Above a particular electric field, known as the dielectricstrength Eds, the dielectric in a capacitor becomes con-ductive. The voltage at which this occurs is called thebreakdown voltage of the device, and is given by the prod-uct of the dielectric strength and the separation betweenthe conductors,[18]

Vbd = Edsd

Themaximum energy that can be stored safely in a capac-itor is limited by the breakdown voltage. Due to the scal-ing of capacitance and breakdown voltage with dielectricthickness, all capacitors made with a particular dielectrichave approximately equal maximum energy density, tothe extent that the dielectric dominates their volume.[19]

For air dielectric capacitors the breakdown field strengthis of the order 2 to 5 MV/m; for mica the breakdown is100 to 300MV/m; for oil, 15 to 25MV/m; it can bemuchless when other materials are used for the dielectric.[20]The dielectric is used in very thin layers and so abso-lute breakdown voltage of capacitors is limited. Typicalratings for capacitors used for general electronics appli-cations range from a few volts to 1 kV. As the voltageincreases, the dielectric must be thicker, making high-voltage capacitors larger per capacitance than those ratedfor lower voltages. The breakdown voltage is criticallyaffected by factors such as the geometry of the capaci-tor conductive parts; sharp edges or points increase theelectric field strength at that point and can lead to a localbreakdown. Once this starts to happen, the breakdownquickly tracks through the dielectric until it reaches theopposite plate, leaving carbon behind and causing a short(or relatively low resistance) circuit. The results can beexplosive as the short in the capacitor draws current fromthe surrounding circuitry and dissipates the energy.[21]

The usual breakdown route is that the field strength be-comes large enough to pull electrons in the dielectric fromtheir atoms thus causing conduction. Other scenarios arepossible, such as impurities in the dielectric, and, if thedielectric is of a crystalline nature, imperfections in thecrystal structure can result in an avalanche breakdown asseen in semi-conductor devices. Breakdown voltage isalso affected by pressure, humidity and temperature.[22]

5.3.2 Equivalent circuit

An ideal capacitor only stores and releases electrical en-ergy, without dissipating any. In reality, all capacitorshave imperfections within the capacitor’s material thatcreate resistance. This is specified as the equivalent se-ries resistance or ESR of a component. This adds a realcomponent to the impedance:

5.3. NON-IDEAL BEHAVIOR 43

Two different circuit models of a real capacitor

RC = Z +RESR =1

jωC+RESR

As frequency approaches infinity, the capacitiveimpedance (or reactance) approaches zero and the ESRbecomes significant. As the reactance becomes negli-gible, power dissipation approaches PRMS = VRMS²/RESR.Similarly to ESR, the capacitor’s leads add equivalent se-ries inductance or ESL to the component. This is usuallysignificant only at relatively high frequencies. As induc-tive reactance is positive and increases with frequency,above a certain frequency capacitance will be canceledby inductance. High-frequency engineering involves ac-counting for the inductance of all connections and com-ponents.If the conductors are separated by a material with a smallconductivity rather than a perfect dielectric, then a smallleakage current flows directly between them. The capaci-tor therefore has a finite parallel resistance,[12] and slowlydischarges over time (timemay vary greatly depending onthe capacitor material and quality).

5.3.3 Q factor

The quality factor (or Q) of a capacitor is the ratio ofits reactance to its resistance at a given frequency, and isa measure of its efficiency. The higher the Q factor ofthe capacitor, the closer it approaches the behavior of anideal, lossless, capacitor.The Q factor of a capacitor can be found through the fol-lowing formula:

Q =XC

RC=

1

ωCRC,

where ω is angular frequency, C is the capacitance, XC

is the capacitive reactance, andRC is the series resistanceof the capacitor.

5.3.4 Ripple current

Ripple current is the AC component of an applied source(often a switched-mode power supply) whose frequencymay be constant or varying. Ripple current causes heatto be generated within the capacitor due to the dielec-tric losses caused by the changing field strength togetherwith the current flow across the slightly resistive supplylines or the electrolyte in the capacitor. The equivalentseries resistance (ESR) is the amount of internal seriesresistance one would add to a perfect capacitor to modelthis. Some types of capacitors, primarily tantalum andaluminum electrolytic capacitors, as well as some film ca-pacitors have a specified rating value for maximum ripplecurrent.

• Tantalum electrolytic capacitors with solid man-ganese dioxide electrolyte are limited by ripple cur-rent and generally have the highest ESR ratings inthe capacitor family. Exceeding their ripple limitscan lead to shorts and burning parts.

• Aluminum electrolytic capacitors, the most com-mon type of electrolytic, suffer a shortening of lifeexpectancy at higher ripple currents. If ripple cur-rent exceeds the rated value of the capacitor, it tendsto result in explosive failure.

• Ceramic capacitors generally have no ripple currentlimitation and have some of the lowest ESR ratings.

• Film capacitors have very low ESR ratings but ex-ceeding rated ripple current may cause degradationfailures.

5.3.5 Capacitance instability

The capacitance of certain capacitors decreases as thecomponent ages. In ceramic capacitors, this is causedby degradation of the dielectric. The type of dielectric,ambient operating and storage temperatures are the mostsignificant aging factors, while the operating voltage hasa smaller effect. The aging process may be reversed byheating the component above the Curie point. Aging isfastest near the beginning of life of the component, andthe device stabilizes over time.[23] Electrolytic capacitorsage as the electrolyte evaporates. In contrast with ceramiccapacitors, this occurs towards the end of life of the com-ponent.

44 CHAPTER 5. CAPACITOR

Temperature dependence of capacitance is usually ex-pressed in parts per million (ppm) per °C. It can usuallybe taken as a broadly linear function but can be noticeablynon-linear at the temperature extremes. The temperaturecoefficient can be either positive or negative, sometimeseven amongst different samples of the same type. In otherwords, the spread in the range of temperature coefficientscan encompass zero. See the data sheet in the leakagecurrent section above for an example.Capacitors, especially ceramic capacitors, and older de-signs such as paper capacitors, can absorb sound wavesresulting in a microphonic effect. Vibration movesthe plates, causing the capacitance to vary, in turn in-ducing AC current. Some dielectrics also generatepiezoelectricity. The resulting interference is especiallyproblematic in audio applications, potentially causingfeedback or unintended recording. In the reverse micro-phonic effect, the varying electric field between the ca-pacitor plates exerts a physical force, moving them as aspeaker. This can generate audible sound, but drains en-ergy and stresses the dielectric and the electrolyte, if any.

5.3.6 Current and voltage reversal

Current reversal occurs when the current changes direc-tion. Voltage reversal is the change of polarity in a cir-cuit. Reversal is generally described as the percentageof the maximum rated voltage that reverses polarity. InDC circuits, this will usually be less than 100% (often inthe range of 0 to 90%), whereas AC circuits experience100% reversal.In DC circuits and pulsed circuits, current and voltage re-versal are affected by the damping of the system. Voltagereversal is encountered in RLC circuits that are under-damped. The current and voltage reverse direction, form-ing a harmonic oscillator between the inductance and ca-pacitance. The current and voltage will tend to oscillateand may reverse direction several times, with each peakbeing lower than the previous, until the system reachesan equilibrium. This is often referred to as ringing. Incomparison, critically damped or over-damped systemsusually do not experience a voltage reversal. Reversal isalso encountered in AC circuits, where the peak currentwill be equal in each direction.For maximum life, capacitors usually need to be able tohandle the maximum amount of reversal that a systemwill experience. An AC circuit will experience 100%voltage reversal, while under-dampedDC circuits will ex-perience less than 100%. Reversal creates excess elec-tric fields in the dielectric, causes excess heating of boththe dielectric and the conductors, and can dramaticallyshorten the life expectancy of the capacitor. Reversal rat-ings will often affect the design considerations for the ca-pacitor, from the choice of dielectric materials and volt-age ratings to the types of internal connections used.[24]

5.3.7 Dielectric absorption

Capacitors made with some types of dielectric materialshow "dielectric absorption" or “soakage”. On discharg-ing a capacitor and disconnecting it, after a short time itmay develop a voltage due to hysteresis in the dielectric.This effect can be objectionable in applications such asprecision sample and hold circuits.

5.3.8 Leakage

Leakage is equivalent to a resistor in parallel with the ca-pacitor. Constant exposure to heat can cause dielectricbreakdown and excessive leakage, a problem often seenin older vacuum tube circuits, particularly where oiledpaper and foil capacitors were used. In many vacuumtube circuits, interstage coupling capacitors are used toconduct a varying signal from the plate of one tube tothe grid circuit of the next stage. A leaky capacitor cancause the grid circuit voltage to be raised from its nor-mal bias setting, causing excessive current or signal dis-tortion in the downstream tube. In power amplifiers thiscan cause the plates to glow red, or current limiting resis-tors to overheat, even fail. Similar considerations apply tocomponent fabricated solid-state (transistor) amplifiers,but owing to lower heat production and the use of mod-ern polyester dielectric barriers this once-common prob-lem has become relatively rare.

5.3.9 Electrolytic failure from disuse

Aluminum electrolytic capacitors are conditioned whenmanufactured by applying a voltage sufficient to initiatethe proper internal chemical state. This state is main-tained by regular use of the equipment. In former times,roughly 30 years ago, if a system using electrolytic capac-itors is unused for a long period of time it can lose its con-ditioning. Sometimes they fail with a short circuit whennext operated. For further information see Aluminumelectrolytic capacitor#Capacitor behavior after storage ordisuse

5.4 Capacitor types

Main article: Types of capacitor

Practical capacitors are available commercially in manydifferent forms. The type of internal dielectric, the struc-ture of the plates and the device packaging all stronglyaffect the characteristics of the capacitor, and its appli-cations.Values available range from very low (picofarad range;while arbitrarily low values are in principle possible, stray

5.4. CAPACITOR TYPES 45

(parasitic) capacitance in any circuit is the limiting factor)to about 5 kF supercapacitors.Above approximately 1 microfarad electrolytic capacitorsare usually used because of their small size and low costcompared with other types, unless their relatively poorstability, life and polarised nature make them unsuitable.Very high capacity supercapacitors use a porous carbon-based electrode material.

5.4.1 Dielectric materials

Capacitor materials. From left: multilayer ceramic, ceramic disc,multilayer polyester film, tubular ceramic, polystyrene, metalizedpolyester film, aluminum electrolytic. Major scale divisions arein centimetres.

Most types of capacitor include a dielectric spacer, whichincreases their capacitance. These dielectrics are mostoften insulators. However, low capacitance devices areavailable with a vacuum between their plates, which al-lows extremely high voltage operation and low losses.Variable capacitors with their plates open to the atmo-sphere were commonly used in radio tuning circuits.Later designs use polymer foil dielectric between themoving and stationary plates, with no significant air spacebetween them.In order to maximise the charge that a capacitor can hold,the dielectric material needs to have as high a permittivityas possible, while also having as high a breakdown voltageas possible.Several solid dielectrics are available, including paper,plastic, glass, mica and ceramic materials. Paper wasused extensively in older devices and offers relatively highvoltage performance. However, it is susceptible to wa-ter absorption, and has been largely replaced by plasticfilm capacitors. Plastics offer better stability and ageingperformance, which makes them useful in timer circuits,although they may be limited to low operating temper-atures and frequencies. Ceramic capacitors are gener-ally small, cheap and useful for high frequency applica-tions, although their capacitance varies strongly with volt-age and they age poorly. They are broadly categorizedas class 1 dielectrics, which have predictable variationof capacitance with temperature or class 2 dielectrics,which can operate at higher voltage. Glass and micacapacitors are extremely reliable, stable and tolerant tohigh temperatures and voltages, but are too expensivefor most mainstream applications. Electrolytic capaci-tors and supercapacitors are used to store small and larger

amounts of energy, respectively, ceramic capacitors areoften used in resonators, and parasitic capacitance oc-curs in circuits wherever the simple conductor-insulator-conductor structure is formed unintentionally by the con-figuration of the circuit layout.Electrolytic capacitors use an aluminum or tantalum platewith an oxide dielectric layer. The second electrode is aliquid electrolyte, connected to the circuit by another foilplate. Electrolytic capacitors offer very high capacitancebut suffer from poor tolerances, high instability, gradualloss of capacitance especially when subjected to heat, andhigh leakage current. Poor quality capacitors may leakelectrolyte, which is harmful to printed circuit boards.The conductivity of the electrolyte drops at low tempera-tures, which increases equivalent series resistance. Whilewidely used for power-supply conditioning, poor high-frequency characteristics make them unsuitable for manyapplications. Electrolytic capacitors will self-degrade ifunused for a period (around a year), and when full poweris applied may short circuit, permanently damaging thecapacitor and usually blowing a fuse or causing failure ofrectifier diodes (for instance, in older equipment, arcingin rectifier tubes). They can be restored before use (anddamage) by gradually applying the operating voltage, of-ten done on antique vacuum tube equipment over a periodof 30 minutes by using a variable transformer to supplyAC power. Unfortunately, the use of this technique maybe less satisfactory for some solid state equipment, whichmay be damaged by operation below its normal powerrange, requiring that the power supply first be isolatedfrom the consuming circuits. Such remedies may not beapplicable to modern high-frequency power supplies asthese produce full output voltage even with reduced in-put.Tantalum capacitors offer better frequency and tempera-ture characteristics than aluminum, but higher dielectricabsorption and leakage.[25]

Polymer capacitors (OS-CON, OC-CON, KO, AO) usesolid conductive polymer (or polymerized organic semi-conductor) as electrolyte and offer longer life and lowerESR at higher cost than standard electrolytic capacitors.A feedthrough capacitor is a component that, while notserving as its main use, has capacitance and is used toconduct signals through a conductive sheet.Several other types of capacitor are available for specialistapplications. Supercapacitors store large amounts of en-ergy. Supercapacitors made from carbon aerogel, carbonnanotubes, or highly porous electrode materials, offer ex-tremely high capacitance (up to 5 kF as of 2010) and canbe used in some applications instead of rechargeable bat-teries. Alternating current capacitors are specifically de-signed to work on line (mains) voltage AC power circuits.They are commonly used in electricmotor circuits and areoften designed to handle large currents, so they tend to bephysically large. They are usually ruggedly packaged, of-ten in metal cases that can be easily grounded/earthed.

46 CHAPTER 5. CAPACITOR

They also are designed with direct current breakdownvoltages of at least five times the maximum AC voltage.

5.4.2 Structure

Capacitor packages: SMD ceramic at top left; SMD tantalum atbottom left; through-hole tantalum at top right; through-hole elec-trolytic at bottom right. Major scale divisions are cm.

The arrangement of plates and dielectric has many vari-ations depending on the desired ratings of the capaci-tor. For small values of capacitance (microfarads andless), ceramic disks use metallic coatings, with wire leadsbonded to the coating. Larger values can bemade bymul-tiple stacks of plates and disks. Larger value capacitorsusually use a metal foil or metal film layer deposited onthe surface of a dielectric film to make the plates, and adielectric film of impregnated paper or plastic – these arerolled up to save space. To reduce the series resistanceand inductance for long plates, the plates and dielectricare staggered so that connection is made at the commonedge of the rolled-up plates, not at the ends of the foil ormetalized film strips that comprise the plates.The assembly is encased to prevent moisture entering thedielectric – early radio equipment used a cardboard tubesealed with wax. Modern paper or film dielectric capaci-tors are dipped in a hard thermoplastic. Large capacitorsfor high-voltage use may have the roll form compressedto fit into a rectangular metal case, with bolted terminalsand bushings for connections. The dielectric in larger ca-pacitors is often impregnated with a liquid to improve itsproperties.Capacitors may have their connecting leads arrangedin many configurations, for example axially or radially.“Axial” means that the leads are on a common axis, typ-ically the axis of the capacitor’s cylindrical body – theleads extend from opposite ends. Radial leads might moreaccurately be referred to as tandem; they are rarely actu-ally aligned along radii of the body’s circle, so the termis inexact, although universal. The leads (until bent) areusually in planes parallel to that of the flat body of the ca-pacitor, and extend in the same direction; they are often

Several axial-lead electrolytic capacitors

parallel as manufactured.Small, cheap discoidal ceramic capacitors have existedsince the 1930s, and remain in widespread use. Since the1980s, surface mount packages for capacitors have beenwidely used. These packages are extremely small and lackconnecting leads, allowing them to be soldered directlyonto the surface of printed circuit boards. Surface mountcomponents avoid undesirable high-frequency effects dueto the leads and simplify automated assembly, althoughmanual handling is made difficult due to their small size.Mechanically controlled variable capacitors allow theplate spacing to be adjusted, for example by rotatingor sliding a set of movable plates into alignment witha set of stationary plates. Low cost variable capac-itors squeeze together alternating layers of aluminumand plastic with a screw. Electrical control of capaci-tance is achievable with varactors (or varicaps), which arereverse-biased semiconductor diodes whose depletion re-gion width varies with applied voltage. They are used inphase-locked loops, amongst other applications.

5.5 Capacitor markings

See also: Preferred number § E series

Most capacitors have numbers printed on their bodies toindicate their electrical characteristics. Larger capacitorslike electrolytics usually display the actual capacitance to-gether with the unit (for example, 220 μF). Smaller ca-pacitors like ceramics, however, use a shorthand consist-ing of three numeric digits and a letter, where the digitsindicate the capacitance in pF (calculated as XY × 10Zfor digits XYZ) and the letter indicates the tolerance (J,K or M for ±5%, ±10% and ±20% respectively).Additionally, the capacitor may show its working voltage,temperature and other relevant characteristics.For typographical reasons, some manufacturers print“MF” on capacitors to indicate microfarads (μF).[26]

5.6. APPLICATIONS 47

5.5.1 Example

A capacitor with the text 473K 330V on its body has acapacitance of 47 × 103 pF = 47 nF (±10%) with a work-ing voltage of 330 V. The working voltage of a capacitoris the highest voltage that can be applied across it withoutundue risk of breaking down the dielectric layer.

5.6 Applications

Main article: Applications of capacitors

This mylar-film, oil-filled capacitor has very low inductance andlow resistance, to provide the high-power (70megawatt) and highspeed (1.2 microsecond) discharge needed to operate a dye laser.

5.6.1 Energy storage

A capacitor can store electric energy when disconnectedfrom its charging circuit, so it can be used like a tem-porary battery, or like other types of rechargeable energystorage system.[27] Capacitors are commonly used in elec-tronic devices to maintain power supply while batteriesare being changed. (This prevents loss of information involatile memory.)Conventional capacitors provide less than 360 joulesper kilogram of energy density, whereas a conventionalalkaline battery has a density of 590 kJ/kg.In car audio systems, large capacitors store energy for the

amplifier to use on demand. Also for a flash tube a ca-pacitor is used to hold the high voltage.

5.6.2 Pulsed power and weapons

Groups of large, specially constructed, low-inductancehigh-voltage capacitors (capacitor banks) are used to sup-ply huge pulses of current for many pulsed power appli-cations. These include electromagnetic forming, Marxgenerators, pulsed lasers (especially TEA lasers), pulseforming networks, radar, fusion research, and particle ac-celerators.Large capacitor banks (reservoir) are used as en-ergy sources for the exploding-bridgewire detonators orslapper detonators in nuclear weapons and other specialtyweapons. Experimental work is under way using banks ofcapacitors as power sources for electromagnetic armourand electromagnetic railguns and coilguns.

5.6.3 Power conditioning

A 10,000 microfarad capacitor in an amplifier power supply

Reservoir capacitors are used in power supplies wherethey smooth the output of a full or half wave rectifier.They can also be used in charge pump circuits as the en-ergy storage element in the generation of higher voltagesthan the input voltage.Capacitors are connected in parallel with the power cir-cuits of most electronic devices and larger systems (suchas factories) to shunt away and conceal current fluctua-tions from the primary power source to provide a “clean”power supply for signal or control circuits. Audio equip-ment, for example, uses several capacitors in this way, toshunt away power line hum before it gets into the signalcircuitry. The capacitors act as a local reserve for the DCpower source, and bypass AC currents from the powersupply. This is used in car audio applications, when astiffening capacitor compensates for the inductance andresistance of the leads to the lead-acid car battery.

48 CHAPTER 5. CAPACITOR

Power factor correction

A high-voltage capacitor bank used for power factor correctionon a power transmission system

In electric power distribution, capacitors are used forpower factor correction. Such capacitors often come asthree capacitors connected as a three phase load. Usually,the values of these capacitors are given not in farads butrather as a reactive power in volt-amperes reactive (var).The purpose is to counteract inductive loading from de-vices like electric motors and transmission lines to makethe load appear to be mostly resistive. Individual mo-tor or lamp loads may have capacitors for power factorcorrection, or larger sets of capacitors (usually with auto-matic switching devices) may be installed at a load centerwithin a building or in a large utility substation.

5.6.4 Suppression and coupling

Signal coupling

Main article: capacitive couplingBecause capacitors pass AC but block DC signals (whencharged up to the applied dc voltage), they are often usedto separate the AC and DC components of a signal. Thismethod is known asAC coupling or “capacitive coupling”.Here, a large value of capacitance, whose value need notbe accurately controlled, but whose reactance is small atthe signal frequency, is employed.

Polyester film capacitors are frequently used as coupling capac-itors.

Decoupling

Main article: decoupling capacitor

A decoupling capacitor is a capacitor used to protect onepart of a circuit from the effect of another, for instance tosuppress noise or transients. Noise caused by other cir-cuit elements is shunted through the capacitor, reducingthe effect they have on the rest of the circuit. It is mostcommonly used between the power supply and ground.An alternative name is bypass capacitor as it is used tobypass the power supply or other high impedance com-ponent of a circuit.Decoupling capacitors need not always be discrete com-ponents. Capacitors used in these applications may bebuilt in to a printed circuit board, between the vari-ous layers. These are often referred to as embeddedcapacitors.[28] The layers in the board contributing to thecapacitive properties also function as power and groundplanes, and have a dielectric in between them, enablingthem to operate as a parallel plate capacitor.

High-pass and low-pass filters

Further information: High-pass filter and Low-pass filter

Noise suppression, spikes, and snubbers

Further information: High-pass filter and Low-pass filter

When an inductive circuit is opened, the current throughthe inductance collapses quickly, creating a large volt-age across the open circuit of the switch or relay. If theinductance is large enough, the energy will generate aspark, causing the contact points to oxidize, deteriorate,or sometimes weld together, or destroying a solid-stateswitch. A snubber capacitor across the newly openedcircuit creates a path for this impulse to bypass the con-tact points, thereby preserving their life; these were com-

5.6. APPLICATIONS 49

monly found in contact breaker ignition systems, for in-stance. Similarly, in smaller scale circuits, the spark maynot be enough to damage the switch but will still radiateundesirable radio frequency interference (RFI), which afilter capacitor absorbs. Snubber capacitors are usuallyemployed with a low-value resistor in series, to dissipateenergy and minimize RFI. Such resistor-capacitor com-binations are available in a single package.Capacitors are also used in parallel to interrupt units of ahigh-voltage circuit breaker in order to equally distributethe voltage between these units. In this case they arecalled grading capacitors.In schematic diagrams, a capacitor used primarily for DCcharge storage is often drawn vertically in circuit dia-grams with the lower, more negative, plate drawn as anarc. The straight plate indicates the positive terminal ofthe device, if it is polarized (see electrolytic capacitor).

5.6.5 Motor starters

Main article: motor capacitor

In single phase squirrel cage motors, the primary wind-ing within the motor housing is not capable of starting arotational motion on the rotor, but is capable of sustain-ing one. To start the motor, a secondary “start” wind-ing has a series non-polarized starting capacitor to in-troduce a lead in the sinusoidal current. When the sec-ondary (start) winding is placed at an angle with respectto the primary (run) winding, a rotating electric field iscreated. The force of the rotational field is not constant,but is sufficient to start the rotor spinning. When the ro-tor comes close to operating speed, a centrifugal switch(or current-sensitive relay in series with the main wind-ing) disconnects the capacitor. The start capacitor is typ-ically mounted to the side of the motor housing. Theseare called capacitor-start motors, that have relatively highstarting torque. Typically they can have up-to four timesas much starting torque than a split-phase motor and areused on applications such as compressors, pressure wash-ers and any small device requiring high starting torques.Capacitor-run induction motors have a permanently con-nected phase-shifting capacitor in series with a secondwinding. The motor is much like a two-phase inductionmotor.Motor-starting capacitors are typically non-polarizedelectrolytic types, while running capacitors are conven-tional paper or plastic film dielectric types.

5.6.6 Signal processing

The energy stored in a capacitor can be used to representinformation, either in binary form, as in DRAMs, or inanalogue form, as in analog sampled filters and CCDs.Capacitors can be used in analog circuits as components

of integrators or more complex filters and in negativefeedback loop stabilization. Signal processing circuitsalso use capacitors to integrate a current signal.

Tuned circuits

Capacitors and inductors are applied together in tunedcircuits to select information in particular frequencybands. For example, radio receivers rely on variable ca-pacitors to tune the station frequency. Speakers use pas-sive analog crossovers, and analog equalizers use capaci-tors to select different audio bands.The resonant frequency f of a tuned circuit is a functionof the inductance (L) and capacitance (C) in series, andis given by:

f =1

2π√LC

where L is in henries and C is in farads.

5.6.7 Sensing

Main article: capacitive sensing

Main article: Capacitive displacement sensor

Most capacitors are designed to maintain a fixed physi-cal structure. However, various factors can change thestructure of the capacitor, and the resulting change in ca-pacitance can be used to sense those factors.Changing the dielectric:

The effects of varying the characteristics of thedielectric can be used for sensing purposes.Capacitors with an exposed and porous dielec-tric can be used tomeasure humidity in air. Ca-pacitors are used to accurately measure the fuellevel in airplanes; as the fuel covers more of apair of plates, the circuit capacitance increases.

Changing the distance between the plates:

Capacitors with a flexible plate can be usedto measure strain or pressure. Industrial pres-sure transmitters used for process control usepressure-sensing diaphragms, which form a ca-pacitor plate of an oscillator circuit. Capaci-tors are used as the sensor in condenser micro-phones, where one plate is moved by air pres-sure, relative to the fixed position of the other

50 CHAPTER 5. CAPACITOR

plate. Some accelerometers use MEMS capac-itors etched on a chip to measure the magni-tude and direction of the acceleration vector.They are used to detect changes in accelera-tion, in tilt sensors, or to detect free fall, as sen-sors triggering airbag deployment, and in manyother applications. Some fingerprint sensorsuse capacitors. Additionally, a user can adjustthe pitch of a theremin musical instrument bymoving their hand since this changes the effec-tive capacitance between the user’s hand andthe antenna.

Changing the effective area of the plates:

Capacitive touch switches are now used onmany consumer electronic products.

5.6.8 Oscillators

Further information: Hartley oscillatorA capacitor can possess spring-like qualities in an oscil-

Example of a simple oscillator that requires a capacitor to func-tion

lator circuit. In the image example, a capacitor acts toinfluence the biasing voltage at the npn transistor’s base.The resistance values of the voltage-divider resistors andthe capacitance value of the capacitor together control theoscillatory frequency.

5.7 Hazards and safety

Capacitors may retain a charge long after power is re-moved from a circuit; this charge can cause dangerous or

even potentially fatal shocks or damage connected equip-ment. For example, even a seemingly innocuous de-vice such as a disposable camera flash unit powered bya 1.5 volt AA battery contains a capacitor which may becharged to over 300 volts. This is easily capable of deliv-ering a shock. Service procedures for electronic devicesusually include instructions to discharge large or high-voltage capacitors, for instance using a Brinkley stick.Capacitors may also have built-in discharge resistors todissipate stored energy to a safe level within a few sec-onds after power is removed. High-voltage capacitors arestored with the terminals shorted, as protection from po-tentially dangerous voltages due to dielectric absorption.Some old, large oil-filled paper or plastic film capac-itors contain polychlorinated biphenyls (PCBs). It isknown that waste PCBs can leak into groundwater un-der landfills. Capacitors containing PCB were labelledas containing “Askarel” and several other trade names.PCB-filled paper capacitors are found in very old (pre-1975) fluorescent lamp ballasts, and other applications.Capacitors may catastrophically fail when subjected tovoltages or currents beyond their rating, or as they reachtheir normal end of life. Dielectric or metal intercon-nection failures may create arcing that vaporizes the di-electric fluid, resulting in case bulging, rupture, or evenan explosion. Capacitors used in RF or sustained high-current applications can overheat, especially in the centerof the capacitor rolls. Capacitors used within high-energycapacitor banks can violently explode when a short in onecapacitor causes sudden dumping of energy stored in therest of the bank into the failing unit. High voltage vacuumcapacitors can generate soft X-rays even during normaloperation. Proper containment, fusing, and preventivemaintenance can help to minimize these hazards.High-voltage capacitors can benefit from a pre-charge tolimit in-rush currents at power-up of high voltage directcurrent (HVDC) circuits. This will extend the life of thecomponent and may mitigate high-voltage hazards.

• Swollen caps of electrolytic capacitors – specialdesign of semi-cut caps prevents capacitors frombursting

• This high-energy capacitor from a defibrillator candeliver over 500 joules of energy. A resistor is con-nected between the terminals for safety, to allow thestored energy to be released.

• Catastrophic failure

5.8 See also• Capacitance meter

• Capacitor plague

• Circuit design

5.10. BIBLIOGRAPHY 51

• Electric displacement field

• Electroluminescence

• Electronic oscillator

• Gimmick capacitor

• Vacuum variable capacitor

5.9 References[1] Bird, John (2010). Electrical and Electronic Princi-

ples and Technology. Routledge. pp. 63–76. ISBN9780080890562. Retrieved 2013-03-17.

[2] Williams, Henry Smith. “A History of Science VolumeII, Part VI: The Leyden Jar Discovered”. Retrieved 2013-03-17.

[3] Keithley, Joseph F. (1999). The Story of Electrical andMagnetic Measurements: From 500 BC to the 1940s. JohnWiley & Sons. p. 23. ISBN 9780780311930. Retrieved2013-03-17.

[4] Houston, Edwin J. (1905). Electricity in Every-day Life.P. F. Collier & Son. p. 71. Retrieved 2013-03-17.

[5] Isaacson, Walter (2003). Benjamin Franklin: An Amer-ican Life. Simon and Schuster. p. 136. ISBN9780743260848. Retrieved 2013-03-17.

[6] Franklin, Benjamin (1749-04-29). “Experiments & Ob-servations on Electricity: Letter IV to Peter Collinson”(PDF). p. 28. Retrieved 2009-08-09.

[7] Morse, Robert A. (September 2004). “Franklin andElectrostatics—Ben Franklin as my Lab Partner” (PDF).Wright Center for Science Education. Tufts University. p.23. Retrieved 2009-08-10. After Volta’s discovery of theelectrochemical cell in 1800, the term was then applied toa group of electrochemical cells

[8] “eFunda: Glossary: Units: Electric Capacitance: Jar”.eFunda. Retrieved 2013-03-17.

[9] “Sketch of Alessandro Volta”. The Popular ScienceMonthly (New York: Bonnier Corporation): 118–119.May 1892. ISSN 0161-7370.

[10] Ulaby, p.168

[11] Ulaby, p.157

[12] Ulaby, p.169

[13] Hammond, Percy (1964). Electromagnetism for Engi-neers: An Introductory Course. The Commonwealth andInternational Library of Science, Technology, Engineer-ing and Liberal Studies. Applied Electricity and Electron-ics Division 3. Pergamon Press. pp. 44–45.

[14] Dorf, p.263

[15] Dorf, p.260

[16] “Capacitor charging and discharging”. All About Circuits.Retrieved 2009-02-19.

[17] Pillai, K. P. P. (1970). “Fringing field of finiteparallel-plate capacitors”. Proceedings of the Insti-tution of Electrical Engineers 117 (6): 1201–1204.doi:10.1049/piee.1970.0232.

[18] Ulaby, p.170

[19] Pai, S. T.; Qi Zhang (1995). Introduction to High PowerPulse Technology. Advanced Series in Electrical andComputer Engineering 10. World Scientific. ISBN9789810217143. Retrieved 2013-03-17.

[20] Dyer, Stephen A. (2004). Wiley Survey of Instrumentationand Measurement. John Wiley & Sons. p. 397. ISBN9780471221654. Retrieved 2013-03-17.

[21] Scherz, Paul (2006). Practical Electronics for Inventors(2nd ed.). McGraw Hill Professional. p. 100. ISBN9780071776448. Retrieved 2013-03-17.

[22] Bird, John (2007). Electrical Circuit Theory and Technol-ogy. Routledge. p. 501. ISBN 9780750681391. Re-trieved 2013-03-17.

[23] “Ceramic Capacitor Aging Made Simple”. Johanson Di-electrics. 2012-05-21. Retrieved 2013-03-17.

[24] “The Effect of Reversal on Capacitor Life” (PDF). Engi-neering Bulletin 96-004. Sorrento Electronics. November2003. Retrieved 2013-03-17.

[25] Guinta, Steve. “Ask The Applications Engineer – 21”.Analog Devices. Retrieved 2013-03-17.

[26] Kaplan, Daniel M.; White, Christopher G. Hands-OnElectronics: A Practical Introduction to Analog and Dig-ital Circuits. p. 19.

[27] Miller, Charles. Illustrated Guide to the National ElectricalCode, p. 445 (Cengage Learning 2011).

[28] Alam, Mohammed; Michael H. Azarian; Michael Oster-man; Michael Pecht (2010). “Effectiveness of embeddedcapacitors in reducing the number of surface mount ca-pacitors for decoupling applications”. Circuit World 36(1): 22. doi:10.1108/03056121011015068.

5.10 Bibliography

• Dorf, Richard C.; Svoboda, James A. (2001).Introduction to Electric Circuits (5th ed.). New York:John Wiley & Sons. ISBN 9780471386896.

• Philosophical Transactions of the Royal SocietyLXXII, Appendix 8, 1782 (Volta coins the wordcondenser)

• Ulaby, Fawwaz Tayssir (1999). Fundamentals ofApplied Electromagnetics. Upper Saddle River, NewJersey: Prentice Hall. ISBN 9780130115546.

52 CHAPTER 5. CAPACITOR

• Zorpette, Glenn (2005). “Super Charged: ATiny South Korean Company is Out to MakeCapacitors Powerful enough to Propel the NextGeneration of Hybrid-Electric Cars”. IEEESpectrum (North American ed.) 42 (1): 32.doi:10.1109/MSPEC.2005.1377872.

• Deshpande, R.P. (2014). Capacitors. McGraw-Hill.ISBN 9780071848565.

5.11 External links• Capacitors: Interactive Tutorial National HighMag-netic Field Laboratory

• Currier, Dean P. (2000). “Adventures in Cyber-sound – Ewald Christian von Kleist”. Archived fromthe original on 2008-06-25.

• “The First Condenser – A Beer Glass”. SparkMu-seum.

• Howstuffworks.com: How Capacitors Work

• CapSite 2015: Introduction to Capacitors

• Capacitor Tutorial – Includes how to read capacitortemperature codes

• Introduction to Capacitor and Capacitor codes

• Low ESR Capacitor Manufacturers

• How Capacitor Works – Capacitor Markings andColor Codes

Chapter 6

Inductor

Axial lead inductors (100 µH)

An inductor, also called a coil or reactor, is a passivetwo-terminal electrical component which resists changesin electric current passing through it. It consists of a con-ductor such as a wire, usually wound into a coil. Whena current flows through it, energy is stored temporarilyin a magnetic field in the coil. When the current flow-ing through an inductor changes, the time-varying mag-netic field induces a voltage in the conductor, accordingto Faraday’s law of electromagnetic induction, which op-poses the change in current that created it. As a result,inductors always oppose a change in current, in the sameway that a flywheel oppose a change in rotational veloc-ity. Care should be taken not to confuse this with theresistance provided by a resistor.An inductor is characterized by its inductance, the ratioof the voltage to the rate of change of current, whichhas units of henries (H). Inductors have values that typ-ically range from 1 µH (10−6H) to 1 H. Many induc-tors have a magnetic core made of iron or ferrite insidethe coil, which serves to increase the magnetic field andthus the inductance. Along with capacitors and resistors,inductors are one of the three passive linear circuit el-ements that make up electric circuits. Inductors arewidely used in alternating current (AC) electronic equip-ment, particularly in radio equipment. They are usedto block AC while allowing DC to pass; inductors de-signed for this purpose are called chokes. They are alsoused in electronic filters to separate signals of differentfrequencies, and in combination with capacitors to maketuned circuits, used to tune radio and TV receivers.

6.1 Overview

Inductance (L) results from the magnetic field around acurrent-carrying conductor; the electric current throughthe conductor creates a magnetic flux. Mathemati-cally speaking, inductance is determined by how muchmagnetic flux φ through the circuit is created by a givencurrent i[1][2][3][4]

L = ϕi (1)

Inductors that have ferromagnetic cores are nonlinear; theinductance changes with the current, in this more generalcase inductance is defined as

L =dϕ

di

Any wire or other conductor will generate a magneticfield when current flows through it, so every conductorhas some inductance. The inductance of a circuit de-pends on the geometry of the current path as well as themagnetic permeability of nearby materials. An inductoris a component consisting of a wire or other conductorshaped to increase the magnetic flux through the circuit,usually in the shape of a coil or helix. Winding the wireinto a coil increases the number of times the magneticflux lines link the circuit, increasing the field and thus theinductance. The more turns, the higher the inductance.The inductance also depends on the shape of the coil, sep-aration of the turns, and many other factors. By addinga "magnetic core" made of a ferromagnetic material likeiron inside the coil, the magnetizing field from the coilwill induce magnetization in the material, increasing themagnetic flux. The high permeability of a ferromagneticcore can increase the inductance of a coil by a factor ofseveral thousand over what it would be without it.

6.1.1 Constitutive equation

Any change in the current through an inductor creates achanging flux, inducing a voltage across the inductor. ByFaraday’s law of induction, the voltage induced by anychange in magnetic flux through the circuit is[4]

53

54 CHAPTER 6. INDUCTOR

v =dϕ

dt

From (1) above[4]

v = ddt (Li) = L di

dt (2)

So inductance is also a measure of the amount ofelectromotive force (voltage) generated for a given rateof change of current. For example, an inductor with aninductance of 1 henry produces an EMF of 1 volt whenthe current through the inductor changes at the rate of1 ampere per second. This is usually taken to be theconstitutive relation (defining equation) of the inductor.The dual of the inductor is the capacitor, which storesenergy in an electric field rather than a magnetic field. Itscurrent-voltage relation is obtained by exchanging currentand voltage in the inductor equations and replacing L withthe capacitance C.

6.1.2 Lenz’s law

The polarity (direction) of the induced voltage is given byLenz’s law, which states that it will be such as to opposethe change in current. For example, if the current throughan inductor is increasing, the induced voltage will be pos-itive at the terminal through which the current enters andnegative at the terminal through which it leaves. The en-ergy from the external circuit necessary to overcome thispotential “hill” is being stored in the magnetic field of theinductor; the inductor is said to be "charging" or “ener-gizing”. If the current is decreasing, the induced voltagewill be negative at the terminal through which the currententers. Energy from the magnetic field is being returnedto the circuit; the inductor is said to be “discharging”.

6.1.3 Ideal and real inductors

In circuit theory, inductors are idealized as obeying themathematical relation (2) above precisely. An “ideal in-ductor” has inductance, but no resistance or capacitance,and does not dissipate or radiate energy. However realinductors have side effects which cause their behavior todepart from this simple model. They have resistance (dueto the resistance of the wire and energy losses in corematerial), and parasitic capacitance (due to the electricfield between the turns of wire which are at slightly differ-ent potentials). At high frequencies the capacitance be-gins to affect the inductor’s behavior; at some frequency,real inductors behave as resonant circuits, becoming self-resonant. Above the resonant frequency the capacitivereactance becomes the dominant part of the impedance.At higher frequencies, resistive losses in the windings in-crease due to skin effect and proximity effect.

Inductors with ferromagnetic cores have additional en-ergy losses due to hysteresis and eddy currents in the core,which increase with frequency. At high currents, ironcore inductors also show gradual departure from ideal be-havior due to nonlinearity caused by magnetic saturationof the core. An inductor may radiate electromagneticenergy into surrounding space and circuits, and may ab-sorb electromagnetic emissions from other circuits, caus-ing electromagnetic interference (EMI). Real-world in-ductor applications may consider these parasitic parame-ters as important as the inductance.

6.2 Applications

Large 50MVAR three-phase iron-core loading inductor at a Ger-man utility substation

A ferrite “bead” choke, consisting of an encircling ferrite cylinder,removes electronic noise from a computer power cord.

Inductors are used extensively in analog circuits and sig-nal processing. Applications range from the use of largeinductors in power supplies, which in conjunction with fil-ter capacitors remove residual hums known as the mainshum or other fluctuations from the direct current output,to the small inductance of the ferrite bead or torus in-stalled around a cable to prevent radio frequency inter-ference from being transmitted down the wire. Inductors

6.3. INDUCTOR CONSTRUCTION 55

Example of signal filtering. In this configuration, the inductorblocks AC current, while allowing DC current to pass.

Example of signal filtering. In this configuration, the inductordecouples DC current, while allowing AC current to pass.

are used as the energy storage device in many switched-mode power supplies to produce DC current. The induc-tor supplies energy to the circuit to keep current flowingduring the “off” switching periods.An inductor connected to a capacitor forms a tuned cir-cuit, which acts as a resonator for oscillating current.Tuned circuits are widely used in radio frequency equip-ment such as radio transmitters and receivers, as narrowbandpass filters to select a single frequency from a com-posite signal, and in electronic oscillators to generate si-nusoidal signals.Two (or more) inductors in proximity that have coupledmagnetic flux (mutual inductance) form a transformer,which is a fundamental component of every electricutility power grid. The efficiency of a transformer maydecrease as the frequency increases due to eddy currentsin the core material and skin effect on the windings. Thesize of the core can be decreased at higher frequencies.For this reason, aircraft use 400 hertz alternating currentrather than the usual 50 or 60 hertz, allowing a great sav-ing in weight from the use of smaller transformers.[5]

Inductors are also employed in electrical transmissionsystems, where they are used to limit switching currentsand fault currents. In this field, they are more commonlyreferred to as reactors.Because inductors have complicated side effects (detailedbelow) which cause them to depart from ideal behav-ior, because they can radiate electromagnetic interfer-

ence (EMI), and most of all because of their bulk whichprevents them from being integrated on semiconduc-tor chips, the use of inductors is declining in modernelectronic devices, particularly compact portable devices.Real inductors are increasingly being replaced by activecircuits such as the gyrator which can synthesize induc-tance using capacitors.

6.3 Inductor construction

A ferrite core inductor with two 47 mH windings.

An inductor usually consists of a coil of conduct-ing material, typically insulated copper wire, wrappedaround a core either of plastic or of a ferromagnetic (orferrimagnetic) material; the latter is called an “iron core”inductor. The high permeability of the ferromagneticcore increases the magnetic field and confines it closelyto the inductor, thereby increasing the inductance. Lowfrequency inductors are constructed like transformers,with cores of electrical steel laminated to prevent eddycurrents. 'Soft' ferrites are widely used for cores aboveaudio frequencies, since they do not cause the large en-ergy losses at high frequencies that ordinary iron alloysdo. Inductors come in many shapes. Most are con-structed as enamel coated wire (magnet wire) wrappedaround a ferrite bobbin with wire exposed on the outside,while some enclose the wire completely in ferrite and arereferred to as “shielded”. Some inductors have an ad-justable core, which enables changing of the inductance.Inductors used to block very high frequencies are some-times made by stringing a ferrite bead on a wire.Small inductors can be etched directly onto a printed cir-

56 CHAPTER 6. INDUCTOR

cuit board by laying out the trace in a spiral pattern. Somesuch planar inductors use a planar core.Small value inductors can also be built on integrated cir-cuits using the same processes that are used to maketransistors. Aluminium interconnect is typically used,laid out in a spiral coil pattern. However, the small di-mensions limit the inductance, and it is far more commonto use a circuit called a "gyrator" that uses a capacitor andactive components to behave similarly to an inductor.

6.4 Types of inductor

6.4.1 Air core inductor

Resonant oscillation transformer from a spark gap transmitter.Coupling can be adjusted by moving the top coil on the supportrod. Shows high Q construction with spaced turns of large diam-eter tubing.

The term air core coil describes an inductor that doesnot use a magnetic core made of a ferromagnetic mate-rial. The term refers to coils wound on plastic, ceramic,or other nonmagnetic forms, as well as those that haveonly air inside the windings. Air core coils have lowerinductance than ferromagnetic core coils, but are oftenused at high frequencies because they are free from en-ergy losses called core losses that occur in ferromagneticcores, which increase with frequency. A side effect thatcan occur in air core coils in which the winding is notrigidly supported on a form is 'microphony': mechanical

vibration of the windings can cause variations in the in-ductance.

Radio frequency inductor

Collection of RF inductors, showing techniques to reducelosses. The three top left and the ferrite loopstick or rodantenna,[6][7][8][9] bottom, have basket windings.

At high frequencies, particularly radio frequencies (RF),inductors have higher resistance and other losses. Inaddition to causing power loss, in resonant circuits thiscan reduce the Q factor of the circuit, broadening thebandwidth. In RF inductors, which are mostly air coretypes, specialized construction techniques are used tominimize these losses. The losses are due to these ef-fects:

• Skin effect: The resistance of a wire to high fre-quency current is higher than its resistance to directcurrent because of skin effect. Radio frequency al-ternating current does not penetrate far into the bodyof a conductor but travels along its surface. There-fore, in a solid wire, most of the cross sectional areaof the wire is not used to conduct the current, whichis in a narrow annulus on the surface. This effect in-creases the resistance of the wire in the coil, whichmay already have a relatively high resistance due toits length and small diameter.

• Proximity effect: Another similar effect that alsoincreases the resistance of the wire at high frequen-cies is proximity effect, which occurs in parallelwires that lie close to each other. The individualmagnetic field of adjacent turns induces eddy cur-rents in the wire of the coil, which causes the currentin the conductor to be concentrated in a thin strip onthe side near the adjacent wire. Like skin effect, thisreduces the effective cross-sectional area of the wireconducting current, increasing its resistance.

6.4. TYPES OF INDUCTOR 57

High Q tank coil in a shortwave transmitter

(left) Spiderweb coil (right) Adjustable ferrite slug-tunedRF coil with basketweave winding and litz wire

• Dielectric losses: The high frequency electric fieldnear the conductors in a tank coil can cause the mo-tion of polar molecules in nearby insulating mate-rials, dissipating energy as heat. So coils used fortuned circuits are often not wound on coil forms butare suspended in air, supported by narrow plastic orceramic strips.

• Parasitic capacitance: The capacitance betweenindividual wire turns of the coil, called parasiticcapacitance, does not cause energy losses but canchange the behavior of the coil. Each turn of thecoil is at a slightly different potential, so the electricfield between neighboring turns stores charge on thewire, so the coil acts as if it has a capacitor in par-allel with it. At a high enough frequency this capac-itance can resonate with the inductance of the coilforming a tuned circuit, causing the coil to becomeself-resonant.

To reduce parasitic capacitance and proximity effect, RFcoils are constructed to avoid having many turns lyingclose together, parallel to one another. The windings ofRF coils are often limited to a single layer, and the turnsare spaced apart. To reduce resistance due to skin effect,in high-power inductors such as those used in transmit-ters the windings are sometimes made of a metal strip or

tubing which has a larger surface area, and the surface issilver-plated.

• Basket-weave coils: To reduce proximity effect andparasitic capacitance, multilayer RF coils are woundin patterns in which successive turns are not parallelbut crisscrossed at an angle; these are often calledhoneycomb or basket-weave coils. These are occa-sionally wound on a vertical insulating supports withdowels or slots, with the wire weaving in and outthrough the slots.

• Spiderweb coils: Another construction techniquewith similar advantages is flat spiral coils.These areoften wound on a flat insulating support with radialspokes or slots, with the wire weaving in and outthrough the slots; these are called spiderweb coils.The form has an odd number of slots, so successiveturns of the spiral lie on opposite sides of the form,increasing separation.

• Litz wire: To reduce skin effect losses, some coilsare wound with a special type of radio frequencywire called litz wire. Instead of a single solid con-ductor, litz wire consists of several smaller wirestrands that carry the current. Unlike ordinarystranded wire, the strands are insulated from eachother, to prevent skin effect from forcing the cur-rent to the surface, and are twisted or braided to-gether. The twist pattern ensures that each wirestrand spends the same amount of its length on theoutside of the wire bundle, so skin effect distributesthe current equally between the strands, resultingin a larger cross-sectional conduction area than anequivalent single wire.

6.4.2 Ferromagnetic core inductor

Ferromagnetic-core or iron-core inductors use amagneticcore made of a ferromagnetic or ferrimagnetic materialsuch as iron or ferrite to increase the inductance. A mag-netic core can increase the inductance of a coil by a factorof several thousand, by increasing the magnetic field dueto its higher magnetic permeability. However the mag-netic properties of the core material cause several sideeffects which alter the behavior of the inductor and re-quire special construction:

• Core losses: A time-varying current in a ferromag-netic inductor, which causes a time-varying mag-netic field in its core, causes energy losses in the corematerial that are dissipated as heat, due to two pro-cesses:

• Eddy currents: From Faraday’s law of induc-tion, the changing magnetic field can inducecirculating loops of electric current in the con-ductive metal core. The energy in these cur-rents is dissipated as heat in the resistance of

58 CHAPTER 6. INDUCTOR

A variety of types of ferrite core inductors and transformers

the core material. The amount of energy lostincreases with the area inside the loop of cur-rent.

• Hysteresis: Changing or reversing the mag-netic field in the core also causes losses due tothe motion of the tiny magnetic domains it iscomposed of. The energy loss is proportionalto the area of the hysteresis loop in the BHgraph of the core material. Materials with lowcoercivity have narrow hysteresis loops and solow hysteresis losses.

For both of these processes, the energy loss percycle of alternating current is constant, so corelosses increase linearly with frequency. Onlinecore loss calculators[10] are available to calcu-late the energy loss. Using inputs such as in-put voltage, output voltage, output current, fre-quency, ambient temperature, and inductancethese calculators can predict the losses of theinductors core and AC/DC based on the oper-ating condition of the circuit being used.[11]

• Nonlinearity: If the current through a ferromag-netic core coil is high enough that the magnetic coresaturates, the inductance will not remain constantbut will change with the current through the de-vice. This is called nonlinearity and results in dis-tortion of the signal. For example, audio signals cansuffer intermodulation distortion in saturated induc-tors. To prevent this, in linear circuits the currentthrough iron core inductors must be limited belowthe saturation level. Some laminated cores have anarrow air gap in them for this purpose, and pow-dered iron cores have a distributed air gap. This al-lows higher levels of magnetic flux and thus highercurrents through the inductor before it saturates.[12]

Laminated core inductor

Laminated iron core ballast inductor for a metal halide lamp

Low-frequency inductors are often made with laminatedcores to prevent eddy currents, using construction similarto transformers. The core is made of stacks of thin steelsheets or laminations oriented parallel to the field, withan insulating coating on the surface. The insulation pre-vents eddy currents between the sheets, so any remainingcurrents must be within the cross sectional area of the in-dividual laminations, reducing the area of the loop andthus reducing the energy losses greatly. The laminationsare made of low-coercivity silicon steel, to reduce hys-teresis losses.

Ferrite-core inductor

For higher frequencies, inductors are made with cores offerrite. Ferrite is a ceramic ferrimagnetic material thatis nonconductive, so eddy currents cannot flow within it.The formulation of ferrite is xxFe2O4 where xx repre-sents various metals. For inductor cores soft ferrites areused, which have low coercivity and thus low hysteresislosses. Another similar material is powdered iron ce-mented with a binder.

Toroidal core inductor

Main article: Toroidal inductors and transformersIn an inductor wound on a straight rod-shaped core, themagnetic field lines emerging from one end of the coremust pass through the air to reenter the core at the otherend. This reduces the field, becausemuch of themagneticfield path is in air rather than the higher permeability corematerial. A higher magnetic field and inductance can be

6.4. TYPES OF INDUCTOR 59

Toroidal inductor in the power supply of a wireless router

achieved by forming the core in a closed magnetic cir-cuit. The magnetic field lines form closed loops withinthe core without leaving the core material. The shape of-ten used is a toroidal or doughnut-shaped ferrite core. Be-cause of their symmetry, toroidal cores allow a minimumof the magnetic flux to escape outside the core (calledleakage flux), so they radiate less electromagnetic inter-ference than other shapes. Toroidal core coils are manu-factured of various materials, primarily ferrite, powderediron and laminated cores.[13]

Choke

Main article: Choke (electronics)A choke is designed specifically for blocking higher-

An MF or HF radio choke for tenths of an ampere, and a ferritebead VHF choke for several amperes.

frequency alternating current (AC) in an electrical cir-cuit, while allowing lower frequency or DC current topass. It usually consists of a coil of insulated wire oftenwound on a magnetic core, although some consist of adonut-shaped “bead” of ferrite material strung on a wire.Like other inductors, chokes resist changes to the cur-rent passing through them, and so alternating currents ofhigher frequency, which reverse direction rapidly, are re-sisted more than currents of lower frequency; the choke’s

impedance increases with frequency. Its low electrical re-sistance allows both AC and DC to pass with little powerloss, but it can limit the amount of AC passing through itdue to its reactance.

6.4.3 Variable inductor

(left) Inductor with a threaded ferrite slug (visible at top)that can be turned to move it into or out of the coil. 4.2cm high. (right) A variometer used in radio receivers inthe 1920sProbably the most common type of variable inductor to-

A “roller coil”, an adjustable air-core RF inductor used in thetuned circuits of radio transmitters. One of the contacts to thecoil is made by the small grooved wheel, which rides on the wire.Turning the shaft rotates the coil, moving the contact wheel up ordown the coil, allowing more or fewer turns of the coil into thecircuit, to change the inductance.

day is one with a moveable ferrite magnetic core, which

60 CHAPTER 6. INDUCTOR

can be slid or screwed in or out of the coil. Moving thecore farther into the coil increases the permeability, in-creasing the magnetic field and the inductance. Manyinductors used in radio applications (usually less than100 MHz) use adjustable cores in order to tune such in-ductors to their desired value, since manufacturing pro-cesses have certain tolerances (inaccuracy). Sometimessuch cores for frequencies above 100 MHz are madefrom highly conductive non-magnetic material such asaluminum. They decrease the inductance because themagnetic field must bypass them.Air core inductors can use sliding contacts or multipletaps to increase or decrease the number of turns includedin the circuit, to change the inductance. A typemuch usedin the past but mostly obsolete today has a spring contactthat can slide along the bare surface of the windings. Thedisadvantage of this type is that the contact usually short-circuits one or more turns. These turns act like a single-turn short-circuited transformer secondary winding; thelarge currents induced in them cause power losses.A type of continuously variable air core inductor is thevariometer. This consists of two coils with the same num-ber of turns connected in series, one inside the other. Theinner coil is mounted on a shaft so its axis can be turnedwith respect to the outer coil. When the two coils’ axesare collinear, with themagnetic fields pointing in the samedirection, the fields add and the inductance is maximum.When the inner coil is turned so its axis is at an anglewith the outer, the mutual inductance between them issmaller so the total inductance is less. When the innercoil is turned 180° so the coils are collinear with theirmagnetic fields opposing, the two fields cancel each otherand the inductance is very small. This type has the advan-tage that it is continuously variable over a wide range. Itis used in antenna tuners and matching circuits to matchlow frequency transmitters to their antennas.Another method to control the inductance without anymoving parts requires an additional DC current biaswinding which controls the permeability of an easily sat-urable core material. See Magnetic amplifier.

6.5 Circuit theory

The effect of an inductor in a circuit is to oppose changesin current through it by developing a voltage across it pro-portional to the rate of change of the current. An ideal in-ductor would offer no resistance to a constant direct cur-rent; however, only superconducting inductors have trulyzero electrical resistance.The relationship between the time-varying voltage v(t)across an inductor with inductance L and the time-varying current i(t) passing through it is described by thedifferential equation:

v(t) = Ldi(t)

dt

When there is a sinusoidal alternating current (AC)through an inductor, a sinusoidal voltage is induced. Theamplitude of the voltage is proportional to the product ofthe amplitude (IP) of the current and the frequency (f)of the current.

i(t) = IP sin(2πft)di(t)

dt= 2πfIP cos(2πft)

v(t) = 2πfLIP cos(2πft)

In this situation, the phase of the current lags that of thevoltage by π/2 (90°). For sinusoids, as the voltage acrossthe inductor goes to its maximum value, the current goesto zero, and as the voltage across the inductor goes to zero,the current through it goes to its maximum value.If an inductor is connected to a direct current source withvalue I via a resistance R, and then the current source isshort-circuited, the differential relationship above showsthat the current through the inductor will discharge withan exponential decay:

i(t) = Ie−RL t

6.5.1 Reactance

The ratio of the peak voltage to the peak current in an in-ductor energised from a sinusoidal source is called thereactance and is denoted XL. The suffix is to distin-guish inductive reactance from capacitive reactance dueto capacitance.

XL =VPIP

=2πfLIP

IP

Thus,

XL = 2πfL

Reactance is measured in the same units as resistance(ohms) but is not actually a resistance. A resistance willdissipate energy as heat when a current passes. This doesnot happen with an inductor; rather, energy is stored inthe magnetic field as the current builds and later returnedto the circuit as the current falls. Inductive reactance isstrongly frequency dependent. At low frequency the re-actance falls, and for a steady current (zero frequency)the inductor behaves as a short-circuit. At increasing fre-quency, on the other hand, the reactance increases and ata sufficiently high frequency the inductor approaches anopen circuit.

6.6. Q FACTOR 61

6.5.2 Laplace circuit analysis (s-domain)

When using the Laplace transform in circuit analysis, theimpedance of an ideal inductor with no initial current isrepresented in the s domain by:

Z(s) = Ls

where

L is the inductance, ands is the complex frequency.

If the inductor does have initial current, it can be repre-sented by:

• adding a voltage source in series with the inductor,having the value:

LI0

where

L is the inductance, andI0 is the initial current in the inductor.

(Note that the source should have a polarity that is alignedwith the initial current)

• or by adding a current source in parallel with theinductor, having the value:

I0s

where

I0 is the initial current in the inductor.s is the complex frequency.

6.5.3 Inductor networks

Main article: Series and parallel circuits

Inductors in a parallel configuration each have the samepotential difference (voltage). To find their total equiva-lent inductance (Lₑ ):

L L L1 2 n

1

Leq=

1

L1+

1

L2+ · · ·+ 1

Ln

The current through inductors in series stays the same,but the voltage across each inductor can be different. Thesum of the potential differences (voltage) is equal to thetotal voltage. To find their total inductance:

L2L1 Ln

Leq = L1 + L2 + · · ·+ Ln

These simple relationships hold true only when there isno mutual coupling of magnetic fields between individualinductors.

6.5.4 Stored energy

Neglecting losses, the energy (measured in joules, in SI)stored by an inductor is equal to the amount of work re-quired to establish the current through the inductor, andtherefore the magnetic field. This is given by:

Estored =1

2LI2

where L is inductance and I is the current through theinductor.This relationship is only valid for linear (non-saturated)regions of the magnetic flux linkage and current relation-ship. In general if one decides to find the energy storedin a LTI inductor that has initial current in a specific timebetween t0 and t1 can use this:

E =

∫ t1

t0

P (t) dt =1

2LI(t1)

2 − 1

2LI(t0)

2

6.6 Q factor

An ideal inductor would have no resistance or energylosses. However, real inductors have winding resistancefrom the metal wire forming the coils. Since the wind-ing resistance appears as a resistance in series with theinductor, it is often called the series resistance. The in-ductor’s series resistance converts electric current throughthe coils into heat, thus causing a loss of inductive quality.The quality factor (or Q) of an inductor is the ratio of itsinductive reactance to its resistance at a given frequency,and is a measure of its efficiency. The higher the Q fac-tor of the inductor, the closer it approaches the behavior

62 CHAPTER 6. INDUCTOR

of an ideal, lossless, inductor. High Q inductors are usedwith capacitors to make resonant circuits in radio trans-mitters and receivers. The higher the Q is, the narrowerthe bandwidth of the resonant circuit.The Q factor of an inductor can be found through the fol-lowing formula, where L is the inductance, R is the induc-tor’s effective series resistance, ω is the radian operatingfrequency, and the product ωL is the inductive reactance:

Q =ωL

R

Notice that Q increases linearly with frequency if L andR are constant. Although they are constant at low fre-quencies, the parameters vary with frequency. For exam-ple, skin effect, proximity effect, and core losses increaseR with frequency; winding capacitance and variations inpermeability with frequency affect L.Qualitatively, at low frequencies and within limits, in-creasing the number of turns N improves Q because Lvaries as N2 while R varies linearly with N. Similarly, in-creasing the radius r of an inductor improves Q becauseL varies as r2 while R varies linearly with r. So high Q aircore inductors often have large diameters andmany turns.Both of those examples assume the diameter of the wirestays the same, so both examples use proportionally morewire (copper). If the total mass of wire is held constant,then there would be no advantage to increasing the num-ber of turns or the radius of the turns because the wirewould have to be proportionally thinner.Using a high permeability ferromagnetic core can greatlyincrease the inductance for the same amount of copper,so the core can also increase the Q. Cores however alsointroduce losses that increase with frequency. The corematerial is chosen for best results for the frequency band.At VHF or higher frequencies an air core is likely to beused.Inductors wound around a ferromagnetic core maysaturate at high currents, causing a dramatic decrease ininductance (and Q). This phenomenon can be avoided byusing a (physically larger) air core inductor. A well de-signed air core inductor may have a Q of several hundred.

6.7 Inductance formulas

The table below lists some common simplified formulasfor calculating the approximate inductance of several in-ductor constructions.

6.8 See also

• Gyrator – a network element that can simulate aninductor

• Induction coil

• Induction cooking

• Induction loop

• RL circuit

• RLC circuit

• Magnetomotive force

• Reactance (electronics) – opposition to a change ofelectric current or voltage

• Saturable reactor – a type of adjustable inductor

• Solenoid

6.9 Notes[1] Singh, Yaduvir (2011). Electro Magnetic Field Theory.

Pearson Education India. p. 65. ISBN 8131760618.

[2] Wadhwa, C. L. (2005). Electrical Power Systems. NewAge International. p. 18. ISBN 8122417221.

[3] Pelcovits, Robert A.; Josh Farkas (2007). Barron’s APPhysics C. Barron’s Educatonal Series. p. 646. ISBN0764137107.

[4] Purcell, Edward M.; David J. Morin (2013). Electricityand Magnetism. Cambridge Univ. Press. p. 364. ISBN1107014026.

[5] “Aircraft electrical systems”. Wonderquest.com. Re-trieved 2010-09-24.

[6] “An Unassuming Antenna - The Ferrite Loopstick”. Ra-dio Time Traveller. January 23, 2011. Retrieved March5, 2014.

[7] Frost, Phil (December 23, 2013). “What’s an appropriatecore material for a loopstick antenna?". Amateur Radiobeta. Stack Exchange, Inc. Retrieved March 5, 2014.

[8] Poisel, Richard (2011). Antenna Systems and ElectronicWarfare Applications. Artech House. p. 280. ISBN1608074846.

[9] Yadava, R. L. (2011). Antenna and Wave Propagation.PHI Learning Pvt. Ltd. p. 261. ISBN 8120342917.

[10] Vishay. “Products - Inductors - IHLP inductor loss calcu-lator tool landing page”. Vishay. Retrieved 2010-09-24.

[11] View: Everyone Only Notes. “IHLP inductor loss calcu-lator tool”. element14. Retrieved 2010-09-24.

[12] “Inductors 101” (PDF). vishay. Retrieved 2010-09-24.

[13] “Inductor and Magnetic Product Terminology” (PDF).Vishay Dale. Retrieved 2012-09-24.

[14] Nagaoka, Hantaro (1909-05-06). “The Inductance Coef-ficients of Solenoids” (PDF) 27. Journal of the College ofScience, Imperial University, Tokyo, Japan. p. 18. Re-trieved 2011-11-10.

6.11. EXTERNAL LINKS 63

[15] Kenneth L. Kaiser, Electromagnetic Compatibility Hand-book, p. 30.64, CRC Press, 2004 ISBN 0849320879.

[16] Rosa, Edward B. (1908). “The Self and Mu-tual Inductances of Linear Conductors” (PDF). Bul-letin of the Bureau of Standards 4 (2): 301–344.doi:10.6028/bulletin.088

[17] Rosa 1908, equation (11a), subst. radius ρ = d/2 and cgsunits

[18] Terman 1943, pp. 48–49, convert to natural logarithmsand inches to mm.

[19] Terman (1943, p. 48) states for l < 100 d, include d/2lwithin the parentheses.

[20] ARRL Handbook, 66th Ed. American Radio RelayLeague (1989).

[21] For the second formula, Terman 1943, p. 58 which citesto Wheeler 1928.

[22] Terman 1943, p. 58

[23] Terman 1943, p. 57

6.10 References• Terman, Frederick (1943). “Radio Engineers’Handbook”. McGraw-Hill

• Wheeler, H. A. (October 1928). “Simple Induc-tance Formulae for Radio Coils”. Proc. I. R. E. 16(10): 1398. doi:10.1109/JRPROC.1928.221309

6.11 External linksGeneral

• How stuff works The initial concept, made very sim-ple

• Capacitance and Inductance –A chapter from an on-line textbook

• Spiral inductor models. Article on inductor charac-teristics and modeling.

• Online coil inductance calculator. Online calcula-tor calculates the inductance of conventional andtoroidal coils using formulas 3, 4, 5, and 6, above.

• AC circuits

• Understanding coils and transforms

• Bowley, Roger (2009). “Inductor”. Sixty Symbols.Brady Haran for the University of Nottingham.

• Inductors 101 Instructional Guide

Chapter 7

Diode

For data diodes, see Unidirectional network. For otheruses, see Diodes (disambiguation).

In electronics, a diode is a two-terminal electronic

Closeup of a diode, showing the square-shaped semiconductorcrystal (black object on left).

component with asymmetric conductance; it has low (ide-ally zero) resistance to current in one direction, and high(ideally infinite) resistance in the other. A semiconduc-tor diode, the most common type today, is a crystallinepiece of semiconductor material with a p–n junction con-nected to two electrical terminals.[5] Avacuum tube diodehas two electrodes, a plate (anode) and a heated cath-ode. Semiconductor diodes were the first semiconductorelectronic devices. The discovery of crystals' rectifyingabilities was made by German physicist Ferdinand Braunin 1874. The first semiconductor diodes, called cat’swhisker diodes, developed around 1906, were made ofmineral crystals such as galena. Today, most diodesare made of silicon, but other semiconductors such asselenium or germanium are sometimes used.[6]

7.1 Main functions

The most common function of a diode is to allow an elec-tric current to pass in one direction (called the diode’sforward direction), while blocking current in the oppo-site direction (the reverse direction). Thus, the diode canbe viewed as an electronic version of a check valve. This

unidirectional behavior is called rectification, and is usedto convert alternating current to direct current, includ-ing extraction of modulation from radio signals in radioreceivers—these diodes are forms of rectifiers.However, diodes can have more complicated behaviorthan this simple on–off action, due to their nonlinearcurrent-voltage characteristics. Semiconductor diodesbegin conducting electricity only if a certain thresholdvoltage or cut-in voltage is present in the forward direc-tion (a state in which the diode is said to be forward-biased). The voltage drop across a forward-biased diodevaries only a little with the current, and is a function oftemperature; this effect can be used as a temperature sen-sor or voltage reference.Semiconductor diodes’ current–voltage characteristic canbe tailored by varying the semiconductor materials anddoping, introducing impurities into the materials. Thesetechniques are used to create special-purpose diodes thatperform many different functions. For example, diodesare used to regulate voltage (Zener diodes), to protect cir-cuits from high voltage surges (avalanche diodes), to elec-tronically tune radio and TV receivers (varactor diodes),to generate radio-frequency oscillations (tunnel diodes,Gunn diodes, IMPATT diodes), and to produce light(light-emitting diodes). Tunnel, Gunn and IMPATTdiodes exhibit negative resistance, which is useful inmicrowave and switching circuits.

7.2 History

Thermionic (vacuum tube) diodes and solid state (semi-conductor) diodes were developed separately, at approxi-mately the same time, in the early 1900s, as radio receiverdetectors. Until the 1950s vacuum tube diodes weremoreoften used in radios because the early point-contact typesemiconductor diodes (cat’s-whisker detectors) were lessstable, and because most receiving sets had vacuum tubesfor amplification that could easily have diodes includedin the tube (for example the 12SQ7 double diode triode),and vacuum tube rectifiers and gas-filled rectifiers han-dled some high voltage/high current rectification tasks be-yond the capabilities of semiconductor diodes (such asselenium rectifiers) available at the time.

64

7.2. HISTORY 65

Various semiconductor diodes. Bottom: A bridge rectifier. Inmost diodes, a white or black painted band identifies the cathodeterminal, that is, the terminal that positive charge (conventionalcurrent) will flow out of when the diode is conducting.[1][2][3][4]

7.2.1 Vacuum tube diodes

Further information: Vacuum tube

In 1873, Frederick Guthrie discovered the basic principleof operation of thermionic diodes.[7][8] Guthrie discov-ered that a positively charged electroscope could be dis-charged by bringing a grounded piece of white-hot metalclose to it (but not actually touching it). The same didnot apply to a negatively charged electroscope, indicating

Glass Envelope

Plate (anode)

Filament (cathode)

Structure of a vacuum tube diode. The filament may be bare, ormore commonly (as shown here), embedded within and insulatedfrom an enclosing cathode.

that the current flow was only possible in one direction.Thomas Edison independently rediscovered the princi-ple on February 13, 1880. At the time, Edison was in-vestigating why the filaments of his carbon-filament lightbulbs nearly always burned out at the positive-connectedend. He had a special bulb made with a metal plate sealedinto the glass envelope. Using this device, he confirmedthat an invisible current flowed from the glowing filamentthrough the vacuum to the metal plate, but only when theplate was connected to the positive supply.Edison devised a circuit where his modified light bulb ef-fectively replaced the resistor in a DC voltmeter. Edisonwas awarded a patent for this invention in 1884.[9] Sincethere was no apparent practical use for such a device atthe time, the patent application was most likely simplya precaution in case someone else did find a use for theso-called Edison effect.About 20 years later, John Ambrose Fleming (scientificadviser to the Marconi Company and former Edison em-ployee) realized that the Edison effect could be used asa precision radio detector. Fleming patented the firsttrue thermionic diode, the Fleming valve, in Britain onNovember 16, 1904[10] (followed by U.S. Patent 803,684in November 1905).

66 CHAPTER 7. DIODE

7.2.2 Solid-state diodes

In 1874 German scientist Karl Ferdinand Braun discov-ered the “unilateral conduction” of crystals.[11][12] Braunpatented the crystal rectifier in 1899.[13] Copper oxideand selenium rectifiers were developed for power appli-cations in the 1930s.Indian scientist Jagadish Chandra Bose was the first touse a crystal for detecting radio waves in 1894.[14] Thecrystal detector was developed into a practical device forwireless telegraphy by Greenleaf Whittier Pickard, whoinvented a silicon crystal detector in 1903 and receiveda patent for it on November 20, 1906.[15] Other experi-menters tried a variety of other substances, of which themost widely used was the mineral galena (lead sulfide).Other substances offered slightly better performance, butgalena was most widely used because it had the advantageof being cheap and easy to obtain. The crystal detectorin these early crystal radio sets consisted of an adjustablewire point-contact (the so-called “cat’s whisker”), whichcould be manually moved over the face of the crystal inorder to obtain optimum signal. This troublesome devicewas superseded by thermionic diodes by the 1920s, butafter high purity semiconductor materials became avail-able, the crystal detector returned to dominant use withthe advent of inexpensive fixed-germanium diodes in the1950s. Bell Labs also developed a germanium diode formicrowave reception, and AT&T used these in their mi-crowave towers that criss-crossed the nation starting inthe late 1940s, carrying telephone and network televi-sion signals. Bell Labs did not develop a satisfactorythermionic diode for microwave reception.

7.2.3 Etymology

At the time of their invention, such devices were knownas rectifiers. In 1919, the year tetrodes were invented,William Henry Eccles coined the term diode from theGreek roots di (from δί), meaning “two”, and ode (fromὁδός), meaning “path”. (However, the word diode itself,as well as triode, tetrode, pentode, hexode, was already inuse as a term of multiplex telegraphy; see, for example,The telegraphic journal and electrical review, September10, 1886, p. 252).

Rectifiers

Main article: Rectifier

Although all diodes rectify, the term 'rectifier' is normallyreserved for higher currents and voltages than would nor-mally be found in the rectification of lower power signals;examples include:

• Power supply rectifiers (half-wave, full-wave,bridge)

• Flyback diodes

7.3 Thermionic diodes

Glass tube

Anode

Heater

Heatedcathode

Diode vacuum tube construction

The symbol for an indirect heated vacuum-tube diode. From topto bottom, the components are the anode, the cathode, and theheater filament.

A thermionic diode is a thermionic-valve device (alsoknown as a vacuum tube, tube, or valve), consisting

7.4. SEMICONDUCTOR DIODES 67

of a sealed evacuated glass envelope containing twoelectrodes: a cathode heated by a filament, and a plate(anode). Early examples were fairly similar in appear-ance to incandescent light bulbs.In operation, a separate current through the filament(heater), a high resistance wire made of nichrome, heatsthe cathode red hot (800–1000 °C), causing it to releaseelectrons into the vacuum, a process called thermionicemission. The cathode is coated with oxides of alkalineearth metals such as barium and strontium oxides, whichhave a low work function, to increase the number of elec-trons emitted. (Some valves use direct heating, in whicha tungsten filament acts as both heater and cathode.) Thealternating voltage to be rectified is applied between thecathode and the concentric plate electrode. When theplate has a positive voltage with respect to the cathode,it electrostatically attracts the electrons from the cathode,so a current of electrons flows through the tube from cath-ode to plate. However when the polarity is reversed andthe plate has a negative voltage, no current flows, becausethe cathode electrons are not attracted to it. The unheatedplate does not emit any electrons itself. So electrons canonly flow through the tube in one direction, from cathodeto plate.In a mercury-arc valve, an arc forms between a refrac-tory conductive anode and a pool of liquid mercury act-ing as cathode. Such units were made with ratings up tohundreds of kilowatts, and were important in the devel-opment of HVDC power transmission. Some types ofsmaller thermionic rectifiers sometimes had mercury va-por fill to reduce their forward voltage drop and to in-crease current rating over thermionic hard-vacuum de-vices.Throughout the vacuum tube era, valve diodes were usedin analog signal applications and as rectifiers in DC powersupplies in consumer electronics such as radios, televi-sions, and sound systems. They were replaced in powersupplies beginning in the 1940s by selenium rectifiers andthen by semiconductor diodes by the 1960s. Today theyare still used in a few high power applications where theirability to withstand transients and their robustness givesthem an advantage over semiconductor devices. The re-cent (2012) resurgence of interest among audiophiles andrecording studios in old valve audio gear such as guitaramplifiers and home audio systems has provided a mar-ket for the legacy consumer diode valves.

7.4 Semiconductor diodes

7.4.1 Electronic symbols

Main article: Electronic symbol

The symbol used for a semiconductor diode in a circuitdiagram specifies the type of diode. There are alternative

symbols for some types of diodes, though the differencesare minor.

• Diode

• Light Emitting Diode (LED)

• Photodiode

• Schottky diode

• Transient Voltage Suppression (TVS)

• Tunnel diode

• Varicap

• Zener diode

• Typical diode packages in same alignment as diodesymbol. Thin bar depicts the cathode.

7.4.2 Point-contact diodes

A point-contact diode works the same as the junctiondiodes described below, but their construction is simpler.A block of n-type semiconductor is built, and a conduct-ing sharp-point contact made with some group-3 metalis placed in contact with the semiconductor. Some metalmigrates into the semiconductor tomake a small region ofp-type semiconductor near the contact. The long-popular1N34 germanium version is still used in radio receivers asa detector and occasionally in specialized analog electron-ics.

7.4.3 Junction diodes

p–n junction diode

Main article: p–n diode

A p–n junction diode is made of a crystal ofsemiconductor, usually silicon, but germanium andgallium arsenide are also used. Impurities are added toit to create a region on one side that contains negativecharge carriers (electrons), called n-type semiconductor,and a region on the other side that contains positive chargecarriers (holes), called p-type semiconductor. When twomaterials i.e. n-type and p-type are attached together, amomentary flow of electrons occur from n to p side result-ing in a third region where no charge carriers are present.This region is called the depletion region due to the ab-sence of charge carriers (electrons and holes in this case).The diode’s terminals are attached to the n-type and p-type regions. The boundary between these two regions,called a p–n junction, is where the action of the diodetakes place. The crystal allows electrons to flow from theN-type side (called the cathode) to the P-type side (calledthe anode), but not in the opposite direction.

68 CHAPTER 7. DIODE

Schottky diode

Main article: Schottky diode

Another type of junction diode, the Schottky diode, isformed from a metal–semiconductor junction rather thana p–n junction, which reduces capacitance and increasesswitching speed.

7.4.4 Current–voltage characteristic

I–V (current vs. voltage) characteristics of a p–n junction diode

A semiconductor diode’s behavior in a circuit is givenby its current–voltage characteristic, or I–V graph (seegraph below). The shape of the curve is determinedby the transport of charge carriers through the so-calleddepletion layer or depletion region that exists at the p–njunction between differing semiconductors. When a p–njunction is first created, conduction-band (mobile) elec-trons from the N-doped region diffuse into the P-dopedregion where there is a large population of holes (va-cant places for electrons) with which the electrons “re-combine”. When a mobile electron recombines with ahole, both hole and electron vanish, leaving behind an im-mobile positively charged donor (dopant) on the N sideand negatively charged acceptor (dopant) on the P side.The region around the p–n junction becomes depleted ofcharge carriers and thus behaves as an insulator.However, the width of the depletion region (called thedepletion width) cannot grow without limit. For eachelectron–hole pair that recombines, a positively chargeddopant ion is left behind in the N-doped region, and anegatively charged dopant ion is left behind in the P-doped region. As recombination proceeds more ions arecreated, an increasing electric field develops through thedepletion zone that acts to slow and then finally stop re-combination. At this point, there is a “built-in” potentialacross the depletion zone.If an external voltage is placed across the diode with thesame polarity as the built-in potential, the depletion zone

continues to act as an insulator, preventing any significantelectric current flow (unless electron–hole pairs are ac-tively being created in the junction by, for instance, light;see photodiode). This is the reverse bias phenomenon.However, if the polarity of the external voltage opposesthe built-in potential, recombination can once again pro-ceed, resulting in substantial electric current through thep–n junction (i.e. substantial numbers of electrons andholes recombine at the junction). For silicon diodes, thebuilt-in potential is approximately 0.7 V (0.3 V for ger-manium and 0.2 V for Schottky). Thus, if an externalcurrent passes through the diode, the voltage across thediode increases logarithmic with the current such that theP-doped region is positive with respect to the N-dopedregion and the diode is said to be “turned on” as it hasa forward bias. The diode is commonly said to have aforward “threshold” voltage, which it conducts above andis cutoff below. However, this is only an approximationas the forward characteristic is according to the Shockleyequation absolutely smooth (see graph below).A diode’s I–V characteristic can be approximated by fourregions of operation:

1. At very large reverse bias, beyond the peak inversevoltage or PIV, a process called reverse breakdownoccurs that causes a large increase in current (i.e.,a large number of electrons and holes are cre-ated at, and move away from the p–n junction)that usually damages the device permanently. Theavalanche diode is deliberately designed for use inthe avalanche region. In the Zener diode, the con-cept of PIV is not applicable. A Zener diode con-tains a heavily doped p–n junction allowing elec-trons to tunnel from the valence band of the p-typematerial to the conduction band of the n-type ma-terial, such that the reverse voltage is “clamped”to a known value (called the Zener voltage), andavalanche does not occur. Both devices, however,do have a limit to themaximum current and power inthe clamped reverse-voltage region. Also, followingthe end of forward conduction in any diode, thereis reverse current for a short time. The device doesnot attain its full blocking capability until the reversecurrent ceases.

2. At reverse biases more positive than the PIV, hasonly a very small reverse saturation current. In thereverse bias region for a normal P–N rectifier diode,the current through the device is very low (in theµA range). However, this is temperature dependent,and at sufficiently high temperatures, a substantialamount of reverse current can be observed (mA ormore).

3. With a small forward bias, where only a small for-ward current is conducted, the current–voltage curveis exponential in accordance with the ideal diodeequation. There is a definite forward voltage at

7.4. SEMICONDUCTOR DIODES 69

which the diode starts to conduct significantly. Thisis called the knee voltage or cut-in voltage and isequal to the barrier potential of the p-n junction.This is a feature of the exponential curve, and isseenmore prominently on a current scale more com-pressed than in the diagram here.

4. At larger forward currents the current-voltage curvestarts to be dominated by the ohmic resistance of thebulk semiconductor. The curve is no longer expo-nential, it is asymptotic to a straight line whose slopeis the bulk resistance. This region is particularly im-portant for power diodes. The effect can be modeledas an ideal diode in series with a fixed resistor.

In a small silicon diode at rated currents, the voltage dropis about 0.6 to 0.7 volts. The value is different for otherdiode types—Schottky diodes can be rated as low as 0.2V, germanium diodes 0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have values of 1.4 V and 4.0V respectively.At higher currents the forward voltage drop of the diodeincreases. A drop of 1 V to 1.5 V is typical at full ratedcurrent for power diodes.

7.4.5 Shockley diode equation

The Shockley ideal diode equation or the diode law(named after transistor co-inventor William BradfordShockley) gives the I–V characteristic of an ideal diode ineither forward or reverse bias (or no bias). The followingequation is called the Shockley ideal diode equation whenn, the ideality factor, is set equal to 1 :

I = IS(eVD/(nVT) − 1

),

where

I is the diode current,IS is the reverse bias saturation current (orscale current),VD is the voltage across the diode,VT is the thermal voltage, andn is the ideality factor, also known as the qualityfactor or sometimes emission coefficient. Theideality factor n typically varies from 1 to 2(though can in some cases be higher), depend-ing on the fabrication process and semiconduc-tor material and in many cases is assumed tobe approximately equal to 1 (thus the notationn is omitted). The ideality factor does not formpart of the Shockley ideal diode equation, andwas added to account for imperfect junctionsas observed in real transistors. The factor ismainly accounting for carrier recombination as

the charge carriers cross the depletion region.By setting n = 1 above, the equation reduces tothe Shockley ideal diode equation.

The thermal voltage VT is approximately 25.85 mV at300 K, a temperature close to “room temperature” com-monly used in device simulation software. At any tem-perature it is a known constant defined by:

VT =kT

q,

where k is the Boltzmann constant, T is the absolute tem-perature of the p–n junction, and q is the magnitude ofcharge of an electron (the elementary charge).The reverse saturation current, IS, is not constant for agiven device, but varies with temperature; usually moresignificantly than VT, so that VD typically decreases as Tincreases.The Shockley ideal diode equation or the diode law is de-rived with the assumption that the only processes givingrise to the current in the diode are drift (due to electricalfield), diffusion, and thermal recombination–generation(R–G) (this equation is derived by setting n = 1 above). Italso assumes that the R–G current in the depletion regionis insignificant. This means that the Shockley ideal diodeequation doesn't account for the processes involved in re-verse breakdown and photon-assisted R–G. Additionally,it doesn't describe the “leveling off” of the I–V curve athigh forward bias due to internal resistance. Introduc-ing the ideality factor, n, accounts for recombination andgeneration of carriers.Under reverse bias voltages the exponential in the diodeequation is negligible, and the current is a constant (nega-tive) reverse current value of −IS. The reverse breakdownregion is not modeled by the Shockley diode equation.For even rather small forward bias voltages the exponen-tial is very large, since the thermal voltage is very smallin comparison. The subtracted '1' in the diode equationis then negligible and the forward diode current can beapproximated by

I = ISeVD/(nVT)

The use of the diode equation in circuit problems is illus-trated in the article on diode modeling.

7.4.6 Small-signal behavior

For circuit design, a small-signal model of the diode be-havior often proves useful. A specific example of diodemodeling is discussed in the article on small-signal cir-cuits.

70 CHAPTER 7. DIODE

7.4.7 Reverse-recovery effect

Following the end of forward conduction in a p–n typediode, a reverse current can flow for a short time. Thedevice does not attain its blocking capability until the mo-bile charge in the junction is depleted.The effect can be significant when switching large cur-rents very quickly.[16] A certain amount of “reverse re-covery time” tᵣ (on the order of tens of nanoseconds to afewmicroseconds) may be required to remove the reverserecovery charge Qᵣ from the diode. During this recoverytime, the diode can actually conduct in the reverse direc-tion. This might give rise to a large constant current inthe reverse direction for a short period of time and whilethe diode is reverse biased. The magnitude of such re-verse current is determined by the operating circuit (i.e.,the series resistance) and the diode is called to be in thestorage-phase.[17] In certain real-world cases it can be im-portant to consider the losses incurred by this non-idealdiode effect.[18] However, when the slew rate of the cur-rent is not so severe (e.g. Line frequency) the effect canbe safely ignored. For most applications, the effect is alsonegligible for Schottky diodes.The reverse current ceases abruptly when the storedcharge is depleted; this abrupt stop is exploited in steprecovery diodes for generation of extremely short pulses.

7.5 Types of semiconductor diode

Several types of diodes. The scale is centimeters.

There are several types of p–n junction diodes, which em-phasize either a different physical aspect of a diode of-ten by geometric scaling, doping level, choosing the right

C

D

A

B

A

Typical datasheet drawing showing the dimensions of a DO-41diode package

electrodes, are just an application of a diode in a specialcircuit, or are really different devices like the Gunn andlaser diode and the MOSFET:Normal (p–n) diodes, which operate as described above,are usually made of doped silicon or, more rarely,germanium. Before the development of silicon powerrectifier diodes, cuprous oxide and later selenium wasused; its low efficiency gave it a much higher forward

7.5. TYPES OF SEMICONDUCTOR DIODE 71

voltage drop (typically 1.4 to 1.7 V per “cell”, with multi-ple cells stacked to increase the peak inverse voltage rat-ing in high voltage rectifiers), and required a large heatsink (often an extension of the diode’s metal substrate),much larger than a silicon diode of the same current rat-ings would require. The vast majority of all diodes are thep–n diodes found in CMOS integrated circuits, which in-clude two diodes per pin and many other internal diodes.Avalanche diodes

These are diodes that conduct in the reverse di-rection when the reverse bias voltage exceedsthe breakdown voltage. These are electricallyvery similar to Zener diodes (and are oftenmis-takenly called Zener diodes), but break downby a different mechanism: the avalanche ef-fect. This occurs when the reverse electric fieldacross the p–n junction causes a wave of ion-ization, reminiscent of an avalanche, leading toa large current. Avalanche diodes are designedto break down at a well-defined reverse volt-age without being destroyed. The differencebetween the avalanche diode (which has a re-verse breakdown above about 6.2 V) and theZener is that the channel length of the formerexceeds the mean free path of the electrons, sothere are collisions between them on the wayout. The only practical difference is that thetwo types have temperature coefficients of op-posite polarities.

Cat’s whisker or crystal diodes

These are a type of point-contact diode. Thecat’s whisker diode consists of a thin or sharp-enedmetal wire pressed against a semiconduct-ing crystal, typically galena or a piece of coal.The wire forms the anode and the crystal formsthe cathode. Cat’s whisker diodes were alsocalled crystal diodes and found application incrystal radio receivers. Cat’s whisker diodesare generally obsolete, but may be availablefrom a few manufacturers.

Constant current diodes

These are actually JFETs[19] with the gateshorted to the source, and function like a two-terminal current-limiting analog to the voltage-limiting Zener diode. They allow a currentthrough them to rise to a certain value, and thenlevel off at a specific value. Also called CLDs,constant-current diodes, diode-connected tran-sistors, or current-regulating diodes.

Esaki or tunnel diodes

These have a region of operation showingnegative resistance caused by quantum tunnel-ing,[20] allowing amplification of signals andvery simple bistable circuits. Due to the highcarrier concentration, tunnel diodes are veryfast, may be used at low (mK) temperatures,high magnetic fields, and in high radiationenvironments.[21] Because of these properties,they are often used in spacecraft.

Gunn diodes

These are similar to tunnel diodes in that theyare made of materials such as GaAs or InPthat exhibit a region of negative differential re-sistance. With appropriate biasing, dipole do-mains form and travel across the diode, allow-ing high frequency microwave oscillators to bebuilt.

Light-emitting diodes (LEDs)

In a diode formed from a direct band-gapsemiconductor, such as gallium arsenide, car-riers that cross the junction emit photons whenthey recombine with the majority carrier onthe other side. Depending on the material,wavelengths (or colors)[22] from the infraredto the near ultraviolet may be produced.[23]The forward potential of these diodes de-pends on the wavelength of the emitted pho-tons: 2.1 V corresponds to red, 4.0 V to vi-olet. The first LEDs were red and yellow,and higher-frequency diodes have been devel-oped over time. All LEDs produce incoher-ent, narrow-spectrum light; “white” LEDs areactually combinations of three LEDs of a dif-ferent color, or a blue LED with a yellowscintillator coating. LEDs can also be usedas low-efficiency photodiodes in signal appli-cations. An LED may be paired with a photo-diode or phototransistor in the same package,to form an opto-isolator.

Laser diodes

When an LED-like structure is contained in aresonant cavity formed by polishing the parallelend faces, a laser can be formed. Laser diodesare commonly used in optical storage devicesand for high speed optical communication.

Thermal diodes

This term is used both for conventional p–n diodes used to monitor temperature due

72 CHAPTER 7. DIODE

to their varying forward voltage with tem-perature, and for Peltier heat pumps forthermoelectric heating and cooling. Peltierheat pumps may be made from semiconduc-tor, though they do not have any rectifyingjunctions, they use the differing behaviour ofcharge carriers in N and P type semiconductorto move heat.

Photodiodes

All semiconductors are subject to opticalcharge carrier generation. This is typi-cally an undesired effect, so most semicon-ductors are packaged in light blocking ma-terial. Photodiodes are intended to senselight(photodetector), so they are packaged inmaterials that allow light to pass, and are usu-ally PIN (the kind of diode most sensitive tolight).[24] A photodiode can be used in solarcells, in photometry, or in optical communica-tions. Multiple photodiodes may be packagedin a single device, either as a linear array or asa two-dimensional array. These arrays shouldnot be confused with charge-coupled devices.

PIN diodes

A PIN diode has a central un-doped, or in-trinsic, layer, forming a p-type/intrinsic/n-typestructure.[25] They are used as radio frequencyswitches and attenuators. They are also usedas large-volume, ionizing-radiation detectorsand as photodetectors. PIN diodes are alsoused in power electronics, as their central layercan withstand high voltages. Furthermore, thePIN structure can be found in many powersemiconductor devices, such as IGBTs, powerMOSFETs, and thyristors.

Schottky diodes

Schottky diodes are constructed from a metalto semiconductor contact. They have a lowerforward voltage drop than p–n junction diodes.Their forward voltage drop at forward cur-rents of about 1 mA is in the range 0.15 Vto 0.45 V, which makes them useful in volt-age clamping applications and prevention oftransistor saturation. They can also be used aslow loss rectifiers, although their reverse leak-age current is in general higher than that ofother diodes. Schottky diodes are majoritycarrier devices and so do not suffer from mi-nority carrier storage problems that slow downmany other diodes—so they have a faster re-verse recovery than p–n junction diodes. They

also tend to have much lower junction capaci-tance than p–n diodes, which provides for highswitching speeds and their use in high-speedcircuitry and RF devices such as switched-mode power supply, mixers, and detectors.

Super barrier diodes

Super barrier diodes are rectifier diodes that in-corporate the low forward voltage drop of theSchottky diode with the surge-handling capa-bility and low reverse leakage current of a nor-mal p–n junction diode.

Gold-doped diodes

As a dopant, gold (or platinum) acts as recom-bination centers, which helps a fast recombina-tion of minority carriers. This allows the diodeto operate at signal frequencies, at the expenseof a higher forward voltage drop. Gold-dopeddiodes are faster than other p–n diodes (but notas fast as Schottky diodes). They also have lessreverse-current leakage than Schottky diodes(but not as good as other p–n diodes).[26][27] Atypical example is the 1N914.

Snap-off or Step recovery diodes

The term step recovery relates to the form ofthe reverse recovery characteristic of these de-vices. After a forward current has been passingin an SRD and the current is interrupted or re-versed, the reverse conduction will cease veryabruptly (as in a step waveform). SRDs can,therefore, provide very fast voltage transitionsby the very sudden disappearance of the chargecarriers.

Stabistors or Forward Reference Diodes

The term stabistor refers to a special type ofdiodes featuring extremely stable forward volt-age characteristics. These devices are spe-cially designed for low-voltage stabilization ap-plications requiring a guaranteed voltage over awide current range and highly stable over tem-perature.

Transient voltage suppression diode (TVS)

These are avalanche diodes designed specifi-cally to protect other semiconductor devicesfrom high-voltage transients.[28] Their p–njunctions have a much larger cross-sectionalarea than those of a normal diode, allowingthem to conduct large currents to ground with-out sustaining damage.

7.7. RELATED DEVICES 73

Varicap or varactor diodes

These are used as voltage-controlledcapacitors. These are important in PLL(phase-locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits,such as those in television receivers, to lockquickly. They also enabled tunable oscillatorsin early discrete tuning of radios, where acheap and stable, but fixed-frequency, crystaloscillator provided the reference frequency fora voltage-controlled oscillator.

Zener diodes

These can be made to conduct in reverse bias(backward), and are correctly termed reversebreakdown diodes. This effect, called Zenerbreakdown, occurs at a precisely defined volt-age, allowing the diode to be used as a precisionvoltage reference. The term Zener diode is col-loquially applied to several types of breakdowndiodes, but strictly speaking Zener diodes havea breakdown voltage of below 5 volts, whilstthose above that value are usually avalanchediodes. In practical voltage reference circuits,Zener and switching diodes are connected inseries and opposite directions to balance thetemperature coefficient to near-zero. Some de-vices labeled as high-voltage Zener diodes areactually avalanche diodes (see above). Two(equivalent) Zeners in series and in reverse or-der, in the same package, constitute a transientabsorber (or Transorb, a registered trademark).The Zener diode is named for Dr. ClarenceMelvin Zener of Carnegie Mellon University,inventor of the device.

Other uses for semiconductor diodes include sensingtemperature, and computing analog logarithms (seeOperational amplifier applications#Logarithmic output).

7.6 Numbering and codingschemes

There are a number of common, standard andmanufacturer-driven numbering and coding schemes fordiodes; the two most common being the EIA/JEDECstandard and the European Pro Electron standard:

7.6.1 EIA/JEDEC

The standardized 1N-series numbering EIA370 systemwas introduced in the US by EIA/JEDEC (Joint ElectronDevice Engineering Council) about 1960. Most diodes

have a 1-prefix designation (e.g., 1N4003). Amongthe most popular in this series were: 1N34A/1N270(germanium signal), 1N914/1N4148 (silicon signal),1N4001−1N4007 (silicon 1A power rectifier) and1N54xx (silicon 3A power rectifier)[29][30][31]

7.6.2 JIS

The JIS semiconductor designation system has all semi-conductor diode designations starting with “1S”.

7.6.3 Pro Electron

The European Pro Electron coding system for active com-ponents was introduced in 1966 and comprises two lettersfollowed by the part code. The first letter represents thesemiconductor material used for the component (A = ger-manium and B = silicon) and the second letter representsthe general function of the part (for diodes: A = low-power/signal, B = variable capacitance, X = multiplier, Y= rectifier and Z = voltage reference), for example:

• AA-series germanium low-power/signal diodes(e.g.: AA119)

• BA-series silicon low-power/signal diodes (e.g.:BAT18 silicon RF switching diode)

• BY-series silicon rectifier diodes (e.g.: BY1271250V, 1A rectifier diode)

• BZ-series silicon Zener diodes (e.g.: BZY88C4V74.7V Zener diode)

Other common numbering / coding systems (generallymanufacturer-driven) include:

• GD-series germanium diodes (e.g.: GD9) – this is avery old coding system

• OA-series germanium diodes (e.g.: OA47) – acoding sequence developed by Mullard, a UK com-pany

As well as these common codes, many manufacturers ororganisations have their own systems too – for example:

• HP diode 1901-0044 = JEDEC 1N4148

• UK military diode CV448 = Mullard type OA81 =GEC type GEX23

7.7 Related devices• Rectifier

• Transistor

74 CHAPTER 7. DIODE

• Thyristor or silicon controlled rectifier (SCR)

• TRIAC

• DIAC

• Varistor

In optics, an equivalent device for the diode but with laserlight would be the Optical isolator, also known as an Op-tical Diode, that allows light to only pass in one direction.It uses a Faraday rotator as the main component.

7.8 Applications

7.8.1 Radio demodulation

The first use for the diode was the demodulation ofamplitude modulated (AM) radio broadcasts. The his-tory of this discovery is treated in depth in the radio ar-ticle. In summary, an AM signal consists of alternatingpositive and negative peaks of a radio carrier wave, whoseamplitude or envelope is proportional to the original au-dio signal. The diode (originally a crystal diode) rectifiesthe AM radio frequency signal, leaving only the positivepeaks of the carrier wave. The audio is then extractedfrom the rectified carrier wave using a simple filter andfed into an audio amplifier or transducer, which gener-ates sound waves.

7.8.2 Power conversion

Main article: RectifierRectifiers are constructed from diodes, where they

Schematic of basic AC-to-DC power supply

are used to convert alternating current (AC) electric-ity into direct current (DC). Automotive alternators area common example, where the diode, which rectifiesthe AC into DC, provides better performance than thecommutator or earlier, dynamo. Similarly, diodes arealso used in Cockcroft–Walton voltage multipliers to con-vert AC into higher DC voltages.

7.8.3 Over-voltage protection

Diodes are frequently used to conduct damaging highvoltages away from sensitive electronic devices. They

are usually reverse-biased (non-conducting) under normalcircumstances. When the voltage rises above the normalrange, the diodes become forward-biased (conducting).For example, diodes are used in (stepper motor and H-bridge) motor controller and relay circuits to de-energizecoils rapidly without the damaging voltage spikes thatwould otherwise occur. (Any diode used in such an ap-plication is called a flyback diode). Many integrated cir-cuits also incorporate diodes on the connection pins toprevent external voltages from damaging their sensitivetransistors. Specialized diodes are used to protect fromover-voltages at higher power (see Diode types above).

7.8.4 Logic gates

Diodes can be combined with other components to con-struct AND and OR logic gates. This is referred to asdiode logic.

7.8.5 Ionizing radiation detectors

In addition to light, mentioned above, semiconductordiodes are sensitive to more energetic radiation. Inelectronics, cosmic rays and other sources of ionizing ra-diation cause noise pulses and single and multiple bit er-rors. This effect is sometimes exploited by particle de-tectors to detect radiation. A single particle of radia-tion, with thousands or millions of electron volts of en-ergy, generates many charge carrier pairs, as its energyis deposited in the semiconductor material. If the deple-tion layer is large enough to catch the whole shower orto stop a heavy particle, a fairly accurate measurementof the particle’s energy can be made, simply by measur-ing the charge conducted and without the complexity ofa magnetic spectrometer, etc. These semiconductor ra-diation detectors need efficient and uniform charge col-lection and low leakage current. They are often cooledby liquid nitrogen. For longer-range (about a centime-tre) particles, they need a very large depletion depth andlarge area. For short-range particles, they need any con-tact or un-depleted semiconductor on at least one surfaceto be very thin. The back-bias voltages are near break-down (around a thousand volts per centimetre). Germa-nium and silicon are common materials. Some of thesedetectors sense position as well as energy. They have afinite life, especially when detecting heavy particles, be-cause of radiation damage. Silicon and germanium arequite different in their ability to convert gamma rays toelectron showers.Semiconductor detectors for high-energy particles areused in large numbers. Because of energy loss fluctua-tions, accurate measurement of the energy deposited isof less use.

7.9. ABBREVIATIONS 75

7.8.6 Temperature measurements

A diode can be used as a temperature measuring device,since the forward voltage drop across the diode dependson temperature, as in a silicon bandgap temperature sen-sor. From the Shockley ideal diode equation given above,it might appear that the voltage has a positive temperaturecoefficient (at a constant current), but usually the varia-tion of the reverse saturation current term is more sig-nificant than the variation in the thermal voltage term.Most diodes therefore have a negative temperature coef-ficient, typically −2 mV/˚C for silicon diodes. The tem-perature coefficient is approximately constant for temper-atures above about 20 kelvins. Some graphs are givenfor 1N400x series,[32] and CY7 cryogenic temperaturesensor.[33]

7.8.7 Current steering

Diodes will prevent currents in unintended directions. Tosupply power to an electrical circuit during a power fail-ure, the circuit can draw current from a battery. Anuninterruptible power supply may use diodes in this wayto ensure that current is only drawn from the battery whennecessary. Likewise, small boats typically have two cir-cuits each with their own battery/batteries: one used forengine starting; one used for domestics. Normally, bothare charged from a single alternator, and a heavy-dutysplit-charge diode is used to prevent the higher-chargebattery (typically the engine battery) from dischargingthrough the lower-charge battery when the alternator isnot running.Diodes are also used in electronic musical keyboards. Toreduce the amount of wiring needed in electronic musi-cal keyboards, these instruments often use keyboard ma-trix circuits. The keyboard controller scans the rows andcolumns to determine which note the player has pressed.The problem with matrix circuits is that, when severalnotes are pressed at once, the current can flow backwardsthrough the circuit and trigger "phantom keys" that cause“ghost” notes to play. To avoid triggering unwanted notes,most keyboard matrix circuits have diodes soldered withthe switch under each key of the musical keyboard. Thesame principle is also used for the switch matrix in solid-state pinball machines.

7.8.8 Waveform Clipper

Main article: Clipper (electronics)

Diodes can be used to limit the positive or negative ex-cursion of a signal to a prescribed voltage.

7.8.9 Clamper

Main article: Clamper (electronics)A diode clamp circuit can take a periodic alternating cur-

This simple diode clamp will clamp the negative peaks of the in-coming waveform to the common rail voltage

rent signal that oscillates between positive and negativevalues, and vertically displace it such that either the pos-itive, or the negative peaks occur at a prescribed level.The clamper does not restrict the peak-to-peak excursionof the signal, it moves the whole signal up or down so asto place the peaks at the reference level.

7.9 Abbreviations

Diodes are usually referred to as D for diode on PCBs.Sometimes the abbreviation CR for crystal rectifier isused.[34]

7.10 See also• Active rectification

• Diode modelling

• Junction diode

• Lambda diode

• p–n junction

• Small-signal model

7.11 References[1] Tooley, Mike (2012). Electronic Circuits: Fundamentals

and Applications, 3rd Ed. Routlege. p. 81. ISBN 1-136-40731-6.

[2] Lowe, Doug (2013). “Electronics Components: Diodes”.Electronics All-In-One Desk Reference For Dummies. JohnWiley & Sons. Retrieved January 4, 2013.

76 CHAPTER 7. DIODE

[3] Crecraft, David; Stephen Gergely (2002). AnalogElectronics: Circuits, Systems and Signal Processing.Butterworth-Heinemann. p. 110. ISBN 0-7506-5095-8.

[4] Horowitz, Paul; Winfield Hill (1989). The Art of Electron-ics, 2nd Ed. London: Cambridge University Press. p. 44.ISBN 0-521-37095-7.

[5] “Physical Explanation – General Semiconductors”. 2010-05-25. Retrieved 2010-08-06.

[6] “The Constituents of Semiconductor Components”.2010-05-25. Retrieved 2010-08-06.

[7] Guthrie, Frederick (October 1873) “On a relation betweenheat and static electricity,” The London, Edinburgh andDublin PhilosophicalMagazine and Journal of Science, 4thseries, 46 : 257–266.

[8] 1928 Nobel Lecture: Owen W. Richardson, “Thermionicphenomena and the laws which govern them”, December12, 1929

[9] Edison, Thomas A. “Electrical Meter” U.S. Patent307,030 Issue date: Oct 21, 1884

[10] “Road to the Transistor”. Jmargolin.com. Retrieved2008-09-22.

[11] Braun, Ferdinand (1874) “Ueber die Stromleitung durchSchwefelmetalle” (On current conduction in metal sul-phides), Annalen der Physik und Chemie, 153 : 556–563.

[12] Karl Ferdinand Braun. chem.ch.huji.ac.il

[13] “Diode”. Encyclobeamia.solarbotics.net.

[14] Sarkar, Tapan K. (2006). History of wireless. USA: JohnWiley and Sons. pp. 94, 291–308. ISBN 0-471-71814-9.

[15] Pickard, Greenleaf Whittier “Means for receiving intel-ligence communicated by electric waves” U.S. Patent836,531 Issued: August 30, 1906

[16] Diode reverse recovery in a boost converter. ECEN5817.ecee.colorado.edu

[17] Elhami Khorasani, A.; Griswold, M.; Alford, T. L.(2014). “Gate-Controlled Reverse Recovery for Charac-terization of LDMOS Body Diode”. IEEE Electron DeviceLetters 35 (11): 1079. doi:10.1109/LED.2014.2353301.

[18] Inclusion of Switching Loss in the Averaged EquivalentCircuit Model. ECEN5797. ecee.colorado.edu

[19] Current regulator diodes. Digikey.com (2009-05-27).Retrieved 2013-12-19.

[20] Jonscher, A. K. (1961). “The physics of the tunneldiode”. British Journal of Applied Physics 12 (12):654. Bibcode:1961BJAP...12..654J. doi:10.1088/0508-3443/12/12/304.

[21] Dowdey, J. E., and Travis, C. M. (1964). “AnAnalysis of Steady-State Nuclear Radiation Damageof Tunnel Diodes”. IEEE Transactions on NuclearScience 11 (5): 55. Bibcode:1964ITNS...11...55D.doi:10.1109/TNS2.1964.4315475.

[22] Classification of components. Digikey.com (2009-05-27). Retrieved 2013-12-19.

[23] “Component Construction”. 2010-05-25. Retrieved2010-08-06.

[24] Component Construction. Digikey.com (2009-05-27).Retrieved 2013-12-19.

[25] “Physics and Technology”. 2010-05-25. Retrieved 2010-08-06.

[26] Fast Recovery Epitaxial Diodes (FRED) Characteristics –Applications – Examples. (PDF). Retrieved 2013-12-19.

[27] Sze, S. M. (1998) Modern Semiconductor Device Physics,Wiley Interscience, ISBN 0-471-15237-4

[28] Protecting Low Current Loads in Harsh Electrical Envi-ronments. Digikey.com (2009-05-27). Retrieved 2013-12-19.

[29] “About JEDEC”. Jedec.org. Retrieved 2008-09-22.

[30] “Introduction dates of common transistors and diodes?".EDAboard.com. 2010-06-10. Retrieved 2010-08-06.

[31] I.D.E.A. “Transistor Museum Construction Projects PointContact Germanium Western Electric Vintage HistoricSemiconductors Photos Alloy Junction Oral History”.Semiconductormuseum.com. Retrieved 2008-09-22.

[32] 1N400x Diode Family Forward Voltage. Cliftonlaborato-ries.com. Retrieved 2013-12-19.

[33] Cryogenic Temperature Sensors. omega.com

[34] John Ambrose Fleming (1919). The Principles of Elec-tric Wave Telegraphy and Telephony. London: Longmans,Green. p. 550.

7.12 External links• Diodes and Rectifiers – Chapter on All About Cir-cuits

• Structure and Functional Behavior of PIN Diodes –PowerGuru

Interactive and animations

• Interactive Explanation of Semiconductor Diode,University of Cambridge

• Schottky Diode Flash Tutorial Animation

Datasheets

• Discrete Databook (Historical 1978), NationalSemiconductor (now Texas Instruments)

• Discrete Databook (Historical 1982), SGS (nowSTMicroelectronics)

• Discrete Databook (Historical 1985), Fairchild

Chapter 8

Wire

For other uses, see Wire (disambiguation).A wire is a single, usually cylindrical, flexible strand or

Wires overhead

rod of metal. Wires are used to bear mechanical loads orelectricity and telecommunications signals. Wire is com-monly formed by drawing the metal through a hole in adie or draw plate. Wire gauges come in various standardsizes, as expressed in terms of a gauge number. The termwire is also used more loosely to refer to a bundle ofsuch strands, as in 'multistranded wire', which is morecorrectly termed a wire rope in mechanics, or a cable inelectricity.Wire comes in solid core, stranded, or braided forms.Although usually circular in cross-section, wire can bemade in square, hexagonal, flattened rectangular, or othercross-sections, either for decorative purposes, or fortechnical purposes such as high-efficiency voice coils inloudspeakers. Edge-wound[1] coil springs, such as theSlinky toy, are made of special flattened wire.

8.1 History

In antiquity, jewelry often contains, in the form of chainsand applied decoration, large amounts of wire that is ac-curately made and which must have been produced bysome efficient, if not technically advanced, means. Insome cases, strips cut from metal sheet were made intowire by pulling them through perforations in stone beads.

Wire wrapped jewelry

This causes the strips to fold round on themselves to formthin tubes. This strip drawing technique was in use inEgypt by the 2nd Dynasty. From the middle of the 2ndmillennium BC most of the gold wires in jewellery arecharacterised by seam lines that follow a spiral path alongthe wire. Such twisted strips can be converted into solidround wires by rolling them between flat surfaces or thestrip wire drawing method. The strip twist wire manufac-turing method was superseded by drawing in the ancientOldWorld sometime between about the 8th and 10th cen-turies AD.[2] There is some evidence for the use of draw-ing further East prior to this period.[3]

Square and hexagonal wires were possibly made using aswaging technique. In this method a metal rod was struckbetween grooved metal blocks, or between a groovedpunch and a grooved metal anvil. Swaging is of great an-tiquity, possibly dating to the beginning of the 2nd mil-

77

78 CHAPTER 8. WIRE

lennium BC in Egypt and in the Bronze and Iron Ages inEurope for torcs and fibulae.Twisted square section wires are a very common filigreedecoration in early Etruscan jewellery.In about the middle of the 2nd millennium BC a new cat-egory of decorative tube was introduced which imitated aline of granules. True beaded wire, produced by mechan-ically distorting a round-section wire, appeared in theEastern Mediterranean and Italy in the seventh centuryBC, perhaps disseminated by the Phoenicians. Beadedwire continued to be used in jewellery into modern times,although it largely fell out of favour in about the tenth cen-tury AD when two drawn round wires, twisted togetherto form what are termed 'ropes’, provided a simpler-to-make alternative. A forerunner to beaded wire may bethe notched strips andwires which first occur from around2000 BC in Anatolia.Wire was drawn in England from the medieval period.The wire was used to make wool cards and pins, manu-factured goods whose import was prohibited by EdwardIV in 1463.[4] The first wire mill in Great Britain wasestablished at Tintern in about 1568 by the founders ofthe Company of Mineral and Battery Works, who had amonopoly on this.[5] Apart from their second wire millat nearby Whitebrook,[6] there were no other wire millsbefore the second half of the 17th century. Despite theexistence of mills, the drawing of wire down to fine sizescontinued to be done manually.Wire is usually drawn of cylindrical form; but it may bemade of any desired section by varying the outline of theholes in the draw-plate through which it is passed in theprocess of manufacture. The draw-plate or die is a pieceof hard cast-iron or hard steel, or for fine work it maybe a diamond or a ruby. The object of utilising preciousstones is to enable the dies to be used for a considerableperiod without losing their size, and so producing wire ofincorrect diameter. Diamond dies must be rebored whenthey have lost their original diameter of hole, but metaldies are brought down to size again by hammering up thehole and then drifting it out to correct diameter with apunch.

8.2 Uses

Wire has many uses. It forms the raw material of manyimportant manufacturers, such as the wire netting indus-try, engineered springs, wire-cloth making and wire ropespinning, in which it occupies a place analogous to atextile fiber. Wire-cloth of all degrees of strength andfineness of mesh is used for sifting and screening ma-chinery, for draining paper pulp, for window screens, andfor many other purposes. Vast quantities of aluminium,copper, nickel and steel wire are employed for telephoneand data cables, and as conductors in electric powertransmission, and heating. It is in no less demand for

fencing, and much is consumed in the construction ofsuspension bridges, and cages, etc. In the manufactureof stringed musical instruments and scientific instrumentswire is again largely used. Carbon and stainless springsteel wire have significant applications for engineeredsprings for critical automotive or industrial manufacturedparts/components. Among its other sources of consump-tion it is sufficient to mention pin and hairpin making, theneedle and fish-hook industries, nail, peg and rivet mak-ing, and carding machinery; indeed there are few indus-tries into which it does not enter.Not all metals and metallic alloys possess the physicalproperties necessary to make useful wire. The metalsmust in the first place be ductile and strong in tension, thequality on which the utility of wire principally depends.Themetals suitable for wire, possessing almost equal duc-tility, are platinum, silver, iron, copper, aluminium andgold; and it is only from these and certain of their alloyswith other metals, principally brass and bronze, that wireis prepared (For a detailed discussion on copper wire, seemain article: Copper wire and cable.).By careful treatment extremely thin wire can be pro-duced. Special purpose wire is however made from othermetals (e.g. tungsten wire for light bulb and vacuum tubefilaments, because of its high melting temperature). Cop-per wires are also plated with other metals, such as tin,nickel, and silver to handle different temperatures, pro-vide lubrication, provide easier stripping of rubber fromcopper.

8.3 Production

Wire mill (1913)

Main article: Wire drawing

Wire is often reduced to the desired diameter and prop-erties by repeated drawing through progressively smallerdies, or traditionally holes in draw plates. After a num-ber of passes the wire may be annealed to facilitate more

8.5. FORMS OF WIRE 79

drawing or, if it is a finished product, to maximise ductil-ity and conductivity.

8.4 Finishing, jacketing, and insu-lating

Electrical wires are usually covered with insulating ma-terials, such as plastic, rubber-like polymers, or varnish.Insulating and jacketing of wires and cables is nowadaysdone by passing them through an extruder. Formerly,materials used for insulation included treated cloth or pa-per and various oil-based products. Since the mid-1960s,plastic and polymers exhibiting properties similar to rub-ber have predominated.Two or more wires may be wrapped concentrically, sepa-rated by insulation, to form coaxial cable. The wire or ca-ble may be further protected with substances like paraffin,some kind of preservative compound, bitumen, lead, alu-minum sheathing, or steel taping. Stranding or coveringmachines wind material onto wire which passes throughquickly. Some of the smallest machines for cotton cover-ing have a large drum, which grips the wire and moves itthrough toothed gears; the wire passes through the centreof disks mounted above a long bed, and the disks carryeach a number of bobbins varying from six to twelve ormore in different machines. A supply of covering ma-terial is wound on each bobbin, and the end is led on tothe wire, which occupies a central position relatively tothe bobbins; the latter being revolved at a suitable speedbodily with their disks, the cotton is consequently servedon to the wire, winding in spiral fashion so as to overlap.If a large number of strands are required the disks are du-plicated, so that as many as sixty spools may be carried,the second set of strands being laid over the first.

Coaxial cable, one example of a jacketed and insulated wire.

For heavier cables that are used for electric light andpower as well as submarine cables, the machines aresomewhat different in construction. The wire is still car-ried through a hollow shaft, but the bobbins or spools ofcovering material are set with their spindles at right an-gles to the axis of the wire, and they lie in a circular cage

which rotates on rollers below. The various strands com-ing from the spools at various parts of the circumferenceof the cage all lead to a disk at the end of the hollowshaft. This disk has perforations through which each ofthe strands pass, thence being immediately wrapped onthe cable, which slides through a bearing at this point.Toothed gears having certain definite ratios are used tocause the winding drum for the cable and the cage for thespools to rotate at suitable relative speeds which do notvary. The cages are multiplied for stranding with a largenumber of tapes or strands, so that a machine may havesix bobbins on one cage and twelve on the other.

8.5 Forms of wire

Further information: Copper wire and cable#Types ofcopper wire and cable

8.5.1 Solid wire

Solid wire, also called solid-core or single-strand wire,consists of one piece of metal wire. Solid wire is usefulfor wiring breadboards. Solid wire is cheaper to manu-facture than stranded wire and is used where there is littleneed for flexibility in the wire. Solid wire also providesmechanical ruggedness; and, because it has relatively lesssurface area which is exposed to attack by corrosives, pro-tection against the environment.

8.5.2 Stranded wire

Stranded copper wire

Stranded wire is composed of a number of small gaugewire bundled or wrapped together to form a larger con-

80 CHAPTER 8. WIRE

ductor. Stranded wire is more flexible than solid wire ofthe same total cross-sectional area. Stranded wire tendsto be a better conductor than solid wire because the indi-vidual wires collectively comprise a greater surface area.Stranded wire is used when higher resistance to metalfatigue is required. Such situations include connectionsbetween circuit boards in multi-printed-circuit-board de-vices, where the rigidity of solid wire would produce toomuch stress as a result of movement during assembly orservicing; A.C. line cords for appliances; musical instru-ment cables; computer mouse cables; welding electrodecables; control cables connecting moving machine parts;mining machine cables; trailing machine cables; and nu-merous others.At high frequencies, current travels near the surface ofthe wire because of the skin effect, resulting in increasedpower loss in the wire. Stranded wire might seem to re-duce this effect, since the total surface area of the strandsis greater than the surface area of the equivalent solidwire, but ordinary stranded wire does not reduce the skineffect because all the strands are short-circuited togetherand behave as a single conductor. A stranded wire willhave higher resistance than a solid wire of the same diam-eter because the cross-section of the stranded wire is notall copper; there are unavoidable gaps between the strands(this is the circle packing problem for circles within a cir-cle). A stranded wire with the same cross-section of con-ductor as a solid wire is said to have the same equivalentgauge and is always a larger diameter.However, for many high-frequency applications,proximity effect is more severe than skin effect, and insome limited cases, simple stranded wire can reduceproximity effect. For better performance at high fre-quencies, litz wire, which has the individual strandsinsulated and twisted in special patterns, may be used.

8.5.3 Braided wire

A braided wire is composed of a number of small strandsof wire braided together. Similar to stranded wires,braided wires are better conductors than solid wires.Braided wires do not break easily when flexed. Braidedwires are often suitable as an electromagnetic shield innoise-reduction cables.

8.5.4 Number of strands

The more individual wire strands in a wire bundle,the more flexible, kink-resistant, break-resistant, andstronger the wire is. But more strands increase cost.The lowest number of strands usually seen is 7: one in themiddle, 6 surrounding it. The next level up is 19, which isanother layer of 12 strands on top of the 7. After that thenumber varies, but 37 and 49 are common, then in the 70to 100 range (the number is no longer exact). Even larger

numbers than that are typically found only in very largecables.For application where the wire moves, 19 is the lowestthat should be used (7 should only be used in applicationswhere the wire is placed and then does not move), and 49is much better. For applications with constant repeatedmovement, such as assembly robots and headphone wires,70 to 100 is mandatory.For applications that need even more flexibility (weldingis the usual example, but also any need to move wire intight areas), even more strands are used. One example isa 2/0 wire made from 5,292 strands of #36 gauge wire.The strands are organized by first creating a bundle of 7strands. Then 7 of these bundles are put together into su-per bundles. Finally 108 super bundles are used to makethe final cable. Each group of wires is wound in a he-lix so that when the wire is flexed, the part of a bundlethat is stretched moves around the helix to a part that iscompressed to allow the wire to have less stress.

8.6 Varieties

Germanium diode bound with gold wire.

• Hook-up wire is small-to-medium gauge, solid orstranded, insulated wire, used for making internalconnections inside electrical or electronic devices.It is often tin-plated to facilitate soldering.

• Wire bonding is the application of microscopicwires for making electrical connections insidesemiconductor components and integrated circuits.

• Magnet wire is solid wire, usually copper, which, toallow closer winding when making electromagneticcoils, is insulated only with varnish, rather than thethicker plastic or other insulation commonly used onelectrical wire. It is used for the winding of motors,transformers, inductors, generators, speaker coils,etc. (For further information about copper mag-net wire, see: Copper wire and cable#Magnet wire(Winding wire).).

• Coaxial cable is a cable consisting of an inner con-ductor, surrounded by a tubular insulating layer typ-

8.8. NOTES 81

ically made from a flexible material with a high di-electric constant, all of which is then surroundedby another conductive layer (typically of fine wo-ven wire for flexibility, or of a thin metallic foil),and then finally covered again with a thin insulat-ing layer on the outside. The term coaxial comesfrom the inner conductor and the outer shield shar-ing the same geometric axis. Coaxial cables are of-ten used as a transmission line for radio frequencysignals. In a hypothetical ideal coaxial cable theelectromagnetic field carrying the signal exists onlyin the space between the inner and outer conductors.Practical cables achieve this objective to a high de-gree. A Coaxial Cable provides protection of signalsfrom external electromagnetic interference, and ef-fectively guides signals with low emission along thelength of the cable.

• Speaker wire is used to make the electrical con-nection between loudspeakers and audio amplifiers.Modern speaker wire consists of electrical conduc-tors individually insulated by plastic.

• Resistance wire is wire with higher than normal re-sistivity, often used for heating elements or for mak-ing wire-wound resistors. Nichromewire is themostcommon type.

8.7 See also• For transmission see: Power cable, High-voltage ca-ble and HVDC

• Barbed wire

• Cable

• Chicken wire

• Electrical connector

• Electrical wiring

• Litz wire

• Piano wire

• Razor wire

• THHN

• Tinsel wire

• Wire (album)

• Wire (band)

• Wire bonding

• Wire gauge

• Wire netting

• Wire rope

• Wire wrapped jewelry

• Wollaston wire

8.8 Notes[1] Swiger Coil Systems. “Edgewound Coils”. Swiger Coil

Systems, AWabtec Company. Retrieved 1 January 2011.

[2] Jack Ogden, ‘Classical Gold wire: Some Aspects of itsManufacture and Use’, Jewellery Studies, 5, 1991, pp. 95–105.

[3] Jack Ogden, ‘Connections between Islam, Europe, and theFar East in theMedieval Period: The Evidence of the Jew-elry Technology’. Eds P. Jett, J Douglas, B. McCarthy,J Winter. Scientific Research in the Field of Asian Art.Fiftieth-Anniversary Symposium Proceedings. ArchetypePublications, London in association with the Freer Galleryof Art, Smithsonian Institution, 2003.

[4] H. R. Schubert, 'The wiredrawers of Bristol' Journal Iron& Steel Institute 159 (1948), 16-22.

[5] M. B. Donald, Elizabethan Monopolies: Company of Min-eral and Battery Works (Olver & Boyd, Edinburgh 1961),95-141.

[6] D. G. Tucker, 'The seventeenth century wireworks atWhitebrook, Monmouthshire' Bull. Hist. Metall. Gp 7(1)(1973), 28-35.

8.9 References• This article incorporates text from a publication nowin the public domain: Chisholm, Hugh, ed. (1911)."Wire". Encyclopædia Britannica 28 (11th ed.).Cambridge University Press. p. 738.

8.10 External links• Wire Gauge to Diameter—Diameter to Wire GaugeConverter - Online calculator converts gauge to di-ameter or diameter to gauge for any wire size.

Chapter 9

Printed circuit board

Not to be confused with printed electronics.“Printed circuit” redirects here. For the defunct com-pany, see Printed Circuit Corporation.A printed circuit board (PCB) mechanically supports

Part of a 1983 Sinclair ZX Spectrum computer board; a popu-lated PCB, showing the conductive traces, vias (the through-holepaths to the other surface), and some mounted electronic compo-nents

and electrically connects electronic components usingconductive tracks, pads and other features etched fromcopper sheets laminated onto a non-conductive substrate.PCBs can be single sided (one copper layer), double sided(two copper layers) ormulti-layer (outer and inner layers).Multi-layer PCBs allow for much higher component den-sity. Conductors on different layers are connected withplated-through holes called vias. Advanced PCBs maycontain components - capacitors, resistors or active de-vices - embedded in the substrate.Printed circuit boards are used in all but the simplest elec-tronic products. Alternatives to PCBs include wire wrapand point-to-point construction. PCBs require the addi-tional design effort to lay out the circuit, but manufac-turing and assembly can be automated. Manufacturingcircuits with PCBs is cheaper and faster than with otherwiring methods as components are mounted and wiredwith one single part. Furthermore, operator wiring errorsare eliminated.When the board has only copper connections and no em-bedded components, it is more correctly called a printedwiring board (PWB) or etched wiring board. Althoughmore accurate, the term printed wiring board has falleninto disuse. A PCB populated with electronic compo-nents is called a printed circuit assembly (PCA), printed

circuit board assembly or PCB assembly (PCBA). The IPCpreferred term for assembled boards is circuit card assem-bly (CCA),[1] and for assembled backplanes it is backplaneassemblies. The term PCB is used informally both forbare and assembled boards.The world market for bare PCBs reached nearly $60 bil-lion in 2012.[2]

9.1 Design

A board designed in 1967; the sweeping curves in the traces areevidence of freehand design using self-adhesive tape.

Initially PCBs were designed manually by creating aphotomask on a clear mylar sheet, usually at two or fourtimes the true size. Starting from the schematic diagramthe component pin pads were laid out on the mylar andthen traces were routed to connect the pads. Rub-on drytransfers of common component footprints increased ef-ficiency. Traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted inlayout. To fabricate the board, the finished photomaskwas photolithographically reproduced onto a photoresistcoated on the blank copper-clad boards.Nowadays PCBs are designed with dedicated layout soft-ware, generally in the following steps:[3]

1. Schematic capture through an electronic design au-tomation (EDA) tool.

82

9.2. MANUFACTURING 83

2. Card dimensions and template are decided based onrequired circuitry and case of the PCB.

3. The positions of the components and heat sinks aredetermined.

4. Layer stack of the PCB is decided, with one to tensof layers depending on complexity. Ground andpower planes are decided. A power plane is thecounterpart to a ground plane and behaves as an ACsignal ground while providing DC power to the cir-cuits mounted on the PCB. Signal interconnectionsare traced on signal planes. Signal planes can be onthe outer as well as inner layers. For optimal EMIperformance high frequency signals are routed in in-ternal layers between power or ground planes.[4]

5. Line impedance is determined using dielectric layerthickness, routing copper thickness and trace-width.Trace separation is also taken into account in caseof differential signals. Microstrip, stripline or dualstripline can be used to route signals.

6. Components are placed. Thermal considerationsand geometry are taken into account. Vias and landsare marked.

7. Signal traces are routed. Electronic design automa-tion tools usually create clearances and connectionsin power and ground planes automatically.

8. Gerber files are generated formanufacturing.[5][6][7][8]

9.2 Manufacturing

PCB manufacturing consists of many steps.

9.2.1 PCB CAM

Manufacturing starts from the PCB fabrication data gen-erated by CAD.[5] The Gerber or Excellon files in the fab-rication data are never used directly on the manufactur-ing equipment but always read into the CAM (ComputerAided Manufacturing) software. CAM performs the fol-lowing functions:[9]

1. Input of the Gerber data[5][8]

2. Verification of the data; optionally DFM

3. Compensation for deviations in the manufacturingprocesses (e.g. scaling to compensate for distortionsduring lamination)

4. Panelization

5. Output of the digital tools (copper patterns, solderresist image, legend image, drill files, automated op-tical inspection data, electrical test files,...)[5]

9.2.2 Panelization

Panelization is a procedure whereby a number of PCBsare grouped for manufacturing onto a larger board - thepanel. Usually a panel consists of a single design butsometimes multiple designs are mixed on a single panel.There are two types of panels: assembly panels - oftencalled arrays - and bare board manufacturing panels. Theassembler often mount components on panels rather thansingle PCBs because this is efficient.[10] The bare boardmanufactures always uses panels, not only for efficiency,but because of the requirements the plating process. Thusa manufacturing panel can consist of a grouping of in-dividual PCBs or of arrays, depending on what must bedelivered.[5]

The panel is eventually broken apart into individualPCBs; this is called depaneling. Separating the individ-ual PCBs is frequently aided by drilling or routing per-forations along the boundaries of the individual circuits,much like a sheet of postage stamps. Another method,which takes less space, is to cut V-shaped grooves acrossthe full dimension of the panel. The individual PCBs canthen be broken apart along this line of weakness.[11] To-day depaneling is often done by lasers which cut the boardwith no contact. Laser panelization reduces stress on thefragile circuits.

9.2.3 Copper patterning

The first step is to replicate the pattern in the fabricator’sCAM system on a protectivemask on the copper foil PCBlayers. Subsequent etching removes the unwanted cop-per. (Alternatively, a conductive ink can be ink-jetted ona blank (non-conductive) board. This technique is alsoused in the manufacture of hybrid circuits.)

1. Silk screen printing uses etch-resistant inks to cre-ate the protective mask.

2. Photoengraving uses a photomask and developer toselectively remove a UV-sensitive photoresist coat-ing and thus create a photoresist mask. Directimaging techniques are sometimes used for high-resolution requirements. Experiments were madewith thermal resist.[12]

3. PCB milling uses a two or three-axis mechanicalmilling system to mill away the copper foil from thesubstrate. A PCB milling machine (referred to asa 'PCB Prototyper') operates in a similar way to aplotter, receiving commands from the host softwarethat control the position of the milling head in the x,y, and (if relevant) z axis.

4. Laser resist ablation Spray black paint onto cop-per clad laminate, place into CNC laser plotter. Thelaser raster-scans the PCB and ablates (vaporizes)the paint where no resist is wanted. (Note: laser

84 CHAPTER 9. PRINTED CIRCUIT BOARD

copper ablation is rarely used and is considered ex-perimental.)

The method chosen depends on the number of boards tobe produced and the required resolution.

Large volume

• Silk screen printing– used for PCBs with bigger fea-tures

• Photoengraving–used when finer features are re-quired.

Small volume

• Print onto transparent film and use as photo maskalong with photo-sensitized boards. (i.e., pre-sensitized boards), then etch. (Alternatively, use afilm photoplotter)

• Laser resist ablation.

• PCB milling.

Hobbyist

• Laser-printed resist: Laser-print onto transparencyfilm, heat-transfer with an iron or modified lamina-tor onto bare laminate, touch up with a marker, thenetch.

• Vinyl film and resist, non-washable marker, someother methods. Labor-intensive, only suitable forsingle boards.

9.2.4 Subtractive, additive and semi-additive processes

Subtractive methods remove copper from an entirelycopper-coated board to leave only the desired copper pat-tern: In additive methods the pattern is electroplated ontoa bare substrate using a complex process. The advantageof the additive method is that less material is needed andless waste is produced. In the full additive process thebare laminate is covered with a photosensitive film whichis imaged (exposed to light through a mask and then de-veloped which removes the unexposed film). The ex-posed areas are sensitized in a chemical bath, usually con-taining palladium and similar to that used for through holeplating which makes the exposed area capable of bondingmetal ions. The laminate is then plated with copper in thesensitized areas. When the mask is stripped, the PCB isfinished.Semi-additive is the most common process: The unpat-terned board has a thin layer of copper already on it. A re-verse mask is then applied. (Unlike a subtractive process

The two processing methods used to produce a double-sided PWBwith plated through holes.

mask, this mask exposes those parts of the substrate thatwill eventually become the traces.) Additional copper isthen plated onto the board in the unmasked areas; coppermay be plated to any desired weight. Tin-lead or othersurface platings are then applied. The mask is strippedaway and a brief etching step removes the now-exposedbare original copper laminate from the board, isolatingthe individual traces. Some single-sided boards whichhave plated-through holes are made in this way. GeneralElectric made consumer radio sets in the late 1960s usingadditive boards.The (semi-)additive process is commonly used for multi-layer boards as it facilitates the plating-through of theholes to produce conductive vias in the circuit board.

9.2.5 Chemical etching

Chemical etching is usually done with ammonium persul-fate or ferric chloride. For PTH (plated-through holes),additional steps of electroless deposition are done afterthe holes are drilled, then copper is electroplated to buildup the thickness, the boards are screened, and plated withtin/lead. The tin/lead becomes the resist leaving the barecopper to be etched away.The simplest method, used for small-scale production andoften by hobbyists, is immersion etching, in which the

9.2. MANUFACTURING 85

board is submerged in etching solution such as ferric chlo-ride. Compared with methods used for mass production,the etching time is long. Heat and agitation can be appliedto the bath to speed the etching rate. In bubble etching,air is passed through the etchant bath to agitate the solu-tion and speed up etching. Splash etching uses a motor-driven paddle to splash boards with etchant; the processhas become commercially obsolete since it is not as fastas spray etching. In spray etching, the etchant solution isdistributed over the boards by nozzles, and recirculatedby pumps. Adjustment of the nozzle pattern, flow rate,temperature, and etchant composition gives predictablecontrol of etching rates and high production rates.[13]

Asmore copper is consumed from the boards, the etchantbecomes saturated and less effective; different etchantshave different capacities for copper, with some as highas 150 grams of copper per litre of solution. In com-mercial use, etchants can be regenerated to restore theiractivity, and the dissolved copper recovered and sold.Small-scale etching requires attention to disposal of usedetchant, which is corrosive and toxic due to its metal con-tent.The etchant removes copper on all surfaces exposed bythe resist. “Undercut” occurs when etchant attacks thethin edge of copper under the resist; this can reduce con-ductor widths and cause open-circuits. Careful control ofetch time is required to prevent undercut. Where metal-lic plating is used as a resist, it can “overhang” which cancause short-circuits between adjacent traces when closelyspaced. Overhang can be removed by wire-brushing theboard after etching.[13]

9.2.6 Inner layer automated optical inspec-tion (AOI)

The inner layers are given a complete machine inspectionbefore lamination because afterwards mistakes cannot becorrected. The automatic optical inspection system scansthe board and compares it with the digital image gener-ated from the original design data. [14]

9.2.7 Lamination

Multi-layer printed circuit boards have trace layers insidethe board. This is achieved by laminating a stack of mate-rials in a press by applying pressure and heat for a periodof time. This results in an inseparable one piece prod-uct. For example, a four-layer PCB can be fabricated bystarting from a two-sided copper-clad laminate, etch thecircuitry on both sides, then laminate to the top and bot-tom prepreg and copper foil. It is then drilled, plated, andetched again to get traces on top and bottom layers.

Eyelets (hollow).

9.2.8 Drilling

Holes through a PCB are typically drilled with small-diameter drill bits made of solid coated tungsten car-bide. Coated tungsten carbide is recommended sincemany board materials are very abrasive and drilling mustbe high RPM and high feed to be cost effective. Drillbits must also remain sharp so as not to mar or tear thetraces. Drilling with high-speed-steel is simply not feasi-ble since the drill bits will dull quickly and thus tear thecopper and ruin the boards. The drilling is performed byautomated drilling machines with placement controlledby a drill tape or drill file. These computer-generated filesare also called numerically controlled drill (NCD) files or"Excellon files". The drill file describes the location andsize of each drilled hole.Holes may be made conductive, by electroplating or in-serting metal eyelets (hollow), to electrically and ther-mally connect board layers. Some conductive holes areintended for the insertion of through-hole-componentleads. Others, typically smaller and used to connect boardlayers, are called vias.When very small vias are required, drilling with me-chanical bits is costly because of high rates of wear andbreakage. In this case, the vias may be laser drilled—evaporated by lasers. Laser-drilled vias typically have aninferior surface finish inside the hole. These holes arecalled micro vias.[15][16]

It is also possible with controlled-depth drilling, laserdrilling, or by pre-drilling the individual sheets of thePCB before lamination, to produce holes that connectonly some of the copper layers, rather than passingthrough the entire board. These holes are called blind viaswhen they connect an internal copper layer to an outerlayer, or buried vias when they connect two or more in-ternal copper layers and no outer layers.The hole walls for boards with two or more layers canbe made conductive and then electroplated with copperto form plated-through holes.[17] These holes electricallyconnect the conducting layers of the PCB. For multi-layerboards, those with three layers or more, drilling typi-

86 CHAPTER 9. PRINTED CIRCUIT BOARD

cally produces a smear of the high temperature decom-position products of bonding agent in the laminate sys-tem. Before the holes can be plated through, this smearmust be removed by a chemical de-smear process, or byplasma-etch. The de-smear process ensures that a goodconnection is made to the copper layers when the hole isplated through. On high reliability boards a process calledetch-back is performed chemically with a potassium per-manganate based etchant or plasma.[18] The etch-back re-moves resin and the glass fibers so that the copper layersextend into the hole and as the hole is plated become in-tegral with the deposited copper.

9.2.9 Plating and coating

PCBs[19] are plated with solder, tin, or gold over nickelas a resist for etching away the unneeded underlyingcopper.[20]

After PCBs are etched and then rinsed with water, thesolder mask is applied, and then any exposed copperis coated with solder, nickel/gold, or some other anti-corrosion coating.[21][22]

Matte solder is usually fused to provide a better bond-ing surface or stripped to bare copper. Treatments, suchas benzimidazolethiol, prevent surface oxidation of barecopper. The places to which components will bemountedare typically plated, because untreated bare copper oxi-dizes quickly, and therefore is not readily solderable. Tra-ditionally, any exposed copper was coated with solder byhot air solder levelling (HASL). The HASL finish pre-vents oxidation from the underlying copper, thereby guar-anteeing a solderable surface.[23] This solder was a tin-lead alloy, however new solder compounds are now usedto achieve compliance with the RoHS directive in the EUand US, which restricts the use of lead. One of theselead-free compounds is SN100CL,made up of 99.3% tin,0.7% copper, 0.05% nickel, and a nominal of 60ppm ger-manium.It is important to use solder compatible with both thePCB and the parts used. An example is ball grid array(BGA) using tin-lead solder balls for connections losingtheir balls on bare copper traces or using lead-free solderpaste.Other platings used are OSP (organic surface protectant),immersion silver (IAg), immersion tin, electroless nickelwith immersion gold coating (ENIG), electroless nickelelectroless palladium immersion gold (ENEPIG) and di-rect gold plating (over nickel). Edge connectors, placedalong one edge of some boards, are often nickel platedthen gold plated. Another coating consideration is rapiddiffusion of coating metal into Tin solder. Tin forms in-termetallics such as Cu5Sn6 and Ag3Cu that dissolve intothe Tin liquidus or solidus(@50C), stripping surface coat-ing or leaving voids.Electrochemical migration (ECM) is the growth of con-

ductive metal filaments on or in a printed circuit board(PCB) under the influence of a DC voltage bias.[24][25]Silver, zinc, and aluminum are known to grow whiskersunder the influence of an electric field. Silver also growsconducting surface paths in the presence of halide andother ions, making it a poor choice for electronics use.Tin will grow “whiskers” due to tension in the plated sur-face. Tin-Lead or solder plating also grows whiskers,only reduced by the percentage Tin replaced. Reflowto melt solder or tin plate to relieve surface stress low-ers whisker incidence. Another coating issue is tin pest,the transformation of tin to a powdery allotrope at lowtemperature.[26]

9.2.10 Solder resist application

Areas that should not be soldered may be covered withsolder resist (solder mask). One of the most com-mon solder resists used today is called LPI (liquidphotoimageable).[27] A photo-sensitive coating is appliedto the surface of the PWB, then exposed to light throughthe solder mask image film, and finally developed wherethe unexposed areas are washed away. Dry film soldermask is similar to the dry film used to image the PWBfor plating or etching. After being laminated to the PWBsurface it is imaged and develop as LPI. Once commonbut no longer commonly used because of its low accuracyand resolution is to screen print epoxy ink. Solder resistalso provides protection from the environment.

9.2.11 Legend printing

A legend is often printed on one or both sides of the PCB.It contains the component designators, switch settings,test points and other indications helpful in assembling,testing and servicing the circuit board.[28][29]

There are three methods to print the legend.

1. Silk screen printing epoxy ink was the establishedmethod. It was so common that legend is often mis-named silk or silkscreen.

2. Liquid photo imaging is a more accurate methodthan screen printing.

3. Ink jet printing is new but increasingly used. Ink jetcan print variable data such as a text or bar code witha serial number.

9.2.12 Bare-board test

Unpopulated boards are usually bare-board tested for“shorts” and “opens”. A short is a connection betweentwo points that should not be connected. An open is amissing connection between points that should be con-nected. For high-volume production a fixture or a rigid

9.2. MANUFACTURING 87

needle adapter is used to make contact with copper landson the board. Building the adapter is a significant fixedcost and is only economical for high-volume or high-valueproduction. For small or medium volume productionflying probe testers are used where test probes are movedover the board by an XY drive to make contact with thecopper lands.[30] The CAM system instructs the electricaltester to apply a voltage to each contact point as requiredand to check that this voltage appears on the appropriatecontact points and only on these.

9.2.13 Assembly

PCB with test connection pads

After the printed circuit board (PCB) is completed, elec-tronic components must be attached to form a functionalprinted circuit assembly,[31][32] or PCA (sometimes calleda “printed circuit board assembly” PCBA). In through-hole construction, component leads are inserted in holes.In surface-mount (SMT - surface mount technology) con-struction, the components are placed on pads or lands onthe outer surfaces of the PCB. In both kinds of construc-tion, component leads are electrically and mechanicallyfixed to the board with a molten metal solder.There are a variety of soldering techniques used to attachcomponents to a PCB. High volume production is usuallydone with SMT placement machine and bulk wave sol-dering or reflow ovens, but skilled technicians are able tosolder very tiny parts (for instance 0201 packages whichare 0.02 in. by 0.01 in.)[33] by hand under a microscope,using tweezers and a fine tip soldering iron for small vol-ume prototypes. Some parts may be extremely difficultto solder by hand, such as BGA packages.Often, through-hole and surface-mount constructionmust be combined in a single assembly because some re-quired components are available only in surface-mountpackages, while others are available only in through-holepackages. Another reason to use both methods is thatthrough-hole mounting can provide needed strength forcomponents likely to endure physical stress, while com-ponents that are expected to go untouched will take up

less space using surface-mount techniques. For furthercomparison, see the SMT page.

After the board has been populated it may be tested in avariety of ways:

• While the power is off, visual inspection, automatedoptical inspection. JEDEC guidelines for PCB com-ponent placement, soldering, and inspection arecommonly used to maintain quality control in thisstage of PCB manufacturing.

• While the power is off, analog signature analysis,power-off testing.

• While the power is on, in-circuit test, where physicalmeasurements (for example, voltage) can be done.

• While the power is on, functional test, just checkingif the PCB does what it had been designed to do.

To facilitate these tests, PCBs may be designed with extrapads to make temporary connections. Sometimes thesepads must be isolated with resistors. The in-circuit testmay also exercise boundary scan test features of somecomponents. In-circuit test systems may also be used toprogram nonvolatile memory components on the board.In boundary scan testing, test circuits integrated into var-ious ICs on the board form temporary connections be-tween the PCB traces to test that the ICs are mountedcorrectly. Boundary scan testing requires that all the ICsto be tested use a standard test configuration procedure,the most common one being the Joint Test Action Group(JTAG) standard. The JTAG test architecture providesa means to test interconnects between integrated circuitson a board without using physical test probes. JTAGtool vendors provide various types of stimulus and so-phisticated algorithms, not only to detect the failing nets,but also to isolate the faults to specific nets, devices, andpins.[34]

When boards fail the test, technicians may desolder andreplace failed components, a task known as rework.

9.2.14 Protection and packaging

PCBs intended for extreme environments often have aconformal coating, which is applied by dipping or spray-ing after the components have been soldered. The coatprevents corrosion and leakage currents or shorting dueto condensation. The earliest conformal coats were wax;modern conformal coats are usually dips of dilute solu-tions of silicone rubber, polyurethane, acrylic, or epoxy.Another technique for applying a conformal coating is forplastic to be sputtered onto the PCB in a vacuum cham-ber. The chief disadvantage of conformal coatings is thatservicing of the board is rendered extremely difficult.[35]

Many assembled PCBs are static sensitive, and there-fore must be placed in antistatic bags during transport.

88 CHAPTER 9. PRINTED CIRCUIT BOARD

When handling these boards, the user must be grounded(earthed). Improper handling techniques might transmitan accumulated static charge through the board, dam-aging or destroying components. Even bare boards aresometimes static sensitive. Traces have become so finethat it’s quite possible to blow an etch off the board (orchange its characteristics) with a static charge. This is es-pecially true on non-traditional PCBs such as MCMs andmicrowave PCBs.

9.3 PCB characteristics

Much of the electronics industry’s PCB design, assembly,and quality control follows standards published by the IPCorganization.

9.3.1 Through-hole technology

Through-hole (leaded) resistors

The first PCBs used through-hole technology, mountingelectronic components by leads inserted through holes onone side of the board and soldered onto copper traceson the other side. Boards may be single-sided, with anunplated component side, or more compact double-sidedboards, with components soldered on both sides. Hor-izontal installation of through-hole parts with two axialleads (such as resistors, capacitors, and diodes) is doneby bending the leads 90 degrees in the same direction, in-serting the part in the board (often bending leads locatedon the back of the board in opposite directions to im-prove the part’s mechanical strength), soldering the leads,and trimming off the ends. Leads may be soldered eithermanually or by a wave soldering machine.[36]

Through-hole PCB technology almost completely re-placed earlier electronics assembly techniques such aspoint-to-point construction. From the second generationof computers in the 1950s until surface-mount technol-ogy became popular in the late 1980s, every componenton a typical PCB was a through-hole component.

Through-hole manufacture adds to board cost by requir-ing many holes to be drilled accurately, and limits theavailable routing area for signal traces on layers immedi-ately below the top layer on multi-layer boards since theholes must pass through all layers to the opposite side.Once surface-mounting came into use, small-sized SMDcomponents were used where possible, with through-hole mounting only of components unsuitably large forsurface-mounting due to power requirements or mechan-ical limitations, or subject to mechanical stress whichmight damage the PCB.

• Through-hole devices mounted on the circuit boardof a mid-1980s home computer

• A box of drill bits used for making holes in printedcircuit boards. While tungsten-carbide bits are veryhard, they eventually wear out or break. Makingholes is a considerable part of the cost of a through-hole printed circuit board.

9.3.2 Surface-mount technology

Main article: Surface-mount technologySurface-mount technology emerged in the 1960s, gained

Surface mount components, including resistors, transistors andan integrated circuit

momentum in the early 1980s and became widely usedby the mid-1990s. Components were mechanically re-designed to have small metal tabs or end caps that couldbe soldered directly onto the PCB surface, instead ofwire leads to pass through holes. Components becamemuch smaller and component placement on both sides ofthe board became more common than with through-holemounting, allowing much smaller PCB assemblies withmuch higher circuit densities. Surface mounting lendsitself well to a high degree of automation, reducing la-bor costs and greatly increasing production rates. Com-ponents can be supplied mounted on carrier tapes. Sur-face mount components can be about one-quarter to one-tenth of the size and weight of through-hole components,

9.3. PCB CHARACTERISTICS 89

and passive components much cheaper; prices of semi-conductor surface mount devices (SMDs) are determinedmore by the chip itself than the package, with little priceadvantage over larger packages. Some wire-ended com-ponents, such as 1N4148 small-signal switch diodes, areactually significantly cheaper than SMD equivalents.

9.3.3 Circuit properties of the PCB

Each trace consists of a flat, narrow part of the copper foilthat remains after etching. The resistance, determinedby width and thickness, of the traces must be sufficientlylow for the current the conductor will carry. Power andground traces may need to be wider than signal traces.In a multi-layer board one entire layer may be mostlysolid copper to act as a ground plane for shielding andpower return. For microwave circuits, transmission linescan be laid out in the form of stripline and microstripwith carefully controlled dimensions to assure a consis-tent impedance. In radio-frequency and fast switchingcircuits the inductance and capacitance of the printedcircuit board conductors become significant circuit ele-ments, usually undesired; but they can be used as a de-liberate part of the circuit design, obviating the need foradditional discrete components.

9.3.4 Materials

Excluding exotic products using special materials or pro-cesses all printed circuit boards manufactured today canbe built using the following four materials:

1. Laminates

2. Copper-clad laminates

3. Resin impregnated B-stage cloth (Pre-preg)

4. Copper foil

Laminates

Laminates are manufactured by curing under pressureand temperature layers of cloth or paper with thermosetresin to form an integral final piece of uniform thickness.The size can be up to 4 by 8 feet (1.2 by 2.4 m) in widthand length. Varying cloth weaves (threads per inch orcm), cloth thickness, and resin percentage are used toachieve the desired final thickness and dielectric charac-teristics. Available standard laminate thickness are listedin Table 1:Notes:

[1] Although this specification has been superseded and thenew specification does not list standard sizes,[38] these arestill the most common sizes stocked and ordered for man-ufacturer.

The cloth or fiber material used, resin material, and thecloth to resin ratio determine the laminate’s type designa-tion (FR-4, CEM-1, G-10, etc.) and therefore the charac-teristics of the laminate produced. Important character-istics are the level to which the laminate is fire retardant,the dielectric constant (eᵣ), the loss factor (tδ), the tensilestrength, the shear strength, the glass transition tempera-ture (T ), and the Z-axis expansion coefficient (howmuchthe thickness changes with temperature).There are quite a few different dielectrics that can be cho-sen to provide different insulating values depending onthe requirements of the circuit. Some of these dielectricsare polytetrafluoroethylene (Teflon), FR-4, FR-1, CEM-1 or CEM-3. Well known prepreg materials used in thePCB industry are FR-2 (phenolic cotton paper), FR-3(cotton paper and epoxy), FR-4 (woven glass and epoxy),FR-5 (woven glass and epoxy), FR-6 (matte glass andpolyester), G-10 (woven glass and epoxy), CEM-1 (cot-ton paper and epoxy), CEM-2 (cotton paper and epoxy),CEM-3 (non-woven glass and epoxy), CEM-4 (wovenglass and epoxy), CEM-5 (woven glass and polyester).Thermal expansion is an important consideration espe-cially with ball grid array (BGA) and naked die technolo-gies, and glass fiber offers the best dimensional stability.FR-4 is by far themost commonmaterial used today. Theboard with copper on it is called “copper-clad laminate”.

Copper thickness

Copper thickness of PCBs can be specified as units oflength (in micrometers or mils) but is often specifiedas weight of copper per area (in ounce per square foot)which is easier to measure. One ounce per square foot is1.344 mils or 34 micrometres thickness.The printed circuit board industry defines heavy copperas layers exceeding three ounces of copper, or approx-imately 0.0042 inches (4.2 mils, 105 μm) thick. PCBdesigners and fabricators often use heavy copper whendesign and manufacturing circuit boards in order to in-crease current-carrying capacity as well as resistance tothermal strains. Heavy copper plated vias transfer heatto external heat sinks. IPC 2152 is a standard for deter-mining current-carrying capacity of printed circuit boardtraces.

Safety certification (US)

Safety Standard UL 796 covers component safety re-quirements for printed wiring boards for use as compo-nents in devices or appliances. Testing analyzes charac-teristics such as flammability, maximum operating tem-perature, electrical tracking, heat deflection, and directsupport of live electrical parts.

90 CHAPTER 9. PRINTED CIRCUIT BOARD

9.4 Multiwire boards

Multiwire is a patented technique of interconnectionwhich uses machine-routed insulated wires embedded ina non-conducting matrix (often plastic resin). It was usedduring the 1980s and 1990s. (Kollmorgen TechnologiesCorp, U.S. Patent 4,175,816 filed 1978) Multiwire is stillavailable in 2010 through Hitachi. There are other com-petitive discrete wiring technologies that have been de-veloped (Jumatech , layered sheets).Since it was quite easy to stack interconnections (wires)inside the embedding matrix, the approach allowed de-signers to forget completely about the routing of wires(usually a time-consuming operation of PCB design):Anywhere the designer needs a connection, the machinewill draw a wire in straight line from one location/pin toanother. This led to very short design times (no complexalgorithms to use even for high density designs) as well asreduced crosstalk (which is worse when wires run paral-lel to each other—which almost never happens in Multi-wire), though the cost is too high to compete with cheaperPCB technologies when large quantities are needed.Corrections can bemade to aMultiwire boardmore easilythan to a PCB.[39]

9.5 Cordwood construction

A cordwood module

Cordwood construction can save significant space andwas often used with wire-ended components in appli-cations where space was at a premium (such as mis-sile guidance and telemetry systems) and in high-speedcomputers, where short traces were important. In“cordwood” construction, axial-leaded components weremounted between two parallel planes. The componentswere either soldered together with jumper wire, or theywere connected to other components by thin nickel rib-bon welded at right angles onto the component leads. Toavoid shorting together different interconnection layers,thin insulating cards were placed between them. Perfo-rations or holes in the cards allowed component leads toproject through to the next interconnection layer. Onedisadvantage of this system was that special nickel-leadedcomponents had to be used to allow the interconnectingwelds to be made. Differential thermal expansion of thecomponent could put pressure on the leads of the com-ponents and the PCB traces and cause physical damage(as was seen in several modules on the Apollo program).

Additionally, components located in the interior are diffi-cult to replace. Some versions of cordwood constructionused soldered single-sided PCBs as the interconnectionmethod (as pictured), allowing the use of normal-leadedcomponents.Before the advent of integrated circuits, this method al-lowed the highest possible component packing density;because of this, it was used by a number of computer ven-dors including Control Data Corporation. The cordwoodmethod of construction was used only rarely once semi-conductor electronics and PCBs became widespread.

9.6 History

Development of the methods used in modern printed cir-cuit boards started early in the 20th century. In 1903,a German inventor, Albert Hanson, described flat foilconductors laminated to an insulating board, in multi-ple layers. Thomas Edison experimented with chemicalmethods of plating conductors onto linen paper in 1904.Arthur Berry in 1913 patented a print-and-etchmethod inBritain, and in the United States Max Schoop obtained apatent[40] to flame-spraymetal onto a board through a pat-terned mask. Charles Durcase in 1927 patented a methodof electroplating circuit patterns.[41]

The Austrian engineer Paul Eisler invented the printedcircuit as part of a radio set while working in Englandaround 1936. Around 1943 the USA began to use thetechnology on a large scale to make proximity fuses foruse in World War II.[41] After the war, in 1948, the USAreleased the invention for commercial use. Printed cir-cuits did not become commonplace in consumer electron-ics until the mid-1950s, after the Auto-Sembly processwas developed by the United States Army. At around thesame time in Britain work along similar lines was carriedout by Geoffrey Dummer, then at the RRDE.

A PCB as a design on a computer (left) and realized as a boardassembly populated with components (right). The board is doublesided, with through-hole plating, green solder resist and a whitelegend. Both surface mount and through-hole components havebeen used.

Before printed circuits (and for a while after their inven-tion), point-to-point construction was used. For proto-types, or small production runs, wire wrap or turret board

9.7. SEE ALSO 91

A PCB in a computer mouse. The component side (left) and theprinted side (right).

The component side of a PCB in a computer mouse; some exam-ples for common components and their reference designations inthe legend.

Component and solderside

can be more efficient. Predating the printed circuit inven-tion, and similar in spirit, was John Sargrove's 1936–1947Electronic Circuit Making Equipment (ECME) whichsprayed metal onto a Bakelite plastic board. The ECMEcould produce 3 radios per minute.DuringWorldWar II, the development of the anti-aircraftproximity fuse required an electronic circuit that could

withstand being fired from a gun, and could be producedin quantity. The Centralab Division of Globe Union sub-mitted a proposal which met the requirements: a ceramicplate would be screenprinted with metallic paint for con-ductors and carbon material for resistors, with ceramicdisc capacitors and subminiature vacuum tubes solderedin place.[42] The technique proved viable, and the result-ing patent on the process, which was classified by the U.S.Army, was assigned to GlobeUnion. It was not until 1984that the Institute of Electrical and Electronics Engineers(IEEE) awarded Mr. Harry W. Rubinstein, the formerhead of Globe Union’s Centralab Division, its covetedCledo Brunetti Award for early key contributions to thedevelopment of printed components and conductors on acommon insulating substrate.[43] As well, Mr. Rubinsteinwas honored in 1984 by his alma mater, the University ofWisconsin-Madison, for his innovations in the technol-ogy of printed electronic circuits and the fabrication ofcapacitors.[44]

Originally, every electronic component had wire leads,and the PCB had holes drilled for each wire of eachcomponent. The components’ leads were then passedthrough the holes and soldered to the PCB trace. Thismethod of assembly is called through-hole construction.In 1949, Moe Abramson and Stanislaus F. Danko of theUnited States Army Signal Corps developed the Auto-Sembly process in which component leads were insertedinto a copper foil interconnection pattern and dip sol-dered. The patent they obtained in 1956 was assigned tothe U.S. Army.[45] With the development of board lam-ination and etching techniques, this concept evolved intothe standard printed circuit board fabrication process inuse today. Soldering could be done automatically by pass-ing the board over a ripple, or wave, of molten solder ina wave-soldering machine. However, the wires and holesare wasteful since drilling holes is expensive and the pro-truding wires are merely cut off.From the 1980s small surfacemount parts have been usedincreasingly instead of through-hole components; this hasled to smaller boards for a given functionality and lowerproduction costs, but with some additional difficulty inservicing faulty boards.Historically many measurements related to PCB designwere specified in multiples of a thousandth of an inch,often called “mils”. For example, DIP and most otherthrough-hole components have pins located on a gridspacing of 100 mils, in order to be breadboard-friendly.Surface-mount SOIC components have a pin pitch of 50mils. SOP components have a pin pitch of 25 mils. LevelB technology recommends a minimum trace width of 8mils, which allows “double-track” – two traces betweenDIP pins.[46][47]

92 CHAPTER 9. PRINTED CIRCUIT BOARD

Schematic Capture (KiCad)

PCB layout (KiCad)

3D View (KiCad)

9.7 See also

• Breadboard

• C.I.D.+

• Design for manufacturability (PCB)

• Electronic packaging

• Electronic waste

• Multi-chip module

• Occam process – another process for the manufac-turing of PCBs

• Printed electronics – creation of components byprinting

• Printed circuit board milling

• Stripboard

• Veroboard

PCB materials

• Conductive ink

• Laminate materials:

• BT-Epoxy• Composite epoxy material, CEM-1,5• Cyanate Ester• FR-2• FR-4, the most common PCB material• Polyimide• PTFE, Polytetrafluoroethylene (Teflon)

PCB layout software

• List of EDA companies

• Comparison of EDA software

9.8 References[1] IPC-14.38

[2] http://www.ipc.org/ContentPage.aspx?pageid=World-PCB-Market-Grew-in-2012 IPC World PCBProduction Report 2013

[3] http://www.cs.berkeley.edu/~{}prabal/teaching/cs194-05-s08/cs194-designflow.ppt Printed CircuitBoard Design Flow Methodology

[4] See appendix D of IPC-2251

[5] Tavernier, Karel. “PCB Fabrication Data - A Guide”.Ucamco. Retrieved 8 January 2015.

[6] Vermeire, Filip. “PCB Fabrication Data Example 1”.Ucamco. Ucamco. Retrieved 7 January 2015.

[7] Vermeire, Filip. “PCB Fabrication Data Example 2”.Ucamco. Ucamco. Retrieved 7 January 2015.

[8] “The Gerber File Format Specification”. Ucamco. Re-trieved 8 January 2015.

[9] “Front-end tool data preparation”. Eurocircuits. Re-trieved 2 Sep 2013.

9.8. REFERENCES 93

[10] “Making a PCB - Educational movies”. Eurocircuits. Eu-rocircuits. Retrieved 20 January 2015.

[11] Kraig Mitzner, Complete PCB Design Using OrCad Cap-ture and Layout, pages 443–446, Newnes, 2011 ISBN0080549209.

[12] Itshak Taff, Hai Benron. “Liquid Photoresists for ThermalDirect Imaging”. The Board Authority, October 1999.

[13] R. S. Khandpur,Printed circuit boards: design, fabrication,assembly and testing, Tata-McGraw Hill, 2005 ISBN 0-07-058814-7, pages 373–378

[14] “Inner layer inspection”. Eurocircuits. Retrieved 31 Aug2013.

[15] http://www.somacis.com/prodotti/tecnologie_detail.php?language=en&tec=8&title=laser-drilling

[16] http://www.magazines007.com/pdf/PCB-May2013.pdf|title= Microvia Fabrication: When to drill, When to Blast

[17] “Making Holes Conductive”. Electronic Chemicals. Re-trieved 5 Sep 2012.

[18] “Electro-Brite E-Prep Desmear/Etchback”. OM Group,Inc. Retrieved 5 Sep 2012.

[19] Appendix F Sample Fabrication Sequence for a Stan-dard Printed Circuit Board, Linkages: ManufacturingTrends in Electronics Interconnection Technology, Na-tional Academy of Sciences

[20] Production Methods and Materials 3.1 General PrintedWiring Board Project Report – Table of Contents, Designfor the Environment (DfE), US EPA

[21] George Milad and Don Gudeczauskas. “Solder Joint Re-liability of Gold Surface Finishes (ENIG, ENEPIG andDIG) for PWB Assembled with Lead Free SAC Alloy.”

[22] “Nickel/Gold tab plating line”

[23] Soldering 101 – A Basic Overview

[24] IPC Publication IPC-TR-476A, “Electrochemical Migra-tion: Electrically Induced Failures in Printed Wiring As-semblies,” Northbrook, IL, May 1997.

[25] S.Zhan, M. H. Azarian and M. Pecht, “Reliability Issuesof No-Clean Flux Technology with Lead-free Solder Al-loy for High Density Printed Circuit Boards”, 38th Inter-national Symposium on Microelectronics, pp. 367–375,Philadelphia, PA, September 25–29, 2005.

[26] Clyde F. Coombs Printed Circuits Handbook McGraw–Hill Professional, 2007 ISBN 0-07-146734-3, pages 45–19

[27] “liquid photoimageable solder masks” (PDF). Coates Cir-cuit Products. Retrieved 2 Sep 2012.

[28] “Silk-screen and cure”. Eurocircuits. Retrieved 31 Aug2013.

[29] “Towards a more rational silkscreen”. Optimum DesignAssociates. Retrieved 31 Aug 2013.

[30] “Electrical test”. Eurocircuits. Retrieved 13 Apr 2015.

[31] Ayob, M.; Kendall, G. (2008). “A Survey of Sur-face Mount Device Placement Machine Optimi-sation: Machine Classification”. European Jour-nal of Operational Research 186 (3): 893–914.doi:10.1016/j.ejor.2007.03.042.

[32] Ayob, M.; Kendall, G. (2005). “A Triple Ob-jective Function with a Chebychev Dynamic Pick-and-place Point Specification Approach to Optimisethe Surface Mount Placement Machine”. EuropeanJournal of Operational Research 164 (3): 609–626.doi:10.1016/j.ejor.2003.09.034.

[33] Borkes, Tom. “SMTATechScanCompendium: 0201De-sign, Assembly and Process” (PDF). SurfaceMount Tech-nology Association. Retrieved 2010-01-11.

[34] JTAG Tutorial (http://www.corelis.com/education/JTAG_Tutorial.htm#History)

[35] Shibu. Intro To Embedded Systems 1E. TataMcGraw-Hill.p. 293. ISBN 978-0-07-014589-4.

[36] Electronic Packaging:Solder Mounting Technologies inK.H. Buschow et al (ed), Encyclopedia of Materials:Science and Technology, Elsevier, 2001 ISBN 0-08-043152-6, pages 2708–2709

[37] “Design Standard for Rigid Printed Boards and RigidPrinted Board Assemblies”. IPC. September 1991. IPC-4101.

[38] “Specification for Base Materials for Rigid and Multi-layer Printed Boards” (IPC-4101). ANSI/IPC. December1997. ANSI/IPC-D-275.

[39] David E. Weisberg. “Chapter 14: Intergraph”. 2008. p.14-8.

[40] US 1256599

[41] Charles A. Harper, Electronic materials and processeshandbook, McGraw-Hill,2003 ISBN 0-07-140214-4,pages 7.3 and 7.4

[42] Brunetti, Cledo (22 November 1948). New Advancesin Printed Circuits. Washington DC: National Bureau ofStandards.

[43] IEEE Cledo Brunetti Award, http://www.ieee.org/documents/brunetti_rl.pdf

[44] Engineers’ Day, 1984 Award Recipients, College of En-gineering, University ofWisconsin-Madison, http://www.engr.wisc.edu/eday/eday1984.html

[45] US 2756485 assigned to US Army. July 31, 1956.

[46] Kraig Mitzner. “Complete PCB Design Using OrCadCapture and Layout”. 2011.

[47] “TINA PCB DesignManual”.

94 CHAPTER 9. PRINTED CIRCUIT BOARD

9.9 External links• A collection of board & module construction tech-niques (Italian, 2 pp.)

• PCB Fabrication Data - A Guide

• The Gerber Format Specification

Chapter 10

Electric current

A simple electric circuit, where current is represented by the letteri. The relationship between the voltage (V), resistance (R), andcurrent (I) is V=IR; this is known as Ohm’s Law.

An electric current is a flow of electric charge. In electriccircuits this charge is often carried by moving electrons ina wire. It can also be carried by ions in an electrolyte, orby both ions and electrons such as in a plasma.[1]

The SI unit for measuring an electric current is theampere, which is the flow of electric charge across a sur-face at the rate of one coulomb per second. Electric cur-rent is measured using a device called an ammeter.[2]

Electric currents cause Joule heating, which creates lightin incandescent light bulbs. They also create magneticfields, which are used inmotors, inductors and generators.The particles that carry the charge in an electric currentare called charge carriers. In metals, one or more elec-trons from each atom are loosely bound to the atom, andcanmove freely about within themetal. These conductionelectrons are the charge carriers in metal conductors.

10.1 Symbol

The conventional symbol for current is I, which origi-nates from the French phrase intensité de courant, or inEnglish current intensity.[3][4] This phrase is frequentlyused when discussing the value of an electric current,but modern practice often shortens this to simply current.The I symbol was used by André-Marie Ampère, afterwhom the unit of electric current is named, in formulating

the eponymous Ampère’s force law, which he discoveredin 1820.[5] The notation travelled from France to GreatBritain, where it became standard, although at least onejournal did not change from using C to I until 1896.[6]

10.2 Conventions

Flow of positive charge

Flow of electrons

The electrons, the charge carriers in an electrical circuit, flow inthe opposite direction of the conventional electric current.

In metals, which make up the wires and other conductorsin most electrical circuits, the positively charged atomicnuclei are held in a fixed position, and the electrons arefree to move, carrying their charge from one place to an-other. In other materials, notably the semiconductors, thecharge carriers can be positive or negative, depending onthe dopant used. Positive and negative charge carriersmay even be present at the same time, as happens in anelectrochemical cell.A flow of positive charges gives the same electric current,and has the same effect in a circuit, as an equal flow ofnegative charges in the opposite direction. Since currentcan be the flow of either positive or negative charges, orboth, a convention is needed for the direction of currentthat is independent of the type of charge carriers. Thedirection of conventional current is arbitrarily defined asthe same direction as positive charges flow.The consequence of this convention is that electrons, thecharge carriers in metal wires and most other parts of

95

96 CHAPTER 10. ELECTRIC CURRENT

The symbol for a battery in a circuit diagram.

electric circuits, flow in the opposite direction of conven-tional current flow in an electrical circuit.

10.2.1 Reference direction

Since the current in a wire or component can flow in eitherdirection, when a variable I is defined to represent thatcurrent, the direction representing positive current mustbe specified, usually by an arrow on the circuit schematicdiagram. This is called the reference direction of current I.If the current flows in the opposite direction, the variableI has a negative value.When analyzing electrical circuits, the actual direction ofcurrent through a specific circuit element is usually un-known. Consequently, the reference directions of cur-rents are often assigned arbitrarily. When the circuit issolved, a negative value for the variable means that theactual direction of current through that circuit element isopposite that of the chosen reference direction. In elec-tronic circuits, the reference current directions are oftenchosen so that all currents are toward ground. This of-ten corresponds to the actual current direction, becausein many circuits the power supply voltage is positive withrespect to ground.

10.3 Ohm’s law

Main article: Ohm’s law

Ohm’s law states that the current through a conduc-tor between two points is directly proportional to thepotential difference across the two points. Introducingthe constant of proportionality, the resistance,[7] one ar-rives at the usual mathematical equation that describesthis relationship:[8]

I =V

R

where I is the current through the conductor in units ofamperes, V is the potential difference measured acrossthe conductor in units of volts, and R is the resistance ofthe conductor in units of ohms. More specifically, Ohm’slaw states that the R in this relation is constant, indepen-dent of the current.[9]

10.4 AC and DC

The abbreviations AC and DC are often used to meansimply alternating and direct, as when they modify cur-rent or voltage.[10][11]

10.4.1 Direct current

Main article: Direct current

Direct current (DC) is the unidirectional flow of electriccharge. Direct current is produced by sources such asbatteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct cur-rent may flow in a conductor such as a wire, but can alsoflow through semiconductors, insulators, or even througha vacuum as in electron or ion beams. The electriccharge flows in a constant direction, distinguishing it fromalternating current (AC). A term formerly used for directcurrent was galvanic current.[12]

10.4.2 Alternating current

Main article: Alternating current

In alternating current (AC, also ac), the movement ofelectric charge periodically reverses direction. In directcurrent (DC, also dc), the flow of electric charge is onlyin one direction.AC is the form of electric power delivered to businessesand residences. The usual waveform of an AC powercircuit is a sine wave. Certain applications use different

10.8. ELECTROMAGNETISM 97

waveforms, such as triangular or square waves. Audioand radio signals carried on electrical wires are also ex-amples of alternating current. An important goal inthese applications is recovery of information encoded (ormodulated) onto the AC signal.

10.5 Occurrences

Natural observable examples of electrical current includelightning, static electricity, and the solar wind, the sourceof the polar auroras.Man-made occurrences of electric current include theflow of conduction electrons in metal wires such as theoverhead power lines that deliver electrical energy acrosslong distances and the smaller wires within electrical andelectronic equipment. Eddy currents are electric currentsthat occur in conductors exposed to changing magneticfields. Similarly, electric currents occur, particularly inthe surface, of conductors exposed to electromagneticwaves. When oscillating electric currents flow at the cor-rect voltages within radio antennas, radio waves are gen-erated.In electronics, other forms of electric current include theflow of electrons through resistors or through the vacuumin a vacuum tube, the flow of ions inside a battery or aneuron, and the flow of holes within a semiconductor.

10.6 Current measurement

Current can be measured using an ammeter.At the circuit level, there are various techniques that canbe used to measure current:

• Shunt resistors[13]

• Hall effect current sensor transducers

• Transformers (however DC cannot be measured)

• Magnetoresistive field sensors[14]

10.7 Resistive heating

Main article: Joule heating

Joule heating, also known as ohmic heating and resistiveheating, is the process by which the passage of an elec-tric current through a conductor releases heat. It was firststudied by James Prescott Joule in 1841. Joule immerseda length of wire in a fixed mass of water and measuredthe temperature rise due to a known current through thewire for a 30 minute period. By varying the current andthe length of the wire he deduced that the heat produced

was proportional to the square of the current multipliedby the electrical resistance of the wire.

Q ∝ I2R

This relationship is known as Joule’s First Law. TheSI unit of energy was subsequently named the joule andgiven the symbol J. The commonly known unit of power,the watt, is equivalent to one joule per second.

10.8 Electromagnetism

10.8.1 Electromagnet

Main article: ElectromagnetElectric current produces a magnetic field. The magnetic

According to Ampère’s law, an electric current produces amagnetic field.

field can be visualized as a pattern of circular field linessurrounding the wire that persists as long as there is cur-rent.Magnetism can also produce electric currents. Whena changing magnetic field is applied to a conductor, anElectromotive force (EMF) is produced, and when thereis a suitable path, this causes current.Electric current can be directly measured with agalvanometer, but this method involves breaking theelectrical circuit, which is sometimes inconvenient. Cur-rent can also be measured without breaking the circuit bydetecting the magnetic field associated with the current.Devices used for this include Hall effect sensors, currentclamps, current transformers, and Rogowski coils.

98 CHAPTER 10. ELECTRIC CURRENT

10.8.2 Radio waves

Main article: Radio waves

When an electric current flows in a suitably shaped con-ductor at radio frequencies radio waves can be generated.These travel at the speed of light and can cause electriccurrents in distant conductors.

10.9 Conduction mechanisms invarious media

Main article: Electrical conductivity

In metallic solids, electric charge flows by means ofelectrons, from lower to higher electrical potential. Inother media, any stream of charged objects (ions, for ex-ample) may constitute an electric current. To provide adefinition of current independent of the type of chargecarriers, conventional current is defined as moving in thesame direction as the positive charge flow. So, in metalswhere the charge carriers (electrons) are negative, con-ventional current is in the opposite direction as the elec-trons. In conductors where the charge carriers are posi-tive, conventional current is in the same direction as thecharge carriers.In a vacuum, a beam of ions or electrons may be formed.In other conductive materials, the electric current is dueto the flow of both positively and negatively charged parti-cles at the same time. In still others, the current is entirelydue to positive charge flow. For example, the electric cur-rents in electrolytes are flows of positively and negativelycharged ions. In a common lead-acid electrochemicalcell, electric currents are composed of positive hydrogenions (protons) flowing in one direction, and negative sul-fate ions flowing in the other. Electric currents in sparksor plasma are flows of electrons as well as positive andnegative ions. In ice and in certain solid electrolytes, theelectric current is entirely composed of flowing ions.

10.9.1 Metals

A solid conductive metal contains mobile, or free elec-trons, which function as conduction electrons. Theseelectrons are bound to the metal lattice but no longer toan individual atom. Metals are particularly conductivebecause there are a large number of these free electrons,typically one per atom in the lattice. Even with no ex-ternal electric field applied, these electrons move aboutrandomly due to thermal energy but, on average, there iszero net current within the metal. At room temperature,the average speed of these random motions is 106 me-tres per second.[15] Given a surface through which a metalwire passes, electrons move in both directions across the

surface at an equal rate. As George Gamow wrote in hispopular science book, One, Two, Three...Infinity (1947),“The metallic substances differ from all other materialsby the fact that the outer shells of their atoms are boundrather loosely, and often let one of their electrons go free.Thus the interior of a metal is filled up with a large num-ber of unattached electrons that travel aimlessly aroundlike a crowd of displaced persons. When a metal wireis subjected to electric force applied on its opposite ends,these free electrons rush in the direction of the force, thusforming what we call an electric current.”When a metal wire is connected across the two termi-nals of a DC voltage source such as a battery, the sourceplaces an electric field across the conductor. The momentcontact is made, the free electrons of the conductor areforced to drift toward the positive terminal under the in-fluence of this field. The free electrons are therefore thecharge carrier in a typical solid conductor.For a steady flow of charge through a surface, the cur-rent I (in amperes) can be calculated with the followingequation:

I =Q

t,

where Q is the electric charge transferred through the sur-face over a time t. If Q and t are measured in coulombsand seconds respectively, I is in amperes.More generally, electric current can be represented as therate at which charge flows through a given surface as:

I =dQdt .

10.9.2 Electrolytes

Main article: Conductivity (electrolytic)

Electric currents in electrolytes are flows of electricallycharged particles (ions). For example, if an electric fieldis placed across a solution of Na+ and Cl− (and conditionsare right) the sodium ionsmove towards the negative elec-trode (cathode), while the chloride ions move towards thepositive electrode (anode). Reactions take place at bothelectrode surfaces, absorbing each ion.Water-ice and certain solid electrolytes called proton con-ductors contain positive hydrogen ions ("protons") thatare mobile. In these materials, electric currents are com-posed of moving protons, as opposed to the moving elec-trons in metals.In certain electrolyte mixtures, brightly coloured ions arethe moving electric charges. The slow progress of thecolour makes the current visible.[16]

10.9. CONDUCTION MECHANISMS IN VARIOUS MEDIA 99

10.9.3 Gases and plasmas

In air and other ordinary gases below the breakdown field,the dominant source of electrical conduction is via rel-atively few mobile ions produced by radioactive gases,ultraviolet light, or cosmic rays. Since the electricalconductivity is low, gases are dielectrics or insulators.However, once the applied electric field approaches thebreakdown value, free electrons become sufficiently ac-celerated by the electric field to create additional freeelectrons by colliding, and ionizing, neutral gas atoms ormolecules in a process called avalanche breakdown. Thebreakdown process forms a plasma that contains enoughmobile electrons and positive ions to make it an electri-cal conductor. In the process, it forms a light emittingconductive path, such as a spark, arc or lightning.Plasma is the state of matter where some of the electronsin a gas are stripped or “ionized” from their molecules oratoms. A plasma can be formed by high temperature, orby application of a high electric or alternating magneticfield as noted above. Due to their lower mass, the elec-trons in a plasma accelerate more quickly in response toan electric field than the heavier positive ions, and hencecarry the bulk of the current. The free ions recombineto create new chemical compounds (for example, break-ing atmospheric oxygen into single oxygen [O2 → 2O],which then recombine creating ozone [O3]).[17]

10.9.4 Vacuum

Since a "perfect vacuum" contains no charged particles, itnormally behaves as a perfect insulator. However, metalelectrode surfaces can cause a region of the vacuum tobecome conductive by injecting free electrons or ionsthrough either field electron emission or thermionic emis-sion. Thermionic emission occurs when the thermal en-ergy exceeds the metal’s work function, while field elec-tron emission occurs when the electric field at the surfaceof the metal is high enough to cause tunneling, whichresults in the ejection of free electrons from the metalinto the vacuum. Externally heated electrodes are oftenused to generate an electron cloud as in the filament orindirectly heated cathode of vacuum tubes. Cold elec-trodes can also spontaneously produce electron cloudsvia thermionic emission when small incandescent regions(called cathode spots or anode spots) are formed. Theseare incandescent regions of the electrode surface that arecreated by a localized high current. These regions maybe initiated by field electron emission, but are then sus-tained by localized thermionic emission once a vacuumarc forms. These small electron-emitting regions canform quite rapidly, even explosively, on a metal surfacesubjected to a high electrical field. Vacuum tubes andsprytrons are some of the electronic switching and am-plifying devices based on vacuum conductivity.

10.9.5 Superconductivity

Main article: Superconductivity

Superconductivity is a phenomenon of exactly zeroelectrical resistance and expulsion of magnetic fields oc-curring in certain materials when cooled below a charac-teristic critical temperature. It was discovered by HeikeKamerlingh Onnes on April 8, 1911 in Leiden. Likeferromagnetism and atomic spectral lines, superconduc-tivity is a quantummechanical phenomenon. It is charac-terized by the Meissner effect, the complete ejection ofmagnetic field lines from the interior of the superconduc-tor as it transitions into the superconducting state. Theoccurrence of the Meissner effect indicates that super-conductivity cannot be understood simply as the ideal-ization of perfect conductivity in classical physics.

10.9.6 Semiconductor

Main article: Semiconductor

In a semiconductor it is sometimes useful to think of thecurrent as due to the flow of positive "holes" (the mobilepositive charge carriers that are places where the semi-conductor crystal is missing a valence electron). This isthe case in a p-type semiconductor. A semiconductorhas electrical conductivity intermediate in magnitude be-tween that of a conductor and an insulator. This means aconductivity roughly in the range of 10−2 to 104 siemensper centimeter (S⋅cm−1).In the classic crystalline semiconductors, electrons canhave energies only within certain bands (i.e. ranges oflevels of energy). Energetically, these bands are locatedbetween the energy of the ground state, the state in whichelectrons are tightly bound to the atomic nuclei of the ma-terial, and the free electron energy, the latter describingthe energy required for an electron to escape entirely fromthe material. The energy bands each correspond to a largenumber of discrete quantum states of the electrons, andmost of the states with low energy (closer to the nucleus)are occupied, up to a particular band called the valenceband. Semiconductors and insulators are distinguishedfrom metals because the valence band in any given metalis nearly filled with electrons under usual operating con-ditions, while very few (semiconductor) or virtually none(insulator) of them are available in the conduction band,the band immediately above the valence band.The ease of exciting electrons in the semiconductor fromthe valence band to the conduction band depends on theband gap between the bands. The size of this energy bandgap serves as an arbitrary dividing line (roughly 4 eV)between semiconductors and insulators.With covalent bonds, an electron moves by hopping to aneighboring bond. The Pauli exclusion principle requires

100 CHAPTER 10. ELECTRIC CURRENT

that the electron be lifted into the higher anti-bondingstate of that bond. For delocalized states, for examplein one dimension – that is in a nanowire, for every energythere is a state with electrons flowing in one direction andanother state with the electrons flowing in the other. Fora net current to flow, more states for one direction thanfor the other direction must be occupied. For this to oc-cur, energy is required, as in the semiconductor the nexthigher states lie above the band gap. Often this is statedas: full bands do not contribute to the electrical conduc-tivity. However, as a semiconductor’s temperature risesabove absolute zero, there is more energy in the semi-conductor to spend on lattice vibration and on excitingelectrons into the conduction band. The current-carryingelectrons in the conduction band are known as free elec-trons, though they are often simply called electrons if thatis clear in context.

10.10 Current density and Ohm’slaw

Main article: Current density

Current density is a measure of the density of an electriccurrent. It is defined as a vector whose magnitude is theelectric current per cross-sectional area. In SI units, thecurrent density is measured in amperes per square metre.

I =

∫J⃗ · dA⃗

where I is current in the conductor, J⃗ is the currentdensity, and dA⃗ is the differential cross-sectional areavector.The current density (current per unit area) J⃗ in mate-rials with finite resistance is directly proportional to theelectric field E⃗ in the medium. The proportionality con-stant is called the conductivity σ of the material, whosevalue depends on the material concerned and, in general,is dependent on the temperature of the material:

J⃗ = σE⃗

The reciprocal of the conductivity σ of the material iscalled the resistivity ρ of the material and the aboveequation, when written in terms of resistivity becomes:

J⃗ =E⃗

ρ

E⃗ = ρJ⃗

Conduction in semiconductor devices may occur by acombination of drift and diffusion, which is proportional

to diffusion constant D and charge density αq . The cur-rent density is then:

J = σE +Dq∇n,

with q being the elementary charge and n the electrondensity. The carriers move in the direction of decreasingconcentration, so for electrons a positive current resultsfor a positive density gradient. If the carriers are holes,replace electron density n by the negative of the hole den-sity p .In linear anisotropic materials, σ, ρ and D are tensors.In linear materials such as metals, and under low frequen-cies, the current density across the conductor surface isuniform. In such conditions, Ohm’s law states that thecurrent is directly proportional to the potential differencebetween two ends (across) of that metal (ideal) resistor(or other ohmic device):

I =V

R,

where I is the current, measured in amperes; V is thepotential difference, measured in volts; and R is theresistance, measured in ohms. For alternating currents,especially at higher frequencies, skin effect causes thecurrent to spread unevenly across the conductor cross-section, with higher density near the surface, thus increas-ing the apparent resistance.

10.11 Drift speed

The mobile charged particles within a conductor moveconstantly in random directions, like the particles of agas. To create a net flow of charge, the particles mustalso move together with an average drift rate. Electronsare the charge carriers in metals and they follow an erraticpath, bouncing from atom to atom, but generally driftingin the opposite direction of the electric field. The speedthey drift at can be calculated from the equation:

I = nAvQ ,

where

I is the electric currentn is number of charged particles per unit vol-ume (or charge carrier density)A is the cross-sectional area of the conductorv is the drift velocity, andQ is the charge on each particle.

10.13. REFERENCES 101

Typically, electric charges in solids flow slowly. For ex-ample, in a copper wire of cross-section 0.5 mm2, carry-ing a current of 5 A, the drift velocity of the electrons ison the order of a millimetre per second. To take a dif-ferent example, in the near-vacuum inside a cathode raytube, the electrons travel in near-straight lines at about atenth of the speed of light.Any accelerating electric charge, and therefore anychanging electric current, gives rise to an electromagneticwave that propagates at very high speed outside the sur-face of the conductor. This speed is usually a significantfraction of the speed of light, as can be deduced fromMaxwell’s Equations, and is therefore many times fasterthan the drift velocity of the electrons. For example,in AC power lines, the waves of electromagnetic energypropagate through the space between the wires, movingfrom a source to a distant load, even though the electronsin the wires only move back and forth over a tiny distance.The ratio of the speed of the electromagnetic wave to thespeed of light in free space is called the velocity factor,and depends on the electromagnetic properties of the con-ductor and the insulating materials surrounding it, and ontheir shape and size.The magnitudes (but, not the natures) of these three ve-locities can be illustrated by an analogy with the threesimilar velocities associated with gases.

• The low drift velocity of charge carriers is analogousto air motion; in other words, winds.

• The high speed of electromagnetic waves is roughlyanalogous to the speed of sound in a gas (these wavesmove through the medium much faster than any in-dividual particles do)

• The randommotion of charges is analogous to heat –the thermal velocity of randomly vibrating gas par-ticles.

10.12 See also

• Current 3-vector

• Direct current

• Electric shock

• Electrical measurements

• History of electrical engineering

• Hydraulic analogy

• International System of Quantities

• SI electromagnetism units

10.13 References[1] Anthony C. Fischer-Cripps (2004). The electronics com-

panion. CRC Press. p. 13. ISBN 978-0-7503-1012-3.

[2] Lakatos, John; Oenoki, Keiji; Judez, Hector; Oenoki,Kazushi; Hyun Kyu Cho (March 1998). “Learn PhysicsToday!". Lima, Peru: Colegio Dr. Franklin D. Roosevelt.Retrieved 2009-03-10.

[3] T. L. Lowe, JohnRounce, Calculations for A-level Physics,p. 2, Nelson Thornes, 2002 ISBN 0-7487-6748-7.

[4] Howard M. Berlin, Frank C. Getz, Principles of ElectronicInstrumentation and Measurement, p. 37, Merrill Pub.Co., 1988 ISBN 0-675-20449-6.

[5] A-M Ampère, Recuil d'Observations Électro-dynamiques,p. 56, Paris: Chez Crochard Libraire 1822 (in French).

[6] Electric Power, vol. 6, p. 411, 1894.

[7] Consoliver, Earl L., and Mitchell, Grover I. (1920).Automotive ignition systems. McGraw-Hill. p. 4.

[8] Robert A. Millikan and E. S. Bishop (1917). Elements ofElectricity. American Technical Society. p. 54.

[9] Oliver Heaviside (1894). Electrical papers 1. Macmillanand Co. p. 283. ISBN 0-8218-2840-1.

[10] N. N. Bhargava and D. C. Kulshreshtha (1983). BasicElectronics & Linear Circuits. Tata McGraw-Hill Educa-tion. p. 90. ISBN 978-0-07-451965-3.

[11] National Electric Light Association (1915). Electrical me-terman’s handbook. Trow Press. p. 81.

[12] Andrew J. Robinson, Lynn Snyder-Mackler (2007).Clinical Electrophysiology: Electrotherapy and Electro-physiologic Testing (3rd ed.). Lippincott Williams &Wilkins. p. 10. ISBN 978-0-7817-4484-3.

[13] What is a Current Sensor and How is it Used?. Fo-cus.ti.com. Retrieved on 2011-12-22.

[14] Andreas P. Friedrich, Helmuth Lemme The UniversalCurrent Sensor. Sensorsmag.com (2000-05-01). Re-trieved on 2011-12-22.

[15] “TheMechanismOfConduction InMetals”, ThinkQuest.

[16] Rudolf Holze, Experimental Electrochemistry: A Labora-tory Textbook, page 44, John Wiley & Sons, 2009 ISBN3527310983.

[17] “Lab Note #106 Environmental Impact of Arc Suppres-sion". Arc Suppression Technologies. April 2011. Re-trieved March 15, 2012.

10.14 External links• Allaboutcircuits.com, a useful site introducing elec-tricity and electronics

Chapter 11

Integrated circuit

“Silicon chip” redirects here. For the electronics maga-zine, see Silicon Chip.“Microchip” redirects here. For other uses, seeMicrochip (disambiguation).An integrated circuit or monolithic integrated cir-

Erasable programmable read-only memory integrated circuits.These packages have a transparent window that shows the dieinside. The window allows the memory to be erased by exposingthe chip to ultraviolet light.

Integrated circuit from an EPROM memory microchip showingthe memory blocks, the supporting circuitry and the fine silverwires which connect the integrated circuit die to the legs of thepackaging.

cuit (also referred to as an IC, a chip, or a microchip)is a set of electronic circuits on one small plate (“chip”)

Synthetic detail of an integrated circuit through four layers ofplanarized copper interconnect, down to the polysilicon (pink),wells (greyish), and substrate (green)

of semiconductor material, normally silicon. This can bemade much smaller than a discrete circuit made from in-dependent electronic components. ICs can be made verycompact, having up to several billion transistors and otherelectronic components in an area the size of a fingernail.Thewidth of each conducting line in a circuit can bemadesmaller and smaller as the technology advances; in 2008it dropped below 100 nanometers,[1] and now is tens ofnanometers.[2]

ICs were made possible by experimental discoveriesshowing that semiconductor devices could perform thefunctions of vacuum tubes and bymid-20th-century tech-nology advancements in semiconductor device fabrica-tion. The integration of large numbers of tiny transistorsinto a small chip was an enormous improvement overthe manual assembly of circuits using discrete electroniccomponents. The integrated circuit’s mass production ca-pability, reliability and building-block approach to circuitdesign ensured the rapid adoption of standardized inte-grated circuits in place of designs using discrete transis-tors.ICs have two main advantages over discrete circuits:cost and performance. Cost is low because the chips,with all their components, are printed as a unit byphotolithography rather than being constructed one tran-sistor at a time. Furthermore, packaged ICs use much

102

11.2. INVENTION 103

less material than discrete circuits. Performance is highbecause the IC’s components switch quickly and consumelittle power (compared to their discrete counterparts) asa result of the small size and close proximity of the com-ponents. As of 2012, typical chip areas range from a fewsquare millimeters to around 450 mm2, with up to 9 mil-lion transistors per mm2.Integrated circuits are used in virtually all electronicequipment today and have revolutionized the world ofelectronics. Computers, mobile phones, and other digitalhome appliances are now inextricable parts of the struc-ture of modern societies, made possible by the low costof integrated circuits.

11.1 Terminology

An integrated circuit is defined as:[3]

A circuit in which all or some of the circuitelements are inseparably associated and elec-trically interconnected so that it is consideredto be indivisible for the purposes of construc-tion and commerce.

Circuits meeting this definition can be constructed usingmany different technologies, including thin-film transis-tor, thick film technology, or hybrid integrated circuit.However, in general usage integrated circuit has cometo refer to the single-piece circuit construction originallyknown as a monolithic integrated circuit.[4][5]

11.2 Invention

Main article: Invention of the integrated circuit

Early developments of the integrated circuit go back to1949, when German engineer Werner Jacobi (SiemensAG)[6] filed a patent for an integrated-circuit-like semi-conductor amplifying device[7] showing five transistors ona common substrate in a 3-stage amplifier arrangement.Jacobi disclosed small and cheap hearing aids as typicalindustrial applications of his patent. An immediate com-mercial use of his patent has not been reported.The idea of the integrated circuit was conceived byGeoffrey W.A. Dummer (1909–2002), a radar scien-tist working for the Royal Radar Establishment of theBritish Ministry of Defence. Dummer presented the ideato the public at the Symposium on Progress in QualityElectronic Components in Washington, D.C. on 7 May1952.[8] He gave many symposia publicly to propagatehis ideas, and unsuccessfully attempted to build such acircuit in 1956.A precursor idea to the IC was to create small ceramicsquares (wafers), each containing a single miniaturized

component. Components could then be integrated andwired into a bidimensional or tridimensional compactgrid. This idea, which seemed very promising in 1957,was proposed to the US Army by Jack Kilby and led tothe short-lived Micromodule Program (similar to 1951’sProject Tinkertoy).[9] However, as the project was gain-ing momentum, Kilby came up with a new, revolutionarydesign: the IC.

Jack Kilby's original integrated circuit

Newly employed by Texas Instruments, Kilby recordedhis initial ideas concerning the integrated circuit in July1958, successfully demonstrating the first working inte-grated example on 12 September 1958.[10] In his patentapplication of 6 February 1959,[11] Kilby described hisnew device as “a body of semiconductor material …wherein all the components of the electronic circuit arecompletely integrated.”[12] The first customer for the newinvention was the US Air Force.[13]

Kilby won the 2000 Nobel Prize in Physics for his part inthe invention of the integrated circuit.[14] His work wasnamed an IEEE Milestone in 2009.[15]

Half a year after Kilby, Robert Noyce at Fairchild Semi-conductor developed his own idea of an integrated cir-cuit that solved many practical problems Kilby’s had not.Noyce’s design was made of silicon, whereas Kilby’s chipwas made of germanium. Noyce credited Kurt Lehovecof Sprague Electric for the principle of p–n junction iso-lation caused by the action of a biased p–n junction (thediode) as a key concept behind the IC.[16]

Fairchild Semiconductor was also home of the firstsilicon-gate IC technology with self-aligned gates, thebasis of all modern CMOS computer chips. The tech-nology was developed by Italian physicist Federico Fag-gin in 1968, who later joined Intel in order to developthe very first single-chip Central Processing Unit (CPU)(Intel 4004), for which he received the National Medal ofTechnology and Innovation in 2010.

104 CHAPTER 11. INTEGRATED CIRCUIT

11.3 Generations

In the early days of simple integrated circuits, the tech-nology’s large scale limited each chip to only a few tran-sistors, and the low degree of integrationmeant the designprocess was relatively simple. Manufacturing yields werealso quite low by today’s standards. As the technologyprogressed, millions, then billions[17] of transistors couldbe placed on one chip, and good designs required thor-ough planning, giving rise to new design methods.

11.3.1 SSI, MSI and LSI

The first integrated circuits contained only a few transis-tors. Called “small-scale integration” (SSI), digital cir-cuits containing transistors numbering in the tens pro-vided a few logic gates for example, while early linearICs such as the Plessey SL201 or the Philips TAA320had as few as two transistors. The term Large Scale In-tegration was first used by IBM scientist Rolf Landauerwhen describing the theoretical concept, from there camethe terms for SSI, MSI, VLSI, and ULSI.SSI circuits were crucial to early aerospace projects, andaerospace projects helped inspire development of thetechnology. Both theMinuteman missile and Apollo pro-gram needed lightweight digital computers for their iner-tial guidance systems; the Apollo guidance computer ledand motivated the integrated-circuit technology,[20] whilethe Minuteman missile forced it into mass-production.The Minuteman missile program and various other Navyprograms accounted for the total $4 million integratedcircuit market in 1962, and by 1968, U.S. Governmentspace and defense spending still accounted for 37% ofthe $312 million total production. The demand by theU.S. Government supported the nascent integrated circuitmarket until costs fell enough to allow firms to penetratethe industrial and eventually the consumer markets. Theaverage price per integrated circuit dropped from $50.00in 1962 to $2.33 in 1968.[21] Integrated circuits began toappear in consumer products by the turn of the decade, atypical application being FM inter-carrier sound process-ing in television receivers.The next step in the development of integrated cir-cuits, taken in the late 1960s, introduced devices whichcontained hundreds of transistors on each chip, called“medium-scale integration” (MSI).They were attractive economically because while theycost little more to produce than SSI devices, they allowedmore complex systems to be produced using smaller cir-cuit boards, less assembly work (because of fewer sepa-rate components), and a number of other advantages.Further development, driven by the same economic fac-tors, led to “large-scale integration” (LSI) in the mid-1970s, with tens of thousands of transistors per chip.Integrated circuits such as 1K-bit RAMs, calculator

chips, and the first microprocessors, that began to bemanufactured in moderate quantities in the early 1970s,had under 4000 transistors. True LSI circuits, ap-proaching 10,000 transistors, began to be producedaround 1974, for computer main memories and second-generation microprocessors.

11.3.2 VLSI

Main article: Very-large-scale integrationThe final step in the development process, starting in

Upper interconnect layers on an Intel 80486DX2 microprocessordie

the 1980s and continuing through the present, was “very-large-scale integration” (VLSI). The development startedwith hundreds of thousands of transistors in the early1980s, and continues beyond several billion transistors asof 2009.Multiple developments were required to achieve this in-creased density. Manufacturers moved to smaller de-sign rules and cleaner fabrication facilities, so that theycould make chips with more transistors and maintain ade-quate yield. The path of process improvements was sum-marized by the International Technology Roadmap forSemiconductors (ITRS). Design tools improved enoughto make it practical to finish these designs in a reasonabletime. The more energy-efficient CMOS replaced NMOSand PMOS, avoiding a prohibitive increase in power con-sumption.In 1986 the first one-megabit RAM chips were intro-duced, containing more than one million transistors. Mi-croprocessor chips passed the million-transistor mark in1989 and the billion-transistor mark in 2005.[22] Thetrend continues largely unabated, with chips introduced in2007 containing tens of billions ofmemory transistors.[23]

11.5. COMPUTER ASSISTED DESIGN 105

11.3.3 ULSI, WSI, SOC and 3D-IC

To reflect further growth of the complexity, the termULSI that stands for “ultra-large-scale integration” wasproposed for chips of more than 1 million transistors.[24]

Wafer-scale integration (WSI) is a means of building verylarge integrated circuits that uses an entire silicon wafer toproduce a single “super-chip”. Through a combination oflarge size and reduced packaging, WSI could lead to dra-matically reduced costs for some systems, notably mas-sively parallel supercomputers. The name is taken fromthe term Very-Large-Scale Integration, the current stateof the art when WSI was being developed.[25]

A system-on-a-chip (SoC or SOC) is an integrated cir-cuit in which all the components needed for a computeror other system are included on a single chip. The designof such a device can be complex and costly, and build-ing disparate components on a single piece of silicon maycompromise the efficiency of some elements. However,these drawbacks are offset by lower manufacturing andassembly costs and by a greatly reduced power budget:because signals among the components are kept on-die,much less power is required (see Packaging).[26]

A three-dimensional integrated circuit (3D-IC) has twoor more layers of active electronic components that areintegrated both vertically and horizontally into a singlecircuit. Communication between layers uses on-die sig-naling, so power consumption is much lower than inequivalent separate circuits. Judicious use of short verti-cal wires can substantially reduce overall wire length forfaster operation.[27]

11.4 Advances in integrated cir-cuits

The die from an Intel 8742, an 8-bit microcontroller that includesa CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes ofEPROM, and I/O in the same chip

Among the most advanced integrated circuits are the

microprocessors or "cores", which control everythingfrom computers and cellular phones to digital microwaveovens. Digital memory chips and application-specific in-tegrated circuits (ASICs) are examples of other familiesof integrated circuits that are important to the moderninformation society. While the cost of designing and de-veloping a complex integrated circuit is quite high, whenspread across typically millions of production units theindividual IC cost is minimized. The performance of ICsis high because the small size allows short traces which inturn allows low power logic (such as CMOS) to be usedat fast switching speeds.ICs have consistently migrated to smaller feature sizesover the years, allowing more circuitry to be packed oneach chip. This increased capacity per unit area canbe used to decrease cost or increase functionality—seeMoore’s law which, in its modern interpretation, statesthat the number of transistors in an integrated circuitdoubles every two years. In general, as the feature sizeshrinks, almost everything improves—the cost per unitand the switching power consumption go down, and thespeed goes up. However, ICs with nanometer-scale de-vices are not without their problems, principal amongwhich is leakage current (see subthreshold leakage fora discussion of this), although innovations in high-κ di-electrics aim to solve these problems. Since these speedand power consumption gains are apparent to the enduser, there is fierce competition among the manufactur-ers to use finer geometries. This process, and the ex-pected progress over the next few years, is described bythe International Technology Roadmap for Semiconduc-tors (ITRS).In current research projects, integrated circuits are alsodeveloped for sensoric applications in medical implantsor other bioelectronic devices. Particular sealing strate-gies have to be taken in such biogenic environments toavoid corrosion or biodegradation of the exposed semi-conductor materials.[28] As one of the few materials wellestablished in CMOS technology, titanium nitride (TiN)turned out as exceptionally stable and well suited for elec-trode applications in medical implants.[29][30]

11.5 Computer assisted design

Main articles: Electronic design automation andHardware description language

11.6 Classification

Integrated circuits can be classified into analog, digitaland mixed signal (both analog and digital on the samechip).Digital integrated circuits can contain anywhere from

106 CHAPTER 11. INTEGRATED CIRCUIT

A CMOS 4511 IC in a DIP

one to millions of logic gates, flip-flops, multiplexers,and other circuits in a few square millimeters. Thesmall size of these circuits allows high speed, low powerdissipation, and reduced manufacturing cost comparedwith board-level integration. These digital ICs, typicallymicroprocessors, DSPs, and microcontrollers, work us-ing binary mathematics to process “one” and “zero” sig-nals.Analog ICs, such as sensors, power management circuits,and operational amplifiers, work by processing continu-ous signals. They perform functions like amplification,active filtering, demodulation, and mixing. Analog ICsease the burden on circuit designers by having expertlydesigned analog circuits available instead of designing adifficult analog circuit from scratch.ICs can also combine analog and digital circuits on a sin-gle chip to create functions such as A/D converters andD/A converters. Such mixed-signal circuits offer smallersize and lower cost, but must carefully account for signalinterference.Modern electronic component distributors often furthersub-categorize the huge variety of integrated circuits nowavailable:

• Digital ICs are further sub-categorized as logicICs, memory chips, interface ICs (level shifters,serializer/deserializer, etc.), Power ManagementICs, and programmable devices.

• Analog ICs are further sub-categorized as linear ICsand RF ICs.

• mixed-signal integrated circuits are further sub-categorized as data acquisition ICs (including A/Dconverters, D/A converter, digital potentiometers)and clock/timing ICs.

11.7 Manufacturing

11.7.1 Fabrication

Main article: Semiconductor fabricationThe semiconductors of the periodic table of the chemical

Rendering of a small standard cell with three metal layers(dielectric has been removed). The sand-colored structures aremetal interconnect, with the vertical pillars being contacts, typ-ically plugs of tungsten. The reddish structures are polysilicongates, and the solid at the bottom is the crystalline silicon bulk.

FEO

Lback

-end /

"Advance

d P

ack

agin

g"

BEO

L

Cr, Cu and Au liners

lead-freesolder bump

poly-Si gate

STIp-wellUSG

tungsten

buried SiO2

p-silicon wafer

n-wellUSG

SOD

SODCu1

PSGSiN barrier

layer

CoSi2

SiC seal layer

PE-TEOS

Cu 2

SiC etch stop layer

Ta/TaN barrier layer

SiN seal layer

seal layer (nitride or oxide)

PSG

Cu 5 SOD

SOD

n-Si n-Si p-Si p-Si

Cu 4 Cu 4Cu 4

Cu 5

SiC etch stop layer

spacer

front-

end

Cu 3

Cu 2 Cu 2

Legend:Silicon (Si)Polysilicon (Poly-Si)

Cobalt disilicide (CoSi2)Silicon dioxide (TEOS oxide, SiO2)

n-Si p-Si

Spin-on dielectric (SOD)Phosphor-silicate glass (PSG)Tungsten (W)Copper (Cu)Silicon nitride (SiN)Silicon nitride (SiN)Silicon carbide (SiC)

Undoped silicon glass (USG, SiO2)

Schematic structure of a CMOS chip, as built in the early 2000s.The graphic shows LDD-MISFET’s on an SOI substrate with fivemetallization layers and solder bump for flip-chip bonding. Italso shows the section for FEOL (front-end of line), BEOL (back-end of line) and first parts of back-end process.

11.7. MANUFACTURING 107

elements were identified as the most likely materials for asolid-state vacuum tube. Starting with copper oxide, pro-ceeding to germanium, then silicon, the materials weresystematically studied in the 1940s and 1950s. Today,monocrystalline silicon is the main substrate used for ICsalthough some III-V compounds of the periodic tablesuch as gallium arsenide are used for specialized applica-tions like LEDs, lasers, solar cells and the highest-speedintegrated circuits. It took decades to perfect methods ofcreating crystals without defects in the crystalline struc-ture of the semiconducting material.Semiconductor ICs are fabricated in a layer process whichincludes three key process steps – imaging, depositionand etching. The main process steps are supplementedby doping and cleaning.Mono-crystal silicon wafers (or for special applications,silicon on sapphire or gallium arsenide wafers) are used asthe substrate. Photolithography is used to mark differentareas of the substrate to be doped or to have polysilicon,insulators or metal (typically aluminium) tracks depositedon them.

• Integrated circuits are composed of many overlap-ping layers, each defined by photolithography, andnormally shown in different colors. Some lay-ers mark where various dopants are diffused intothe substrate (called diffusion layers), some definewhere additional ions are implanted (implant lay-ers), some define the conductors (polysilicon ormetal layers), and some define the connections be-tween the conducting layers (via or contact lay-ers). All components are constructed from a specificcombination of these layers.

• In a self-aligned CMOS process, a transistor isformed wherever the gate layer (polysilicon ormetal) crosses a diffusion layer.

• Capacitive structures, in form very much like theparallel conducting plates of a traditional electricalcapacitor, are formed according to the area of the“plates”, with insulating material between the plates.Capacitors of a wide range of sizes are common onICs.

• Meandering stripes of varying lengths are some-times used to form on-chip resistors, though mostlogic circuits do not need any resistors. The ratioof the length of the resistive structure to its width,combined with its sheet resistivity, determines theresistance.

• More rarely, inductive structures can be built as tinyon-chip coils, or simulated by gyrators.

Since a CMOS device only draws current on the transitionbetween logic states, CMOS devices consume much lesscurrent than bipolar devices.

A random access memory is themost regular type of inte-grated circuit; the highest density devices are thus mem-ories; but even a microprocessor will have memory onthe chip. (See the regular array structure at the bottomof the first image.) Although the structures are intricate– with widths which have been shrinking for decades –the layers remain much thinner than the device widths.The layers of material are fabricated much like a photo-graphic process, although light waves in the visible spec-trum cannot be used to “expose” a layer of material, asthey would be too large for the features. Thus photonsof higher frequencies (typically ultraviolet) are used tocreate the patterns for each layer. Because each featureis so small, electron microscopes are essential tools for aprocess engineer who might be debugging a fabricationprocess.Each device is tested before packaging using automatedtest equipment (ATE), in a process known as wafer test-ing, or wafer probing. The wafer is then cut into rectan-gular blocks, each of which is called a die. Each gooddie (plural dice, dies, or die) is then connected into apackage using aluminium (or gold) bond wires which arethermosonically bonded[31] to pads, usually found aroundthe edge of the die. . Thermosonic bonding was firstintroduced by A. Coucoulas which provided a reliablemeans of forming these vital electrical connections to theoutside world. After packaging, the devices go through fi-nal testing on the same or similar ATE used during waferprobing. Industrial CT scanning can also be used. Testcost can account for over 25% of the cost of fabrica-tion on lower-cost products, but can be negligible on low-yielding, larger, or higher-cost devices.As of 2005, a fabrication facility (commonly knownas a semiconductor fab) costs over US$1 billion toconstruct.[32] The cost of a fabrication facility rises overtime (Rock’s law) because much of the operation is auto-mated. Today, the most advanced processes employ thefollowing techniques:

• The wafers are up to 300 mm in diameter (widerthan a common dinner plate).

• Use of 32 nanometer or smaller chip manufacturingprocess. Intel, IBM, NEC, and AMD are using ~32nanometers for their CPU chips. IBM and AMDintroduced immersion lithography for their 45 nmprocesses[33]

• Copper interconnects where copper wiring replacesaluminium for interconnects.

• Low-K dielectric insulators.

• Silicon on insulator (SOI)

• Strained silicon in a process used by IBM known asstrained silicon directly on insulator (SSDOI)

108 CHAPTER 11. INTEGRATED CIRCUIT

• Multigate devices such as tri-gate transistors beingmanufactured by Intel from 2011 in their 22 nm pro-cess.

11.7.2 Packaging

Main article: Integrated circuit packagingThe earliest integrated circuits were packaged in ceramic

A Soviet MSI nMOS chip made in 1977, part of a four-chip cal-culator set designed in 1970[34]

flat packs, which continued to be used by the military fortheir reliability and small size for many years. Commer-cial circuit packaging quickly moved to the dual in-linepackage (DIP), first in ceramic and later in plastic. In the1980s pin counts of VLSI circuits exceeded the practicallimit for DIP packaging, leading to pin grid array (PGA)and leadless chip carrier (LCC) packages. Surface mountpackaging appeared in the early 1980s and became pop-ular in the late 1980s, using finer lead pitch with leadsformed as either gull-wing or J-lead, as exemplified bysmall-outline integrated circuit – a carrier which occu-pies an area about 30–50% less than an equivalent DIP,with a typical thickness that is 70% less. This packagehas “gull wing” leads protruding from the two long sidesand a lead spacing of 0.050 inches.In the late 1990s, plastic quad flat pack (PQFP) and thinsmall-outline package (TSOP) packages became themostcommon for high pin count devices, though PGA pack-ages are still often used for high-end microprocessors.Intel and AMD are currently transitioning from PGApackages on high-end microprocessors to land grid array(LGA) packages.Ball grid array (BGA) packages have existed since the1970s. Flip-chip Ball Grid Array packages, which al-low for much higher pin count than other package types,were developed in the 1990s. In an FCBGA package thedie is mounted upside-down (flipped) and connects to thepackage balls via a package substrate that is similar to aprinted-circuit board rather than by wires. FCBGA pack-ages allow an array of input-output signals (called Area-I/O) to be distributed over the entire die rather than being

confined to the die periphery.Traces out of the die, through the package, and into theprinted circuit board have very different electrical prop-erties, compared to on-chip signals. They require specialdesign techniques and need much more electric powerthan signals confined to the chip itself.When multiple dies are put in one package, it is calledSiP, for System In Package. When multiple dies are com-bined on a small substrate, often ceramic, it’s called anMCM, or Multi-Chip Module. The distinction betweena bigMCMand a small printed circuit board is sometimesfuzzy.

11.7.3 Chip labeling and manufacturedate

Most integrated circuits large enough to include identify-ing information include four common sections: the man-ufacturer’s name or logo, the part number, a part pro-duction batch number and serial number, and a four-digitcode that identifies when the chip was manufactured. Ex-tremely small surface mount technology parts often bearonly a number used in a manufacturer’s lookup table tofind the chip characteristics.The manufacturing date is commonly represented as atwo-digit year followed by a two-digit week code, suchthat a part bearing the code 8341 was manufactured inweek 41 of 1983, or approximately in October 1983.

11.8 Intellectual property

Main article: Integrated circuit layout design protection

The possibility of copying by photographing each layerof an integrated circuit and preparing photomasks for itsproduction on the basis of the photographs obtained is themain reason for the introduction of legislation for the pro-tection of layout-designs.The Semiconductor Chip Pro-tection Act (SCPA) of 1984 established a new type ofintellectual property protection for mask works that arefixed in semiconductor chips. It did so by amending title17 of the United States chapter 9 [35]

A diplomatic conference was held at Washington, D.C.,in 1989, which adopted a Treaty on Intellectual Propertyin Respect of Integrated Circuits (IPIC Treaty).The Treaty on Intellectual Property in respect of Inte-grated Circuits, also called Washington Treaty or IPICTreaty (signed at Washington on 26 May 1989) is cur-rently not in force, but was partially integrated into theTRIPS agreement.National laws protecting IC layout designs have beenadopted in a number of countries.

11.10. SILICON LABELLING AND GRAFFITI 109

11.9 Other developments

In the 1980s, programmable logic devices were devel-oped. These devices contain circuits whose logical func-tion and connectivity can be programmed by the user,rather than being fixed by the integrated circuit manu-facturer. This allows a single chip to be programmedto implement different LSI-type functions such as logicgates, adders and registers. Current devices called field-programmable gate arrays can now implement tens ofthousands of LSI circuits in parallel and operate up to 1.5GHz.The techniques perfected by the integrated circuits indus-try over the last three decades have been used to createvery small mechanical devices driven by electricity us-ing a technology known as microelectromechanical sys-tems. These devices are used in a variety of commer-cial and military applications. Example commercial ap-plications include DLP projectors, inkjet printers, andaccelerometers andMEMS gyroscopes used to deploy au-tomobile airbags.As of 2014, the vast majority of all transistors are fabri-cated in a single layer on one side of a chip of silicon in aflat 2-dimensional planar process. Researchers have pro-duced prototypes of several promising alternatives, suchas:

• fabricating transistors over the entire surface of asmall sphere of silicon.[36][37]

• various approaches to stacking several layers oftransistors to make a three-dimensional integratedcircuit, such as through-silicon via, “monolithic3D”,[38] stacked wire bonding,[39] etc.

• transistors built from other materials: graphenetransistors, molybdenite transistors, carbon nan-otube field-effect transistor, gallium nitride tran-sistor, transistor-like nanowire electronic devices,organic field-effect transistor, etc.

• modifications to the substrate, typically to make"flexible transistors" for a flexible display or otherflexible electronics, possibly leading to a roll-awaycomputer.

In the past, radios could not be fabricated in the samelow-cost processes as microprocessors. But since 1998,a large number of radio chips have been developed usingCMOS processes. Examples include Intel’s DECT cord-less phone, or Atheros's 802.11 card.Future developments seem to follow themulti-core multi-microprocessor paradigm, already used by the Intel andAMD dual-core processors. Rapport Inc. and IBMstarted shipping the KC256 in 2006, a 256-core micro-processor. Intel, as recently as February–August 2011,unveiled a prototype, “not for commercial sale” chip that

bears 80 cores. Each core is capable of handling its owntask independently of the others. This is in response tothe heat-versus-speed limit that is about to be reachedusing existing transistor technology (see: thermal designpower). This design provides a new challenge to chip pro-gramming. Parallel programming languages such as theopen-source X10 programming language are designed toassist with this task.[40]

Since the early 2000s, the integration of optical function-ality (optical computing) into silicon chips has been ac-tively pursued in both academic research and in indus-try resulting in the successful commercialization of sili-con based integrated optical transceivers combining opti-cal devices (modulators, detectors, routing) with CMOSbased electronics.[41]

11.10 Silicon labelling and graffiti

To allow identification during production most siliconchips will have a serial number in one corner. It is alsocommon to add the manufacturer’s logo. Ever since ICswere created, some chip designers have used the siliconsurface area for surreptitious, non-functional images orwords. These are sometimes referred to as chip art, sili-con art, silicon graffiti or silicon doodling.

11.11 ICs and IC families

• The 555 timer IC

• The 741 operational amplifier

• 7400 series TTL logic building blocks

• 4000 series, the CMOS counterpart to the 7400 se-ries (see also: 74HC00 series)

• Intel 4004, the world’s first microprocessor, whichled to the famous 8080 CPU and then the IBM PC's8088, 80286, 486 etc.

• The MOS Technology 6502 and Zilog Z80 micro-processors, used in many home computers of theearly 1980s

• The Motorola 6800 series of computer-relatedchips, leading to the 68000 and 88000 series (usedin some Apple computers and in the 1980s Com-modore Amiga series).

• The LM-series of analog integrated circuits.

11.12 See also

• Automatic test pattern generation

110 CHAPTER 11. INTEGRATED CIRCUIT

• BCDMOS

• Bipolar junction transistor

• Cleanroom

• Computer engineering

• Current mirror

• Datasheet Archive

• Depletion-load NMOS logic

• Electrical engineering

• Field-programmable gate array

• Gate array

• Hardware description language

• Integrated circuit development

• Integrated circuit vacuum tube

• integrated injection logic

• Ion implantation

• Joint Test Action Group

• LDMOS

• Linear feedback shift register

• Logic family

• Memristor

• Monolithic microwave integrated circuit

• MOSFET

• Multi-threshold CMOS

• Photonic integrated circuit

• Silicon-germanium

• Silicon photonics

• Simulation

• Sound chip

• SPICE

• Zero insertion force

11.13 References[1] “Intel to Invest More than $5 Billion to Build New Factory

in Arizona”. Retrieved 3 February 2013.

[2] “Intel® 22nm Technology”. Retrieved 26 July 2014.

[3] “Integrated circuit (IC)". JEDEC.

[4] Andrew Wylie (2009). “The first monolithic integratedcircuits”. Retrieved 14 March 2011. Nowadays whenpeople say 'integrated circuit' they usually mean a mono-lithic IC, where the entire circuit is constructed in a singlepiece of silicon.

[5] Horowitz, Paul; Hill, Winfield (1989). The Art of Elec-tronics (2nd ed.). Cambridge University Press. p. 61.ISBN 0-521-37095-7. Integrated circuits, which havelargely replaced circuits constructed from discrete transis-tors, are themselves merely arrays of transistors and othercomponents built from a single chip of semiconductor ma-terial.

[6] “Integrated circuits help Invention”. Integratedcir-cuithelp.com. Retrieved 2012-08-13.

[7] DE 833366 W. Jacobi/SIEMENS AG: „Halbleiterver-stärker“ priority filing on 14 April 1949, published on 15May 1952.

[8] “The Hapless Tale of Geoffrey Dummer”, (n.d.),(HTML), Electronic Product News, accessed 8 July 2008.

[9] George Rostky, (n. d.), “Micromodules: the ultimatepackage”, (HTML), EE Times, accessed 8 July 2008.

[10] The Chip that Jack Built, (c. 2008), (HTML), Texas In-struments, Retrieved 29 May 2008.

[11] Jack S. Kilby, Miniaturized Electronic Circuits, UnitedStates Patent Office, US Patent 3,138,743, filed 6 Febru-ary 1959, issued 23 June 1964.

[12] Winston, Brian (1998). Media Technology and Society: AHistory : From the Telegraph to the Internet. Routledge.p. 221. ISBN 978-0-415-14230-4.

[13] “Texas Instruments – 1961 First IC-based computer”.Ti.com. Retrieved 2012-08-13.

[14] Nobel Web AB, (10 October 2000),(The Nobel Prize inPhysics 2000, Retrieved 29 May 2008

[15] "Milestones:First Semiconductor Integrated Circuit (IC),1958”. IEEE Global History Network. IEEE. Retrieved 3August 2011.

[16] Kurt Lehovec’s patent on the isolation p–n junction: U.S.Patent 3,029,366 granted on 10 April 1962, filed 22 April1959. Robert Noyce credits Lehovec in his article –“Microelectronics”, Scientific American, September 1977,Volume 23, Number 3, pp. 63–9.

[17] Peter Clarke, Intel enters billion-transistor processor era,EE Times, 14 October 2005

[18] http://www.iutbayonne.univ-pau.fr/~{}dalmau/documents/cours/archi/MICROPancien.pdf

11.14. FURTHER READING 111

[19] Bulletin de la Societe fribourgeoise des sciences naturelles,Volumes 62 à 63 (in French). 1973.

[20] Mindell, David A. (2008). Digital Apollo: Human andMachine in Spaceflight. TheMIT Press. ISBN 978-0-262-13497-2.

[21] Ginzberg, Eli (1976). Economic impact of large publicprograms: the NASA Experience. Olympus PublishingCompany. p. 57. ISBN 0-913420-68-9.

[22] Peter Clarke, EE Times: Intel enters billion-transistor pro-cessor era, 14 November 2005

[23] Antone Gonsalves, EE Times, “Samsung begins produc-tion of 16-Gb flash”, 30 April 2007

[24] Meindl, J.D. “Ultra-large scale integration”. ieee.org.IEEE. Retrieved 21 September 2014.

[25] Shanefield, Daniel. “Wafer scale integration”. google.com/patents. Retrieved 21 September 2014.

[26] Klaas, Jeff. “System-on-a-chip”. google.com/patents. Re-trieved 21 September 2014.

[27] Topol, A.W.; Tulipe, D.C.La; Shi, L; et., al. “Three-dimensional integrated circuits”. ieee.org. InternationalBusiness Machines Corporation (IBM). Retrieved 21September 2014.

[28] A.H.D. Graham, J. Robbins, C.R. Bowen, J. Taylor(2011). “Commercialisation of CMOS Integrated CircuitTechnology in Multi-Electrode Arrays for Neuroscienceand Cell-Based Biosensors”. Sensors 11: 4943–4971.doi:10.3390/s110504943.

[29] H. Hämmerle, K. Kobuch, K. Kohler, W. Nisch, H. Sachs,M. Stelzle (2002). “Biostability of micro-photodiode ar-rays for subretinal implantation”. Biomat. 23: 797–804.doi:10.1016/S0142-9612(01)00185-5.

[30] M. Birkholz, K.-E. Ehwald, D. Wolansky, I. Costina, C.Baristyran-Kaynak, M. Fröhlich, H. Beyer, A. Kapp, F.Lisdat (2010). “Corrosion-resistant metal layers froma CMOS process for bioelectronic applications” (PDF).Surf. Coat. Technol. 204 (12–13): 2055–2059.doi:10.1016/j.surfcoat.2009.09.075.

[31] Coucoulas, A., http://commons.wikimedia.org/wiki/File:Hot_Work_Ultrasonic_(Thermosonic)_Bonding_549-556.pdf “Hot Work Ultrasonic Bonding – AMethod Of Facilitating Metal Flow By RestorationProcesses”, Proc. 20th IEEE Electronic ComponentsConf. Washington, D.C., May 1970, pp. 549–556.https://sites.google.com/site/hotworkultrasonicbonding/

[32] For example, Intel Fab 28 cost $3.5 billion, whileits neighboring Fab 18 cost $1.5 billion http://www.theinquirer.net/default.aspx?article=29958

[33] “Breaking News-IBM, AMD Expect 45-NanometerChips in Mid-2008”. Itjungle.com. 2006-12-12. Re-trieved 2013-09-08.

[34] “145 series ICs (in Russian)". Retrieved 22 April 2012.

[35] //copyright.gov/circs/circ100.pdf

[36] “Spherical semiconductor radio temperature sensor”. Na-tureInterface. 2002.

[37] NOBUO TAKEDA. “MEMS applications of Ball Semi-conductor Technology”.

[38] Zvi Or-Bach. “Why SOI is the Future Technology ofSemiconductors”. 2013.

[39] “Samsung’s Eight-Stack Flash Shows up in Apple’s iPhone4”. 2010.

[40] Biever, C. “Chip revolution poses problems for program-mers”, New Scientist (Vol 193, Number 2594)

[41] A. Narasimha et al. (2008). “A 40-Gb/s QSFP optoelec-tronic transceiver in a 0.13 µmCMOS silicon-on-insulatortechnology”. Proceedings of the Optical Fiber Communi-cation Conference (OFC): OMK7.

11.14 Further reading• The first monolithic integrated circuits

• Baker, R. J. (2010). CMOS: Circuit Design, Layout,and Simulation, Third Edition. Wiley-IEEE. ISBN978-0-470-88132-3. http://cmosedu.com/

• Hodges, David; Jackson, Horace; Saleh, Resve(2003). Analysis and Design of Digital IntegratedCircuits. McGraw-Hill Science/Engineering/Math.ISBN 978-0-07-228365-5.

• Rabaey, J. M.; Chandrakasan, A.; Nikolic, B.(2003). Digital Integrated Circuits (2nd ed.). ISBN0-13-090996-3.

• Mead, Carver; Conway, Lynn (1980). Introductionto VLSI systems. Addison Wesley Publishing Com-pany. ISBN 978-0-201-04358-7.

• Veendrick, H. J. M. (2008). Nanometer CMOS ICs,from Basics to ASICs. Springer. p. 770. ISBN978-1-4020-8332-7. http://springer.com/cn/book/9781402083327?referer=springer.com

• Arjun N. Saxena (2009). Invention of IntegratedCircuits: Untold Important Facts. World Scientific.ISBN 978-981-281-446-3.

• Veendrick, H.J.M. (2011). Bits on Chips. p.253. ISBN 978-1-61627-947-9.https://openlibrary.org/works/OL15759799W/Bits_on_Chips/

11.15 External links

General

• Krazit, Tom "– AMD’s new 65-nanometer chips sipenergy but trail Intel,”C-net, 2006-12-21. Retrievedon 8 January 2007

112 CHAPTER 11. INTEGRATED CIRCUIT

• a large chart listing ICs by generic number includingaccess to most of the datasheets for the parts.

• Stephen P. Marsh (2006). Practical MMIC design.Artech House. ISBN 978-1-59693-036-0.

Author S.P. Marsh

• Introduction to Circuit Boards and Integrated Cir-cuits 6/21/2011

Patents

• US3,138,743 – Miniaturized electronic circuit – J.S. Kilby

• US3,138,747 – Integrated semiconductor circuit de-vice – R. F. Stewart

• US3,261,081 – Method of making miniaturizedelectronic circuits – J. S. Kilby

• US3,434,015 – Capacitor for miniaturized elec-tronic circuits or the like – J. S. Kilby

Silicon graffiti

• The Chipworks silicon art gallery

Integrated circuit die manufacturing

• IC Die Photography – A gallery of IC die pho-tographs

• Zeptobars – Yet another gallery of IC die pho-tographs

• Silicon Chip Wafer Fab Mailbag on YouTube – Alook at some equipment and wafers used in the man-ufacturing of silicon chip wafers

Chapter 12

Breadboard

This article is about electronics. For other uses, seeBreadboard (disambiguation).A breadboard is a construction base for prototyping of

Solderless breadboard with 400 connection points

electronics. Originally it was literally a bread board, a pol-ished piece of wood used for slicing bread. In the 1970sthe solderless breadboard (AKA plugboard, a termi-nal array board) became available and nowadays the term“breadboard” is commonly used to refer to these. “Bread-board” is also a synonym for "prototype".Because the solderless breadboard does not requiresoldering, it is reusable. This makes it easy to use for cre-ating temporary prototypes and experimenting with cir-cuit design. For this reason, solderless breadboards arealso extremely popular with students and in technologi-cal education. Older breadboard types did not have thisproperty. A stripboard (veroboard) and similar prototyp-ing printed circuit boards, which are used to build semi-permanent soldered prototypes or one-offs, cannot easilybe reused. A variety of electronic systems may be proto-typed by using breadboards, from small analog and digitalcircuits to complete central processing units (CPUs).

12.1 Evolution

In the early days of radio, amateurs nailed bare copperwires or terminal strips to a wooden board (often literallya board to slice bread on) and soldered electronic compo-nents to them.[1] Sometimes a paper schematic diagram

This 1920s TRF radio manufactured by Signal was constructedon a wooden breadboard.

was first glued to the board as a guide to placing terminals,then components and wires were installed over their sym-bols on the schematic. Using thumbtacks or small nailsas mounting posts was also common.Breadboards have evolved over time, with the term nowbeing used for all kinds of prototype electronic devices.For example, US Patent 3,145,483,[2] filed in 1961 andgranted in 1964, describes a wooden plate breadboardwith mounted springs and other facilities. US Patent3,496,419,[3] filed in 1967 and granted in 1970, refersto a particular printed circuit board layout as a PrintedCircuit Breadboard. Both examples refer to and describeother types of breadboards as prior art.The breadboard most commonly used today is usuallymade of white plastic and is a pluggable (solderless)breadboard. It was designed by Ronald J. Portugal of EIInstruments Inc. in 1971.[4]

12.1.1 Alternatives

Alternative methods to create prototypes are point-to-point construction (reminiscent of the original woodenbreadboards), wire wrap, wiring pencil, and boards likethe stripboard. Complicated systems, such as moderncomputers comprising millions of transistors, diodes, andresistors, do not lend themselves to prototyping usingbreadboards, as their complex designs can be difficult to

113

114 CHAPTER 12. BREADBOARD

Wire wrap backplane

lay out and debug on a breadboard.Modern circuit designs are generally developed using aschematic capture and simulation system, and tested insoftware simulation before the first prototype circuits arebuilt on a printed circuit board. Integrated circuit designsare a more extreme version of the same process: sinceproducing prototype silicon is costly, extensive softwaresimulations are performed before fabricating the first pro-totypes. However, prototyping techniques are still usedfor some applications such as RF circuits, or where soft-ware models of components are inexact or incomplete.You could also use a square grid of pairs of holes whereone hole per pair connects to its row and the other con-nects to its column. This same shape can be in a cir-cle with rows and columns each spiraling opposite clock-wise/counterclockwise.

12.2 Solderless breadboard

12.2.1 Typical specifications

A modern solderless breadboard consists of a perfo-rated block of plastic with numerous tin plated phosphorbronze or nickel silver alloy spring clips under the per-forations. The clips are often called tie points or contactpoints. The number of tie points is often given in the spec-ification of the breadboard.The spacing between the clips (lead pitch) is typically 0.1in (2.54 mm). Integrated circuits (ICs) in dual in-linepackages (DIPs) can be inserted to straddle the center-line of the block. Interconnecting wires and the leadsof discrete components (such as capacitors, resistors, andinductors) can be inserted into the remaining free holesto complete the circuit. Where ICs are not used, discretecomponents and connecting wires may use any of theholes. Typically the spring clips are rated for 1 ampere at5 volts and 0.333 amperes at 15 volts (5 watts).

12.2.2 Bus and terminal strips

The hole pattern for a typical etched prototyping PCB (printedcircuit board) is similar to the node pattern of the solderlessbreadboards shown above.

Solderless breadboards are available from several differ-ent manufacturers, but most share a similar layout. Thelayout of a typical solderless breadboard is made up fromtwo types of areas, called strips. Strips consist of inter-connected electrical terminals.

Terminal strips The main areas, to hold most of theelectronic components.

In the middle of a terminal strip of a breadboard, onetypically finds a notch running in parallel to the longside. The notch is to mark the centerline of the ter-minal strip and provides limited airflow (cooling) toDIP ICs straddling the centerline. The clips on theright and left of the notch are each connected in a ra-dial way; typically five clips (i.e., beneath five holes)in a row on each side of the notch are electricallyconnected. The five clip columns on the left of thenotch are often marked as A, B, C, D, and E, whilethe ones on the right are marked F, G, H, I and J.When a “skinny” dual in-line pin package (DIP) in-tegrated circuit (such as a typical DIP-14 or DIP-16,which have a 0.3-inch (7.6 mm) separation betweenthe pin rows) is plugged into a breadboard, the pinsof one side of the chip are supposed to go into col-umn E while the pins of the other side go into col-umn F on the other side of the notch.

Bus strips To provide power to the electronic compo-nents.

A bus strip usually contains two columns: one forground and one for a supply voltage. However, somebreadboards only provide a single-column powerdistributions bus strip on each long side. Typicallythe column intended for a supply voltage is markedin red, while the column for ground is marked inblue or black. Some manufacturers connect all ter-minals in a column. Others just connect groups

12.2. SOLDERLESS BREADBOARD 115

of, for example, 25 consecutive terminals in a col-umn. The latter design provides a circuit designerwith some more control over crosstalk (inductivelycoupled noise) on the power supply bus. Often thegroups in a bus strip are indicated by gaps in thecolor marking.

Bus strips typically run down one or both sides of aterminal strip or between terminal strips. On largebreadboards additional bus strips can often be foundon the top and bottom of terminal strips.

Some manufacturers provide separate bus and terminalstrips. Others just provide breadboard blocks which con-tain both in one block. Often breadboard strips or blocksof one brand can be clipped together to make a largerbreadboard.In a more robust variant, one or more breadboard stripsare mounted on a sheet of metal. Typically, that backingsheet also holds a number of binding posts. These postsprovide a clean way to connect an external power supply.This type of breadboard may be slightly easier to handle.Several images in this article show such solderless bread-boards.

Diagram

A “full size” terminal breadboard strip typically consistsof around 56 to 65 rows of connectors, each row contain-ing the above-mentioned two sets of connected clips (Ato E and F to J). Together with bus strips on each side thismakes up a typical 784 to 910 tie point solderless bread-board. “Small size” strips typically come with around 30rows. Miniature solderless breadboards as small as 17rows (no bus strips, 170 tie points) can be found, but theseare only suitable for small and simple designs.

12.2.3 Jump wires

Stranded 22AWG jump wires with solid tips

Jump wires (also called jumper wires) for solderlessbreadboarding can be obtained in ready-to-use jump wire

sets or can be manually manufactured. The latter canbecome tedious work for larger circuits. Ready-to-usejump wires come in different qualities, some even withtiny plugs attached to the wire ends. Jump wire mate-rial for ready-made or homemade wires should usually be22 AWG (0.33 mm2) solid copper, tin-plated wire - as-suming no tiny plugs are to be attached to the wire ends.The wire ends should be stripped 3⁄16 to 5⁄16 in (4.8 to7.9 mm). Shorter stripped wires might result in bad con-tact with the board’s spring clips (insulation being caughtin the springs). Longer stripped wires increase the like-lihood of short-circuits on the board. Needle-nose pli-ers and tweezers are helpful when inserting or removingwires, particularly on crowded boards.Differently colored wires and color-coding discipline areoften adhered to for consistency. However, the numberof available colors is typically far fewer than the num-ber of signal types or paths. Typically, a few wire colorsare reserved for the supply voltages and ground (e.g., red,blue, black), some are reserved for main signals, and therest are simply used where convenient. Some ready-to-use jump wire sets use the color to indicate the length ofthe wires, but these sets do not allow a meaningful color-coding schema.

12.2.4 Inside a breadboard: construction

The following images show the inside of a bus strip.

• Inside breadboard 1

• Inside breadboard 2

• Inside breadboard 3

• Inside breadboard 4

• Inside breadboard 5

• Inside breadboard 6

12.2.5 Advanced solderless breadboards

Some manufacturers provide high-end versions of solder-less breadboards. These are typically high-quality bread-board modules mounted on a flat casing. The casing con-tains additional equipment for breadboarding, such as apower supply, one or more signal generators, serial inter-faces, LED or LCD display modules, and logic probes.[5]

Solderless breadboard modules can also be foundmounted on devices like microcontroller evaluationboards. They provide an easy way to add additional pe-riphery circuits to the evaluation board.

116 CHAPTER 12. BREADBOARD

12.2.6 High frequencies and dead bugs

For high-frequency development, a metal breadboard af-fords a desirable solderable ground plane, often an un-etched piece of printed circuit board; integrated circuitsare sometimes stuck upside down to the breadboard andsoldered to directly, a technique sometimes called “deadbug” construction because of its appearance. Examplesof dead bug with ground plane construction are illustratedin a Linear Technologies application note.[6] For otheruses of this technique see dead bugs.

12.2.7 Limitations

An example of a complex circuit built on a breadboard. Thecircuit is an Intel 8088 single board computer.

Due to relatively large stray capacitance compared to aproperly laid out PCB (approx 2pF between adjacent con-tact columns[7] ), high inductance of some connectionsand a relatively high and not very reproducible contactresistance, solderless breadboards are limited to opera-tion at relatively low frequencies, usually less than 10MHz, depending on the nature of the circuit. The rel-atively high contact resistance can already be a problemfor some DC and very low frequency circuits. Solderlessbreadboards are further limited by their voltage and cur-rent ratings.Solderless breadboards usually cannot accommodatesurface-mount technology devices (SMD) or componentswith grid spacing other than 0.1 in (2.54 mm). Fur-ther, they cannot accommodate components with multi-ple rows of connectors if these connectors don't match thedual in-line layout—it is impossible to provide the correctelectrical connectivity. Sometimes small PCB adapterscalled “breakout adapters” can be used to fit the com-ponent to the board. Such adapters carry one or morecomponents and have 0.1 in (2.54 mm) spaced male con-nector pins in a single in-line or dual in-line layout, forinsertion into a solderless breadboard. Larger compo-nents are usually plugged into a socket on the adapter,

while smaller components (e.g., SMD resistors) are usu-ally soldered directly onto the adapter. The adapter isthen plugged into the breadboard via the 0.1 in (2.54mm)connectors. However, the need to solder the componentsonto the adapter negates some of the advantage of usinga solderless breadboard.Very complex circuits can become unmanageable on asolderless breadboard due to the large amount of wiringrequired. The very convenience of easy plugging and un-plugging of connections also makes it too easy to acci-dentally disturb a connection, and the system becomesunreliable. It is possible to prototype systems with thou-sands of connecting points, but great care must be takenin careful assembly, and such a system becomes unreli-able as contact resistance develops over time. At somepoint, very complex systems must be implemented in amore reliable interconnection technology, to have a like-lihood of working over a usable time period.

12.3 Gallery• A solderless breadboard with a completed circuit.

• A binary counter wired up on a large solderlessbreadboard.

• Logical 4-bit adder with output bits linked to LEDson a typical breadboard.

• Close-up of a solderless breadboard. An IC strad-dling the centerline is probed with an oscilloscopeprobe. The solderless breadboard is mounted on ablue painted metal plate base. Red and black bind-ing posts are also present on the base; the black oneis partly obscured by the oscilloscope probe.

• Example breadboard drawing. Two bus strips andone terminal strip in one block. 25 consecutive ter-minals in a bus strip connected (indicated by gaps inthe red and blue lines). Four binding posts depictedat the top.

12.4 See also• Brassboard

• Expansion spring

• Fahnestock clip

• Iterative design

• Perfboard

• Stripboard

• Veroboard

• Wire wrap

12.6. EXTERNAL LINKS 117

12.5 References[1] Description of the term breadboard

[2] U.S. Patent 3,145,483 Test Board for Electronic Circuits

[3] U.S. Patent 3,496,419 Printed Circuit Breadboard

[4] US patent D228136, Ronald J. Portugal, “breadboard forelectronic components or the like”, issued 1973-08-14

[5] Powered breadboard

[6] Linear technologies AN47. Dead-bug breadboards withground plane, and other prototyping techniques, illus-trated in Figures F1 to F24, from p.AN47-98. There is in-formation on breadboarding on pages AN47-26 to AN47-29.

[7] Jones, David. “EEVblog #568 - Solderless BreadboardCapacitance”. EEVblog. Retrieved 15 January 2014.

12.6 External links• Large parallel processing design prototyped on 50connected breadboards

Chapter 13

Perfboard

Top of a copper clad Perfboard with solder pads for each hole.

Perfboard is a material for prototyping electronic cir-cuits also called (DOT PCB). It is a thin, rigid sheet withholes pre-drilled at standard intervals across a grid, usu-ally a square grid of 2.54 mm (0.1 in) spacing. Theseholes are ringed by round or square copper pads. Inex-pensive perfboard may have pads on only one side of theboard, while better quality perfboard can have pads onboth sides (plate-through holes). Since each pad is elec-trically isolated, the builder makes all connections witheither wire wrap or miniature point to point wiring tech-niques. Discrete components are soldered to the proto-type board such as resistors, capacitors, and integratedcircuits. The substrate is typically made of paper lami-nated with phenolic resin (such as FR-2) or a fiberglass-reinforced epoxy laminate (FR-4).The 0.1 in grid system accommodates integrated circuitsin DIP packages and many other types of through-holecomponents. Perfboard is not designed for prototypingsurface mount devices.Before building a circuit on perfboard, the locations ofthe components and connections are typically planned indetail on paper or with software tools. Small scale proto-types, however, are often built ad hoc, using an oversizedperfboard.Software for PCB layout can often be used to generateperfboard layouts as well. In this case, the designer posi-

tions the components so all leads fall on intersections ofa 0.1 in grid. When routing the connections more than 2copper layers can be used, as multiple overlaps are not aproblem for insulated wires.Once the layout is finalized, the components are solderedin their designated locations, paying attention to orien-tation of polarized parts such as electrolytic capacitors,diodes, and integrated circuits. Next, electrical connec-tions are made as called for in the layout.One school of thought is to make as many connections aspossible without adding extra wire. This is done by bend-ing the existing leads on resistors, capacitors, etc. into po-sition, trimming off extra length, and soldering the lead tomake the required electrical connection. Another schoolof thought refuses to bend the excessive leads of com-ponents and use them for wiring, on the ground that thismakes removing a component later hard or impossible,e.g. when a repair is needed.If extra wires need to be used, or are used for principlereasons, they are typically routed entirely on the copperside of perfboards. Because, as opposite to strip boards,nearby holes aren't connected, and the only hole in a padis already occupied by a component’s lead. Wires usedrange from isolated wires, including verowire (enameledcopper wire with a polyurethane insulation supposed tomelt when soldered)), to bare copper wire, depending onindividual preference, and often also on what is currentlyat hand in the workshop.For insulated wires thin solid core wire with temperature-resistant insulation such as Kynar or Tefzel is preferred.The wire gauge is typically 24 - 30 AWG. A special strip-ping tool can be used, incorporating a thin steel bladewith a slit that the wire is simply inserted into and thenpulled loose, leaving a clean stripped end. This wirewas developed initially for circuit assembly by the wirewrap technique but also serves well for miniature point-to-point wiring on perfboard. Bare copper wire is use-ful when merging a number of connections to form anelectrical bus such as the circuit’s ground, and when thereis enough space to properly route connections, instead ofwiring them rats-nest style.Intentional solder bridges can be used to connect adjacentpads when necessary. Careful hand–eye coordination is

118

13.1. SEE ALSO 119

needed to avoid causing inadvertent short circuits.Circuits assembled on perfboard are not necessarily frag-ile but may be less impact-resistant than printed circuitboards.Perfboard differs from stripboard in that each pad onperfboard is isolated. Stripboard is made with rows ofcopper conductors that form default connections, whichare broken into isolated segments as required by scrap-ing through the copper. This is similar to the pattern ofdefault connections on a solderless breadboard. However,the absence of default connectivity on perfboard gives thedesigner more freedom in positioning components andlends itself more readily to software-aided design thanstripboard or breadboard.

Bottom of a copper clad Perfboard with a ground plane

A 555 timer circuit on perforated board

13.1 See also• Stripboard (Veroboard)

• Breadboard (Protoboard)

Chapter 14

Stripboard

For film preproduction, see Production board.Stripboard is the generic name for a widely used type of

A piece of unused stripboard

electronics prototyping board characterized by a 0.1 inch(2.54 mm) regular (rectangular) grid of holes, with wideparallel strips of copper cladding running in one direc-tion all the way across one side of the board. It is com-monly also known by the name of the original productVeroboard, which is a trademark, in the UK, of Britishcompany Vero Technologies Ltd and Canadian companyPixel Print Ltd. In using the board, breaks aremade in thetracks, usually around holes, to divide the strips into mul-tiple electrical nodes. With care, it is possible to breakbetween holes to allow for components that have two pinrows only one position apart such as twin row headers forIDCs.Stripboard is not designed for surface-mount compo-nents, though it is possible to mount many such com-ponents on the track side, particularly if tracks arecut/shaped with a knife or small cutting disc in a rotarytool.

14.1 Variations

Stripboard is available from many vendors. All versionshave copper strips on one side. Some are made usingprinted circuit board etching and drilling techniques, al-though some have milled strips and punched holes. Theoriginal Veroboard used FR-2 synthetic-resin-bonded pa-per (SRBP) (also known as phenolic board) as the baseboard material. Some versions of stripboard now usehigher quality FR-4 (fiberglass-reinforced epoxy lami-nate) material.[1]

14.2 Hole spacing

Stripboard holes are drilled on 0.1 inch (2.54 mm) cen-ters. This spacing allows components having pins witha 0.1 inch (2.54 mm) spacing to be inserted. Compati-ble parts include DIP ICs, sockets for ICs, some types ofconnectors, and other devices.Stripboards have evolved over time into several variantsand related products. For example, a larger version us-ing a 0.15 inch (3.81 mm) grid and larger holes is avail-able, but is generally less popular (presumably because itdoesn't match up with standard IC pin spacing).

14.3 Board dimensions

Stripboard is available in a variety of sizes. One commonsize (at least in the United Kingdom) is 160 mm x 100mm.[2]

14.4 Assemblies

The components are usually placed on the plain side ofthe board, with their leads protruding through the holes.The leads are then soldered to the copper tracks on theother side of the board to make the desired connections,and any excess wire is cut off. The continuous tracks maybe easily and neatly cut as desired to form breaks betweenconductors using a 3 mm twist drill, a hand cutter made

120

14.6. PROTOTYPE BOARDS 121

An example of a populated stripboard

for the purpose, or a knife. Tracks may be linked up oneither side of the board using wire. With practice, veryneat and reliable assemblies can be created, though sucha method is labour-intensive and therefore unsuitable forproduction assemblies except in very small quantity.External wire connections to the board are made eitherby soldering the wires through the holes or, for wires toothick to pass through the holes, by soldering them to spe-cially made pins called Veropins which fit tightly into theholes. Alternatively, some types of connectors have asuitable pin spacing to be inserted directly into the board.

14.5 Comparison with other sys-tems

14.5.1 Wire wrap

For high density prototyping, especially of digital circuits,wire wrap is faster and more reliable than Stripboard forexperienced personnel.[3]

14.5.2 Breadboard

Veroboard is similar in concept and usage to plug-in breadboard, but is cheaper and more permanent—connections are soldered and while some limited reusemay be possible, more than a few cycles of soldering anddesoldering are likely to render both the components andthe board unusable. In contrast, breadboard connectionsare held by friction, and the breadboard can be reusedmany times. However, a breadboard is not very suitablefor prototyping that needs to remain in a set configurationfor an appreciable period of time nor for physical mock-ups containing a working circuit or for any environmentsubject to vibration or movement.

14.6 Prototype boards

Stripboards have further evolved into a larger class of pro-totype boards, available in different shapes and sizes, withdifferent conductive trace layouts.

14.6.1 TriPad

TriPad stripboard has strips of copper broken up into three-holesections

For example, one variant is called a TriPad board. This issimilar to stripboard, except that the conductive tracks donot run continuously along the board but are broken intosections, each of which spans three holes. This allowsthe legs of two or three components to be easily linkedtogether in the circuit conveniently without the need fortrack breaks to be made. However, in order to link morethan three holes together, wire links or bridges must beformed and this can result in a less compact layout thanis possible with ordinary stripboard.

14.6.2 Perf+

Another variant is Perf+.[4] This is best described as aselective stripboard. Instead of having all the holes con-nected together in a strip, a Perf+ board can have holesconnected to the bus using a small dab of solder. On theother side the busses run in another direction, allowing

122 CHAPTER 14. STRIPBOARD

Closeup of a corner of a Perf+ prototyping board showing thepad shapes

compact layouts of complicated circuits by passing sig-nals over each other on different layers of the board.

14.6.3 Other

Other prototype board variants have generic layouts tosimplify building prototypes with integrated circuits, typ-ically in DIP shapes, or with transistors (pads forming tri-angles). In particular, some boards mimic the layout ofbreadboards, to simplify moving a non-permanent pro-totype on a breadboard to a permanent construction ona PCB. Some types of boards have patterns for connec-tors on the periphery, like DB9 or IDC headers, to allowconnectors with non-standard pin spacings to be easilyused.[5] Some come in special physical shapes, to be usedto prototype plug-in boards for computer bus systems.

14.7 See also

• Point-to-point construction

• Breadboard

• Perfboard

• Veroboard

14.8 References[1] BusBoard Prototype Systems Ltd. “ST3U StripBoard

Datasheet” Retrieved on 2010-10-20.

[2] Prototype and development boards from RS ComponentsThe board size with the largest number of products listedis 160 mm x 100 mm.

[3] Bilotta, Anthony J.: Connections in Electronic Assemblies.Marcel Dekker: 1985. ISBN 0-8247-7319-5

[4] Original Kickstarter for Perf+. “Perf+ the perfboard rein-vented” Retrieved on 2015-4-17.

[5] BusBoard Prototype Systems Ltd. “PR3UC ProtoBoardWith Connectors Datasheet” Retrieved on 2010-10-20.

Chapter 15

Analogue electronics

Analogue electronics (or analog in American English)are electronic systems with a continuously variable sig-nal, in contrast to digital electronics where signals usu-ally take only two levels. The term “analogue” describesthe proportional relationship between a signal and a volt-age or current that represents the signal. The word ana-logue is derived from the Greek word ανάλογος (analo-gos) meaning “proportional”.[1]

15.1 Analogue signals

Main article: Analogue signal

An analogue signal uses some attribute of the mediumto convey the signal’s information. For example, ananeroid barometer uses the angular position of a nee-dle as the signal to convey the information of changes inatmospheric pressure.[2] Electrical signals may representinformation by changing their voltage, current, frequency,or total charge. Information is converted from someother physical form (such as sound, light, temperature,pressure, position) to an electrical signal by a transducerwhich converts one type of energy into another (e.g. amicrophone).[3]

The signals take any value from a given range, and eachunique signal value represents different information. Anychange in the signal is meaningful, and each level of thesignal represents a different level of the phenomenon thatit represents. For example, suppose the signal is beingused to represent temperature, with one volt represent-ing one degree Celsius. In such a system 10 volts wouldrepresent 10 degrees, and 10.1 volts would represent 10.1degrees.Another method of conveying an analogue signal is to usemodulation. In this, some base carrier signal has one of itsproperties altered: amplitude modulation (AM) involvesaltering the amplitude of a sinusoidal voltage waveformby the source information, frequency modulation (FM)changes the frequency. Other techniques, such as phasemodulation or changing the phase of the carrier signal,are also used.[4]

In an analogue sound recording, the variation in pressure

of a sound striking a microphone creates a correspond-ing variation in the current passing through it or voltageacross it. An increase in the volume of the sound causesthe fluctuation of the current or voltage to increase pro-portionally while keeping the same waveform or shape.Mechanical, pneumatic, hydraulic and other systems mayalso use analogue signals.

15.2 Inherent noise

Analogue systems invariably include noise that is ran-dom disturbances or variations, some caused by the ran-dom thermal vibrations of atomic particles. Since allvariations of an analogue signal are significant, any dis-turbance is equivalent to a change in the original signaland so appears as noise.[5] As the signal is copied andre-copied, or transmitted over long distances, these ran-dom variations becomemore significant and lead to signaldegradation. Other sources of noise may include externalelectrical signals or poorly designed components. Thesedisturbances are reduced by shielding and by using low-noise amplifiers (LNA).[6]

15.3 Analogue vs digital electronics

Since the information is encoded differently in analogueand digital electronics, the way they process a signalis consequently different. All operations that can beperformed on an analogue signal such as amplification,filtering, limiting, and others, can also be duplicated inthe digital domain. Every digital circuit is also an ana-logue circuit, in that the behaviour of any digital circuitcan be explained using the rules of analogue circuits.The first electronic devices invented and mass-producedwere analogue. The use of microelectronics has madedigital devices cheap and widely available.

123

124 CHAPTER 15. ANALOGUE ELECTRONICS

15.3.1 Noise

Because of the way information is encoded in analoguecircuits, they are much more susceptible to noise thandigital circuits, since a small change in the signal can rep-resent a significant change in the information present inthe signal and can cause the information present to be lost.Since digital signals take on one of only two different val-ues, a disturbance would have to be about one-half themagnitude of the digital signal to cause an error. Thisproperty of digital circuits can be exploited to make signalprocessing noise-resistant. In digital electronics, becausethe information is quantized, as long as the signal staysinside a range of values, it represents the same informa-tion. Digital circuits use this principle to regenerate thesignal at each logic gate, lessening or removing noise.[7]

15.3.2 Precision

A number of factors affect how precise a signal is, mainlythe noise present in the original signal and the noise addedby processing (see signal-to-noise ratio). Fundamentalphysical limits such as the shot noise in components limitsthe resolution of analogue signals. In digital electronicsadditional precision is obtained by using additional digitsto represent the signal. The practical limit in the num-ber of digits is determined by the performance of theanalogue-to-digital converter (ADC), since digital opera-tions can usually be performed without loss of precision.The ADC takes an analogue signal and changes it into aseries of binary numbers. The ADC may be used in sim-ple digital display devices, e. g., thermometers or lightmeters but it may also be used in digital sound recordingand in data acquisition. However, a digital-to-analogueconverter (DAC) is used to change a digital signal to ananalogue signal. A DAC takes a series of binary num-bers and converts it to an analogue signal. It is commonto find a DAC in the gain-control system of an op-ampwhich in turn may be used to control digital amplifiersand filters.[8]

15.3.3 Design difficulty

Analogue circuits are typically harder to design, requir-ing more skill, than comparable digital systems. This isone of the main reasons why digital systems have becomemore common than analogue devices. An analogue cir-cuit must be designed by hand, and the process is muchless automated than for digital systems. However, if adigital electronic device is to interact with the real world,it will always need an analogue interface.[9] For example,every digital radio receiver has an analogue preamplifieras the first stage in the receive chain.

15.4 See also• Analogue computer

• Analogue signal

• Digital – for a comparison with analogue

• Analogue recording vs. digital recording

• Analogue chip

• Analogue verification

• Electronic circuit

15.5 References[1] Concise Oxford dictionary (10 ed.). Oxford University

Press Inc. 1999. ISBN 0-19-860287-1.

[2] Plympton, George Washington (1884). The aneroidbarometer: its construction and use. D. Van Nostran Co.

[3] Singmin, Andrew (2001). Beginning Digital ElectronicsThrough Projects. Newnes. p. 9. ISBN 0-7506-7269-2.Signals come from transducers...

[4] Miller, Mark R. (2002). Electronics the Easy Way. Bar-ron’s Educational Series. pp. 232–239. ISBN 0-7641-1981-8. Until the radio came along...

[5] Hsu, Hwei Piao (2003). Schaum’s Outline of Theoryand Problems of Analogue and Digital Communications.McGraw-Hill Professional. p. 202. ISBN 0-07-140228-4. The presence of noise degrades the performance ofcommunication systems.

[6] Carr, Joseph J. (2000). Secrets of RF circuit design.McGraw-Hill Professional. p. 423. ISBN 0-07-137067-6. It is common in microwave systems...

[7] Chen, Wai-Kai (2005). The electrical engineering hand-book. Academic Press. p. 101. ISBN 0-12-170960-4.Noise from an analog (or small-signal) perspective...

[8] Scherz, Paul (2006). Practical electronics for inventors.McGraw-Hill Professional. p. 730. ISBN 0-07-145281-8. In order for analog devices... to communicate withdigital circuits...

[9] Williams, Jim (1991). Analog circuit design. Newnes. p.238. ISBN 0-7506-9640-0. Even within companies pro-ducing both analog and digital products...

Chapter 16

Digital electronics

Three digital circuits

A binary clock, hand-wired on breadboards

An industrial digital controller

Intel 80486DX2 microprocessor

Digital electronics, or digital (electronic) circuits, areelectronics that represent signals by discrete bands ofanalog levels, rather than by continuous ranges (as usedin analogue electronics). All levels within a band repre-sent the same signal state. Because of this discretization,

relatively small changes to the analog signal levels due tomanufacturing tolerance, signal attenuation or parasiticnoise do not leave the discrete envelope, and as a resultare ignored by signal state sensing circuitry.In most cases the number of these states is two, and theyare represented by two voltage bands: one near a refer-ence value (typically termed as “ground” or zero volts),and the other a value near the supply voltage. These cor-respond to the “false” (“0”) and “true” (“1”) values of theBoolean domain, respectively, yielding binary code.Digital techniques are useful because it is easier to get anelectronic device to switch into one of a number of knownstates than to accurately reproduce a continuous range ofvalues.Digital electronic circuits are usually made from large as-semblies of logic gates, simple electronic representationsof Boolean logic functions.[1]

16.1 Advantages

An advantage of digital circuits when compared to analogcircuits is that signals represented digitally can be trans-mitted without degradation due to noise.[2] For example,a continuous audio signal transmitted as a sequence of 1sand 0s, can be reconstructed without error, provided thenoise picked up in transmission is not enough to preventidentification of the 1s and 0s. An hour of music can bestored on a compact disc using about 6 billion binary dig-its.In a digital system, a more precise representation of a sig-nal can be obtained by using more binary digits to repre-sent it. While this requires more digital circuits to pro-cess the signals, each digit is handled by the same kindof hardware, resulting in an easily scalable system. In ananalog system, additional resolution requires fundamen-tal improvements in the linearity and noise characteristicsof each step of the signal chain.Computer-controlled digital systems can be controlled bysoftware, allowing new functions to be added withoutchanging hardware. Often this can be done outside ofthe factory by updating the product’s software. So, the

125

126 CHAPTER 16. DIGITAL ELECTRONICS

product’s design errors can be corrected after the productis in a customer’s hands.Information storage can be easier in digital systems thanin analog ones. The noise-immunity of digital systemspermits data to be stored and retrieved without degrada-tion. In an analog system, noise from aging and wear de-grade the information stored. In a digital system, as longas the total noise is below a certain level, the informationcan be recovered perfectly.

16.2 Disadvantages

In some cases, digital circuits use more energy than ana-log circuits to accomplish the same tasks, thus producingmore heat which increases the complexity of the circuitssuch as the inclusion of heat sinks. In portable or battery-powered systems this can limit use of digital systems.For example, battery-powered cellular telephones oftenuse a low-power analog front-end to amplify and tune inthe radio signals from the base station. However, a basestation has grid power and can use power-hungry, but veryflexible software radios. Such base stations can be easilyreprogrammed to process the signals used in new cellularstandards.Digital circuits are sometimes more expensive, especiallyin small quantities.Most useful digital systems must translate from continu-ous analog signals to discrete digital signals. This causesquantization errors. Quantization error can be reducedif the system stores enough digital data to represent thesignal to the desired degree of fidelity. The Nyquist-Shannon sampling theorem provides an important guide-line as to how much digital data is needed to accuratelyportray a given analog signal.In some systems, if a single piece of digital data is lostor misinterpreted, the meaning of large blocks of relateddata can completely change. Because of the cliff effect,it can be difficult for users to tell if a particular systemis right on the edge of failure, or if it can tolerate muchmore noise before failing.Digital fragility can be reduced by designing a digital sys-tem for robustness. For example, a parity bit or othererror management method can be inserted into the signalpath. These schemes help the system detect errors, andthen either correct the errors, or at least ask for a newcopy of the data. In a state-machine, the state transitionlogic can be designed to catch unused states and trigger areset sequence or other error recovery routine.Digital memory and transmission systems can use tech-niques such as error detection and correction to use addi-tional data to correct any errors in transmission and stor-age.On the other hand, some techniques used in digital sys-

tems make those systems more vulnerable to single-biterrors. These techniques are acceptable when the under-lying bits are reliable enough that such errors are highlyunlikely.A single-bit error in audio data stored directly as linearpulse code modulation (such as on a CD-ROM) causes,at worst, a single click. Instead, many people use audiocompression to save storage space and download time,even though a single-bit error may corrupt the entire song.

16.3 Design issues in digital cir-cuits

Digital circuits are made from analog components. Thedesign must assure that the analog nature of the compo-nents doesn't dominate the desired digital behavior. Dig-ital systems must manage noise and timing margins, par-asitic inductances and capacitances, and filter power con-nections.Bad designs have intermittent problems such as“glitches”, vanishingly fast pulses that may trigger somelogic but not others, "runt pulses" that do not reachvalid “threshold” voltages, or unexpected (“undecoded”)combinations of logic states.Additionally, where clocked digital systems interface toanalog systems or systems that are driven from a differentclock, the digital system can be subject to metastabilitywhere a change to the input violates the set-up time fora digital input latch. This situation will self-resolve, butwill take a random time, and while it persists can result ininvalid signals being propagated within the digital systemfor a short time.Since digital circuits are made from analog components,digital circuits calculate more slowly than low-precisionanalog circuits that use a similar amount of space andpower. However, the digital circuit will calculate morerepeatably, because of its high noise immunity. On theother hand, in the high-precision domain (for example,where 14 or more bits of precision are needed), analogcircuits require much more power and area than digitalequivalents.

16.4 Construction

A digital circuit is often constructed from small elec-tronic circuits called logic gates that can be used to createcombinational logic. Each logic gate represents a functionof boolean logic. A logic gate is an arrangement of elec-trically controlled switches, better known as transistors.Each logic symbol is represented by a different shape.The actual set of shapes was introduced in 1984 underIEEE/ANSI standard 91-1984. “The logic symbol givenunder this standard are being increasingly used now and

16.4. CONSTRUCTION 127

have even started appearing in the literature published bymanufacturers of digital integrated circuits.”[3]

The output of a logic gate is an electrical flow or voltage,that can, in turn, control more logic gates.Logic gates often use the fewest number of transistors inorder to reduce their size, power consumption and cost,and increase their reliability.Integrated circuits are the least expensive way to makelogic gates in large volumes. Integrated circuits are usu-ally designed by engineers using electronic design au-tomation software (see below for more information).Another form of digital circuit is constructed from lookuptables, (many sold as "programmable logic devices",though other kinds of PLDs exist). Lookup tables canperform the same functions as machines based on logicgates, but can be easily reprogrammed without changingthe wiring. This means that a designer can often repairdesign errors without changing the arrangement of wires.Therefore, in small volume products, programmable logicdevices are often the preferred solution. They are usuallydesigned by engineers using electronic design automationsoftware.When the volumes are medium to large, and the logic canbe slow, or involves complex algorithms or sequences, of-ten a small microcontroller is programmed to make anembedded system. These are usually programmed bysoftware engineers.When only one digital circuit is needed, and its design istotally customized, as for a factory production line con-troller, the conventional solution is a programmable logiccontroller, or PLC. These are usually programmed byelectricians, using ladder logic.

16.4.1 Structure of digital systems

Engineers usemanymethods to minimize logic functions,in order to reduce the circuit’s complexity. When thecomplexity is less, the circuit also has fewer errors andless electronics, and is therefore less expensive.The most widely used simplification is a minimizationalgorithm like the Espresso heuristic logic minimizerwithin a CAD system, although historically, binary de-cision diagrams, an automated Quine–McCluskey algo-rithm, truth tables, Karnaugh maps, and Boolean algebrahave been used.

Representation

Representations are crucial to an engineer’s design of dig-ital circuits. Some analysis methods only work with par-ticular representations.The classical way to represent a digital circuit is with anequivalent set of logic gates. Another way, often with

the least electronics, is to construct an equivalent systemof electronic switches (usually transistors). One of theeasiest ways is to simply have amemory containing a truthtable. The inputs are fed into the address of the memory,and the data outputs of the memory become the outputs.For automated analysis, these representations have digitalfile formats that can be processed by computer programs.Most digital engineers are very careful to select computerprograms (“tools”) with compatible file formats.

Combinational vs. Sequential

To choose representations, engineers consider typesof digital systems. Most digital systems divide into"combinational systems" and "sequential systems.” Acombinational system always presents the same outputwhen given the same inputs. It is basically a represen-tation of a set of logic functions, as already discussed.A sequential system is a combinational system with someof the outputs fed back as inputs. This makes the dig-ital machine perform a “sequence” of operations. Thesimplest sequential system is probably a flip flop, a mech-anism that represents a binary digit or "bit".Sequential systems are often designed as state machines.In this way, engineers can design a system’s gross behav-ior, and even test it in a simulation, without consideringall the details of the logic functions.Sequential systems divide into two further subcate-gories. “Synchronous” sequential systems change stateall at once, when a “clock” signal changes state.“Asynchronous” sequential systems propagate changeswhenever inputs change. Synchronous sequential sys-tems are made of well-characterized asynchronous cir-cuits such as flip-flops, that change only when the clockchanges, and which have carefully designed timing mar-gins.

Synchronous Systems

The usual way to implement a synchronous sequentialstate machine is to divide it into a piece of combinationallogic and a set of flip flops called a “state register.” Eachtime a clock signal ticks, the state register captures thefeedback generated from the previous state of the combi-national logic, and feeds it back as an unchanging input tothe combinational part of the state machine. The fastestrate of the clock is set by the most time-consuming logiccalculation in the combinational logic.The state register is just a representation of a binary num-ber. If the states in the state machine are numbered(easy to arrange), the logic function is some combina-tional logic that produces the number of the next state.

128 CHAPTER 16. DIGITAL ELECTRONICS

Asynchronous Systems

As of 2014, almost all digital machines are synchronousdesigns because it is easier to create and verify a syn-chronous design. However, asynchronous logic is thoughtcan be superior because its speed is not constrained by anarbitrary clock; instead, it runs at the maximum speed ofits logic gates. Building an asynchronous system usingfaster parts makes the circuit faster.Many systems need circuits that allow external unsyn-chronized signals to enter synchronous logic circuits.These are inherently asynchronous in their design andmust be analyzed as such. Examples of widely used asyn-chronous circuits include synchronizer flip-flops, switchdebouncers and arbiters.Asynchronous logic components can be hard to designbecause all possible states, in all possible timings must beconsidered. The usual method is to construct a table ofthe minimum andmaximum time that each such state canexist, and then adjust the circuit to minimize the numberof such states. Then the designer must force the circuitto periodically wait for all of its parts to enter a compat-ible state (this is called “self-resynchronization”). With-out such careful design, it is easy to accidentally produceasynchronous logic that is “unstable,” that is, real elec-tronics will have unpredictable results because of the cu-mulative delays caused by small variations in the valuesof the electronic components.

Register Transfer Systems

Many digital systems are data flow machines. These areusually designed using synchronous register transfer logic,using hardware description languages such as VHDL orVerilog.In register transfer logic, binary numbers are stored ingroups of flip flops called registers. The outputs of eachregister are a bundle of wires called a "bus" that carriesthat number to other calculations. A calculation is sim-ply a piece of combinational logic. Each calculation alsohas an output bus, and these may be connected to the in-puts of several registers. Sometimes a register will have amultiplexer on its input, so that it can store a number fromany one of several buses. Alternatively, the outputs ofseveral items may be connected to a bus through buffersthat can turn off the output of all of the devices exceptone. A sequential state machine controls when each reg-ister accepts new data from its input.Asynchronous register-transfer systems (such as comput-ers) have a general solution. In the 1980s, some re-searchers discovered that almost all synchronous register-transfer machines could be converted to asynchronous de-signs by using first-in-first-out synchronization logic. Inthis scheme, the digital machine is characterized as a setof data flows. In each step of the flow, an asynchronous“synchronization circuit” determines when the outputs of

that step are valid, and presents a signal that says, “grabthe data” to the stages that use that stage’s inputs. It turnsout that just a few relatively simple synchronization cir-cuits are needed.

Computer Design

Themost general-purpose register-transfer logic machineis a computer. This is basically an automatic binaryabacus. The control unit of a computer is usually designedas a microprogram run by a microsequencer. A micro-program is much like a player-piano roll. Each table en-try or “word” of the microprogram commands the state ofevery bit that controls the computer. The sequencer thencounts, and the count addresses the memory or combina-tional logic machine that contains the microprogram. Thebits from the microprogram control the arithmetic logicunit, memory and other parts of the computer, includ-ing the microsequencer itself.A “specialized computer”is usually a conventional computer with special-purposecontrol logic or microprogram.In this way, the complex task of designing the controls ofa computer is reduced to a simpler task of programminga collection of much simpler logic machines.Almost all computers are synchronous. However, trueasynchronous computers have also been designed. Oneexample is the Aspida DLX core.[4] Another was of-fered by ARM Holdings. Speed advantages have notmaterialized, because modern computer designs alreadyrun at the speed of their slowest componment, usuallymemory. These do use somewhat less power becausea clock distribution network is not needed. An unex-pected advantage is that asynchronous computers do notproduce spectrally-pure radio noise, so they are used insome mobile-phone base-station controllers. They maybe more secure in cryptographic applications becausetheir electrical and radio emissions can be more difficultto decode.[5]

Computer Architecture

Computer architecture is a specialized engineering activ-ity that tries to arrange the registers, calculation logic,buses and other parts of the computer in the best way forsome purpose. Computer architects have applied largeamounts of ingenuity to computer design to reduce thecost and increase the speed and immunity to program-ming errors of computers. An increasingly common goalis to reduce the power used in a battery-powered com-puter system, such as a cell-phone. Many computer ar-chitects serve an extended apprenticeship as micropro-grammers.

16.4. CONSTRUCTION 129

16.4.2 Automated design tools

To save costly engineering effort, much of the effort ofdesigning large logic machines has been automated. Thecomputer programs are called "electronic design automa-tion tools” or just “EDA.”Simple truth table-style descriptions of logic are often op-timized with EDA that automatically produces reducedsystems of logic gates or smaller lookup tables that stillproduce the desired outputs. The most common exam-ple of this kind of software is the Espresso heuristic logicminimizer.Most practical algorithms for optimizing large logic sys-tems use algebraic manipulations or binary decision dia-grams, and there are promising experiments with geneticalgorithms and annealing optimizations.To automate costly engineering processes, some EDAcan take state tables that describe state machines and au-tomatically produce a truth table or a function table forthe combinational logic of a state machine. The state ta-ble is a piece of text that lists each state, together with theconditions controlling the transitions between them andthe belonging output signals.It is common for the function tables of such computer-generated state-machines to be optimized with logic-minimization software such as Minilog.Often, real logic systems are designed as a series of sub-projects, which are combined using a “tool flow.” The toolflow is usually a “script,” a simplified computer languagethat can invoke the software design tools in the right order.Tool flows for large logic systems such asmicroprocessorscan be thousands of commands long, and combine thework of hundreds of engineers.Writing and debugging tool flows is an established engi-neering specialty in companies that produce digital de-signs. The tool flow usually terminates in a detailed com-puter file or set of files that describe how to physicallyconstruct the logic. Often it consists of instructions todraw the transistors and wires on an integrated circuit ora printed circuit board.Parts of tool flows are “debugged” by verifying the out-puts of simulated logic against expected inputs. The testtools take computer files with sets of inputs and outputs,and highlight discrepancies between the simulated behav-ior and the expected behavior.Once the input data is believed correct, the design itselfmust still be verified for correctness. Some tool flows ver-ify designs by first producing a design, and then scanningthe design to produce compatible input data for the toolflow. If the scanned data matches the input data, then thetool flow has probably not introduced errors.The functional verification data are usually called “testvectors.” The functional test vectors may be preservedand used in the factory to test that newly constructed logic

works correctly. However, functional test patterns don'tdiscover common fabrication faults. Production tests areoften designed by software tools called "test pattern gen-erators". These generate test vectors by examining thestructure of the logic and systematically generating testsfor particular faults. This way the fault coverage canclosely approach 100%, provided the design is properlymade testable (see next section).Once a design exists, and is verified and testable, it of-ten needs to be processed to be manufacturable as well.Modern integrated circuits have features smaller than thewavelength of the light used to expose the photoresist.Manufacturability software adds interference patterns tothe exposure masks to eliminate open-circuits, and en-hance the masks’ contrast.

16.4.3 Design for testability

There are several reasons for testing a logic circuit. Whenthe circuit is first developed, it is necessary to verify thatthe design circuit meets the required functional and tim-ing specifications. When multiple copies of a correctlydesigned circuit are being manufactured, it is essential totest each copy to ensure that the manufacturing processhas not introduced any flaws.[6]

A large logic machine (say, withmore than a hundred log-ical variables) can have an astronomical number of possi-ble states. Obviously, in the factory, testing every state isimpractical if testing each state takes a microsecond, andthere are more states than the number of microsecondssince the universe began. Unfortunately, this ridiculous-sounding case is typical.Fortunately, large logic machines are almost always de-signed as assemblies of smaller logic machines. To savetime, the smaller sub-machines are isolated by perma-nently installed “design for test” circuitry, and are testedindependently.One common test scheme known as “scan design” movestest bits serially (one after another) from external testequipment through one or more serial shift registersknown as “scan chains”. Serial scans have only one ortwo wires to carry the data, and minimize the physicalsize and expense of the infrequently used test logic.After all the test data bits are in place, the design is re-configured to be in “normal mode” and one or more clockpulses are applied, to test for faults (e.g. stuck-at low orstuck-at high) and capture the test result into flip-flopsand/or latches in the scan shift register(s). Finally, the re-sult of the test is shifted out to the block boundary andcompared against the predicted “good machine” result.In a board-test environment, serial to parallel testing hasbeen formalized with a standard called "JTAG" (namedafter the “Joint Test Action Group” that proposed it).Another common testing scheme provides a test mode

130 CHAPTER 16. DIGITAL ELECTRONICS

that forces some part of the logic machine to enter a “testcycle.” The test cycle usually exercises large independentparts of the machine.

16.4.4 Trade-offs

Several numbers determine the practicality of a systemof digital logic: cost, reliability, fanout and speed. En-gineers explored numerous electronic devices to get anideal combination of these traits.

Cost

The cost of a logic gate is crucial. In the 1930s, the earli-est digital logic systems were constructed from telephonerelays because these were inexpensive and relatively reli-able. After that, engineers always used the cheapest avail-able electronic switches that could still fulfill the require-ments.The earliest integrated circuits were a happy accident.They were constructed not to save money, but to saveweight, and permit the Apollo Guidance Computer tocontrol an inertial guidance system for a spacecraft. Thefirst integrated circuit logic gates cost nearly $50 (in 1960dollars, when an engineer earned $10,000/year). To ev-eryone’s surprise, by the time the circuits were mass-produced, they had become the least-expensive methodof constructing digital logic. Improvements in this tech-nology have driven all subsequent improvements in cost.With the rise of integrated circuits, reducing the abso-lute number of chips used represented another way tosave costs. The goal of a designer is not just to make thesimplest circuit, but to keep the component count down.Sometimes this results in slightly more complicated de-signs with respect to the underlying digital logic but nev-ertheless reduces the number of components, board size,and even power consumption.For example, in some logic families, NAND gates are thesimplest digital gate to build. All other logical operationscan be implemented by NAND gates. If a circuit alreadyrequired a single NAND gate, and a single chip normallycarried four NAND gates, then the remaining gates couldbe used to implement other logical operations like logicaland. This could eliminate the need for a separate chipcontaining those different types of gates.

Reliability

The “reliability” of a logic gate describes its mean timebetween failure (MTBF). Digital machines often havemillions of logic gates. Also, most digital machines are“optimized” to reduce their cost. The result is that of-ten, the failure of a single logic gate will cause a digitalmachine to stop working.

Digital machines first became useful when the MTBFfor a switch got above a few hundred hours. Even so,many of these machines had complex, well-rehearsed re-pair procedures, and would be nonfunctional for hoursbecause a tube burned-out, or a moth got stuck in a relay.Modern transistorized integrated circuit logic gates haveMTBFs greater than 82 billion hours (8.2×1010) hours,[7]and need them because they have so many logic gates.

Fanout

Fanout describes howmany logic inputs can be controlledby a single logic output without exceeding the current rat-ings of the gate.[8] The minimum practical fanout is aboutfive. Modern electronic logic using CMOS transistors forswitches have fanouts near fifty, and can sometimes gomuch higher.

Speed

The “switching speed” describes howmany times per sec-ond an inverter (an electronic representation of a “logicalnot” function) can change from true to false and back.Faster logic can accomplish more operations in less time.Digital logic first became useful when switching speedsgot above fifty hertz, because that was faster than a teamof humans operating mechanical calculators. Modernelectronic digital logic routinely switches at five gigahertz(5×109 hertz), and some laboratory systems switch atmore than a terahertz (1×1012 hertz).

16.4.5 Logic families

Main article: logic family

Design started with relays. Relay logic was relatively in-expensive and reliable, but slow. Occasionally a mechan-ical failure would occur. Fanouts were typically aboutten, limited by the resistance of the coils and arcing onthe contacts from high voltages.Later, vacuum tubes were used. These were very fast, butgenerated heat, and were unreliable because the filamentswould burn out. Fanouts were typically five to seven, lim-ited by the heating from the tubes’ current. In the 1950s,special “computer tubes” were developed with filamentsthat omitted volatile elements like silicon. These ran forhundreds of thousands of hours.The first semiconductor logic family was resistor–transistor logic. This was a thousand times more reliablethan tubes, ran cooler, and used less power, but had a verylow fan-in of three. Diode–transistor logic improved thefanout up to about seven, and reduced the power. SomeDTL designs used two power-supplies with alternatinglayers of NPN and PNP transistors to increase the fanout.

16.7. REFERENCES 131

Transistor–transistor logic (TTL) was a great improve-ment over these. In early devices, fanout improved toten, and later variations reliably achieved twenty. TTLwas also fast, with some variations achieving switchingtimes as low as twenty nanoseconds. TTL is still used insome designs.Emitter coupled logic is very fast but uses a lot of power.It was extensively used for high-performance computersmade up of many medium-scale components (such as theIlliac IV).By far, the most common digital integrated circuits builttoday use CMOS logic, which is fast, offers high circuitdensity and low-power per gate. This is used even in large,fast computers, such as the IBM System z.

16.5 Recent developments

In 2009, researchers discovered that memristors can im-plement a boolean state storage (similar to a flip flop,implication and logical inversion), providing a completelogic family with very small amounts of space and power,using familiar CMOS semiconductor processes.[9]

The discovery of superconductivity has enabled the de-velopment of rapid single flux quantum (RSFQ) circuittechnology, which uses Josephson junctions instead oftransistors. Most recently, attempts are being made toconstruct purely optical computing systems capable ofprocessing digital information using nonlinear optical el-ements.

16.6 See also• Boolean algebra

• Combinational logic

• De Morgan’s laws

• Digital signal processing

• Formal verification

• Hardware description language

• Integrated circuit

• Logic family

• Logic gate

• Logic minimization

• Logic simulation

• Logical effort

• Microelectronics

• Ringing

• Claude E. Shannon

• Sequential logic

• Transparent latch

• Unconventional computing

16.7 References[1] Null, Linda; Lobur, Julia (2006). The essentials of com-

puter organization and architecture. Jones & Bartlett Pub-lishers. p. 121. ISBN 0-7637-3769-0. We can build logicdiagrams (which in turn lead to digital circuits) for anyBoolean expression...

[2] Paul Horowitz and Winfield Hill, The Art of Electronics2nd Ed. Cambridge University Press, Cambridge, 1989ISBN 0-521-37095-7 page 471

[3] Maini. A.K. (2007). Digital Electronics Principals, De-vices and Applications. Chichester, England.: JonhWiley& Sons Ltd.

[4] “ASODA sync/async DLX Core”. OpenCores.org. Re-trieved September 5, 2014.

[5] Clarke, Peter. “ARM Offers First Clockless ProcessorCore”. eetimes.com. UBM Tech (Universal Business Me-dia). Retrieved 5 September 2014.

[6] Brown S & Vranesic Z. (2009). Fundamentals of DigitalLogic with VHDL Design. 3rd ed. New York, N.Y.: McGraw Hill.

[7] MIL-HDBK-217F notice 2, section 5.3, for 100,000 gate0.8 micrometre CMOS commercial ICs at 40C; failurerates in 2010 are better, because line sizes have decreasedto 0.045 micrometres, and fewer off-chip connections areneeded per gate.

[8] Kleitz , William. (2002). Digital and MicroprocessorFundamentals: Theory and Application. 4th ed. UpperSaddler Reviver, NJ: Pearson/Prentice Hall

[9] Eero Lehtonen, Mika Laihom, “Stateful implication logicwith memristors”, Proceedings of the 2009 IEEE/ACMInternational Symposium on Nanoscale ArchitecturesIEEE Computer Society Washington, DC, USA ©2009Accessed 2011-12-11

• R. H. Katz, Contemporary Logic Design, The Ben-jamin/Cummings Publishing Company, 1994.

• P. K. Lala, Practical Digital Logic Design and Test-ing, Prentice Hall, 1996.

• Y. K. Chan and S. Y. Lim, Progress In Electromag-netics Research B, Vol. 1, 269–290, 2008,"Syn-thetic Aperture Radar (SAR) Signal Generation,Faculty of Engineering & Technology, MultimediaUniversity, Jalan Ayer Keroh Lama, Bukit Beruang,Melaka 75450, Malaysia

132 CHAPTER 16. DIGITAL ELECTRONICS

16.8 External links• Lessons in Electric Circuits - Volume IV (Digital)

• MIT OpenCourseWare introduction to digital de-sign class materials (“6.004: Computation Struc-tures”)

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 133

16.9 Text and image sources, contributors, and licenses

16.9.1 Text• Electronic circuit Source: http://en.wikipedia.org/wiki/Electronic_circuit?oldid=660025244 Contributors: William Avery, Glenn, Reddi,

Omegatron, Jondel, DavidCary, Lyght, Velella, Wtshymanski, RainbowOfLight, Mindmatrix, Robert K S, Cbdorsett, Eras-mus, Plrk,Haikupoet, Cirfis, Gurch, Chobot, Spacepotato, Toffile, Stephenb, Canageek, TheMandarin, Grafen, Tyrenius, Allens, Snaxe920, Ozzmo-sis, SmackBot, Bigbluefish, Gilliam, SchfiftyThree, Rrburke, Edivorce, TimQ.Wells, RomanSpa, 16@r, Dicklyon, Hu12, Shoeofdeath, Alejrb, Amalas, Snakemike, Nczempin, Circuit dreamer, Pewwer42, Cydebot, Odie5533, Alaibot, Michagal, Nick Number, Dawnseeker2000,Nicolaasuni, VoABot II, 28421u2232nfenfcenc, Allstarecho, M 3bdelqader, MartinBot, Axlq, Jim.henderson, J.delanoy, Pharaoh of theWizards, Trusilver, Ram4nd, Danield101, Mellonbank, VolkovBot, Jeff G., Kakoui, Barneca, Philip Trueman, IlijaKovacevic, Anna Lin-coln, Dendodge, Santacruzing, Aaron Rotenberg, Wikiisawesome, Dsignoff, Kalan, Kehrbykid, MrChupon, Fanatix, Audioamp, Ttony21,Masgatotkaca, Nancy, ClueBot, Tachasmo, Excirial, Azadeh.a, Burner0718, HD86, XLinkBot, Mitch Ames, Addbot, Tcncv, Gnetter,MrOllie, Redheylin, Cristinalee, Bassbonerocks, Shekure, Eagle999, Rjaf29, Teles, ,سعی Yobot, Fraggle81, SolBasic, Evans1982, He-lena srilowa, Zohair.ahmad, AnomieBOT, Materialscientist, Promd33, Capricorn42, Armstrong1113149, Giggy12345, AbigailAbernathy,Anonymous from the 21st century, NotGiven, Amplitude101, Calmer Waters, Serols, DexDor, Slon02, John of Reading, Tommy2010,Bleakgadfly, Johnjosephc, Kilopi, Vladimirdx, Dshavit, ResearchRave, ClueBot NG, Satellizer, Ahmed.engr, Widr, Wbm1058, Naveenpn,Sotos68, Teepu Ahmad, AdventurousSquirrel, Robert Thyder, Ecsdiagram, Glacialfox, MathewTownsend, Batman11337, Lijogrg444,MadCowpoke, Webclient101, Epicgenius, Yamaha5, Jianhui67, Cricetone, TheQ Editor, Tatisimo, MrRedstone9000, KasparBot andAnonymous: 219

• Electronic component Source: http://en.wikipedia.org/wiki/Electronic_component?oldid=666307870 Contributors: Heron, RTC,Mahjongg, Reddi, David Shay, Omegatron, Chrisjj, Altenmann, Alan Liefting, Giftlite, Abdull, ArnoldReinhold, Closeapple, Alansohn,MarkGallagher, Caesura,Wtshymanski, Danhash, Kusma, PeterWöllauer, Versageek, Sleigh, RHaworth, Cbdorsett, Mandarax, Graham87,BD2412, JIP, RxS, Phillipedison1891, Ryan Norton, DavideAndrea, Routy, Chobot, Krishnavedala, DVdm, Bgwhite, YurikBot, Wave-length, Oliviosu~enwiki, RussBot, Toffile, Rsrikanth05, Proidiot, Jeff Carr, Jpbowen, SamuelRiv, Searchme, Light current, Mickpc, Tabby,Fernblatt, Paul Erik, Groyolo, robot, KnightRider~enwiki, SmackBot, Reedy, Lindosland, HenrikS, Oli Filth, Astaroth5, DHN-bot~enwiki, Frap, Indiedude, Rigadoun, Oasiselec, Scetoaux, 16@r, Dicklyon, TerryKing, Zarex, Circuit dreamer, Dgw, AndrewHowse,A876, Editor at Large, Hithisishal, Thijs!bot, Dougsim, Smile a While, Siawase, Leon7, RichardVeryard, MER-C, Arch dude, VoABot II,Swpb, Thunderhead~enwiki, Seba5618, R'n'B, Pharaoh of the Wizards, Gregfitzy, ARTE, Funandtrvl, VolkovBot, Philip Trueman, TXiK-iBoT, Rei-bot, Lordvolton, Monaco377, Wolfrock, Spinningspark, Alex h leclerc, Otxi, BotMultichill, PbBot, Dp67, ClueBot, PipepBot,Rparts, Cp111, Mild Bill Hiccup, DragonBot, LeoFrank, Excirial, PixelBot, Elcap, Apparition11, Crazy Boris with a red beard, Bodhisattv-aBot, Interferometrist, Addbot, Mortense, Fgnievinski, AkhtaBot, Fieldday-sunday, Prxbl, 5 albert square, , OffsBlink, Tide rolls,Hoenny, Teles, Luckas-bot, Yobot, Ptbotgourou, Grebaldar, FUZxxl, KDS4444, DemocraticLuntz, RBM 72, Materialscientist, Xqbot,Armstrong1113149, Mlpearc, Prunesqualer, RibotBOT, Amaury, IShadowed, FrescoBot, Rjwiki09, Pshent, Pinethicket, I dream of horses,LittleWink, Efalkow, FoxBot, ,کاشفعقیل Gauravpolekar, Banhtrung1, Javierito92, Dinamik-bot, Arcadiy, Nyxaus, EmausBot, John ofReading, 8v26901, K6ka, Lucas Thoms, Wemskills2016, Dffgd, AvicAWB, Bamyers99, Wikitürkçe, Staszek Lem, Sethupathy3e, L Kens-ington, Gwen-chan, ClueBot NG, Loew Galitz, O.Koslowski, Cybernew, Widr, Vortex112, Wbm1058, Jeraphine Gryphon, RAKESHBALAN, YFdyh-bot, MrDKing, SujithKJ, Frosty, Kevin12xd, Vahid alpha, Vanamonde93, Rakomwolvesbane, Tentinator, 1Source23,Falcogna, Stub Mandrel, Sarr X, Prabhjotcheema, Jianhui67, 99kmg365, Hoy smallfry, Tjrjehfhffh, Leadingic, Loloyrty, BacLuong, Sam-ran234, Nc4sb8, KasparBot and Anonymous: 207

• Resistor Source: http://en.wikipedia.org/wiki/Resistor?oldid=665622776 Contributors: AxelBoldt, Ap, Css, Andre Engels, Christian List,Aldie, Matusz, Ray Van De Walker, SimonP, Waveguy, Heron, Patrick, RTC, Tim Starling, Mahjongg, Liftarn, Karada, Delirium, Alfio,CesarB, Ahoerstemeier, Cyp, Theresa knott, Darkwind, Glenn, Bogdangiusca, Nikai, Eszett, Timwi, Reddi, Zoicon5, Omegatron, Ed g2s,Wilbern Cobb~enwiki, Chrisjj, Robbot, Hankwang, Tonsofpcs, Jredmond, Smither, Romanm, PxT, Ojigiri~enwiki, Robinh, Xanzzibar,Cyrius, Pengo, Alan Liefting, Giftlite, Everyking, Perl, Markus Kuhn, Leonard G., Joe Sewell, Brockert, Bobblewik, Tagishsimon, Su-pachikn, StuartH, Chowbok, Antandrus, Mako098765, DragonflySixtyseven, Glogger, Gauss, Icairns, GeoGreg, Vishahu, TobinFricke,Ojw, Abdull, Discospinster, Rich Farmbrough, ArnoldReinhold, Alistair1978, Quistnix, Pavel Vozenilek, Paul August, ESkog, Plugwash,Patrickov, El C, Jd waverly, Haxwell, Art LaPella, RoyBoy, Bobo192, NetBot, AnyFile, Harald Hansen, Smalljim, Matt Britt, ColinDouglas Howell, Jojit fb, Kjkolb, Nk, Larry V, Sam Korn, Haham hanuka, Hooperbloob, Nsaa, Ranveig, Red Winged Duck, Alansohn,Jic, Atlant, M7, Zippanova, Comrade009, Theodore Kloba, Wdfarmer, Snowolf, Velella, Wtshymanski, RainbowOfLight, Shoefly, Kusma,Carlos Quesada, DV8 2XL, Gene Nygaard, Kinema, HenryLi, Nilloc, Unixxx, Begemotv2718~enwiki, Jeffrey O. Gustafson, Woohookitty,Mindmatrix, Pol098, Joels341, Stixpjr, Frankie1969, CPES, Gimboid13, PeregrineAY, FreplySpang, Rjwilmsi, Seidenstud, GeorgeBurgess, RobertDahlstrom, SeanMack, Brighterorange, Bratch, Yamamoto Ichiro, Fish and karate, FuelWagon, FlaBot, Jeepo~enwiki,EPAstor, Shultzc, EmielMols, Alfred Centauri, Lmatt, Zotel, King of Hearts, Jidan, Chobot, Antilived, Krishnavedala, Bgwhite, Der-rickOswald, YurikBot, Wavelength, RobotE, Jimp, Phantomsteve, Spudbeach, JabberWok, Ukdragon37, Hydrargyrum, Stephenb, Shad-dack, Guiltyspark343, Shanel, SEWilcoBot, Borbrav, Srinivasasha, RazorICE, InvaderJim42, Mikeblas, DeadEyeArrow, Jeh, Blowdart,Oliverdl, SamuelRiv, Searchme, Richardcavell, FF2010, Uwezi, Light current, 21655, Phgao, Tabby, Nkendrick, DGaw, Mike1024, Al-lens, JSC ltd, Snaxe920, GrinBot~enwiki, Jknacnud, Sbyrnes321, Teo64x, Neier, KnightRider~enwiki, AtomCrusher, SmackBot, Tarret,Bggoldie~enwiki, Unyoyega, Thorseth, Cessator, Ohnoitsjamie, Hugo-cs, Lindosland, Chris the speller, Michbich, Oblemboy, CrookedAs-terisk, Sirex98, Thumperward, Oli Filth, Papa November, Astaroth5, Ruffelo, Audriusa, Ian Burnet~enwiki, Riflemann, Can't sleep,clown will eat me, Милан Јелисавчић, TheGerm, Ateş~enwiki, Geekboy72, JonHarder, VMS Mosaic, RedHillian, DinosaursLoveEx-istence, CanDo, Yrral, M jurrens, DMacks, N Shar, Where, Mion, FelisLeo, Ohconfucius, SashatoBot, KLLvr283, Laogeodritt, Dick-lyon, Mets501, EdC~enwiki, Quodfui, Matthew Kornya, Pi, Daniel5127, Atomobot, Electron20, Jpeguero, Sir Vicious, Ilikefood, Zureks,Pottsy123, Shoez, Jcoffland, W1tgf, Gatorosa, Requestion, MrFish, Kar403, Karimarie, Mblumber, Nbound, Altaphon, Meno25, GogoDodo, Tawkerbot4, DumbBOT, Viridae, Omicronpersei8, Ebraminio, Cinderblock63, Ozguy89, Serych, Epbr123, Mojo Hand, John254,Neilajh, Gerry Ashton, Leon7, Ajo Mama, Matty!, Ketter~enwiki, AntiVandalBot, Edokter, Dinferno, Spencer, Spartaz, Golgofrinchian,Deadbeef, JAnDbot, Pp0u016d, MER-C, Jddriessen, CosineKitty, John a s, Edwin ok, Magioladitis, VoABot II, JamesBWatson, Snthakur,Nikevich, Schily, Aka042, Carlsonmark, Catgut, Daarznieks, Virtlink, Americanhero, Allstarecho, User A1, Vssun, Calltech, Wderousse,Outlook, Dantman, DancingPenguin, MartinBot, Raymondyo, Sigmundg, Rettetast, Jonathan Hall, Nono64, GrahamDavies, Sephers, Led-gendGamer, Tgeairn, J.delanoy, Pharaoh of the Wizards, Peter Chastain, Dispenser, DarkFalls, Slrdtm, Falcon866, NewEnglandYankee,Suckindiesel, Sciport, Guitarlesson, Cmichael, 2help, Cometstyles, WJBscribe, Tchoutka, Uhai, Magatouche, Gaurav joseph, Scwerllguy,Useight, David.lecomte, Xiahou, Squids and Chips, Funandtrvl, Deor, VolkovBot, Lordmontu, Asnr 6, Jeff G., JohnBlackburne, Holme053,

134 CHAPTER 16. DIGITAL ELECTRONICS

Constant314, EchoBravo, Alberon, Philip Trueman, TXiKiBoT, Qureus1, Hqb, Lordvolton, Retiono Virginian, Anna Lincoln, Dendodge,Zolot, LeaveSleaves, DarkFuture, PDFbot, Inductiveload, Dragon587, Enigmaman, Sarc37, Wolfrock, SQL, Synthebot, Jason Leach, En-viroboy, Davidvanee, Spinningspark, Atreusk, Cindamuse, AlleborgoBot, AHMartin, Kbrose, JDHeinzmann, SieBot, Scarian, Gerakibot,Viskonsas, Matthew Yeager, Lucasbfrbot, Yintan, Msadaghd, Crm123, VampireBaru, Hoagg, Bentogoa, A. Carty, Xxrambo, Rocknroll-suicide, Poindexter Propellerhead, Lazyfishnet, IdreamofJeanie, Kudret abi, Ge0rge359, StaticGull, Capitalismojo, Unique ragazzo, Di-jhammond, Felizdenovo, Precious Roy, Denisarona, Beemer69, Tuntable, Loren.wilton, De728631, ClueBot, Binksternet, GorillaWarfare,Khaleghian, CarolSpears, The Thing That Should Not Be, Ggia, AerospaceEngr, Mild Bill Hiccup, Edlerk, Thegeneralguy, Momentofiner-tia, Excirial, Jusdafax, TonyBallioni, Hardkrash, Arjayay, Wstorr, Aitias, Zootboy, Versus22, Moonlit Knight, Berean Hunter, Ginbot86,DumZiBoT, XLinkBot, Kyz 97, MarvinPelfer, Rror, Interferometrist, Skarebo, Madmike159, Udt-21, Karpouzi, Iranway, Mojska, Owl or-der, Nikhilb239, Addbot, Cxz111, Mortense, Bboe, Jojhutton, Fyrael, Olli Niemitalo, Metsavend, CanadianLinuxUser, Cst17, Download,Roux, Favonian, 5 albert square, Delphi234, Bavgang123, Tide rolls, MuZemike, Luckas-bot, Nunikasi, Yobot, Fraggle81, II MusLiMHyBRiD II, Amirobot, MadMan2021, Omaga99, THENWHOWAS PHONE?, Mattia Luigi Nappi, KamikazeBot, Backtothemacman32,Eric-Wester, Tempodivalse, CHUCKisGOD, Aliens are fun!!!!!, AnomieBOT, KDS4444, Quangbao, Ravikant nit, Jim1138, Hat'nCoat,Piano non troppo, RBM 72, Aditya, Realgigabyte, Materialscientist, 4441gh, Citation bot, Tristantech, Felyza, Frankenpuppy, Neurol-ysis, Xqbot, Iadrian yu, Capricorn42, Miracleworker5263, Minnijazzyjade, Whipple11, Yoconst, GrouchoBot, Nedim Ardoğa, SophusBie, Shadowjams, Dakane2, Depictionimage, Prari, FrescoBot, Chugachuga, Furshur, Paco1976, Ercegovac~enwiki, Kenny.Yang, Ben-zolBot, Rjwiki09, Oalp1003, Pinethicket, I dream of horses, Boulaur, ,נלביא Rambo111, Nikey101, Salvidrim!, Lineslarge, Merlion444,December21st2012Freak, Jauhienij, Utility Monster, Abc518, Double sharp, عقیل ,کاشف SchreyP, Uriburu, Vrenator, Reaper Eternal,Seahorseruler, Nascar1996, Minimac, DARTH SIDIOUS 2, Mean as custard, Skamecrazy123, EmausBot, Racerx11, GoingBatty, Hos-sammandour, Challisrussia, Wikipelli, Fæ, Lindseyrose, Trinidade, 1234r00t, H3llBot, EWikist, BrianSfinasSSI, Tolly4bolly, Sbmeirow,Tomásdearg92, Etugam, Anonimski, Autoerrant, Carmichael, Cupaxtai, Itaharesay, RockMagnetist, Maminov2, Capgunslinger, ClueBotNG, Smtchahal, Matthiaspaul, Lanthanum-138, Frietjes, Jakuzem, 10v1walsha, Widr, Vortex112, Karthik262399, Sameenahmedkhan,Helpful Pixie Bot, Minderbart1, Pliu88, Wbm1058, Lowercase sigmabot, AntonioSajonia, Piguy101, Yowanvista, Alexey Villarreal, Dave3740, Tsopatsopa, Glacialfox, Chip123456, Funfun2333, ChrisGualtieri, GoShow, Embrittled, Chromastone1998, Raptormega123, Medi-ran, Khazar2, Dexbot, Oldschool1970, Zikri hidayat, Lugia2453, MWikiOrg, Orlin.tel, Ajay.loveland.jr, Pdecalculus, Binarysequence,Eyesnore, Tentinator, Auburnate, John Blair76, Peter Sendtown, Tanujkumarpandey, Buntybhai, Ginsuloft, 72dodgerpress, Y13bakerm, Ja-conaFrere, Cricetone, JREling1, BatManFascination, JaunJimenez, Trackteur, Owais Khursheed, Nodleh, Jelabon123, Qdavis, Akhil.A.L,Masteerr, Gouravd, JoJMasterRace, JoJMastarRace, Pitchcapper, Sytgod, Infinite0694, KasparBot, Soyungeniodelavida and Anonymous:866

• Transistor Source: http://en.wikipedia.org/wiki/Transistor?oldid=666747838 Contributors: Mav, The Anome, Taw, Rjstott, Jkominek,Sandos, Youssefsan, RAD~enwiki, Little guru, Mudlock, Ray Van De Walker, SimonP, Maury Markowitz, Ellmist, Gbraad, Heron, RTC,JohnOwens, Michael Hardy, Tim Starling, Cprompt, Mahjongg, Nixdorf, Ixfd64, Ahoerstemeier, Cyp, ZoeB, Stevenj, Suisui, Iammaxus,Александър, Kaeslin, Julesd, Glenn, Bogdangiusca, Cyan, Nikai, Tristanb, Jiang, Lommer, HolIgor, Wikiborg, Reddi, Stone, Dfeuer, An-drewman327, Gutza, Zoicon5, PeterGrecian, Timc, Tpbradbury, Marshman, Maximus Rex, Grendelkhan, Omegatron, ReciprocityProject,Thue, Stormie, Bloodshedder, Raul654, Dpbsmith, Flockmeal, Ldo, Phil Boswell, Maheshkale, Robbot, Pigsonthewing, Jakohn, Owain,Fredrik, Pjedicke, Babbage, Jondel, Bkell, Hadal, UtherSRG, Galexander, Jleedev, Alan Liefting, David Gerard, Enochlau, Wjbeaty,Ancheta Wis, Giftlite, Graeme Bartlett, DavidCary, Mat-C, Ferkelparade, Brian Kendig, COMPATT, Fleminra, Capitalistroadster, Drat-man, Chowbok, Gadfium, Plutor, Sonjaaa, Antandrus, Mako098765, Jossi, Untifler, Avihu, Dcandeto, Qdr, Jimaginator, Mike Rosoft,Vesta~enwiki, Mindspillage, Zed~enwiki, Discospinster, Rich Farmbrough, Rhobite, Rmalloy, Pjacobi, ArnoldReinhold, Xezbeth, Mani1,Dmeranda, Dyl, Kbh3rd, Klenje, Plugwash, Jindrich, Srivatsaaithal, CanisRufus, Sfahey, El C, Lankiveil, Barfooz, Sietse Snel, Neilrieck,Spoon!, Bobo192, Smalljim, EricBarbour, R. S. Shaw, Elipongo, Matt Britt, Mikel Ward, Jojit fb, Kjkolb, Wikinaut, DanB~enwiki,Haham hanuka, Hooperbloob, Nsaa, Nazli, Alansohn, Orimosenzon, Jared81, Interiot, Eric Kvaalen, Barium, Atlant, WTGDMan1986,Ashley Pomeroy, Mr snarf, Brinkost, Snowolf, Blobglob, Oneliner, Wtshymanski, Knowledge Seeker, Cburnett, Suruena, Cal 1234,TenOfAllTrades, DV8 2XL, Gene Nygaard, MIT Trekkie, Redvers, TheCoffee, Ahseaton, HenryLi, Flying fish, Begemotv2718~enwiki,Veemonkamiya, Polyparadigm, Matijap, MONGO, Pyrosim, Cbdorsett, Eyreland, Bar0n, Zzyzx11, CPES, Palica, Msiddalingaiah, Gra-ham87, Magister Mathematicae, Haikupoet, Snafflekid, Coneslayer, JVz, Mjm1964, Bernard van der Wees, Tangotango, Colin Hill, Ve-gaswikian, DonSiano, Ligulem, LjL, Rbeas, Yamamoto Ichiro, FlaBot, Naraht, Arnero, Ysangkok, Nihiltres, AJR, Gparker, RexNL,Gurch, DavideAndrea, RobyWayne, Alvin-cs, Kri, JonathanFreed, Jidan, Chobot, Krishnavedala, DVdm, Cornellrockey, Bubbachuck,YurikBot, Wavelength, Marginoferror, Hairy Dude, Jimp, SpuriousQ, Stephenb, Gaius Cornelius, Yyy, Shaddack, Brejc8, Pseudomonas,NawlinWiki, Rohitbd, ONEder Boy, RazorICE, Jpbowen, Speedevil, Scs, Misza13, Scottfisher, Gadget850, DeadEyeArrow, Bota47, Jeh,Searchme, Light current, 21655, Ninly, Theda, Closedmouth, Arthur Rubin, Vdegroot, Cronostvg, Emc2, Wbrameld, Katieh5584, Kung-fuadam, GrinBot~enwiki, Zvika, ModernGeek, Elliskev, That Guy, From That Show!, Minnesota1, Attilios, Siker, SmackBot, Yellow-Monkey, RockMaestro, Dovo, Reedy, Thorseth, Delldot, StephenJMuir, Unforgettableid, Magwich77, Gilliam, Simoxxx, Andy M. Wang,Lindosland, QEDquid, Master Jay, Avin, @modi, Thumperward, Oli Filth, EncMstr, Papa November, SEIBasaurus, DHN-bot~enwiki,Squibman, Audriusa, WDGraham, Foogod, HeKeRnd, Can't sleep, clown will eat me, Writtenright, Sephiroth BCR, KaiserbBot, Lantrix,Yidisheryid, Rrburke, VMSMosaic, Chcknwnm, Nakon, Valenciano, MichaelBillington, BWDuncan, Repairscircuitboards, Jklin, DMacks,Rspanton, Ligulembot, Ohconfucius, The undertow, SashatoBot, Kuru, NeilUK, Danorux, Lazylaces, Evenios, JorisvS, Scetoaux, Iron-Gargoyle, CyrilB, Loadmaster, MarkSutton, Slakr, Optimale, George The Dragon, Rogerbrent, Dicklyon, Waggers, Mets501, EEPROMEagle, Softice6~enwiki, Caiaffa, Tsolosmi, Kvng, KJS77, Cmcginnis, Iridescent, Drlegendre, Yves-Laurent, Paul Foxworthy, DarkCell,Aeons, IanOfNorwich, Tawkerbot2, Daniel5127, G-W, Chetvorno, Elekas, Compy 386, David Carron, ThisIsMyUsername, CmdrObot,Irwangatot, Chrumps, Ilikefood, JohnCD, Rohan2kool, Zureks, Old Guard, Casper2k3, Cydebot, Verdy p, Tawkerbot4, DumbBOT, Edi-tor at Large, Splateagle, Charlvn, Malleus Fatuorum, 6pence, Jessemonroy650, Epbr123, Pcu123456789, Headbomb, Electron9, GerryAshton, Nezzadar, Leon7, CboneG5, Natalie Erin, Escarbot, AntiVandalBot, Luna Santin, Firespray, EarthPerson, Scientific Ameri-can, RapidR, Dvandersluis, Farosdaughter, Rico402, JAnDbot, Xhienne, Dan D. Ric, Em3ryguy, Harryzilber, MER-C, CosineKitty, Eri-coides, Dagnabit, Britcom, Dricherby, Snowolfd4, PhilKnight, Denimadept, Acroterion, I80and, Bongwarrior, VoABot II, Verkhovensky,BigChicken, Robcotton, Schily, Sub40Hz, Bleh999, Allstarecho, Canyouhearmenow, Clipjoint, Matt B., Species8471, Cocytus, Gjd001,VMMK, MartinBot, Chrismon, Tamer ih~enwiki, DatasheetArchive, Compnerd09, Kostisl, R'n'B, Galootius, Esolbiz, LedgendGamer,Transisto, J.delanoy, Hans Dunkelberg, ChrisfromHouston, Uncle Dick, Kevin aylward, Ginsengbomb, Darth Mike, Rod57, Dfries, Tarot-cards, SJP, Bigdumbdinosaur, Mermadak, Imchandan, KylieTastic, Jamesontai, Zuban42, Hmsbeagle, Ale2006, JonS117, Idioma-bot,Reelrt, IFly, Chinneeb, King Lopez, VolkovBot, TreasuryTag, ABF, HeckXX, Constant314, Ryan032, Philip Trueman, TXiKiBoT, Jo-masecu, The Original Wildbear, Davehi1, FDominec, Rei-bot, Axonn77, Soldior60, CanOfWorms, Supertask, LeaveSleaves, Wicked-clown29, Saturn star, Cameronled, Hellcat fighter, Randers1, Enviroboy, RaseaC, Spinningspark, Bucko1992, Northfox, Symane, JimmiHugh, Logan, Kbrose, Anirak1337, Area51david, SieBot, Dwandelt, Tescoid, WereSpielChequers, Jonnic1, Toghome, Vanished User

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 135

8a9b4725f8376, Chmyr, Guillermo90r, Jayzor123, Oda Mari, Davidperson, Lightmouse, Poindexter Propellerhead, Boots232, Apsro-billo, Bludude90210, GAMER 20999, Alf loves chocolate, Nibol, Dolphin51, Denisarona, CodyARay, C0nanPayne, Asher196, Explicit,Loren.wilton, Martarius, ClueBot, The Thing That Should Not Be, Rodhullandemu, Pakaraki, Mattgirling, Garyzx, Mild Bill Hiccup,Boing! said Zebedee, Blanchardb, Urb4nn1nj4, Puchiko, 718 Bot, Masterpiece2000, Masoud691, Habibi 66, Mahya42, Kurdestan, Mor-ristanenbaum, Faranak moradipoor, Rahmaty, PixelBot, Pmronchi, Conical Johnson, Geniusinfranceman, RedSHIFT, Sun Creator, Brewsohare, Rakins007, Tayyabarif, 07mahmooda, Dekisugi, The Red, Carriearchdale, ChrisHodgesUK, Chaosdruid, Thingg, Wstorr, Aitias,NorthernNerd, SoxBot III, Therealmorris, Rtellason, DumZiBoT, Dorit82, Bearsona, Delt01, XLinkBot, Spitfire, WikHead, Noctibus,Drm5555, Kbdankbot, Addbot, Pyfan, DOI bot, Captain-tucker, Ronhjones, Fieldday-sunday, CanadianLinuxUser, Fluffernutter, Spilling-Bot, MrOllie, Mentisock, Download, Glane23, Favonian, 84user, Numbo3-bot, Semiwiki, Lightbot, Hhcox, Zorrobot, Jackelfive, PlankBot,Luckas-bot, OrgasGirl, JSimmonz, Ptbotgourou, Fraggle81, Cc2po, Crispmuncher, DJ LoPaTa, THEN WHO WAS PHONE?, ,Mike1975, TestEditBot, Commissar Mo, OregonD00d, AnomieBOT, Efa, Captain Quirk, Ulric1313, Flewis, LiuyuanChen, Materialsci-entist, RobertEves92, Citation bot, Carlsotr, Carl086, Frankenpuppy, Xqbot, Hammack, Capricorn42, Nokkosukko, Magnus0re, Grou-choBot, Nedim Ardoğa, Yoganate79, Der Falke, Maitchy, Henk.muller, Richard BB, Shadowjams, David Nemati, Mike Dill~enwiki, A.di M., Some standardized rigour, Forrest575757, Prari, FrescoBot, Tobby72, Tiramisoo, Lonaowna, Jc3s5h, Dooley3956, Hébus, Firq,Dman223, Roman12345, E1m1o1, Citation bot 1, Kient123, AstaBOTh15, Pinethicket, Spidey104, Quantumsilverfish, RedBot, Space-Flight89, Jamesinderbyshire, Mikespedia, Tcnuk, Tyler-willard, Bgpaulus, Lissajous, Circuitsmith, Sensitivo, Georgemalliaras, TobeBot,Surendhar Murugan, MarkGT, Privatise, Michael9422, Dinamik-bot, Vrenator, Thomaskutty, Stephen2zidang, Tbhotch, DARTH SID-IOUS 2, SSgator15, DASHBot, EmausBot, John of Reading, Jovianconflict, Immunize, Beatnik8983, RA0808, Mchaiiann, Olof nord,Smappy, AG SILVER92, Tommy2010, REMspectrum, Freetall, Serketan, Markk01, Joao.pimentel.ferreira, Mkratz, MigueldelosSantos,Rails, 2n3055, Sbmeirow, L Kensington, Anonimski, ChuispastonBot, RockMagnetist, LeAwesome0001, TYelliot, 28bot, Profurp, Clue-Bot NG,Wikivinyl, Dratini0, Wikishotaro, Vergamiester, Akjahid, Kjece, Vishal.vnair, Helpful Pixie Bot, J caraball, Tejasvi.ts, Wbm1058,Lowercase sigmabot, BG19bot, Zzyxzaa26, Vagobot, ISTB351, Mondeepsaikia, PearlSt82, Tritomex, Tiscando, Colin5555, Vivek7de,Anamatsu, Sunshine Warrior04, Bluefire272, Klilidiplomus, Simeondahl, Dinesh.lei, Hebert Peró, Chromastone1998, Miguelmadruga,Khazar2, EuroCarGT, JYBot, Dexbot, Havabighed, Dhanmantee, Jochen Burghardt, YaganZ, Vahid alpha, I am One of Many, Joeymank,Sanya7901, Historianbuff, DavidLeighEllis, Wamiq, Babitaarora, Ugog Nizdast, Wordpressstar, Deedmonds, Gokul.gk7, Mh akbarpour,Pri88yank, Monkbot, BatManFascination, JaunJimenez, DaveeBlahBlah, Dsernst, Scipsycho, Bigol77, KasparBot and Anonymous: 1138

• Capacitor Source: http://en.wikipedia.org/wiki/Capacitor?oldid=666960471 Contributors: AxelBoldt, Sodium, Bryan Derksen, Zundark,Ap, Andre Engels, Fredbauder, Aldie, PierreAbbat, Ray Van De Walker, Merphant, Waveguy, Heron, Patrick, Tim Starling, Chan siu-man, Modster, Dominus, Tjfulopp, Lousyd, Kku, Ixfd64, Ahoerstemeier, Mac, Stevenj, Muriel Gottrop~enwiki, Theresa knott, Darkwind,Glenn, Bogdangiusca, Nikai, BAxelrod, Smack, Schneelocke, HolIgor, Timwi, Bemoeial, Wikiborg, Reddi, Denni, Sertrel, Maximus Rex,Furrykef, Populus, Omegatron, Phoebe, Thue, Francs2000, Phil Boswell, Rogper~enwiki, Nufy8, Robbot, Hubertus~enwiki, Naddy, Mod-ulatum, Texture, Gidonb, Jondel, Intangir, Jleedev, Rik G., Wjbeaty, Giftlite, DavidCary, Wolfkeeper, Netoholic, Tom harrison, Tubular,Everyking, CyborgTosser, Niteowlneils, Leonard G., Starsong, Guanaco, Yekrats, Mboverload, Pascal666, Solipsist, Foobar, Edcolins,StuartH, SebastianBreier~enwiki, Geni, Gzuckier, Mako098765, MisfitToys, Am088, ShakataGaNai, Jossi, Hutschi, Anythingyouwant,Icairns, Gscshoyru, Urhixidur, Shen, Joyous!, Sonett72, Deglr6328, Xspartachris, Grunt, Gazpacho, Fpga, Ralph Corderoy, NathanHurst,Discospinster, Guanabot, ArnoldReinhold, Flatline, ZeroOne, Kjoonlee, FrankCostanza, Rmcii, Sietse Snel, RoyBoy, Euyyn, Mickey-mousechen~enwiki, Jevinsweval, Sole Soul, Bobo192, Shenme, Slicky, Bert Hickman, Kjkolb, Tgabor, Hagerman, Pearle, Hooperbloob,Jakew, Jumbuck, Neonumbers, Atlant, Mac Davis, Wdfarmer, Snowolf, Velella, CaseInPoint, Wtshymanski, Suruena, TenOfAllTrades,LFaraone, DV8 2XL, Gene Nygaard, Alai, Mattbrundage, HenryLi, Kenyon, Saeed, Robin F., Woohookitty, Poppafuze, Mindmatrix,RHaworth, StradivariusTV, Robert K S, Pol098, Tylerni7, Rtdrury, Gyanprakash, SCEhardt, Eyreland, SDC, Frankie1969, Wayward, Pfal-stad, Msiddalingaiah, Graham87, Crocodealer, FreplySpang, Snafflekid, Edison, Josh Parris, Sjakkalle, Rjwilmsi, Zbxgscqf, Tangotango,Tawker, Vegaswikian, SeanMack, FlavrSavr, Thedatastream, FlaBot, Bobstay, Arnero, Shultzc, Jak123, Nivix, Alfred Centauri, AlexSims, RexNL, Gurch, Czar, Pewahl, Fosnez, Fresheneesz, Fct, Chobot, Krishnavedala, DVdm, YurikBot, Wavelength, Jimp, Adam1213,RussBot, Gokselgoksel, Crazytales, Red Slash, Hydrargyrum, Akamad, Stephenb, Yyy, Shaddack, Wiki alf, Spike Wilbury, Howcheng,Sangwine, CecilWard, Mikeblas, RUL3R, E2mb0t~enwiki, Zzzzzzus, Ospalh, Syrthiss, Scottfisher, DeadEyeArrow, Bota47, Jeh, Sup-spirit, Dingy, Zelikazi, Smaines, Kev Boy, Wknight94, SamuelRiv, Searchme, Light current, Huangcjz, Knotnic, Tabby, Canley, Fergofrog,LeonardoRob0t, Naught101, JLaTondre, Enkauston, GrinBot~enwiki, Dkasak, Mejor Los Indios, Lunch, Sbyrnes321, Jimerb, Veinor,SmackBot, Amcbride, FunnyYetTasty, Steve carlson, Tarret, Pgk, Thorseth, Freestyle~enwiki, Blue520, BMunage, Jbleecker, Eskimbot,Pedrose, Edgar181, Genisock, Relaxing, Gilliam, Skizzik, RHCD, Lindosland, Quinsareth, Persian Poet Gal, Oli Filth, Pylori, OrangeDog,Papa November, Epastore, Terraguy, Dual Freq, A. B., Langbein Rise, Bread2u, Theneokid, Rheostatik, MKB, Can't sleep, clown willeat me, Милан Јелисавчић, JonHarder, Addshore, SundarBot, Mugaliens, Cyhatch, Fuhghettaboutit, Radagast83, S Roper, Dreadstar, Mjurrens, Minipie8, DMacks, Kotjze, Sadi Carnot, Kukini, Fjjf, DJIndica, Nmnogueira, SashatoBot, Harryboyles, Dbtfz, John, Jidanni, Za-phraud, FrozenMan, Notmicro, JorisvS, Ckatz, CyrilB, A. Parrot, Dicklyon, Optakeover, Dalstadt, Nwwaew, ShakingSpirit, Hgrobe, Hu12,Blackcloak, W0lfie, IanOfNorwich, Tawkerbot2, Chetvorno, Atomobot, Powerslide, GeordieMcBain, Nutster, CmdrObot, Irwangatot,Scohoust, MorkaisChosen, Ilikefood, Prlsmith, JohnCD, Nczempin, Orderinchaos, Jamoche, Zyxoas,WeggeBot, Seven of Nine, Mike5193,RP98007, Cydebot, Lemurdude, Zginder, JustinForce, My Flatley, DumbBOT, Electric squall, Fyedernoggersnodden, Thijs!bot, Wikid77,Drpixie, Ishdarian, Young Pioneer, Electron9, Leon7, FourBlades, Nick Number, Jauricchio, AntiVandalBot, Linksmask1, Opelio, Shirt58,Gef756, Indrek, BinaryFrog, DarthShrine, Lfstevens, Myanw, Andy.Cowley, Zondran, Geobio, Arch dude, Ron7684, Ccrrccrr, Andonic,Coolhandscot, PhilKnight, Meeples, Sangak, Magioladitis, VoABot II, Mondebleu, Xochimec, Nikevich, Catgut, Crunchy Numbers, UserA1, Martynas Patasius, JaGa, Calltech, Oroso, S3000, Audi O Phile~enwiki, Denis tarasov, Axlq, Rettetast, Bissinger, Fuzzyhair2, Avakar,Kateshortforbob, Freeboson, J.delanoy, Pharaoh of the Wizards, Nbauman, Uncle Dick, Jesant13, Monodb, Ganymedstanek, Lannocc1,McSly, Mbbradford, RiverBissonnette, Glens userspace watcher, Warut, Leodj1992, Szzuk, NewEnglandYankee, Vanished user 47736712,Potatoswatter, Ja 62, H1voltage, Alexander Bell, Mlewis000, Samkline, Idioma-bot, Funandtrvl, Deor, Ivor Catt, VolkovBot, Larryisgood,Orphic, Pleasantville, Pasquale.Carelli, Constant314, Philip Trueman, TXiKiBoT, Circuit13, The Original Wildbear, BertSen, Lordvolton,Sankalpdravid, Qxz, Cloudswrest, Oxfordwang, Dendodge, Martin451, PaulTanenbaum, Inductiveload, Nelkins, Yk Yk Yk, Synthebot,Altermike, GlassFET, Michaeltripp, Spinningspark, Antosheryl, Nibios, BeowulfNode, Symane, S.Örvarr.S, Theoneintraining, SieBot,Hertz1888, VVVBot, Trigaranus, Mwaisberg, Bentogoa, A. Carty, Ioverka, PHermans, Hello71, KoshVorlon, Steven Zhang, Lightmouse,Alex.muller, Ngriffeth, Fullobeans, PlantTrees, Treekids, TreeSmiler, Asher196, Dp67, SpectrumAnalyser, ClueBot, Binksternet, Go-rillaWarfare, Snigbrook, Robchat, Wanderer57, GreenSpigot, Mild Bill Hiccup, Ventusa, Edlerk, Enghoff, Pointillist, Nima shoormeij,Excirial, Jusdafax, Robbie098, Anon lynx, Lucas the scot, Dagordon01, Tylerdmace, Iner22, Esbboston, Brews ohare, Simdude2u, Jotter-bot, Promethean, Etcwebb, Editor510, Banime, Thingg, Wstorr, Tleave2000, Berean Hunter, Elcap, DumZiBoT, InternetMeme, AlanM1,XLinkBot, BodhisattvaBot, Rror, Cameracut, Dthomsen8, Noctibus, WikiDao, Airplaneman, Alex Khimich, Addbot, Mortense, Lan-don1980, KickimusButtus, Ronhjones, Jncraton, Pcormon, Cst17, MrOllie, Download, LaaknorBot, Redheylin, Favonian, K Eliza Coyne,

136 CHAPTER 16. DIGITAL ELECTRONICS

LinkFA-Bot, Peti610botH, Himerish, Numbo3-bot, Corny131, StoneCold89, Tide rolls, Luckas-bot, Yobot, Zaereth, Schuym1, Kartano,Jordsan, Amirobot, Mmxx, THEN WHO WAS PHONE?, AnomieBOT, Sonia, Jim1138, Jeni, B137, GRDoss, Materialscientist, Citationbot, Hadaly, OllieFury, ArthurBot, Xqbot, Capricorn42, Jeffrey Mall, Yuiwii, Turk oğlan, ManasShaikh, Mmathiesen, Wingstarsoft, Grou-choBot, Mdewman6, RibotBOT, Epannila, Leonardo Da Vinci, Quantum ammar, Thaflinger, GhalyBot, Grossday, Chongkian, Dougof-borg, Coleycole, GliderMaven, FrescoBot, Feneeth of Borg, RuslanBer, Yiyi303, Soam Vasani~enwiki, Idyllic press, Hasanbabu, CraigPemberton, Rjwiki09, Citation bot 1, Pinethicket, Jonesey95, Tom.Reding, RedBot, 124Nick, Foobarnix, Fumitol, Vin300, Abhishekcha-van79, Hitachi-Train, LogAntiLog, Dinamik-bot, Vrenator, MajorStovall, TorQue Astur, Theo10011, Vladislav Pogorelov, Minimac,Rad peeps, Hyarmendacil, NerdyScienceDude, Cogniac, Bullet train, Mark Kretschmar, EmausBot, WikitanvirBot, Hippopenonomous,Da500063, GoingBatty, Minimac’s Clone, DMChatterton, Tommy2010, Gavinburke, Winner 42, REMspectrum, Frof eyed, ZéroBot,Lindseyrose, Sanalks, Fred Gandt, Sbmeirow, L Kensington, Zueignung, Ego White Tray, DennisIsMe, Itaharesay, Maminov2, TYelliot,ClueBot NG, Ulflund, Matthiaspaul, Vividvilla, Delusion23, 10v1walsha, ScottSteiner, Benfriesen12, Widr, Reify-tech, Vortex112, HelpfulPixie Bot, Doorknob747, Lowercase sigmabot, Mataresephotos, BG19bot, IronOak, Vagobot, Vokesk, AntonioSajonia, Piguy101, MarkArsten, AhsanAli408, Rickey985, Isacp, Sleepsfortheweak, Frizb99, BattyBot, Clienthopeless, DarafshBot, Mahmud Halimi Wardag,HubabubbalubbahubbaYABALICIOUS, SD5bot, JamesHaigh, Kshahinian, Dexbot, Aloysius314, Mogism, Salako1999, Bayezit.dirim, Is-arra (HG), MZLauren, Frosty, Paxmartian, FrostieFrost, Vahid alpha, Madhacker2000, Mark viking, Altered Walter, TREXJET, Fa.aref,Gomunkul51, Murmur75, Gtrsentra, DavidLeighEllis, Glaisher, Jwratner1, Asadwarraich, Cricetone, Monkbot, JREling1, JaunJimenez,MadDoktor23, Applemusher123, NameloCmaS, Krelcoyne, Ruksakba, Goran Diklic and Anonymous: 1034

• Inductor Source: http://en.wikipedia.org/wiki/Inductor?oldid=666006804 Contributors: Eclecticology, Christopher Mahan, Ben-Zin~enwiki, Heron, Mintguy, Youandme, Hephaestos, Patrick, RTC, Michael Hardy, Chan siuman, SebastianHelm, Dgrant,Looxix~enwiki, Glenn, Bogdangiusca, Nikai, Jiang, Smack, Lommer, CAkira, Bemoeial, RickK, Reddi, Zoicon5, Omegatron, Unin-vitedCompany, Rogper~enwiki, Robbot, Romanm, Cyrius, Giftlite, Wolfkeeper, Dratman, Ssd, Starsong, Yekrats, Bobblewik, Chowbok,Utcursch, LucasVB, Gzuckier, GeoGreg, Nickptar, Mike Rosoft, Mormegil, Rich Farmbrough, Pjacobi, ArnoldReinhold, Harriv, Mister-Sheik, Bdieseldorff, Chairboy, Army1987, Meggar, Bert Hickman, Nk, Congruence, Haham hanuka, Hooperbloob, Lornova~enwiki, Jum-buck, Atlant, Keenan Pepper, Benjah-bmm27,Wtshymanski, Apolkhanov, DV8 2XL, Gene Nygaard, Aempirei, Aidanlister, BillC, Pol098,Rtdrury, Cbdorsett, CharlesC, Frankie1969, Eirikr, BD2412, Snafflekid, Rjwilmsi, Joel D. Reid, FlaBot, Neonil~enwiki, Loggie, Al-fred Centauri, Pewahl, Fresheneesz, Lmatt, Srleffler, Antikon, Krishnavedala, Berrinam, YurikBot, Stephenb, Gaius Cornelius, Shaddack,Rsrikanth05, NawlinWiki, Grafen, Gerben49~enwiki, Lexicon, TDogg310, Mkill, DeadEyeArrow, Bota47, Unforgiven24, Searchme,Light current, KNfLrPnKNsT, Arthur Rubin, Nemu, Mike1024, Junglecat, SmackBot, Steve carlson, Thorseth, Eskimbot, BernardFrançois, Gilliam, Ohnoitsjamie, Lindosland, Lovecz, Bluebot, Thumperward, Oli Filth, Papa November, Adpete, DHN-bot~enwiki,Cfallin, Hgrosser, SundarBot, Zhinker, ServAce85, M jurrens, Kbwikipedia, DMacks, Petedarnell, TenPoundHammer, Ohconfucius,SashatoBot, Akendall, Hefo~enwiki, FrozenMan, Copeland.James.H, Gobonobo, CyrilB, Dicklyon, Waggers, Dalstadt, Hu12, Paul Fox-worthy, G-W, Chetvorno, Nczempin, Velle~enwiki, MarsRover, MaxEnt, Christian75, Ebraminio, Acronymsical, J. W. Love, Escarbot,WikiWebbie, Guy Macon, Seaphoto, Lovibond, Salgueiro~enwiki, Myanw, JAnDbot, CosineKitty, Arch dude, Andonic, Elspec, Drhlajos,VoABot II, Mondebleu, Hmo, Rivertorch, ShiftyDave, Cpl Syx, Vssun, Khalid Mahmood, InvertRect, Highsand, Hdt83, Glrx, Pharaoh ofthe Wizards, Kar.ma, AntiSpamBot, Wikigi, Tt801, Funandtrvl, Maxzimet, Worp8d, Amaraiel, Philip Trueman, TXiKiBoT, The Orig-inal Wildbear, Vipinhari, Ulfbastel, Sankalpdravid, JayC, Dendodge, RandomXYZb, Synthebot, RaseaC, Spinningspark, AlleborgoBot,SieBot, TYLER, Yintan, Flyer22, A. Carty, ScAvenger lv, Baseball Bugs, Lightmouse, OKBot, Maelgwnbot, Mhims, Maralia, Ascidian,Dlrohrer2003, ClueBot, PipepBot, Wolfch, GreenSpigot, Mild Bill Hiccup, Night Goblin, Niceguyedc, Harland1, Arunsingh16, DragonBot,No such user, Alexbot, PixelBot, Arjayay, Alertjean, AbJ32, Aitias, Superherogirl7, Berean Hunter, Elcap, Little Mountain 5, LizGere, Ad-dbot, Manuel Trujillo Berges, Breakeydown, Ronhjones, Download, Austin RS, Tide rolls, Grandfatherclok, Lightbot, Teles, Gail, Yobot,THEN WHO WAS PHONE?, Nallimbot, AnomieBOT, KDS4444, Götz, Galoubet, Zangar, Kingpin13, Materialscientist, Oooh.oooh,SvartMan, Citation bot, ArthurBot, Jlg4104, Aditya Cholan, Xqbot, Armstrong1113149, Srich32977, Munozdj, Pirateer, GrouchoBot,Pandamonia, Even stevenson, RibotBOT, Nedim Ardoğa, Immibis, GliderMaven, Rickcwalker, Prari, MetaNest, Steve Quinn, BenzolBot,Citation bot 1, LukeB 11, Pinethicket, FearXtheXfro, Boulaur, HazardX21, Fumitol, Jauhienij, Meisongbei, Theo10011, Defrector, Pen-terwast, Mean as custard, EmausBot, John of Reading, WikitanvirBot, Wiebelfrotzer, Katherine, Enviromet, Your Lord and Master, K6ka,Lindseyrose, Wagino 20100516, BabyBatter, ClueBot NG, Gareth Griffith-Jones, Matthiaspaul, Iwsh, O.Koslowski, Widr, ساجد امجد ,ساجدKarthik262399, Jeraphine Gryphon, AvocatoBot, Amp71, Robert the Devil, Sparkie82, Cky2250, BattyBot, Cyprien 1997, Dexbot, We-bclient101, Vahid alpha, Prateekgoyl, Ï¿½, Xdever, BhavdipGadhiya, Dainte, Alkalite, Cameronroytaylor, Monkbot, BatManFascination,JaunJimenez, Hy1201750, Lando123456789, Mario Castelán Castro, Gkmurtoff, Cali0086, Nc4sb8 and Anonymous: 434

• Diode Source: http://en.wikipedia.org/wiki/Diode?oldid=666628173 Contributors: Tobias Hoevekamp, Mav, Zundark, Rjstott, Aldie,Mudlock, Heron, Youandme, Topory, Edward, Michael Hardy, Tim Starling, Dgrant, Ahoerstemeier, Theresa knott, Snoyes, Jll, Glenn,Bogdangiusca, Nikai, Bassington, GRAHAMUK, EL Willy, Timwi, Dysprosia, Oliver Sedlacek, Maximus Rex, Furrykef, Omegatron,Darkhorse, Jerzy, Donarreiskoffer, Branddobbe, Robbot, Tomchiukc, Rholton, Blainster, Ledgerbob, Wjbeaty, Giftlite, Andries, LeonardG., StuartH, Knutux, Slowking Man, Aledeniz, Mako098765, R-Joe, Aulis Eskola, Richmd, Glogger, Johnflux, Bumm13, GeoGreg, Zfr,Sam Hocevar, Tzarius, Ukexpat, Canterbury Tail, Rfl, Discospinster, TedPavlic, Bert490, R6144, Xezbeth, Alistair1978, Dahamsta, Djord-jes, Nabla, Sietse Snel, Nigelj, Hurricane111, Smalljim, Rbj, Matt Britt, Foobaz, Jojit fb, MPerel, Haham hanuka, Hooperbloob, Jumbuck,Alansohn, GRider, Mo0, Stovetopcookies, TrevorP, Atlant, Riana, Amram99, Cdc, VladimirKorablin, Ross Burgess, Velella,Wtshymanski,Vedant, Cal 1234, Tony Sidaway, DV8 2XL, Gene Nygaard, HenryLi, Bookandcoffee, Mindmatrix, Parboman, StradivariusTV, Pol098,Gruu, Bbatsell, The Lightning Stalker, Lovro, Graham87, Ryan Norton, SteveW, Syndicate, Brighterorange, Ttwaring, Alejo2083, FlaBot,Authalic, RobertG, Arnero, Alfred Centauri, RexNL, Gurch, Nimur, Fresheneesz, Goudzovski, Srleffler, Zotel, Snailwalker, CJLLWright,Chobot, Frappyjohn, JohnDalton, YurikBot, Wavelength, Jimp, Espencer, Stephenb, Okedem, Rsrikanth05, Kb1koi, David R. Ingham, Ro-hitbd, Wiki alf, Mssetiadi, Speedevil, Rwalker, Bota47, Jeh, Searchme, Mholland, Light current, Lt-wiki-bot, Morcheeba, Tabby, Fernblatt,Nkendrick, Allens, Plober, GrinBot~enwiki, Zvika, Sam Gardiner, Jimerb, SmackBot, FocalPoint, KnowledgeOfSelf, Bggoldie~enwiki,Melchoir, Unyoyega, The Photon, Cronium, Gilliam, Skizzik, Lindosland, Bluebot, Kurykh, Avin, DHN-bot~enwiki, Darth Panda, Au-driusa, Chendy, Riflemann, Can't sleep, clown will eat me, Kevinpurcell, Flubbit, Nonforma, Smooth O, Sesc~enwiki, Puelly, Drphilhar-monic, DMacks, ILike2BeAnonymous, Jwheimans, Springnuts, John Reid, Archimerged, Kristleifur~enwiki, JorisvS, Olfzwin, CyrilB,Kevca, Tasc, Darein, Mr Stephen, Amr Bekhit, Rogerbrent, Dicklyon, Xitdiest0day, Spiel496, Kvng, Pjrm, BranStark, OnBeyondZebrax,W0lfie, Az1568, Chetvorno, INkubusse, Mikiemike, CmdrObot, Tarchon, Irwangatot, Sir Vicious, KyraVixen, Nczempin, NickW557,MarsRover, Lazulilasher, Deadferrets, SahRaeH, Gogo Dodo, Quibik, Pi3832, Richard416282, Alaibot, Omicronpersei8, Gimmetrow,Thijs!bot, Epbr123, Fisherjs, Acronymsical, Headbomb, Electron9, Gerry Ashton, PHaze, Nick Number, Andante1980, KrakatoaKatie,Rees11, AntiVandalBot, Abu-Fool Danyal ibn Amir al-Makhiri, Opelio, QuiteUnusual, JAnDbot, Em3ryguy, Pi.1415926535, MER-C,Geobio, Arch dude, Photodude, LittleOldMe, Bongwarrior, VoABot II, JamesBWatson, Mbc362, Jack Schmidling, Cpl Syx, Jhabib,Witchinghour, Brandon Hixson, WLU, TheNoise, MartinBot, STBot, Pringley Joe, R'n'B, J.delanoy, Bongomatic, JohnnyKegs, Silverxxx,

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 137

TheDog, Ertyiopul8, Katalaveno, Daniele.tampieri, Wolfoftheazuresky, MKoltnow, Cometstyles, Treisijs, H1voltage, Sam Blacketer, Deor,VolkovBot, AlnoktaBOT, Philip Trueman, TXiKiBoT, Eddiehimself, Msdaif, Ulfbastel, Schroedi, SQL, Jason Leach, Falcon8765, Spin-ningspark, Jobberone, Why Not A Duck, Mortivik, AlleborgoBot, Symane, Biscuittin, Bboothman, SieBot, Coffee, Tresiden, Cwk-mail, Jp314159, Bentogoa, Nopetro, Siyamraj, Oxymoron83, OKBot, Svick, Anchor Link Bot, TreeSmiler, Escape Orbit, ClueBot,Padre31~enwiki, The Thing That Should Not Be, Ark2120, Learner71, Mild Bill Hiccup, Shinpah1, Ventusa, LizardJr8, Eadthem, F-402, Behnammirzay, Farideh.soheily, Naseh nezami, Brews ohare, Paultseung, Jobetheren, MarkEaston, Thingg, Wstorr, Savastio, Ver-sus22, Johnuniq, SmoJoe, XLinkBot, Ultramince, Koumz, Ovis23, Rror, Mimarx, Kreline, Thatguyflint, Addbot, Mthardy, Proofreader77,Some jerk on the Internet, Elbreapoly, Nestorius, Tanhabot, Forum Mod Daniel, Lionoche~enwiki, ProperFraction, Glane23, Dynamiza-tion, AndersBot, Favonian, Erik Streb, Nanzilla, Shocking Asia, Tide rolls, Zorrobot, Nhoss2, Legobot, Publicly Visible, Luckas-bot,Yobot, Kartano, Fraggle81, , عالم ,محبوب DemocraticLuntz, 1exec1, Jim1138, Kingpin13, Poetman22, Пика Пика, Mate-rialscientist, ArdWar, Maxis ftw, Norkimes, ArthurBot, RealityApologist, LilHelpa, Xqbot, JimVC3, Capricorn42, GrouchoBot, Cor-ruptcopper, Pandamonia, Niimiish, RibotBOT, Nedim Ardoğa, Ajitkumar 2009, Maitchy, Us441, Geheimer, Jackandbos, FrescoBot,Cruiserbmw, Hldsc, Weetoddid, Roman12345, Shekhartit, Migul91, Nextext, Pinethicket, I dream of horses, Edderso, Tom.Reding,Joshuachohan, SpaceFlight89, Jp619, Arisharon, Lissajous, Jauhienij, Mstrogoff, Cirrone, Scopeknowledge, Re bill seeker of archery,DARTH SIDIOUS 2, S3nbon5akura, Xoristzatziki, Salvio giuliano, Mrseanski, EmausBot, John of Reading, Acather96, Wikitanvir-Bot, Balavenkataraju, Hashemfekry9, GoingBatty, RenamedUser01302013, Wikipelli, Hhhippo, ZéroBot, Mkratz, Arpit.withu, Lindsey-rose, Sthubertus, Lion789, GianniG46, Sonygal, Sbmeirow, Jay-Sebastos, Donner60, Tls60, Anonimski, Puffin, ChuispastonBot, Shnako,28bot, Maxdlink, Mikhail Ryazanov, ClueBot NG, Ulflund, KonaBear05, Ulrich67, Vipinratnakaran, Snotbot, Braincricket, Qwertymn-bvc10, Widr, Colossuskid, Titodutta, Calabe1992, Wbm1058, Bibcode Bot, Mataresephotos, BG19bot, Davdforg, Mysterytrey, Wiki13,Karthiksperla, EmadIV, Nicola.Manini, Snow Blizzard, Zedshort, Ulidtko, CensoredBiscuit, Pawan vaskar, ChrisGualtieri, Akash96, Man-astuna, AK456, Smee78, BrightStarSky, Dexbot, Shsi1123, Johnmathew15, Lugia2453, Zee1215, 069952497a, Reatlas, Faizan, User-name1507, Camayoc, Ugog Nizdast, Spyglasses, Citrusbowler, Ginsuloft, Akhil Bandari, Gokul.gk7, Cahhta, Beastemorph, SimeonBF,Monkbot, BatManFascination, DaveeBlahBlah, Cccp3, Beloxxi, Master Gourav Chandra, SomeOtherOldGuy, Radian2012, Kiwi2002,KasparBot, Gourav shende and Anonymous: 701

• Wire Source: http://en.wikipedia.org/wiki/Wire?oldid=664980034 Contributors: Kpjas, David Parker, Bryan Derksen, Malcolm Farmer,Sjc, Rmhermen, Aldie, Karen Johnson, Heron, Patrick, RTC, Michael Hardy, JakeVortex, Delirium, Ahoerstemeier, Mac, Glenn, Smack,Radiojon, Maximus Rex, Wernher, Joy, Pilaf~enwiki, Nurg, Rholton, Bkell, Alan Liefting, Giftlite, Jason Quinn, Solipsist, Darrien, Slowk-ing Man, Yath, Grinner, Biot, Trevor MacInnis, MarkSH, Corti, CALR, Jiy, Rich Farmbrough, Guanabot, ArnoldReinhold, Adam850,Alistair1978, RJHall, MisterSheik, Bobo192, Stesmo, Reinyday, Duk, Cmdrjameson, Duffman~enwiki, Wtshymanski, Bsadowski1, GeneNygaard, Miaow Miaow, SCEhardt, Hughcharlesparker, Banpei~enwiki, Dysepsion, Graham87, JamesBurns, Dwarf Kirlston, Rjwilmsi,Graibeard, Avocado, FlaBot, Margosbot~enwiki, RexNL, Silversmith, Chobot, NSR, YurikBot, Borgx, Charles Gaudette, Peterkingiron,D0li0, Stephenb, Gaius Cornelius, Wimt, Alynna Kasmira, NawlinWiki, ENeville, Brian Crawford, Jeremy Visser, 21655, Zzuuzz, EWing, Vicarious, Segv11, Dusso Janladde, Yvwv, SmackBot, Abhishek.scorp, Verne Equinox, Jfurr1981, Edgar181, Xchbla423, Kaiserb-Bot, Answerthis, Repairscircuitboards, Zzorse, A5b, Ohconfucius, John, Shirifan, MarkSutton, Slakr, Beetstra, Dr.K., Peter R Hastings,Peter Horn, Wizard191, Iridescent, Eastlaw, El aprendelenguas, Cydebot, Robmonk, Thijs!bot, Epbr123, Mercury~enwiki, Dtgriscom,Escarbot, AntiVandalBot, Alphachimpbot, Gökhan, JAnDbot, Leuko, MER-C, Ccrrccrr, Yahel Guhan, Bongwarrior, VoABot II, Mon-debleu, Bwhack, Allstarecho, Chkno, Martynas Patasius, The Real Marauder, DerHexer, Valdo~enwiki, Markco1, MartinBot, Ariel.,Jim.henderson, Glrx, R'n'B, Nono64, J.delanoy, Trusilver, Headgit, Alex:D, Idioma-bot, Nate Dog 93, Cem BSEE~enwiki, Jackd812,Drunkenmonkey, Andy Dingley, Enugala ashok, Jhawkinson, Spinningspark, Nssbm117, Jrshaffer11, Dogah, Brenont, Jimmy-griffin,Steven Zhang, EmanWilm, Lascorz, Dlrohrer2003, ClueBot, Binksternet, GorillaWarfare, WoweeeZoweee, Excirial, Vsombra, Ejay,Razorflame, Nate man123, BOTarate, 7, Gonzonoir, Nahtans, Uli sh, Kbdankbot, CalumH93, Addbot, Proofreader77, Wakablogger2,Non-dropframe, Jncraton, Fieldday-sunday, CanadianLinuxUser, 102orion, Lightbot, Yobot, TaBOT-zerem, Iroony, Flewis, Materialsci-entist, MCloud114, Bob Burkhardt, GB fan, Addihockey10, Jeffrey Mall, Amirajab, Stupedosmanoense, Farzaaaad2000, Freddaveg, MikeDill~enwiki, SD5, FrescoBot, المؤمن ,عبد Ong saluri, Mfwitten, PigFlu Oink, Miagmar, Mr. Jake Anders, JackMOgden, Hellzies, ManuelLabor, TheArguer, John of Reading, GoingBatty, Qpalxm27, Enviromet, Rajkiandris, PBS-AWB, Katherine.munn1, Loiy33, Donner60,Anonimski, Terraflorin, ClueBot NG, Rich Smith, MelbourneStar, Satellizer, Harrjhalley, Widr, Reify-tech, Blast furnace chip worker,MerlIwBot, Propel2234, PFH1987, Pano38, Uluru345, YVSREDDY, Flamekiller123, CatcherInTheRye773, I edeted this page, RileyHuntley, Md jamal molla, Sethdinicola, Dexbot, R5452, DavidLeighEllis, Ginsuloft, JaunJimenez, Fyddlestix, Thunder6666, Welded-wire-mesh and Anonymous: 195

• Printed circuit board Source: http://en.wikipedia.org/wiki/Printed_circuit_board?oldid=665758677 Contributors: Malcolm Farmer,William Avery, Ray Van De Walker, Waveguy, Heron, Camembert, Vkem~enwiki, RTC, D, Michael Hardy, Nixdorf, Liftarn, Aho-erstemeier, Haakon, Ronz, Theresa knott, Fuck You, Julesd, Glenn, Andres, Smack, Arteitle, RickK, Maximus Rex, Furrykef, Wern-her, Robbot, Pigsonthewing, Altenmann, Tobycat, Sunray, Hadal, Pengo, Rsduhamel, Dina, Alan Liefting, Ploum’s, Giftlite, DavidCary,BenFrantzDale, Ds13, Leonard G., Khalid hassani, Darrien, Bobblewik, Pale blue dot, Sam Hocevar, Abdull, Flyhighplato, JTN, RichFarmbrough, Smyth, Bender235, Plugwash, Edward Z. Yang, Nile, Sietse Snel, Jevinsweval, Bobo192, Kghose, Whosyourjudas, Meesta-plu, Robotje, Cmdrjameson, R. S. Shaw, Richi, Giraffedata, DCEdwards1966, Hooperbloob, Avian, Jumbuck, Alansohn, Atlant, Josh-baumgartner, Andrewpmk, Theodore Kloba, Mysdaao, Malo, Ste281, Velella, Wtshymanski, Kusma, DV8 2XL, Saxifrage, Dennis Brat-land, Oleg Alexandrov, Angr, Rintojiang, OwenX, Mindmatrix, Chris Mason, Pol098, Miss Madeline, Kglavin, Davidfstr, BradleyEE,Someone42, Macaddct1984, Hughcharlesparker, Prashanthns, Marudubshinki, Mandarax, BD2412, FreplySpang, Jclemens, Sjakkalle,Rjwilmsi, Guyd, GOD, Scorpiuss, Borborygmus, Nguyen Thanh Quang, N0YKG, FlaBot, Neonil~enwiki, RexNL, Ewlyahoocom, Gurch,Chobot, Sherool, Korg, Gwernol, George Leung, YurikBot, Wavelength, Charles Gaudette, Adam1213, DMahalko, Icarus3, Hydrar-gyrum, Stephenb, Gaius Cornelius, Shaddack, Wiki alf, Brewthatistrue, Janke, Nick, Sangwine, Denisgomes, Coderzombie, Jpbowen,Ndavies2, LodeRunner, Voidxor, Misza13, Scottfisher, Gadget850, Moritasgus, Salmanazar, Searchme, Johncruise, Light current, Phgao,Morcheeba, Closedmouth, Mike1024, Wechselstrom, Tom Duff, Snaxe920, Majtec, Kf4bdy, Peranders, SmackBot, Esradekan, Reedy,KnowledgeOfSelf, Pgk, The Photon, Thunderboltz, Edgar181, Zephyris, Reaver3123, Gilliam, Ohnoitsjamie, Betacommand, Lindosland,KD5TVI, Chris the speller, Optikos, MalafayaBot, George Church, Astaroth5, Audriusa, Frap, RProgrammer, Onorem, Rrburke, Rada-gast83, Nakon, MichaelBillington, Dreadstar, Dcamp314, HarisM, Weregerbil, Rao umair, Nmnogueira, SashatoBot, Akendall, Zaphraud,Treyt021, CaptainVindaloo, Codepro, Mr. Lefty, IronGargoyle, CyrilB, AnotherBrian, Tasc, Beetstra, Amr Bekhit, Sharcho, Ryulong,Rickington, Keycard, Hu12, Phakorn, Screaming.people, Tawkerbot2, Mikebuetow, Mware, Buist2000, Chetvorno, Atomobot, DJGB,JForget, Karloman2, Maolmhuire, Lamkin, Aweinstein~enwiki, TwinsMetsFan, Shoez, Dgw, MarsRover, HenkeB, Casper2k3, Johnlogic,Swoolverton, Steel, Gogo Dodo, Wa2ise, David 39, Quibik, Pga23, Codetiger, Roberta F., DumbBOT, Pacemkr, Editor at Large, Omi-cronpersei8, Pipatron, Repliedthemockturtle, FrancoGG, Chruch, Kablammo,Michagal, GBPackersfan, Andyjsmith, Al Lemos, Bmunden,Electron9, Skidmark, Joeolson, Leon7, Ptndan, Brewsum, Molido, AntiVandalBot, MichaelFrey, Seaphoto, Rehnn83, Edokter, Duaneb,

138 CHAPTER 16. DIGITAL ELECTRONICS

Dvandersluis, JAnDbot, Husond, MER-C, Arch dude, Naughtyca, Sophie means wisdom, PhilKnight, Eintar, Roidroid, No more bon-gos, Kerotan, Jaysweet, VoABot II, Catslash, Avjoska, JamesBWatson, Microcad, Recurring dreams, Indon, Vanished user ty12kl89jq10,Efansay, Dallem~enwiki, Beagel, Madmanguruman, LeeF, Matt B., Akhil999in, MartinBot, Capefearpress, Axlq, SmokeySteve, Glrx,R'n'B, Kateshortforbob, CommonsDelinker, J.delanoy, Lmjohnson, Hans Dunkelberg, Newpcb, DanielEng, Jayden54, Bigdumbdinosaur,DorganBot, Scrapeyard, HighKing, Andy.gock, Funandtrvl, VolkovBot, Jeff G., Philip Trueman, Oshwah, The Original Wildbear, Dav-ehi1, Vipinhari, Chimpex, Midlandstoday, Treads032, Aleksandar225, Vesi.kracheva, Computergeek1507, Jcswright2, Andy Dingley,Spinningspark, Brianga, Quantpole, PGWG, Hokie92, SieBot, Moonriddengirl, YourEyesOnly, Yintan, The very model of a minor gen-eral, Bhimaji, Hawk777, Flyer22, Tiptoety, A. Carty, Nopetro, JSpung, Oxymoron83, Steven Zhang, Lightmouse, MarkMLl, Bergda,Jons63, Escape Orbit, QuantumCAD, ClueBot, The Thing That Should Not Be, Waldoemerson, Thubing, Arakunem, Christopherblizzard,Tfitzp, SecretDisc, Chter, Yuckhil, Shjacks45, Excirial, Conical Johnson, Wipe2000, Brengi, Sun Creator, NuclearWarfare, Mathema-tron84, Kakofonous, Suyogaerospace, Allsvartr, HumphreyW, Party, Ginbot86, Vanished User 1004, Kid42day, XLinkBot, Gnowor, Gxk-endall, Dark Mage, BodhisattvaBot, Dthomsen8, John in kc, NobbiP, Shiloh Trouble, Fionaro, Davidgag, RyanCross, Wyatt915, Addbot,Tomve, Mentorgraphicspcb, Pminmo, Otisjimmy1, Zrowny, Ronhjones, Maziaar83, Prxbl, Sleepaholic, Download, CarsracBot, Cristi-nalee, Eddau~enwiki, 5 albert square, JamesKelch, Tide rolls, Lightbot, Zorrobot, MuZemike, Arbitrarily0, F818076M1bU1, Murdock123,Legobot, Joshmcx, Luckas-bot, Yobot, Themfromspace, Amirobot, Peizo, Nallimbot, Evaders99, Thaiio, MrBurns, TheMightyPirate, Wiz-ardOfOz, AnomieBOT, Tryptofish, Jim1138, Nelatan, RandomAct, Goldmaned, Materialscientist, RobertEves92, Rajanpras, Eumolpo,ArthurBot, Xqbot, Capricorn42, Grim23, JamesFitzgeraldKelch, Another Geoff, Abce2, BulldogBeing, Plusspace pcc, DiodeDave, Dou-glas W. Jones, Bdoughty96, AJCham, Sesu Prime, Prari, GiraldoX, FrescoBot, LucienBOT, LLanders, Edgarrabbit, Liammorriscirexx,Steve Quinn, Tore wiberg, Cannolis, Nixiebunny, Ganesh.fc, Dcshank, I dream of horses, HRoestBot, RedBot, MastiBot, Jodypro, Space-Flight89, Barras, HeyRick1973, Amber422, Lotje, Sergey539, Rentzepopoulos, ویکی ,علی Amaamamm, Mech sj, EdalityBY, Bri-anaecw, Alphacircuit, Bobby122, DARTH SIDIOUS 2, Mean as custard, Gitmlife, EmausBot, Tororunner, Munguia319, Momin313,Pwaterman, Saniyaleena, Solarra, Wikipelli, Probeboi, BSchneed, Linsinger, Thepurlieu, Wikfr, Laurasmithhp, Nudecline, SAJID1231,Geometryofshadows, Sbmeirow, Sayno2quat, Sethupathy3e, Photojack50, Pcblily, Carmichael, Vanished 1850, Ocyan, Fekri83, Lv131,Cgt, ClueBot NG, Jack Greenmaven, Satellizer, Frietjes, Widr, Zacharyklein, Helpful Pixie Bot, JahanXaib, BG19bot, Dsajga, Northamer-ica1000, Frze, Jlan712, Jschwa01, Mandolinist, Taneluc, Chip123456, Fylbecatulous, Cyan.aqua, Anhtrobote, Simonbliss, Ushau97,ChrisGualtieri, Khazar2, Ajv39, JYBot, ThunderStormer, Athomeinkobe, Bjct2000, Popey000, Epicgenius, Sabrina phoebe, Wellen-tech1981, IliyaKovac, Sonĝanto, Tentinator, Wbiliet, Rtrombetta, BerlinaLondona, RockWang (IQE), Naakaller, Harishmanoharan, Noys-ter, JEMZ1995, Chetansynergos, Sjpachal, Dsprc, Wasdichsoveraenderthat, ColdFootedMole, Brucesmith-usa, Terrytexasbutler, ShaileshPatel at APC, Engr Wasim Khan, Pancho507, Supdiop, Saqibijaz158, KasparBot, Pola habib, Michael.holper628 and Anonymous: 807

• Electric current Source: http://en.wikipedia.org/wiki/Electric_current?oldid=667056210 Contributors: AxelBoldt, Carey Evans, Heron,Patrick, D, PhilipMW, Michael Hardy, Tim Starling, Pit~enwiki, Nixdorf, Delirium, Bjpremore~enwiki, Ahoerstemeier, Cyp, Snoyes,Glenn, Nikai, Andres, Cherkash, Rob Hooft, GRAHAMUK, Tantalate, Wikiborg, Reddi, Andrewman327, Zoicon5, Marshman, Omega-tron, Ed g2s, Indefatigable, Epl18, Pakaran, Donarreiskoffer, Robbot, Tonsofpcs, Owain, Vespristiano, Mayooranathan, Fuelbottle, ShoUemura, Wjbeaty, Clementi, Giftlite, Art Carlson, TomViza, Ssd, Jfdwolff, Brockert, SWAdair, LiDaobing, Kjetil r, OverlordQ, KarolLangner, Maximaximax, Rubik-wuerfel, Johnflux, H Padleckas, Kevin B12, Icairns, Raylu, SomeFajitaSomewhere, Trevor MacInnis,Grunt, Danh, Mike Rosoft, Discospinster, Guanabot, Pmsyyz, Masudr, ArnoldReinhold, Mani1, Bender235, FrankCostanza, CanisRufus,Kwamikagami, PhilHibbs, Shanes, Femto, Adambro, Bobo192, Smalljim, Jolomo, Jojit fb, Bert Hickman, Kjkolb, Sam Korn, Hahamhanuka, Hooperbloob, Nsaa, Ranveig, Michael Bertolacci, Red Winged Duck, Alansohn, Jaw959, Malo, Bart133, Caesura, Snowolf,Yossiea~enwiki, Wtmitchell, Bucephalus, Velella, CaseInPoint, Super-Magician, Wtshymanski, Yuckfoo, Sedimin, Bsadowski1, DV82XL, Gene Nygaard, Capecodeph, HenryLi, Zntrip, Roland2~enwiki, Nuno Tavares, TigerShark, Fingers-of-Pyrex, Rocastelo, Stradi-variusTV, Benbest, Robert K S, Raevel, CharlesC, Paxsimius, Mandarax, Graham87, BD2412, Crocodealer, DePiep, Edison, Vary,Seraphimblade, Tawker, Sferrier, Titoxd, Tordail, Mishuletz, Winhunter, Nivix, Alfred Centauri, RexNL, Fresheneesz, Wesolson, Srl-effler, Imnotminkus, Chobot, Karch, DVdm, WriterHound, YurikBot, Wavelength, RussBot, Splash, Madkayaker, Hydrargyrum, Pol-luxian, Salsb, Zephyr9, Vanished user 1029384756, Clarenceos, TDogg310, Ospalh, Bucketsofg, Phandel, Rbyrne6722, DeadEyeArrow,Elkman, Kkmurray, Searchme, WAS 4.250, Light current, Enormousdude, 2over0, Jwissick, KGasso, Dspradau, Orthografer, GraemeL,Katieh5584, Kungfuadam, Some guy, Mejor Los Indios, Sbyrnes321, Treesmill, SmackBot, InverseHypercube, Shoy, CyclePat, Vald,Freestyle~enwiki, FRS, Eaglizard, Dmitry sychov, Gilliam, Ohnoitsjamie, ERcheck, Chris the speller, Bird of paradox, Thumperward,Oli Filth, Lenko, PureRED, EdgeOfEpsilon, Zven, Darth Panda, Chendy, Zsinj, Nick Levine, Onorem, Rrburke, Run!, RedHillian, Va-lenciano, Barney Stratford, Dreadstar, DMacks, Kotjze, Thehakimboy, Dogears, DJIndica, Nmnogueira, Lambiam, John, FrozenMan,CatastrophicToad~enwiki, CyrilB, Stikonas, Rogerbrent, Dicklyon, Mets501, Dacium, NuncAutNunquam, Amitch, BranStark, Iridescent,FSHero, Az1568, Courcelles, Tawkerbot2, Dlohcierekim, Chetvorno, Mattbr, Dgw, MarsRover, Yolcu, Bvcrist, Gogo Dodo, JFreeman,JustinForce, Tawkerbot4, Quibik, Christian75, DumbBOT, Editor at Large, Thijs!bot, Epbr123, Virp, Headbomb, Marek69, John254,James086, Leon7, EdJohnston, Michael A. White, Chewbacca01, Icep, Mlađa, AntiVandalBot, Wang ty87916, Opelio, Jwhamilton, Min-htung91, Arthurmyles, JAnDbot, Husond, Wiki0709, Andonic, SteveSims, Bongwarrior, VoABot II, Roger2909, Romtobbi, Indon, Nposs,28421u2232nfenfcenc, DerHexer, Khalid Mahmood, InvertRect, MartinBot, BetBot~enwiki, Burnedthru, R'n'B, Kateshortforbob, Com-monsDelinker, AlexiusHoratius, Ash, J.delanoy, Littletemchin, Madadem, Trusilver, Geomanjo, DigitalCatalyst, M C Y 1008, Nemo bis,Hillock65, Scoobystones, Hut 6.5, NewEnglandYankee, Potatoswatter, Cometstyles, RB972, Treisijs, Inter16, Pdcook, Lseixas, SoCalSu-perEagle, Mlewis000, Sheliak, Deor, ABF, LokiClock, Constant314, Philip Trueman, The Original Wildbear, Mikethorny, Ekwonder-land, Seraphim, Martin451, Psyche825, Venny85, Andy Dingley, Yk Yk Yk, Enviroboy, Purgatory Fubar, Spinningspark, Big G Ursa,Gallagher69, NHRHS2010, Bernmaster, SieBot, Coffee, K. Annoyomous, Msadaghd, GrooveDog, Bentogoa, JD554, Paolo.dL, Faraday-plank, Poindexter Propellerhead, Svick, Dcook32p, Anchor Link Bot, WikiLaurent, BentzyCo, DRTllbrg, ClueBot, Fribbler, GorillaWar-fare, MacroDaemon, Mild Bill Hiccup, Richerman, Delta1989, No such user, Jusdafax, Abhirocks94, Gtstricky, Lartoven, Promethean,Gciriani, Yadvinder, Wisewarlock, Glen Chagrin, Jfioeawfjdls453, Subash.chandran007, Versus22, Meske, Lxmota, SoxBot III, RMFan1,PatrickBogdziewicz, Rror, Ahirwav, Alexius08, Noctibus, JinJian, Thatguyflint, Cxz111, Willking1979, Manuel Trujillo Berges, Somejerk on the Internet, Sceny, Hda3ku, Fgnievinski, MoysieGT, Gizza gander, SoSaysChappy, LaaknorBot, Chamal N, Glane23, Chzz, 5albert square, Naidevinci, Ehrenkater, Tide rolls, Lightbot, PRRP, Secundus Zephyrus, Bmendonc, Megaman en m, Legobot, Luckas-bot,Yobot, Niklo sv, CinchBug, Tempodivalse, Cnorrisindustry, Orion11M87, AnomieBOT, KDS4444, Killiondude, Jim1138, AdjustShift,Dr. Pathos, RandomAct, Materialscientist, Carlsotr, Raven1977, Xqbot, Athabaska-Clearwater, Capricorn42, SchfiftyThree (Public), Jef-frey Mall, GrouchoBot, Cooltoad4102, Trurle, Oli19, Karlmossmans, JulianDelphiki, Shadowjams, Mike Dill~enwiki, Erik9, , Bekus,GliderMaven, Prari, FrescoBot, Pepper, Wikipe-tan, Sky Attacker, Citation bot 1, Pinethicket, Flekstro, Tinton5, Jusses2, Var0017, Serols,Mak2109, Meaghan, Robo Cop, Turian, Malikserhan, December21st2012Freak, IVAN3MAN, TobeBot, Heyyyyah, SchreyP, Jonkerz,Lotje, Defender of torch, Specs112, Michael.goulais, PleaseStand, Systemdweller, Jo big daddy, TjBot, 123Mike456Winston789, Man-dolinface, EmausBot, John of Reading, Acather96, Gfoley4, GoingBatty, I am from south wales, Tommy2010, Netheril96, Wikipelli,

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 139

AvicBot, JSquish, Fæ, Imperial Monarch, Gdaman5, Dondervogel 2, Pokeyclap7, Stephen CWells, Newlen, Lambrosus, Jsayre64, Rseagull,ChuispastonBot, RockMagnetist, Teapeat, DASHBotAV, Kj13isaac, Xonqnopp, ClueBot NG, Gilderien, Benydogc13, Enopet, Rezabot,ThatAMan, Helpful Pixie Bot, Wbm1058, Lowercase sigmabot, Hallows AG, Metricopolus, Mark Arsten, Cj3975, Shawn WorthingtonLaser Plasma, OSU1980, Vanished user lt94ma34le12, Neshmick, ChrisGualtieri, GoShow, Embrittled, Garamond Lethe, Tabrin-mabra,IWikileaks, Kyohyi, JohnnyJones1018, Dustin V. S., Flat Out, Tigraan, Spyglasses, Ducksandwich, Vavdeev, Grammato, Monkbot, Pulk-itmidha, Non-pupulus-impilium, KasparBot, MrArsGravis, Bubbagump1234 and Anonymous: 723

• Integrated circuit Source: http://en.wikipedia.org/wiki/Integrated_circuit?oldid=666998994 Contributors: Magnus Manske, Derek Ross,Mav, Bryan Derksen, Espen, Scipius, Arvindn, Rmhermen, Christian List, 0, Ray Van De Walker, Waveguy, Heron, RTC, Michael Hardy,Tim Starling, DopefishJustin, Nixdorf, Ixfd64, Iluvcapra, 7265, Egil, Stw, Ahoerstemeier, Mac, Julesd, Pratyeka, Glenn, Harvester, Lom-mer, GRAHAMUK, CAkira, Dcoetzee, Reddi, Stone, Dysprosia, Colin Marquardt, Zoicon5, IceKarma, Tpbradbury, Mrand, Furrykef,Jnc, Omegatron, Wernher, Bevo, Jni, Ckape, Pakcw, Robbot, Fredrik, Chris 73, Donreed, Altenmann, Nurg, Hadal, SC, Mushroom,Stek~enwiki, Ancheta Wis, Alf Boggis, Giftlite, Brouhaha, DavidCary, Laudaka, Mikez, Tom harrison, Everyking, Dratman, Frencheigh,Yekrats, Jce~enwiki, Uzume, Bobblewik, Edcolins, Golbez, Slurslee, Vadmium, Utcursch, Geni, Mike R, Antandrus, Mako098765,Kusunose, Michalj, Jossi, Annom, PFHLai, Jeremykemp, Cynical, Huaiwei, Mschlindwein, McCart42, Deglr6328, Qdr, Canterbury Tail,Mike Rosoft, Discospinster, 4pq1injbok, Rich Farmbrough, FT2, Rmalloy, Pixel8, Gejigeji~enwiki, Sergei Frolov, SpookyMulder, Dyl,Bender235, Andrejj, Kilrogg, Ht1848, MisterSheik, CanisRufus, Walden, Hayabusa future, Edward Z. Yang, Bookofjude, Femto, Bobo192,Viames, Smalljim, Duk, RAM, Liquidhot, Cmdrjameson, R. S. Shaw, Cmacd123, Matt Britt, Jerryseinfeld, Jatos, Wikinaut, Wrs1864,Haham hanuka, Pearle, Jonathunder, Hooperbloob, Jumbuck, Richard Harvey, Neonumbers, Atlant, Andrewpmk, AzaToth, Mysdaao,Angelic Wraith, Jdippold, Rebroad, Wtshymanski, Cburnett, Tony Sidaway, Brholden, Jguk, Rjhanson54, HenryLi, Oleg Alexandrov,Woohookitty, Mindmatrix, Pol098, Tabletop, Cbdorsett, Wikiklrsc, Dionyziz, BlaiseFEgan, Frungi, CharlesC, Dysepsion, RuM, Sin-man, Graham87, Dpv, Snafflekid, Josh Parris, Sjakkalle, Rjwilmsi, Mfwills, Virtualphtn, Kinu, Vegaswikian, Yamamoto Ichiro, Revo331,Mirror Vax, Rz350, Arnero, Intgr, Lmatt, Eman502, Chobot, AmritTuladhar, Gwernol, Wjfox2005, Siddhant, YurikBot, Spacepotato,Sceptre, DMahalko, TheDoober, Toffile, Hydrargyrum, Stephenb, Gaius Cornelius, Pseudomonas, Shanel, Wiki alf, Janke, Trovatore,Ino5hiro, Howcheng, Jpbowen, Zzzzzzus, Mishalak, Scottfisher, BOT-Superzerocool, DeadEyeArrow, Jaymody, Oliverdl, SamuelRiv,Searchme, Tetracube, Light current, Sagsaw, Open2universe, Lt-wiki-bot, Nwk, YolanCh, Closedmouth, Pb30, JQF, CWenger, Wech-selstrom, Phil Holmes, Mais oui!, Whaa?, Lamat~enwiki, Bluezy, GrinBot~enwiki, Twilight Realm, SmackBot, Nihonjoe, Boypv, Delldot,Sam8, Onebravemonkey, Zephyris, Gilliam, Wlmg, Chaojoker, Lindosland, Bluebot, SMP, Thumperward, Miquonranger03, Papa Novem-ber, Simpsons contributor, Jonatan Swift, Southcaltree, Can't sleep, clown will eat me, Harumphy, Konstantino, LouScheffer, Apexprim8,Dharmabum420, MichaelBillington, Dreadstar, ShaunES, RichAromas, A5b, Dmfallak, Bidabadi~enwiki, Ohconfucius, SashatoBot,RFIDEX, Richard L. Peterson, John, Hefo~enwiki, Gobonobo, Jaganath, Igor Markov, Shantanudivekar, Bjankuloski06en~enwiki, Iron-Gargoyle, Bilby, Mr. Vernon, Dicklyon, ClutteredMind, CASHMONEYBLACK, Waggers, PeterJohnBishop, Koweja, Kvng, Vincecate,Hu12, DabMachine, Iridescent, Overlook1977, Saltlakejohn, Delta x, Noodlez84, Supersquid, Pathosbot, Tawkerbot2, Nerfer, Chetvorno,Ismith, Eastlaw, David Carron, MorkaisChosen, KyraVixen, JohnCD, Nczempin, Dgw, FlyingToaster, Andkore, CompRhetoric, SamiF,Corp1117, Cydebot, Hyperdeath, GogoDodo, Anonymi, Corpx, HeWho Is, Odie5533, Tawkerbot4, Shirulashem, Kozuch, Editor at Large,Zalgo, Gimmetrow, Repliedthemockturtle, Thijs!bot, Epbr123, Kubanczyk, Kredal, WillMak050389, Gerry Ashton, Treedee, E. Ripley,Leon7, DJ Creature, Mentifisto, AntiVandalBot, Gioto, Luna Santin, Quintote, Krtek2125, Gökhan, Uusitunnus, JAnDbot, Omeganian,MER-C, Rob Kam, PaleAqua, MSBOT, Magioladitis, Bongwarrior, VoABot II, Cadsuane Melaidhrin, Pixel ;-), Ethan a dawe, Torchi-est, Glen, Elven Spellmaker, Seba5618, Iccaldwell, MartinBot, Grandia01, Seenukushi, Hugo Dufort, Rettetast, Glrx, R'n'B, Commons-Delinker, Emily GABLE, Transisto, J.delanoy, Trusilver, Pagemillroad, Hans Dunkelberg, Uncle Dick, Maurice Carbonaro, MooresLaw,Eliz81, Rod57, Dispenser, Ook com, Towerofsong, Kingtell, Arms & Hearts, Richard D. LeCour, Touch Of Light, Kraftlos, Umpteee,Cometstyles, ShanminDeng, Scott Illini, JavierMC, Randyest, Borat fan, Funandtrvl, Hugo999, ABF, JeffG., AlnoktaBOT, Philip Trueman,TXiKiBoT, Nicholasnice, BuickCenturyDriver, Muro de Aguas, Starrymessenger, A4bot, Murugango, Lordvolton, Ask123, OlavN, AnnaLincoln, Sintaku, Periendu, JhsBot, Leafyplant, Jackfork, LeaveSleaves, Candlemb, Cremepuff222, BigDunc, Andy Dingley, Lamro, Rhop-kins8, Enviroboy, Premelexis, RaseaC, Kwandae, Fire woman 11, Why Not A Duck, Nibios, Brianga, Symane, Philofred, Area51david,SieBot, Tiddly Tom, Caltas, Yintan, Delish90, Mr.Z-bot, Quest for Truth, Flyer22, EnOreg, Hello71, Steven Zhang, Fratrep, Gennady70,Svick, Spartan-James, ShabbatSam, Anchor Link Bot, Sfan00 IMG, ClueBot, Jackollie, The Thing That Should Not Be, WaltBusterkeys,Champfoxhound, Meekywiki, Eeinmrpk, Lazystupididiots, Niceguyedc, MrEccentric, Sandhyavempati, Puchiko, Jdawson76, AndyField-ing, Chinaja, Jtylerw, Nutmegardee, Gretchenpatti, La Pianista, Thingg, Aitias, Tigeron, AHDGraham, Rtellason, Vanished User 1004,DumZiBoT, Christianw7, Koumz, Wikiuser100, Skarebo, Augustojv, Dsimic, Addbot, Ernie Smith, MrOllie, Zzz888, Protonk, Laaknor-Bot, CarsracBot, Cristinalee, Favonian, Jasper Deng, Shekure, Evattb, Lightbot, OlEnglish, Frisbee1, Heinzelmann, Yobot, JackPotte,OrgasGirl, Senator Palpatine, Niklo sv, Hairmetal69, Cepheiden, Crispmuncher, MarkAlexan, THEN WHO WAS PHONE?, Sven nes-tle, Patrickyip, TestEditBot, Aldwindgr8, Backslash Forwardslash, AnomieBOT, Rumpler xiv, Cyrus34, 22Rimfire, Seas would rise whenI gave the word, Captain Quirk, Jim1138, Materialscientist, RobertEves92, Archaeopteryx, Xqbot, Rocketmanburningallhisfueloutthe-realone, Sionus, Capricorn42, JOsborne00, PraeceptorIP, Ute in DC, Leasamimee, RibotBOT, Maitchy, Spellage, FrescoBot, Jc3s5h,RoyGoldsmith, Sae1962, Pinethicket, MBirkholz, HRoestBot, Calmer Waters, Jschnur, RedBot, SpaceFlight89, Lissajous, SkyMachine,ImmortalYawn, X3r13x1z, TobeBot, Ilikenuts23, Edo248, Al Swenson, Maths22, Extra999, Minimac, Danielo103103, DASHBot, Emaus-Bot, GoingBatty, RenamedUser01302013, Zestee, Gathr, Blakedmiller, Wikipelli, WittyMan1986,Werieth, Fæ, Kokopellimama, Jenks24,Joshfinnie, Rashwin95, Yiosie2356, GianniG46, Tolly4bolly, Sbmeirow, L Kensington, Tls60, ChuispastonBot, Sunshine4921, Spicemix,Maxdlink, Rocketrod1960, ClueBot NG, Since 10.28.2010, Gareth Griffith-Jones, Matthiaspaul, MelbourneStar, A520, DobriAtanassov-Batovski, Chipsetc, LeCon Vivek, Cntras, Widr, Krunchyman, Amircrypto, Helpful Pixie Bot, Novusuna, DanDan0101, Wbm1058, Re-tired electrician, WNYY98, Doorknob747, Mataresephotos, Dsajga, Jdbickner, PearlSt82, Wiki13, MusikAnimal, Mark Arsten, Rm1271,Mayuri.sandhanshiv, H.sh8241, Eio, RAVIHCTM, Snow Blizzard, Thinkr123, Ihazacold, Pratyya Ghosh, The Illusive Man, Lophostrix,Khazar2, EuroCarGT, Cheryl Hugle, ZaferXYZ, DJB3.14, Rotlink, Reatlas, Rfassbind, I am One of Many, Anglerphish, AnthonyJ Lock,Geekomat, Cre81ve master, Ugog Nizdast, Taojialibian, ScotXW, 1305199LAL, Joeyao02015678, Sawdust Restaurant, MCDG, SofiaKoutsouveli, Sircakethough, Cole1917, Julietdeltalima, IEditEncyclopedia, Yasbetch, KasparBot, Confusion221 and Anonymous: 769

• Breadboard Source: http://en.wikipedia.org/wiki/Breadboard?oldid=662857942 Contributors: Aldie, Waveguy, Heron, Lumpbucket,Mahjongg, Glenn, Omegatron, Wernher, Aenar, Sanders muc, Alan Liefting, Admbws, DavidCary, Leonard G., Foobar, Oscar, Glogger,Equant, MementoVivere, Imroy, Rich Farmbrough, Mani1, Plugwash, CanisRufus, Fuxx, Drw25, Zr40, Hooperbloob, Linuxlad, Roy-Smith, Wdfarmer, Dominic, Batguano, LukeSurl, Dismas, Bushytails, Mário, Robert K S, Pol098, Tabletop, Cbdorsett, SDC, Rjwilmsi,.digamma, JoshuacUK, Krash, AySz88, FlaBot, Moskvax, Neonil~enwiki, Gurch, Mathrick, Chobot, John Dalton, Bgwhite, YurikBot,Toffile, Hydrargyrum, Gaius Cornelius, Pelago, Mikeblas, DeadEyeArrow, Katieh5584, SmackBot, InverseHypercube, Rovenhot, Com-mander Keane bot, Ohnoitsjamie, Anwar saadat, Bluebot, MagnusW, @modi, Thumperward, Kostmo, Audriusa, Wynand.winterbach,Neo139, OrphanBot, Starshadow, Soosed, Jonnty, Breno, Jodamn, 16@r, Mr Stephen, Amr Bekhit, KurtRaschke, MTSbot~enwiki, Hu12,

140 CHAPTER 16. DIGITAL ELECTRONICS

Doc Daneeka, Angelpeream, Ilikefood, Gogo Dodo, JLD, Kablammo, MangoChicken, Arch dude, Mark Shaw, Fulladder, Deepdive217,Choppingmall, J.delanoy, Snay2, Juliancolton, VolkovBot, Supervictor, Diazleonardo, Steven J. Anderson, ^demonBot2, Jslabovitz, Man-nafredo, BigDunc, Andy Dingley, Spinningspark, Yngvarr, ToePeu.bot, Berserkerus, Saurabhd17, WakingLili, Kelvinite, ClueBot, Tfitzp,Park27094, ChandlerMapBot, Excirial, Da rulz07, Winston365, MorrisRob, Rhododendrites, Faramarz.M, Moonlit Knight, Obrienmi8,Subversive.sound, Addbot, Wsvlqc, Fgnievinski, Tothwolf, LatitudeBot, Fieldday-sunday, Getsilly, Favonian, Lightbot, Legobot, Luckas-bot, Yobot, AnomieBOT, Archon 2488, Zxabot, Materialscientist, Obersachsebot, TheAMmollusc, Armstrong1113149, Kyng, Shaine01,Rstuvw, Prari, FrescoBot, Jvojta, Cannolis, RedBot, Sujoykroy, EmausBot, Nuujinn, TuHan-Bot, ZéroBot, Dolovis, Aadhirai R, Sb-meirow, Lorem Ip, Bahuner, Autoerrant, Bomazi, ClueBot NG, Satellizer, Reify-tech, Scoey123, Wbm1058, Daves73, Per1234, Darafsh-Bot, ChrisGualtieri, Electricmuffin11, Khazar2, Nordevx, Lugia2453, LordMike, Joeinwiki, Bradfordtoney, Greengreengreenred, One OfSeven Billion, Mnater900, Thomas W. Wilson, KasparBot, AqwertApple and Anonymous: 143

• Perfboard Source: http://en.wikipedia.org/wiki/Perfboard?oldid=645008431 Contributors: Klaus Leiss, Rich Farmbrough, Mandarax,George Leung, Toffile, 48v, Tony1, SmackBot, Kostmo, Alphathon, CmdrObot, Nick Number, Magioladitis, CommonsDelinker, Silverxxx,Kyle the bot, Andy Dingley, Darsie from german wiki pedia, Vdaghan, Addbot, Mortense, Tothwolf, Ettrig, Yobot, Jim1138, Erik9bot,Eric.archer, Rnabioullin, Joeinwiki and Anonymous: 21

• Stripboard Source: http://en.wikipedia.org/wiki/Stripboard?oldid=657003737 Contributors: Heron, Mahjongg, Kosebamse, Ahoerste-meier, Glenn, GRAHAMUK, Lewisdg2000, Klaus Leiss, Hubertus~enwiki, Ds13, Mboverload, Bobblewik, MementoVivere, Rich Farm-brough, Plugwash, Hooperbloob, MarkGallagher, Goldom, Nightstallion, MartinSpacek, Pol098, Mandarax, Josh Parris, Ian Dunster, Tof-file, Pelago, Vivenot, DVD R W, SmackBot, Chris the speller, Thumperward, Kostmo, Audriusa, Ghiraddje, S Roper, Gregs, Scarletman,Tawkerbot2, Ilikefood, Electron9, James086, Rehnn83, VoABot II, R'n'B, Juliancolton, VolkovBot, Hqb, SelketBot, Inductiveload, AndyDingley, Biscuittin, Phe-bot, Berserkerus, Leushenko, Wdwd, ClueBot, Tfitzp, DragonBot, Chiefmanzzz, Addbot, Mortense, Tothwolf,Beddingplane, Yobot, Crispmuncher, Piano non troppo, Teleprinter Sleuth, Gwideman, Louperibot, Vrenator, AvicAWB, Eric.archer,Northgeer, ClueBot NG, Shanaey, MerlIwBot, Helpful Pixie Bot, BG19bot, Klilidiplomus, Joeinwiki, JamesMoose, Ginsuloft, Kindianaand Anonymous: 52

• Analogue electronics Source: http://en.wikipedia.org/wiki/Analogue_electronics?oldid=666692020 Contributors: Heron, Jitse Niesen,Alan Liefting, Alf Boggis, Mhowkins, Edward Z. Yang, Afed, Bobo192, Timl, Pearle, TheParanoidOne, Wtshymanski, Cburnett, RJFJR,Sleigh, Stemonitis, Simetrical, SCEhardt, BD2412, George Burgess, ABot, FlaBot, Kerowyn, Gurch, Chobot, RussBot, Sanguinity, Jp-bowen, EAderhold, Light current, Fourohfour, Neurogeek, Allens, SmackBot, Thorseth, Mdd4696, Evanreyes, Commander Keane bot,Lindosland, KaiserbBot, Radagast83, Jaganath, Makyen, Dicklyon, ShelfSkewed, Casper2k3, AndrewHowse, A876, Corpx, Thijs!bot,Mbell, Nick Number, Alphachimpbot, JAnDbot, R'n'B, Hans Dunkelberg, Moqueur roux, STBotD, Derfee, ICE77, Pgavin, AlnoktaBOT,TXiKiBoT, Garett Long, Audioamp, Tresiden, Nestea Zen, Jp314159, Masgatotkaca, Steven Zhang, Binksternet, Brews ohare, JDPhD,Gnowor, Addbot, Hence Jewish Anderstein, GyroMagician, Oldmountains, Quercus solaris, Lightbot, Luckas-bot, Xqbot, FaleBot, Ed-wardkwt, RibotBOT, Kyng, FrescoBot, Micoru, Jschnur, RjwilmsiBot, AndyHe829, Donner60, 28bot, ClueBot NG, MerlIwBot, HelpfulPixie Bot, Wbm1058, KLBot2, Teepu Ahmad, Justincheng12345-bot, Pratyya Ghosh, Skr15081997 and Anonymous: 81

• Digital electronics Source: http://en.wikipedia.org/wiki/Digital_electronics?oldid=661595084 Contributors: AxelBoldt, Zundark, PerryBebbington, Mudlock, Ray Van De Walker, Heron, Michael Hardy, Julesd, Glenn, Smack, Colin Marquardt, Omegatron, Darkhorse, Joy,Raul654, Robbot, Jredmond, Altenmann, Jondel, Connelly, Alf Boggis, DavidCary, Philwelch, Robert Southworth, Nayuki, VampWil-low, Nickptar, Peter bertok, McCart42, Grunt, *drew, El C, Edward Z. Yang, Sietse Snel, Art LaPella, Viames, Matt Britt, Chbarts,Hooperbloob, Jakew, Atlant, Riana, Eagleamn, Wtshymanski, Cburnett, Versageek, Gene Nygaard, Blaxthos, LOL, Cbdorsett, Bbatsell,Graham87, Rjwilmsi, Vegaswikian, Ddawson, ScottJ, Mirror Vax, Gurch, Chobot, Quicksilvre, YurikBot, Wavelength, Borgx, Russ-Bot, Polluxian, Rsrikanth05, William Caputo, Trovatore, Srinivasasha, Jpbowen, Lomn, Kakero, Light current, Closedmouth, Wbrameld,SmackBot, Derek Andrews, Video99, Pieleric, AnOddName, Commander Keane bot, Lindosland, Chris the speller, Oli Filth, Nbarth,Can't sleep, clown will eat me, JonHarder, LouScheffer, Addshore, Decltype, Jon Awbrey, PerceivingMachine, Dicklyon, Iridescent,Tawkerbot2, Nczempin, Circuit dreamer, Tawkerbot4, Jrgetsin, Epbr123, Nick Number, AntiVandalBot, BokicaK, Guy Macon, Seaphoto,Jtaft, JAnDbot, Magioladitis, Meredyth, Vssun, Hbent, ENIAC, MartinBot, STBot, R'n'B, Highqueue, Mu li, Vanished user 342562,ARTE, Bigdumbdinosaur, ICE77, Indubitably, AlnoktaBOT, Kyle the bot, TXiKiBoT, Mamidanna, Murugango, Jackfork, Softtest123,Haseo9999, Audioamp, SieBot, Edd Swain, Flyer22, Universalcosmos, Lightmouse, Extreme BS, Cacycle test, CultureDrone, Pinkadelica,WimdeValk, ClueBot, Jbvogel, Updatepontus, Blanchardb, Tachasmo, Spud4dinner, Alexbot, SchreiberBike, BasilF, JDPhD, Clintkohl,XLinkBot, Gnowor, Jovianeye, Insertesla, Little Mountain 5, NellieBly, Vianello, Spacedriver34545, Shrena modi, Addbot, Mortense,Fieldday-sunday, Shyso~enwiki, MrOllie, Oldmountains, Favonian, Quercus solaris, 5 albert square, Lightbot, Hoenny, Leovizza, Kepry,Legobot, आशीष भटनागर, Yobot, OrgasGirl, Fraggle81, KamikazeBot, Eric-Wester, Ulric1313, Sidfilter, Materialscientist, Лев Дубовой,RibotBOT, Elep2009, FrescoBot, Mustimp, BenzolBot, Bexigao, MondalorBot, Joshuachohan, SpaceFlight89, Strenshon, RobinK, Ofirmichael, Merlion444, Knoppson, Lotje, Onel5969, J36miles, Logical Cowboy, The Mysterious El Willstro, Fæ, Odyssoma, Alan ffm,ArachanoxReal, Artsanta-NJITWILL, LordJeff, DmitriG NJITWILL, ClueBot NG,Matthiaspaul, Widr, Aaidilamindar, Helpful Pixie Bot,Egwu nnanna, Wbm1058, Benzband, Manu31415, CitationCleanerBot, Tony Tan, EnzaiBot, Deathlasersonline, FaerieChilde, Tentinator,Inaaaa, Hoy smallfry, Drmajidn and Anonymous: 246

16.9.2 Images• File:153056995_5ef8b01016_o.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/64/Intel_8742_153056995.jpg Li-cense: CC BY-SA 2.0 Contributors: http://www.flickr.com/photos/biwook/153056995/ Original artist: Ioan Sameli

• File:18MHZ_12MHZ_Crystal_110.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/6e/18MHZ_12MHZ_Crystal_110.jpg License: CC BY 3.0 Contributors: Own work Original artist: Vahid alpha

• File:1920s_TRF_radio_manufactured_by_Signal.jpg Source: https://upload.wikimedia.org/wikipedia/commons/1/12/1920s_TRF_radio_manufactured_by_Signal.jpg License: Public domain Contributors: Own work Original artist: Armstrong1113149

• File:3Com_OfficeConnect_ADSL_Wireless_11g_Firewall_Router_2012-10-28-0869.jpg Source: https://upload.wikimedia.org/wikipedia/commons/c/ca/3Com_OfficeConnect_ADSL_Wireless_11g_Firewall_Router_2012-10-28-0869.jpg License: CC0 Contribu-tors: Own work Original artist: Slick

• File:3_Resistors.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e3/3_Resistors.jpg License: CC BY-SA 2.5 Contribu-tors: Own work Original artist: Afrank99

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 141

• File:400_points_breadboard.jpg Source: https://upload.wikimedia.org/wikipedia/commons/7/73/400_points_breadboard.jpg License:CC BY-SA 2.0 Contributors: BREB-01 (Breadboard) Original artist: oomlout

• File:555_timer_circuit_perforated_board.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/3f/555_timer_circuit_perforated_board.jpg License: Public domain Contributors: Transferred from en.wikipediaOriginal artist: Silverxxx (talk). Original uploader was Silverxxx at en.wikipedia

• File:80486DX2_200x.png Source: https://upload.wikimedia.org/wikipedia/commons/2/2b/80486DX2_200x.png License: CC BY-SA2.5 Contributors: ? Original artist: ?

• File:80486dx2-large.jpg Source: https://upload.wikimedia.org/wikipedia/commons/0/02/80486dx2-large.jpg License: CC-BY-SA-3.0Contributors: ? Original artist: ?

• File:ACtoDCpowersupply.png Source: https://upload.wikimedia.org/wikipedia/commons/4/4e/ACtoDCpowersupply.png License: CCBY 3.0 Contributors: Transferred from en.wikipedia to Commons. Original artist: JaunJimenez (talk) (Uploads)

• File:A_few_Jumper_Wires.jpg Source: https://upload.wikimedia.org/wikipedia/commons/5/5c/A_few_Jumper_Wires.jpg License:CC BY-SA 2.0 Contributors: A few Jumper Wires Original artist: oomlout

• File:Aplikimi_i_feriteve.png Source: https://upload.wikimedia.org/wikipedia/commons/2/27/Aplikimi_i_feriteve.png License: CCBY-SA 3.0 Contributors: Own work Original artist: FIEK-Kompjuterike

• File:Axial_electrolytic_capacitors.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/b4/Axial_electrolytic_capacitors.jpg License: CC BY 3.0 Contributors: http://matarese.com/photo/413-sprague-atom-electrolytics/ Original artist: Mataresephotos

• File:BJT_NPN_symbol.svg Source: https://upload.wikimedia.org/wikipedia/commons/6/66/BJT_NPN_symbol.svg License:CC BY-SA 3.0 Contributors: The source code of this SVG is <a data-x-rel='nofollow' class='external text' href='http://validator.w3.org/check?uri=http%3A%2F%2Fcommons.wikimedia.org%2Fwiki%2FSpecial%3AFilepath%2FBJT_NPN_symbol.svg,<span>,&,</span>,ss=1#source'>valid</a>. Original artist: Omegatron

• File:BJT_PNP_symbol.svg Source: https://upload.wikimedia.org/wikipedia/commons/9/9b/BJT_PNP_symbol.svg License:CC BY-SA 3.0 Contributors: The source code of this SVG is <a data-x-rel='nofollow' class='external text' href='http://validator.w3.org/check?uri=http%3A%2F%2Fcommons.wikimedia.org%2Fwiki%2FSpecial%3AFilepath%2FBJT_PNP_symbol.svg,<span>,&,</span>,ss=1#source'>valid</a>. Original artist: Omegatron

• File:Bardeen_Shockley_Brattain_1948.JPG Source: https://upload.wikimedia.org/wikipedia/commons/c/c2/Bardeen_Shockley_Brattain_1948.JPG License: Public domain Contributors: eBay item Original artist: AT&T; photographer: Jack St. (last part of name notstamped well enough to read), New York, New York.

• File:Battery_symbol2.svg Source: https://upload.wikimedia.org/wikipedia/commons/2/28/Battery_symbol2.svg License: Public domainContributors: Own work Original artist: Jacek FH

• File:Breadboard_complex.jpg Source: https://upload.wikimedia.org/wikipedia/commons/4/47/Breadboard_complex.jpg License: Pub-lic domain Contributors: ? Original artist: ?

• File:Breadboard_scheme.svg Source: https://upload.wikimedia.org/wikipedia/commons/e/ec/Breadboard_scheme.svg License: CC-BY-SA-3.0 Contributors:

• Breadboard-144dpi.gif Original artist: Breadboard-144dpi.gif: en:User:Waveguy• File:Capacitor.jpg Source: https://upload.wikimedia.org/wikipedia/commons/5/5a/Capacitor.jpg License: CC BY-SA 3.0 Contributors:

Transferred from en.wikipedia; transferred to Commons by User:Sreejithk2000 using CommonsHelper.Original artist: Daniel Christensen at en.wikipedia

• File:CapacitorHydraulicAnalogyAnimation.gif Source: https://upload.wikimedia.org/wikipedia/commons/c/c1/CapacitorHydraulicAnalogyAnimation.gif License: CC0 Contributors: Own work Original artist: Sbyrnes321

• File:Capacitor_equivalent_circuits.svg Source: https://upload.wikimedia.org/wikipedia/commons/a/a8/Capacitor_equivalent_circuits.svg License: CC0 Contributors: Own work Original artist: GorillaWarfare

• File:Capacitor_schematic_with_dielectric.svg Source: https://upload.wikimedia.org/wikipedia/commons/c/cd/Capacitor_schematic_with_dielectric.svg License: CC BY-SA 3.0 Contributors: self-made SVG version of Image:Dielectric.png, incorporating Image:Capacitorschematic.svg as its base. Original artist: Papa November

• File:Capacitors_(7189597135).jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/b9/Capacitors_%287189597135%29.jpg License: CC BY-SA 2.0 Contributors: 12739s Original artist: Eric Schrader from San Francisco, CA, United States

• File:Capacitors_in_parallel.svg Source: https://upload.wikimedia.org/wikipedia/commons/f/fa/Capacitors_in_parallel.svg License: CCBY-SA 3.0 Contributors: This SVG electrical schematic was created with the Electrical Symbols Library. Original artist: Omegatron

• File:Capacitors_in_series.svg Source: https://upload.wikimedia.org/wikipedia/commons/7/75/Capacitors_in_series.svg License: CCBY-SA 3.0 Contributors: This SVG electrical schematic was created with the Electrical Symbols Library. Original artist: Omegatron

• File:Carbon-resistor-TR212-1.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d4/Carbon-resistor-TR212-1.jpg Li-cense: CC BY-SA 3.0 Contributors: Own work Original artist: Shaddack

• File:Choke_electronic_component_Epcos_2x47mH_600mA_common_mode.jpg Source: https://upload.wikimedia.org/wikipedia/commons/4/43/Choke_electronic_component_Epcos_2x47mH_600mA_common_mode.jpg License: Public domain Contributors: Pho-tographed by Mike1024 Original artist: Mike1024

• File:Cmos-chip_structure_in_2000s_(en).svg Source: https://upload.wikimedia.org/wikipedia/commons/e/ee/Cmos-chip_structure_in_2000s_%28en%29.svg License: CCBY 2.5 Contributors: self made (from university scripts and scientific papers)Original artist: Cephei-den

• File:Cmosic.JPG Source: https://upload.wikimedia.org/wikipedia/commons/a/a2/Cmosic.JPG License: CC-BY-SA-3.0 Contributors: ?Original artist: Users Washio, Oliverdl on en.wikipedia

• File:Common_Base_amplifier.png Source: https://upload.wikimedia.org/wikipedia/commons/9/9b/Common_Base_amplifier.png Li-cense: CC-BY-SA-3.0 Contributors: ? Original artist: ?

142 CHAPTER 16. DIGITAL ELECTRONICS

• File:Commons-logo.svg Source: https://upload.wikimedia.org/wikipedia/en/4/4a/Commons-logo.svg License: ? Contributors: ? Originalartist: ?

• File:Componentes.JPG Source: https://upload.wikimedia.org/wikipedia/commons/e/ea/Componentes.JPG License: Public domain Con-tributors: Own work Original artist: Kae

• File:Computerplatine_Wire-wrap_backplane_detail_Z80_Doppel-Europa-Format_1977_(close_up).jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e6/Computerplatine_Wire-wrap_backplane_detail_Z80_Doppel-Europa-Format_1977_%28close_up%29.jpg License: CC BY-SA 3.0 Contributors: Own work (own photo) Original artist: Wikinaut

• File:Condensador_electrolitico_150_microF_400V.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/31/Condensador_electrolitico_150_microF_400V.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Willtron

• File:Condensators.JPG Source: https://upload.wikimedia.org/wikipedia/commons/d/de/Condensators.JPG License: CC-BY-SA-3.0Contributors: de:Bild:Kondensatoren.JPG, uploaded there by de:Benutzer:Honina Original artist: de:Benutzer:Aka

• File:Condensor_bank_150kV_-_75MVAR.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/ed/Condensor_bank_150kV_-_75MVAR.jpg License: Public domain Contributors: Own work Original artist: Philippe Mertens

• File:CopperCladPerfboard_1.png Source: https://upload.wikimedia.org/wikipedia/commons/b/b7/CopperCladPerfboard_1.png Li-cense: CC-BY-SA-3.0 Contributors: Own work Original artist: Klaus - Günter Leiss (Klaus_Leiss)

• File:CopperCladPerfboard_2.png Source: https://upload.wikimedia.org/wikipedia/commons/e/e1/CopperCladPerfboard_2.png Li-cense: CC-BY-SA-3.0 Contributors: Own work Original artist: Klaus - Günter Leiss (Klaus_Leiss)

• File:Cordwoodcircuit.agr.jpg Source: https://upload.wikimedia.org/wikipedia/commons/c/c3/Cordwoodcircuit.agr.jpg License: CCBY 2.5 Contributors: Self-published work by ArnoldReinhold Original artist: ArnoldReinhold

• File:Current_notation.svg Source: https://upload.wikimedia.org/wikipedia/commons/2/2e/Current_notation.svg License: CC BY 3.0Contributors: Conventional_Current.png by User:Romtobbi Original artist: User:Flekstro

• File:DO-41_Dimensions.svg Source: https://upload.wikimedia.org/wikipedia/commons/a/aa/DO-41_Dimensions.svg License: Publicdomain Contributors: Own work Original artist: Inductiveload

• File:Danotherm_HS50_power_resistor.jpg Source: https://upload.wikimedia.org/wikipedia/commons/a/a1/Danotherm_HS50_power_resistor.jpg License: CC0 Contributors: {www.danotherm.dk} Original artist: Olli Niemitalo

• File:Darlington_transistor_MJ1000.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d9/Darlington_transistor_MJ1000.jpg License: Attribution Contributors: thomy_pc Original artist: thomy_pc

• File:Diode-closeup.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d5/Diode-closeup.jpg License: CCBY-SA 2.5Con-tributors: Transferred from en.wikipedia to Commons. Original artist: The original uploader was Morcheeba at English Wikipedia

• File:Diode-english-text.svg Source: https://upload.wikimedia.org/wikipedia/commons/8/8e/Diode-english-text.svg License: CCBY-SA3.0 Contributors: Own work Original artist: Svjo

• File:DiodeClamp.png Source: https://upload.wikimedia.org/wikipedia/en/2/2d/DiodeClamp.png License: CC-BY-3.0 Contributors: ?Original artist: ?

• File:Diode_current_wiki.png Source: https://upload.wikimedia.org/wikipedia/commons/2/2a/Diode_current_wiki.png License: GFDLContributors: Own work Original artist: User:Hldsc

• File:Diode_tube_schematic.svg Source: https://upload.wikimedia.org/wikipedia/commons/3/36/Diode_tube_schematic.svg License:CC BY-SA 2.5 Contributors: Own work Original artist: Ojibberish

• File:Dioden2.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/60/Dioden2.jpg License: CC-BY-SA-3.0 Contributors:modified from Dioden.jpg (centimeter instead of meter), created by Honina Original artist: Ulfbastel

• File:Diodes.jpg Source: https://upload.wikimedia.org/wikipedia/commons/4/4b/Diodes.jpg License: CCBY-SA 3.0Contributors: ? Orig-inal artist: ?

• File:Double_side_PCB_process_flow_chart.png Source: https://upload.wikimedia.org/wikipedia/en/6/61/Double_side_PCB_process_flow_chart.png License: CC-BY-3.0 Contributors:Gliffy Flow chart softwareOriginal artist:Dcshank

• File:Drosselspule_im_Umspannwerk_Bisamberg.jpg Source: https://upload.wikimedia.org/wikipedia/commons/8/8a/Drosselspule_im_Umspannwerk_Bisamberg.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Mario Sedlak (<a href='//commons.wikimedia.org/wiki/User_talk:Mario_Sedlak' title='User talk:Mario Sedlak'>talk</a>)

• File:EPROM_Microchip_SuperMacro.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/ee/EPROM_Microchip_SuperMacro.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Zephyris

• File:Edit-clear.svg Source: https://upload.wikimedia.org/wikipedia/en/f/f2/Edit-clear.svg License: Public domain Contributors: TheTango! Desktop Project. Original artist:The people from the Tango! project. And according to the meta-data in the file, specifically: “Andreas Nilsson, and Jakub Steiner (althoughminimally).”

• File:Electrolytic_capacitor.jpg Source: https://upload.wikimedia.org/wikipedia/en/a/a6/Electrolytic_capacitor.jpg License: CC-BY-3.0Contributors:photoOriginal artist:Vahid alpha

• File:Electromagnetism.svg Source: https://upload.wikimedia.org/wikipedia/commons/9/91/Electromagnetism.svg License: CC-BY-SA-3.0 Contributors: Image:Electromagnetism.png Original artist: User:Stannered

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 143

• File:Electronic_component_inductors.jpg Source: https://upload.wikimedia.org/wikipedia/commons/a/a1/Electronic_component_inductors.jpg License: CC-BY-SA-3.0 Contributors: Photograph Original artist: me

• File:Ferrite_bead_no_shell.jpg Source: https://upload.wikimedia.org/wikipedia/commons/5/58/Ferrite_bead_no_shell.jpg License: CCBY-SA 3.0 Contributors: Taken by User:Omegatron using a Canon Powershot SD110 Original artist: Omegatron

• File:Ferrite_slug_tuned_inductor_with_pot_core.JPG Source: https://upload.wikimedia.org/wikipedia/commons/0/08/Ferrite_slug_tuned_inductor_with_pot_core.JPG License: CC0 Contributors: Own work Original artist: Chetvorno

• File:Folder_Hexagonal_Icon.svg Source: https://upload.wikimedia.org/wikipedia/en/4/48/Folder_Hexagonal_Icon.svg License: Cc-by-sa-3.0 Contributors: ? Original artist: ?

• File:Hf_spoler_og_transformatorer.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e4/Hf_spoler_og_transformatorer.jpg License: CC-BY-SA-3.0 Contributors: Transferred from da.wikipedia Original artist: Original uploader wasGlenn at da.wikipedia

• File:HitachiJ100A.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/32/HitachiJ100A.jpg License: CC-BY-SA-3.0 Con-tributors: Transferred from en.wikipedia Original artist: Original uploader was C J Cowie at en.wikipedia

• File:IGFET_N-Ch_Dep_Labelled.svg Source: https://upload.wikimedia.org/wikipedia/commons/e/e8/IGFET_N-Ch_Dep_Labelled.svg License: Public domain Contributors: From Scratch in Inkcape 0.43 Original artist: jjbeard

• File:IGFET_N-Ch_Enh_Labelled.svg Source: https://upload.wikimedia.org/wikipedia/commons/6/62/IGFET_N-Ch_Enh_Labelled.svg License: Public domain Contributors: ? Original artist: ?

• File:IGFET_N-Ch_Enh_Labelled_simplified.svg Source: https://upload.wikimedia.org/wikipedia/commons/6/61/IGFET_N-Ch_Enh_Labelled_simplified.svg License: CC BY-SA 3.0 Contributors: Based on Image:IGFET N-Ch Enh Labelled.svg Original artist:Omegatron

• File:IGFET_P-Ch_Dep_Labelled.svg Source: https://upload.wikimedia.org/wikipedia/commons/1/1b/IGFET_P-Ch_Dep_Labelled.svg License: Public domain Contributors: From Scratch in Inkcape 0.43 Original artist: jjbeard

• File:IGFET_P-Ch_Enh_Labelled.svg Source: https://upload.wikimedia.org/wikipedia/commons/0/0c/IGFET_P-Ch_Enh_Labelled.svg License: Public domain Contributors: From Scratch in Inkcape 0.43 Original artist: jjbeard

• File:IGFET_P-Ch_Enh_Labelled_simplified.svg Source: https://upload.wikimedia.org/wikipedia/commons/c/c4/IGFET_P-Ch_Enh_Labelled_simplified.svg License: CC BY-SA 3.0 Contributors: Based on Image:IGFET P-Ch Enh Labelled.svg, Original artist:User:Omegatron

• File:Inductor.svg Source: https://upload.wikimedia.org/wikipedia/commons/4/4b/Inductor.svg License: Public domain Contributors:Made in Inkscape 0.43 from scratch Original artist: Jjbeard

• File:InductorSignalFilter1.png Source: https://upload.wikimedia.org/wikipedia/en/2/2f/InductorSignalFilter1.png License: CC-BY-3.0Contributors: ? Original artist: ?

• File:InductorSignalFilter2.png Source: https://upload.wikimedia.org/wikipedia/en/d/d7/InductorSignalFilter2.png License: CC-BY-3.0Contributors: ? Original artist: ?

• File:Inductors_in_parallel.svg Source: https://upload.wikimedia.org/wikipedia/commons/e/e8/Inductors_in_parallel.svg License: CCBY-SA 3.0 Contributors: This SVG electrical schematic was created with the Electrical Symbols Library. Original artist: Omegatron

• File:Inductors_in_series.svg Source: https://upload.wikimedia.org/wikipedia/commons/f/ff/Inductors_in_series.svg License: CC BY-SA 3.0 Contributors: This SVG electrical schematic was created with the Electrical Symbols Library. Original artist: Omegatron

• File:Intel_8742_153056995.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/64/Intel_8742_153056995.jpg License:CC BY-SA 2.0 Contributors: http://www.flickr.com/photos/biwook/153056995/ Original artist: Ioan Sameli

• File:JFET_N-Channel_Labelled.svg Source: https://upload.wikimedia.org/wikipedia/commons/4/46/JFET_N-Channel_Labelled.svgLicense: Public domain Contributors: From Scratch in Inkcape 0.43 Original artist: jjbeard

• File:JFET_P-Channel_Labelled.svg Source: https://upload.wikimedia.org/wikipedia/commons/0/09/JFET_P-Channel_Labelled.svgLicense: Public domain Contributors: From Scratch in Inkcape 0.43 Original artist: jjbeard

• File:KTSU_resistors.jpg Source: https://upload.wikimedia.org/wikipedia/commons/1/10/KTSU_resistors.jpg License: CC BY-SA 2.5Contributors: ru.wikipedia Original artist: Сергей Филатов

• File:Kicad_Eeschema_screenshot.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d3/Kicad_Eeschema_screenshot.jpg License: GPL Contributors: the English language Wikipedia (log) Original artist: en:User:Brengi

• File:Kicad_Pcbnew3D_screenshot.jpg Source: https://upload.wikimedia.org/wikipedia/commons/9/92/Kicad_Pcbnew3D_screenshot.jpg License: GPL Contributors: ? Original artist: ?

• File:Kicad_Pcbnew_screenshot.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/ba/Kicad_Pcbnew_screenshot.jpg Li-cense: GPL Contributors: ? Original artist: ?

• File:Kilby_solid_circuit.jpg Source: https://upload.wikimedia.org/wikipedia/en/4/42/Kilby_solid_circuit.jpg License: Fair use Contrib-utors:http://www.ti.com/corp/docs/kilbyctr/downloadphotos.shtml Original artist:Texas Instruments

• File:Kreuzwickelspule.png Source: https://upload.wikimedia.org/wikipedia/commons/6/69/Kreuzwickelspule.png License: Public do-main Contributors: http://de.wikipedia.org/wiki/Datei:Kreuzwickelspule.png Original artist: de:User:PeterFrankfurt

• File:Laser_Trimmed_Precision_Thin_Film_Resistor_Network.JPG Source: https://upload.wikimedia.org/wikipedia/commons/b/b1/Laser_Trimmed_Precision_Thin_Film_Resistor_Network.JPG License: CC BY-SA 4.0 Contributors: screenshot from http://www.eevblog.com/forum/blog/eevblog-730-thin-film-resistor-networks/ Original artist: Binarysequence

144 CHAPTER 16. DIGITAL ELECTRONICS

• File:Leidse_flessen_Museum_Boerhave_december_2003_2.jpg Source: https://upload.wikimedia.org/wikipedia/commons/2/22/Leidse_flessen_Museum_Boerhave_december_2003_2.jpg License: CC-BY-SA-3.0 Contributors: Transferred from en.wikipedia toCommons.Original Image: en::Image:Leidse flessen Museum Boerhave december 2003.jpg Original artist: The original uploader was Alvinrune atEnglish Wikipedia

• File:Micro_switch.jpg Source: https://upload.wikimedia.org/wikipedia/en/6/63/Micro_switch.jpg License: CC-BY-3.0 Contributors:photoOriginal artist:Vahid alpha

• File:Microchips.jpg Source: https://upload.wikimedia.org/wikipedia/commons/5/5c/Microchips.jpg License: CC-BY-SA-3.0 Contribu-tors: Transferred from en.wikipedia; transferred to Commons by User:TenIslands using CommonsHelper. Original artist: Original uploaderwas Zephyris at en.wikipedia

• File:Mouse_printed_circuit_board_both_sides_IMG_0959a.JPG Source: https://upload.wikimedia.org/wikipedia/commons/a/ab/Mouse_printed_circuit_board_both_sides_IMG_0959a.JPG License: CC0 Contributors: Own work Original artist: Own work

• File:Mouse_printed_circuit_board_component_side_IMG_0952_-_d.JPG Source: https://upload.wikimedia.org/wikipedia/commons/4/43/Mouse_printed_circuit_board_component_side_IMG_0952_-_d.JPG License: CC0 Contributors: Own work Originalartist: Eddau

• File:Mylar-film_oil-filled_low-inductance_capacitor_6.5_MFD_@_5000_VDC.jpg Source: https://upload.wikimedia.org/wikipedia/commons/2/2d/Mylar-film_oil-filled_low-inductance_capacitor_6.5_MFD_%40_5000_VDC.jpg License: CC0 Contributors:Own work Original artist: Zaereth

• File:NPN_common_emitter_AC.svg Source: https://upload.wikimedia.org/wikipedia/commons/8/8c/NPN_common_emitter_AC.svgLicense: GFDL Contributors: Own work Original artist: Zedh

• File:Ni000_Hollow_rivets_for_Plated_Through_Hole_PCB_repair_and_small-scale_manufacturing.png Source: https://upload.wikimedia.org/wikipedia/commons/7/7a/Ni000_Hollow_rivets_for_Plated_Through_Hole_PCB_repair_and_small-scale_manufacturing.png License: CC BY-SA 3.0 Contributors: Own work Original artist: Ossip Groth

• File:Nuvola_apps_ksim.png Source: https://upload.wikimedia.org/wikipedia/commons/8/8d/Nuvola_apps_ksim.png License: LGPLContributors: http://icon-king.com Original artist: David Vignoni / ICON KING

• File:Odporová_dekáda_KURBELWIDERSTAND_(A).jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/b8/Odporov%C3%A1_dek%C3%A1da_KURBELWIDERSTAND_%28A%29.jpg License: CC0 Contributors: Own work Original artist:Qwertz0451

• File:Ohm’{}s_Law_with_Voltage_source_TeX.svg Source: https://upload.wikimedia.org/wikipedia/commons/b/b4/Ohm%27s_Law_with_Voltage_source_TeX.svg License: CC0 Contributors: Own work Original artist: GorillaWarfare

• File:Old_Radio_Resistors.jpg Source: https://upload.wikimedia.org/wikipedia/en/d/d4/Old_Radio_Resistors.jpg License: PD Contrib-utors: ? Original artist: ?

• File:OscillatorSchematic.png Source: https://upload.wikimedia.org/wikipedia/en/2/2b/OscillatorSchematic.png License: CC-BY-3.0Contributors: ? Original artist: ?

• File:PCB_Carbon_Printed_Resistor.jpg Source: https://upload.wikimedia.org/wikipedia/commons/8/83/PCB_Carbon_Printed_Resistor.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Altzone

• File:PCB_Spectrum.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/65/PCB_Spectrum.jpg License: CC-BY-SA-3.0Contributors: Bill Bertram Original artist: Bill Bertram

• File:PCB_copper_layer_electroplating_machine.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e8/PCB_copper_layer_electroplating_machine.jpg License: CC BY-SA 3.0 Contributors: Template:Innoquick Electronics Limited (www.iqpcb.com) Orig-inal artist: Swoolverton

• File:PCB_design_and_realisation_smt_and_through_hole.png Source: https://upload.wikimedia.org/wikipedia/commons/6/67/PCB_design_and_realisation_smt_and_through_hole.png License: Public domain Contributors: Photographed by User:Mike1024 Originalartist: User Mike1024

• File:PCBs_hanging_in_electroplating_machine.jpg Source: https://upload.wikimedia.org/wikipedia/commons/9/92/PCBs_hanging_in_electroplating_machine.jpg License: CC BY-SA 3.0 Contributors: Template:Innoquick Electronics Limited(www.iqpcb.com) Originalartist: Swoolverton

• File:PExdcr01CJC.jpg Source: https://upload.wikimedia.org/wikipedia/commons/1/1c/PExdcr01CJC.jpg License: CC-BY-SA-3.0Contributors: Transfered from en.wikipedia Original artist: Original uploader was C J Cowie at en.wikipedia

• File:Parallel_plate_capacitor.svg Source: https://upload.wikimedia.org/wikipedia/commons/3/35/Parallel_plate_capacitor.svg License:Public domain Contributors: own drawing, done in Inkscape 0.44 Original artist: inductiveload

• File:Perf+_prototyping_board.png Source: https://upload.wikimedia.org/wikipedia/commons/8/86/Perf%2B_prototyping_board.pngLicense: CC BY-SA 4.0 Contributors: Own work Original artist: Kindiana

• File:Philco_Surface_Barrier_transistor=1953.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e8/Philco_Surface_Barrier_transistor%3D1953.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Historianbuff

• File:Photo-SMDcapacitors.jpg Source: https://upload.wikimedia.org/wikipedia/commons/8/86/Photo-SMDcapacitors.jpg License:Public domain Contributors: ? Original artist: ?

• File:Plattenkondensator_hg.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d3/Plattenkondensator_hg.jpg License:CC BY 3.0 Contributors: own work, Schulhistorische Sammlung Bremerhaven Original artist: Hannes Grobe (<a href='//commons.wikimedia.org/wiki/User_talk:Hgrobe' title='User talk:Hgrobe'>talk</a>)

• File:Polyester_film_capacitor.jpg Source: https://upload.wikimedia.org/wikipedia/commons/1/13/Polyester_film_capacitor.jpg Li-cense: CC BY 3.0 Contributors: http://matarese.com/photo/418-mallory-150-capacitor/ Original artist: Mataresephotos

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 145

• File:Question_book-new.svg Source: https://upload.wikimedia.org/wikipedia/en/9/99/Question_book-new.svg License: Cc-by-sa-3.0Contributors:Created from scratch in Adobe Illustrator. Based on Image:Question book.png created by User:Equazcion Original artist:Tkgd2007

• File:RC_switch.svg Source: https://upload.wikimedia.org/wikipedia/commons/9/90/RC_switch.svg License: CC BY-SA 3.0 Contribu-tors: Own work Original artist: PureCore

• File:RG-59.jpg Source: https://upload.wikimedia.org/wikipedia/commons/7/73/RG-59.jpg License: CC-BY-SA-3.0 Contributors: ?Original artist: ?

• File:RUS-IC.JPG Source: https://upload.wikimedia.org/wikipedia/commons/7/7e/RUS-IC.JPG License: CC BY-SA 3.0 Contributors:Own work Original artist: Sergei Frolov,Soviet Calculators Collection,http://www.rk86.com/frolov/

• File:Relogio_binario.JPG Source: https://upload.wikimedia.org/wikipedia/commons/6/69/Relogio_binario.JPG License: Public domainContributors: ? Original artist: ?

• File:Replica-of-first-transistor.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/bf/Replica-of-first-transistor.jpg Li-cense: Public domain Contributors: ? Original artist: ?

• File:ResistanceHydraulicAnalogy2.svg Source: https://upload.wikimedia.org/wikipedia/commons/1/19/ResistanceHydraulicAnalogy2.svg License: CC0 Contributors: Own work Original artist: Sbyrnes321

• File:Resistor.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e6/Resistor.jpg License: CC BY-SA 3.0 Contributors:Own work Original artist: Nunikasi

• File:Resistor_shaped_Inductors.png Source: https://upload.wikimedia.org/wikipedia/en/f/f1/Resistor_shaped_Inductors.png License:CC-BY-3.0 Contributors:photoOriginal artist:Vahid alpha

• File:Resistors.svg Source: https://upload.wikimedia.org/wikipedia/commons/2/25/Resistors.svg License: Public domain Contributors:Original work Original artist: Justin Force

• File:Resistors_(1).jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/f8/Resistors_%281%29.jpg License: CC-BY-SA-3.0Contributors: Transferred from en.wikipedia; transferred to Commons by User:Sfan00_IMG using CommonsHelper. Original artist: Orig-inal uploader was Cyp at en.wikipedia

• File:Resistors_in_parallel.svg Source: https://upload.wikimedia.org/wikipedia/commons/0/09/Resistors_in_parallel.svg License: CCBY-SA 3.0 Contributors: This SVG electrical schematic was created with the Electrical Symbols Library. Original artist: Omegatron

• File:Resistors_in_series.svg Source: https://upload.wikimedia.org/wikipedia/commons/1/11/Resistors_in_series.svg License: CC BY-SA 3.0 Contributors: This SVG electrical schematic was created with the Electrical Symbols Library. Original artist: Omegatron

• File:Resistors_on_tape.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/b1/Resistors_on_tape.jpg License: Public do-main Contributors: Own work Original artist: Inductiveload

• File:Rollspule.jpg Source: https://upload.wikimedia.org/wikipedia/commons/2/2c/Rollspule.jpg License: CC BY-SA 3.0 Contributors:Own work Original artist: HBD20

• File:S111FlipChipBack.jpg Source: https://upload.wikimedia.org/wikipedia/commons/0/09/S111FlipChipBack.jpg License: CC0 Con-tributors: Own work Original artist: Douglas W. Jones

• File:SI_base_unit.svg Source: https://upload.wikimedia.org/wikipedia/commons/c/c8/SI_base_unit.svg License: CCBY-SA 3.0Contrib-utors: I (Dono (talk)) created this work entirely by myself. Base on http://www.newscientist.com/data/images/archive/2622/26221501.jpgOriginal artist: Dono (talk)

• File:SMD_aufgelötet.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/fd/SMD_aufgel%C3%B6tet.jpg License: CCBY-SA 3.0 Contributors: Own work Original artist: Hutschi

• File:Sil_resistor.png Source: https://upload.wikimedia.org/wikipedia/en/e/e9/Sil_resistor.png License: PD Contributors:I (Nkendrick (talk)) created this work entirely by myself. Original artist:Nkendrick (talk)

• File:Silicon_chip_3d.png Source: https://upload.wikimedia.org/wikipedia/commons/a/aa/Silicon_chip_3d.png License: Public domainContributors: Transferred from en.wikipedia Original artist: Original uploader was David Carron at en.wikipedia Later version(s) wereuploaded by Tene at en.wikipedia.

• File:Siliconchip_by_shapeshifter.png Source: https://upload.wikimedia.org/wikipedia/commons/c/c6/Siliconchip_by_shapeshifter.png License: CC BY-SA 3.0 Contributors: Transferred from en.wikipedia to Commons. Original artist: David Carron at English Wikipedia

• File:Simple_electrical_schematic_with_Ohms_law.png Source: https://upload.wikimedia.org/wikipedia/commons/a/a0/Simple_electrical_schematic_with_Ohms_law.png License: Public domain Contributors: Own work Original artist: Danield101

• File:Spider_coil.jpg Source: https://upload.wikimedia.org/wikipedia/commons/a/a9/Spider_coil.jpg License: CC BY-SA 3.0 Contribu-tors: Spider coil(kit of w:ja: ) Original artist: ?

• File:Splatine.jpg Source: https://upload.wikimedia.org/wikipedia/commons/4/49/Splatine.jpg License: Public domain Contributors:bearbeitet des Bildes Platine.jpg, erstellt von Honina am 9. Okt 2003 (CEST) Original artist: Ulfbastel

• File:Stranded_lamp_wire.jpg Source: https://upload.wikimedia.org/wikipedia/commons/7/74/Stranded_lamp_wire.jpg License: Publicdomain Contributors: Own work Original artist: Scott Ehardt

• File:Streifenrasterleiterplatte_IMGP5364.jpg Source: https://upload.wikimedia.org/wikipedia/commons/5/51/Streifenrasterleiterplatte_IMGP5364.jpg License: CC BY-SA 2.0 de Contributors: Own work Original artist: Original uploaderwas Smial at de.wikipedia

146 CHAPTER 16. DIGITAL ELECTRONICS

• File:Stripboard.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/f9/Stripboard.jpg License: Public domain Contributors:Own work Original artist: Alexander Jones

• File:Stripboardexample.jpg Source: https://upload.wikimedia.org/wikipedia/commons/5/58/Stripboardexample.jpg License: Public do-main Contributors: Own work Original artist: Alexander Jones

• File:Surface_Mount_Components.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/3d/Surface_Mount_Components.jpg License: CC-BY-SA-3.0 Contributors: en:Image:Surface Mount Components.jpg Original artist: en:User:Zephyris

• File:SydneyWireMill_1913_Canada_a017696.jpg Source: https://upload.wikimedia.org/wikipedia/en/e/e8/SydneyWireMill_1913_Canada_a017696.jpg License: ? Contributors:Source: Library and Archives Canada Original artist: ?

• File:Symbol_book_class2.svg Source: https://upload.wikimedia.org/wikipedia/commons/8/89/Symbol_book_class2.svg License: CCBY-SA 2.5 Contributors: Mad by Lokal_Profil by combining: Original artist: Lokal_Profil

• File:Tantalum_capacitors.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e0/Tantalum_capacitors.jpg License: CCBY 3.0 Contributors: http://matarese.com/photo/419-several-tantalum-capacitors/ Original artist: Mataresephotos

• File:Testpad.JPG Source: https://upload.wikimedia.org/wikipedia/commons/4/4d/Testpad.JPG License: CC-BY-SA-3.0 Contributors:Own work Original artist: Cschirp

• File:Text_document_with_red_question_mark.svg Source: https://upload.wikimedia.org/wikipedia/commons/a/a4/Text_document_with_red_question_mark.svg License: Public domain Contributors: Created by bdesham with Inkscape; based upon Text-x-generic.svgfrom the Tango project. Original artist: Benjamin D. Esham (bdesham)

• File:Transbauformen.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e1/Transbauformen.jpg License: CC-BY-SA-3.0 Contributors: Own work Original artist: Ulfbastel

• File:Transistor_Simple_Circuit_Diagram_with_NPN_Labels.svg Source: https://upload.wikimedia.org/wikipedia/commons/9/91/Transistor_Simple_Circuit_Diagram_with_NPN_Labels.svg License: CC BY-SA 3.0 Contributors: I created a postscript file, and con-verted it to SVG using the pstoedit program. Original artist: Michael9422

• File:Transistor_as_switch.svg Source: https://upload.wikimedia.org/wikipedia/commons/5/5d/Transistor_as_switch.svg License: Pub-lic domain Contributors: Own work Original artist: FDominec

• File:Transistor_on_portuguese_pavement.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/38/Transistor_on_portuguese_pavement.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: Joao.pimentel.ferreira

• File:Transistorer_(croped).jpg Source: https://upload.wikimedia.org/wikipedia/commons/2/21/Transistorer_%28cropped%29.jpg Li-cense: CC-BY-SA-3.0 Contributors: Own work Original artist: Transisto at en.wikipedia

• File:Transmitter_tank_coil.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/b0/Transmitter_tank_coil.jpg License:Public domain Contributors: Downloaded July 22,2013 from <a data-x-rel='nofollow' class='external text' href='http://books.google.com/books?id=KpZEAAAAIAAJ,<span>,&,</span>,pg=PA269,<span>,&,</span>,dq=%22double+helix+oscillation+transformer'>ThePrinciples Underlying Radio Communication, National Bureau of Standards radio pamphlet no. 40, US Signal Corps. December 10, 1918,US Government Printing Office p. 372, fig. 197</a> on Google Books Original artist: Unknown

• File:Transmitter_tank_inductor.jpg Source: https://upload.wikimedia.org/wikipedia/commons/a/ac/Transmitter_tank_inductor.jpgLicense: Public domain Contributors: Retrieved March 12, 2014 from <a data-x-rel='nofollow' class='external text' href='http://www.americanradiohistory.com/Archive-Radio-News/30s/Radio-News-1938-05-R.pdf'>Radio News magazine, Ziff-Davis Publishing Co.,Chicago, Vol. 20, No. 11, May 1938, p. 31</a> American Radio History website Original artist: Unknown

• File:Two_ferrite_beads.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/ed/Two_ferrite_beads.jpg License: CCBY 2.0Contributors: http://flickr.com/photos/oskay/437342545/ Original artist: http://flickr.com/photos/oskay/

• File:Types_of_capacitor.svg Source: https://upload.wikimedia.org/wikipedia/commons/1/1c/Types_of_capacitor.svg License: CC0Contributors: Vectorized from raster image at English Wikipedia. Original artist: Uploader is Jwratner1 at English Wikipedia.

• File:Types_of_winding_by_Zureks.png Source: https://upload.wikimedia.org/wikipedia/commons/3/30/Types_of_winding_by_Zureks.png License: Public domain Contributors: Own work Original artist: Zureks

• File:UniversalPCB.jpg Source: https://upload.wikimedia.org/wikipedia/commons/8/81/UniversalPCB.jpg License: CCBY-SA 3.0 Con-tributors: own work, vlastní dílo Original artist: Tlapicka

• File:Vacuum_diode.svg Source: https://upload.wikimedia.org/wikipedia/commons/a/af/Vacuum_diode.svg License: Public domainCon-tributors: ? Original artist: ?

• File:Variometer.jpg Source: https://upload.wikimedia.org/wikipedia/commons/9/9f/Variometer.jpg License: Public domain Con-tributors: Downloaded April 30, 2013 from <a data-x-rel='nofollow' class='external text' href='http://books.google.com/books?id=1YtRAAAAMAAJ,<span>,&,</span>,pg=PA189#v=onepage,<span>,&,</span>,q,<span>,&,</span>,f=false'>Elmer Eustace Bucher(1920) The Wireless Experimenter’s Manual, Wireless Press, Inc., New York, p. 189, fig. 150a</a> on Google Books Original artist:Unknown

• File:Verschiedene_Kondensatoren_2.JPG Source: https://upload.wikimedia.org/wikipedia/commons/9/92/Verschiedene_Kondensatoren_2.JPG License: CC-BY-SA-3.0 Contributors: Own work Original artist: Fabian ~ (Fabian R at de.wikipedia)

• File:Verschiedene_LEDs.jpg Source: https://upload.wikimedia.org/wikipedia/commons/9/9e/Verschiedene_LEDs.jpg License: CCBY-SA 2.0 Contributors: Own work Original artist: Afrank99

• File:Vorschaltdrossel_Kvg.jpg Source: https://upload.wikimedia.org/wikipedia/commons/f/f2/Vorschaltdrossel_Kvg.jpg License: Pub-lic domain Contributors: Transferred from de.wikipedia to Commons byWdwd using CommonsHelper. Original artist: Ulfbastel at GermanWikipedia

• File:Wiki_letter_w.svg Source: https://upload.wikimedia.org/wikipedia/en/6/6c/Wiki_letter_w.svg License: Cc-by-sa-3.0 Contributors:? Original artist: ?

• File:Wikibooks-logo-en-noslogan.svg Source: https://upload.wikimedia.org/wikipedia/commons/d/df/Wikibooks-logo-en-noslogan.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: User:Bastique, User:Ramac et al.

16.9. TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES 147

• File:Wiktionary-logo-en.svg Source: https://upload.wikimedia.org/wikipedia/commons/f/f8/Wiktionary-logo-en.svg License: Publicdomain Contributors: Vector version of Image:Wiktionary-logo-en.png. Original artist: Vectorized by Fvasconcellos (talk · contribs),based on original logo tossed together by Brion Vibber

• File:Wire-bonded_Germanium_Diode.jpg Source: https://upload.wikimedia.org/wikipedia/commons/e/e3/Wire-bonded_Germanium_Diode.jpg License: CC0 Contributors: Own work Original artist: Anonimski

• File:Wire_wrapped_jewelry.JPG Source: https://upload.wikimedia.org/wikipedia/en/a/a7/Wire_wrapped_jewelry.JPG License: PDContributors: ? Original artist: ?

• File:Wires.jpg Source: https://upload.wikimedia.org/wikipedia/commons/c/c0/Wires.jpg License: CC-BY-SA-3.0 Contributors: Trans-ferred from en.wikipedia; transfer was stated to be made by User:iroony. Original artist: Original uploader was Pilaf at en.wikipedia

• File:Zero_ohm_resistors_cropped.jpg Source: https://upload.wikimedia.org/wikipedia/commons/0/05/Zero_ohm_resistors_cropped.jpg License: Public domain Contributors: Photographed by User:Mike1024 Original artist: User Mike1024 on en.wikipedia

16.9.3 Content license• Creative Commons Attribution-Share Alike 3.0