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EE 3110 Microelectronics I Suketu Naik
1Review Outline
1. Chapter 1: Signals and Amplifiers
2. Chapter 3: Semiconductors
3. Chapter 4: Diodes
EE 3110 Microelectronics I Suketu Naik
21.1 Signals
Signal – contains information
e.g. voice of radio announcer reading the news
Transducer – device which converts signalfrom non-electrical to electrical form
e.g. microphone (sound to electrical)
Process – an operation which allows an observer to understand this information from a signal
generally done electrically
EE 3110 Microelectronics I Suketu Naik
31.4 Amplifiers
Q: Why is signal amplification needed?
A: Because many transducers yield output at low power
levels (mW or nW)
Linearity – is property of an amplifier which ensures a
signal is not “altered” from amplification
Distortion – is any unintended change in output
EE 3110 Microelectronics I Suketu Naik
41.5.1 Voltage Amplifiers
model of amplifier input terminals
sourcevolt.
source andinput
resistances
input vo tag )l e ( ii s
i s
Rv v
R R
model of amplifier output terminals
open-cktoutput
output andvoltageload
resistances
output vo (l )tage Lo vo i
L o
Rv A v
R R
Figure 1.16 (b): voltage amplifier with input signal source
EE 3110 Microelectronics I Suketu Naik
51.5.1 Voltage Amplifiers
Ideal amplifier model – is function of vs and Avo only!!
It is assumed that Ro << RL…
It is assumed that Ri >> Rs…
idealmodel
non-ideal model
i Lo vo s vo s
i s L o
R Rv A v A v
R R R R
Key characteristics of ideal voltage amplifier model
1) Source resistance RS and load resistance RL have no effect on gain
2) High input resistance Ri (>>RS) and low output resistance Ro(<<RL)
EE 3110 Microelectronics I Suketu Naik
6Example 1.3: Cascaded Amplifier Configurations
Figure 1.17: Three-stage amplifier for Example 1.3.
• High Input
Resistance
• Modest
Gain
• Low Input
Resistance
• High Gain
• Low
Output
Resistance
• Unity Gain
EE 3110 Microelectronics I Suketu Naik
7Review Outline
1. Chapter 1: Signals and Amplifiers
2. Chapter 3: Semiconductors
3. Chapter 4: Diodes
EE 3110 Microelectronics I Suketu Naik
8
Valence electron – is an electron that participates in the formation of chemical bonds.
Lies in the outermost electron shell of an element
The number of valence electrons that an atom has determines the kinds of chemical bonds that it can form.
Covalent bond – is a form of chemical bond in which two atoms share a pair of electrons
By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability
3.1. Intrinsic Semiconductors
valence
electron
covalent
bond
EE 3110 Microelectronics I Suketu Naik
93.2 Doped Semiconductors
p-type semiconductor
doped with trivalent
impurity atom
(e.g. Boron)
n-type semiconductor
doped with pentavalent impurity atom (e.g. Phosphorus)
EE 3110 Microelectronics I Suketu Naik
103.3 Current Flow in Semiconductors
Summary
Holes (absence of electrons, p) and free electrons (n):
p-type semiconductor: holes are majority carriers ( pp ),
free electrons (np) are minority carriers
n-type semiconductor: free electrons are majority
carriers (nn), holes are minority carriers ( pn )
Two distinct mechanisms for current flow (movement
of charge carriers)
Drift Current (IS)
Diffusion Current (ID)
EE 3110 Microelectronics I Suketu Naik
11Mobility
Holes have less mobility than free electrons
Why?
Free electrons are loosely tied to the nucleus and are closer
to the conduction band (higher orbits, see slide 19)
Holes are absence of electrons in the covalent bond
between Si atoms and B
Holes are locked or subjected to the stronger atomic force
pulled by the nucleus than the electrons residing in the
higher shells or farther shells
So, holes have a lower mobility
EE 3110 Microelectronics I Suketu Naik
123.4.1 Physical Structure
pn junction (diode) structure
p-type semiconductor
n-type semiconductor
metal contact for connection
EE 3110 Microelectronics I Suketu Naik
13pn junction: modes of operation
(a) Open-circuit:voltage drop across depletion region = V0 , ID = IS
(b) Reverse bias:voltage drop across depletion region = V0 +VR, ID < IS
(c) Forward bias:voltage drop across depletion region = V0 -VF, ID > IS
EE 3110 Microelectronics I Suketu Naik
14Reverse-Bias Case
Observe that increased barriervoltage will be accompanied by…
(1) Increase in stored uncovered charge on both sides of junction
(2) wider depletion region
pp
p0p
0
0
width of depletion region
electrical permiability of silicon (11.7 1.04 12 )
magn
replace with
itude of electron ch
/
0
arge
P
P
(eq3.31)2 1 1
( )
S
R
F cm
Sn p R
VV V
W
q
A D
W x x V Vq N N
action:
Epp
pp
pp
p0 p
pp
concentration of acceptor atoms
concentration of donor atoms
barrier / junction built-in voltage
externally applied reverse-bias volta
P
P
P
g Pe
P
(eq3.3 22)
A
D
R
N
N
V
J
V
Q A
0
pp
0
magnitude of charge store
0
d on either side of depletion re
replace with
gi Pon
( )
J
R
VV V
A DS R
A
Q
D
N Nq V V
N N
action:
EE 3110 Microelectronics I Suketu Naik
15
Observe that decreased barrier voltage will be accompanied by
(1) Decrease in stored uncovered charge on both sides of junction
(2) Smaller depletion region
0
0
pp
pp
pp
0
width of depletion region
electrical permiability of silicon (11.7 1.04 12 )
magnitude of electron charge
con
replac
P
P
P
/
e with
0
2 1 1( )
A
F
S F c
V
W
q
m
Sn p F
A D
N
V V
W x x V Vq N N
action:
E
pp
pp
pp0
pp
centration of acceptor atoms
concentration of donor atoms
barrier / junction built-in voltage
externally applied forward-bias voltage
P
P
P
0
P
2 (
D
F
A DJ S F
A D
N
V
V
N NQ A q V V
N N
0
pp
0
magnitude of charge stored on either side of
rep
dep
lace wit
letion region
P
h
)
J
FV V
Q
V
action:
Forward-Bias Case
EE 3110 Microelectronics I Suketu Naik
16Review Outline
1. Chapter 1: Signals and Amplifiers
2. Chapter 3: Semiconductors
3. Chapter 4: Diodes
EE 3110 Microelectronics I Suketu Naik
174.1 The Ideal Diode
Ideal diode – most fundament nonlinear circuit element
Operates in two modes:
Off (reverse biased, (c)), On (forward biased, (d))
Off (Reverse Biased)
Open Circuit
On (Forward Biased)
Short Circuit
On Off p type n type
EE 3110 Microelectronics I Suketu Naik
184.3.5 Constant Voltage-Drop Model
The constant voltage-drop diode modelassumes that the slope of ID vs. VD is vertical @ 0.7V
Negligible difference between values obtained from the exponential model (most accurate)
Example
EE 3110 Microelectronics I Suketu Naik
194.3.1 Exponential Model:
Q: How does one solve
for ID in circuit to right?
A:
Graphical method
Iterative methodTD VV
SD
DDDD
eII
R
VVI
/
eq 4.6
eq 4.7
TD VV
SD eII/
EE 3110 Microelectronics I Suketu Naik
20Terminal Characteristics of Junction Diodes
I-V curve
consists of three
characteristic
regions
forward bias:
v > 0
reverse bias:
v < 0
breakdown:
v << 0
EE 3110 Microelectronics I Suketu Naik
21Exercise 4.4
Find I and V using
(a) Ideal diode model (b) Constant voltage drop model
Ans: 4.4 (a) 2 mA, 0V (c) 0 mA, -5V
4.4
EE 3110 Microelectronics I Suketu Naik
22
Microelectronic Circuits, Sixth Edition Sedra/Smith Copyright © 2010 by Oxford University Press, Inc.
Figure P4.3
EE 3110 Microelectronics I Suketu Naik
23Examples and Excercises
Example 1:
VDD = 5 V
R = 1 kΩ
ID = 1 mA @ 0.7 V
Model
Type/
Parameter
Ideal diode
model
Constant
voltage-drop
model
Exponential
Model: Iterative
Method
VD 0 V 0.7 V0.738 V (2nd
iteration)
ID 5 mA 4.3mA4.262 mA (2nd
iteration)
Excercises
D4.11, 4.12 (a)
EE 3110 Microelectronics I Suketu Naik
244.3.1 Exponential Model:
Q: How does one solve
for ID in circuit to right?
A:
Graphical method
Iterative methodTD VV
SD
DDDD
eII
R
VVI
/
eq 4.6
eq 4.7
TD VV
SD eII/
EE 3110 Microelectronics I Suketu Naik
254.3.7 Small Signal Model
DC analysis: Use constant voltage drop model
AC analysis: Use resistor as diode
Notation:
DC only – upper-case w/ upper-case
subscript, VD
Time-varying only – lower-case w/
lower-case subscript, vd
total instantaneous – lower-case w/
upper-case subscript, vD
DC
AC (time
varying)
EE 3110 Microelectronics I Suketu Naik
264.3.7 Small Signal Model
Substitute eq.4.9 in eq.4.10
Split this exponential
Redefine total instant current in
terms of DC component (ID)
and time-varying voltage (vd)
Apply power series expansion
to (4.12) and keep upto first
order terms
)()(
)(
/
tvVtv
eII
V
vIti
dDD
VV
sD
T
dDD
TD
1
d
(eq4.14
)
(eq4.8)
(eq4.9)
EE 3110 Microelectronics I Suketu Naik
274.3.7 Small Signal Model
Small signal approximation
total instant current (iD)
small-signal current (id.)
small-signal resistance (rd.)
accurate for vd < 5mV amplitude (not peak to peak)
somewhat accurate for vd > 5mV
( )
( )
1
d
DD D d
T
D D d
d d
d
Td
D
i
Ii t I v
V
i t I i
i vr
Vr
I
(eq4.14
)
EE 3110 Microelectronics I Suketu Naik
28Example 4.5
V+ = 10 V with 1 V peak amp at
60 Hz (power supply ripple)
R = 10 kΩ
ID = 1 mA @ 0.7 V
Calculate dc voltage and the
amplitude of ac signal across
the diode.
EE 3110 Microelectronics I Suketu Naik
294.4 Zener Diodes
ZZZOZ IrVV
VZK ≈ VZO
We will revisit Zener diode in
section 4.6 (limiter circuit)
EE 3110 Microelectronics I Suketu Naik
304.1.2 Application: Rectifier
Rectifier converts
ac signal in to dc
signal
During positive
cycle, current will
flow through the
diode (forward
biased)
During negative
cycle, no current
will flow through
the diode (reverse
biased)
Off On
Off
On On
EE 3110 Microelectronics I Suketu Naik
31Half Wave Rectifier with a Filter Capacitor
EE 3110 Microelectronics I Suketu Naik
32Full-Wave Rectifier
Center-tapping of the transformer, allowing “reversal”
of certain currents…
EE 3110 Microelectronics I Suketu Naik
33Bridge Rectifier