UNIT – I: IC FABRICATION AND CIRCUIT CONFIGURATION FOR LINEAR IC

PART -A (2 Marks)

1. Mention the advantages of integrated circuits.

*Miniaturization and hence increased equipment

density. *Cost reduction due to batch processing. *Increased system reliability due to the elimination of soldered

joints. *Improved functional performance. *Matched devices.

*Increased operating speeds.

*Reduction in power consumption.

2.Write down the various processes used to fabricate IC’s using silicon planar technology. *Silicon wafer preparation. Epitaxial growth *Oxidation. *Photolithography. *Diffusion. *Ion implantation. *Isolation. *Metallization. *Assembly processing and packaging.

3. What is the purpose of oxidation? *SiO2 is an extremely hard protective coating and is unaffected by almost all reagents. *By selective etching of SiO2, diffusion of impurities through carefully defined windows

can be accomplished to fabricate various components.

4. Why aluminium is preferred for metallization?

*It is a good conductor. *it is easy to deposit aluminium films using vacuum deposition.

*It makes good mechanical bonds with silicon.

*It forms a low resistance contact.

5. What are the popular IC packages available? Metal can package. Dual-in-line package. Ceramic flat package.

6. Define an operational amplifier.

An operational amplifier is a direct-coupled, high gain amplifier consisting of one or more

differential amplifier. By properly selecting the external components, it can be used to

perform a variety of mathematical operations.

7.Mention the characteristics of an ideal op-amp. Open loop voltage gain is infinity.

*Input impedance is infinity.

*Output impedance is zero.

*Bandwidth is infinity.

*Zero offset.

8. State the advantages of Integrated circuits over discrete components[AUC

NOV 2013] Reduced size. Low power consumption. High speed of operation.

9.Define offset voltage of an operational amplifier[AUC NOV 2013]

A small voltage applied to the input terminals to make the output voltage as zerowhen the two input terminals are grounded is called input offset voltage.

10. What are the two requirements to be met for a good current source? [AUC MAY 2012]

The output current Io should not be dependent on β. The output resistance of the current source should be very high.

11. List the various methods of realizing high input resistance in a differential amplifier. [AUC MAY 2012]

Use of darlington pair. Use of FET. Use of swamping resistance.

12. What are the applications of current source.[AUC MAY 2011]

Transistor current sources are widely used in analog ICs both as biasingelements and as load devices for amplifier stages.

13. Define slew rate. [AUC MAY 2011]

The slew rate is defined as the maximum rate of change of output voltage causedby a step input voltage.An ideal slew rate is infinite which means that op-amp’s outputvoltage should change instantaneously in response to input step voltage.

14.What is the need for frequency compensation in practical op-amps? [AUC MAY 2011]

Frequency compensation is needed when large bandwidth and lower closed loopgain is desired. Compensating networks are used to control the phase shift and henceto improve the stability.

15. What is the need for constant current source in differential amplifier? [AUC MAY 2011]

superior insensitivity of circuit performance to power supply variations and temperature. more economical than resistors in terms of die area required to provide bias currents of small value. When used as load element, the high incremental resistance of current source results in high voltage gain at low supply voltages.

16.Justify the statement: CMRR value of an ideal op-amp should be infinite. [ AUC MAY 2011]

CMRR ρ = Ad / Ac For an op-amp Ad is large and Ac is zero . Hence CMRR is infinite.

17. Define CMRR. [AUC April 2004,MAY2010]

The relative sensitivity of an op-amp to a difference signal as compared to acommon – mode signal is called the common –mode rejection ratio. It is expressedin decibels. CMRR= Ad/Ac

18. What is the reason for drop in gain at high frequencies in op-amp?[AUC MAY2010]

The open-loop gain of op-amp decreases at higher frequencies due to thepresence of parasitic capacitance. The closed-loop gain increases at higher frequenciesand leads to instability.

19. Draw a neat sketch showing the frequency response of μA741 OP AMP.[AUC Nov

2004]

20. Write down the characteristics of ideal operational amplifier.[AUC May 2005,Nov 2006]

Open loop voltage gain Zout 0

Output impedance Zin Infinity

Input offset current Ios 0

Bandwidth BW 0

CMRR ρ Infinity

Slew rate S Infinity

PSRR PSRR 0

21.Draw the equivalent circuit of an ideal amplifier.[AUC June 2006]

22.An opamp circuit shown in figure has differential gain Ad=5mv.Calculate V0. [AUC Nov 2006]

Vo = -5v2 + 5 V1= 5(V1-V2)

23.Compare the ideal and practical characteristics of op-amp.[Nov 2006]

24.What does the term linear circuits generally convey?[Nov 2007]

In linear circuits the output electrical signals vary in proportion to the applied input signal.

25.Give the circuit schematic of simple current mirror circuit.[AUC Nov 2007]

R2 Q1

1k Q2N3721

0

Q2

Q2N3721

0

26.Define unity gain bandwidth of an Op-Amp.[AUC April 2008]

Unity gain bandwidth is defined as the bandwidth of an Op-Amp when the voltage gain is unity.

27.Define slew rate. What causes it ?[AUC May 2008,May2009]

The slew rate is defined as the maximum rate of change of output voltage caused by a

step inputvoltage.An ideal slew rate is infinite which means that op-amp’s output voltage

should changeinstantaneously in response to input step voltage. 28.State the applications of band gap reference circuit[AUC Nov 2008]

Voltage regulator

ADC and DAC circuits

V-F and F-V converters

29. What is a current mirror circuit? What are its advantages?[AUC Nov 2008]

The circuit in which the output current is forced to equal the input current is called as current mirror circuit.

Advantages:

Requires less components than constant current bias circuits.

Circuit is simple and easy to fabricate.

Using matching transistors, thermal stability is achieved.

30. Define current mirror.[AUC May 2009]

The circuit in which the output current is forced to equal the input current is called as current mirror circuit.

31. List the basic blocks of an op-amp. [AUC Nov2009]

Input stage

Intermediate stage

Level shifting stage

Output stage

32. How can you increase the input resistance of an op-amp.[AUC Nov2009]

Use of darlington pair.

Use of FET.

Use of swamping resistance.

An operational amplifier is a direct-coupled, high gain amplifier consisting of one or more

differential amplifier. By properly selecting the external components, it can be used to

perform a variety of mathematical operations.

33. Mention the characteristics of an ideal op-amp. a. Open loop voltage gain is infinity.

*Input impedance is infinity.

*Output impedance is zero.

*Bandwidth is infinity.

*Zero offset.

UNIT – II: APPLICATIONS OF OP-AMP

PART -A (2 Marks)

1. An input of 3v is fed to the non-inverting terminal of an op-amp. The amplifier has

a Ri of 10KΩ and Rf of 10KΩ .Find the output voltage[AUC April 2004]

V0 =[

2. Draw an integrator circuit using op-amp.[ AUC April 2004]

3. Mention two characteristics of instrumentation amplifier.[ AUC May 2005]

high gain accuracy high CMRR high gain stability with low temperature coefficient low output impedance

4. Mention two applications of Schmitt trigger.[ AUC May

2005] To convert sine wave to square wave.

Over voltage and over current protection circuit.

On /off temperature controllers.

5. Draw an adder circuit using op amp to get the output expression as vo=-

(0.1+v2+5v3)[ AUC May 2006]

6. Draw the circuit of a voltage follower using op-amp and prove that its gain is

exactly equal to unity.?[ AUC May 2006]

Va = Vb = vin

Node a is directly connected to output

V0= Va

V0=Vin

For the circuit voltage gain is unity.

7. Draw the block diagram of a multiplier using log and antilog amplifiers.[ AUC May

2006]

8. State the requirements of an instrumentation amplifier. [AUC Nov 2006]

high gain accuracy

high CMRR

high gain stability with low temperature coefficient

low output impedance

9. Name four applications of operational amplifier based comparator.[ AUC Nov

2006,April 2008]

ero crossing detector

Window detector

Marker generator

Phase meter

10. What is an antilog amplifier? Draw the circuit diagram of an antilog amplifier.[ AUC

Nov 2007]

Amplifier that converts logarithmic numbers back to decimal numbers is called antilog

amplifiers.

D1

D1N4001

I

V4 VOFF = VAMPL = FREQ =

0

RF

1k

I

A 2 4

AD741

V-

-

OS1

OUT

3 +

V+

OS 2

B

U3

7

0

1 6 5

VO

11. What is the principle of regenerative comparator.[ AUC Nov2007]

If positive feedback is added to the comparator circuit, gain can be increased. Hence ,the

transfer curve of comparator becomes more closer to ideal curve. If the loop gain is adjusted

to unity then the gain becomes infinity. This results in an abrupt transition between the

extreme values of the output voltage.

12. Draw the circuit diagram of a non-inverting amplifier ?[ AUC May 2008]

13. Draw the circuit of an integrator[AUC Nov 2008]

14. What is a V to I converter?[ AUC Nov 2008]

Converter that produces output current which is directly proportional to the input voltage is

called as V to I converter.

15. Draw the Schmitt trigger and give its application?[ AUC May2009]

ROM

1k

V1 VOFF = VAMPL = FREQ =

0

AD741

2

-

3

+ U1

R2

1k

4

V-

OS1

OUT

V+

OS 2

7

R1

1k

1 6 vo 5

R3

1k

0

0

Applications

o To convert sine wave to square wave.

o Over voltage and over current protection circuit.

o On /off temperature controllers.

16. Draw the input and output waveforms for an integrator for square wave input.[

AUC May 2010]

17. Mention the applications of an instrumentation amplifier.[ AUC May 2009]

Data acquisition system.

Temperature indicator

Temperature controller.

Light intensity meter.

18. In what way, a precision rectifier using op-amp is superior to a conventional

rectifier. [AUC Nov09 ,MAY 2011]

Conventional rectifier cannot rectify voltages below 0.6V. Precision

rectifiers rectify voltages having amplitude less than 0.7V

19. Draw an op-amp subtractor circuit. . [AUC Nov09]

20. Design an inverter using op-amp [AUC MAY 2010 ,MAY 2011]

21. Design a peak detector using op-amp [AUC MAY 2010]

22. Distinguish between active and passive filter. [AUC MAY 2011]

ACTIVE FILTER PASSIVE FILTER

Tuning is easy Difficult to tune

Does not cause loading effect Causes loading effect to source or load

More economical Cost is high

23. Why active guard drive is necessary for an instrumentation amplifier?[AUC MAY

2012]

The common ground is shared by variety of circuits.

Due to ground loop interference , additional voltage drop develops and lead to

error in low voltage measurement.

Due to distributed cable capacitances degradation of CMRR occurs.

The active guard drive eliminates all these problems.

24. What is comparator? [AUC MAY 2012]

Comparator is a circuit that compares the voltage applied at one of its input to that

applied at its other input and to produce an output voltage which is either Vh or vl

25. Draw a non –inverting amplifier with a voltage gain of 3 [AUC NOV 2013]

Ri Rf

1k 2k

2

Vin 3

4

5

-

+

7

1

AD741 6

U2

26. Give an application for each of the following circuits : voltage follower ,peak

detector ,Schmitt trigger , clamper

Voltage follower : used in isolator circuit

Peak detector : used for amplitude modulation in communication applications.

Schmitt Trigger : square wave generators , ON –OFF controllers.

Clamper : DC restorer in television receivers.