EE 332
DEVICES AND CIRCUITS II
Lecture 3
COMMON EMITTER-COMMON SOURCE
with RE-RS
8/29/2022
1
Lecture Goals
 Common-Emitter with RE circuit
+ Calculating Input resistance, Output resistance,
+ Calculating Voltage gain, Current gain, Power gain
+ Input voltage range for linear condition of amplification circuit
 Common-Source with RS circuit
+ Calculating Input resistance, Output resistance,
+ Calculating Voltage gain, Current gain, Power gain
+ Input voltage range for linear condition of amplification circuit
 Discussion and Summary
Chap 1 - 2
Signal Injection and Extraction: BJT

In forward-active region,






v

i  I exp BE 
C S
V 
T 
v

I


S
i 
exp BE 
 V

E 
T


F
I





v 
i  S exp BE 
B 
V 
T 
F
8/29/2022
3
Signal Injection and Extraction: MOSFET

In pinch-off region,
i 
D
8/29/2022
Kn 
v V
TN
2 GS





2
4
Amplifier Families

Constraints for signal injection and extraction yield three
families of amplifiers
+ Common-Emitter (C-E)/Common- Source (C-S)
+ Common-Base (C-B)/Common- Gate (C-G)
+ Common-Collector (C-C)/Common- Drain (C-D)

All circuit examples here use the four-resistor bias circuits
to establish Q-point of the various amplifiers

Coupling and bypass capacitors are used to change the ac
equivalent circuits.
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 5
COMMON-EMITTER (CE) AMPLIFIER WITH RE
Chap13 - 6
COMMON-EMITTER (CE) AMPLIFIER WITH RE
Chap13 - 7
INPUT RESISTANCE
Chap13 - 8
SIGNAL SOURCE VOLTAGE GAIN
Chap13 - 9
IMPORTANT LIMITS AND MODEL SIMPLIFICATIONS
Chap13 - 10
COMMON-EMITTER VOLTAGE GAIN FOR LARGE
EMITTER RESISTANCE
Chap13 - 11
SMALL-SIGNAL LIMIT FOR CE AMPLIFIER
 r  (o 1)R
E
iB 
 r (1 g m R )
E
R  R // R
B
in
iB
R
v  v  ve  v  gmv R  v (1 gmR )
E
b be
be
be E be
v v
i(R  R ) v
R R
i  i b  I
in  b  I
in (1 g R )
m E
v
v v
iR
v
R
be b be
in
be
in
v
R R
R R
I
in (1 g R )  0,005 I
in (1 g R )
v v
m
m E
E
i be R
R
in
in


V
Chap13 - 12
12
RESISTANCE AT COLLECTOR OF BJT
Chap13 - 13
RESISTANCE AT COLLECTOR OF BJT
Chap13 - 14
RESISTANCE AT COLLECTOR OF BJT
RiC
Output Resistance of overrall CE
Amplifier
Chap13 - 15
Inverting Amplifiers: Common-Emitter and
Common-Source Circuits
AC equivalent for C-E Amplifier
Jaeger/Blalock
7/1/03
AC equivalent for C-S Amplifier
Microelectronic Circuit Design
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Chap 14 - 16
Inverting Amplifiers: Common-Emitter and
Common-Source Circuits
RiD
RiC
RiB
RiG
AC equivalent for C-E Amplifier
Jaeger/Blalock
7/1/03
AC equivalent for C-S Amplifier
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 17
Terminal voltage gain of CS
v
g v R
m gs L
g R
m
CS  ds  
L

Avt
v
v g v R
1 g R
gs
gs m gs S
m S
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
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Chap 14 - 18
Condition of vi for linear amplification
R
R
iG
in

 R // R  R
G
G
iG
vg  vgs  vs  vgs  gmvgsR  vgs (1 gmR ) 
S
S
vg
vgs
 (1 gmR )
S
v v
i(R  R ) vg R  R
I
G 
G (1 g R )
i  i g 
 I
m S
vgs vg vgs
iR
vgs
R
G
G
v
R R
R R
I
G
G (1 g R )
v  vgs
(1 gmR )  0,2(V  V ) I
m S
S
GS TN R
i
R
G
G


V
19
Inverting Amplifiers: Input Resistance and
Overall Voltage Gain
Input resistance looking into the base
terminal is given by
v
RiB  b  r  (o 1)RE
i
RiB  r (1 gm R )
E
For C-S Amplifier, r  

RCS
in
For C-S Amplifier,
Jaeger/Blalock
7/1/03
Overall voltage gain is
v 
v  v  v 
CE  o   o  b   CE  b 
Av
Avt
 v 
v  v  v 
i  b  i 
 i 


CE 
Avt
R
 I

R RiB 
B

  R RiB  
 B


R

CS 
G

Av
Avt

R R 
I
G 
Microelectronic Circuit Design
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





Chap 14 - 20
(Example 1)




Problem: Find Q-point; RiB; Rin; Avt; Av; Ai; Ap; vimax for linear
condition of this amplifier.
Given data: RI, R1, R2, R3, R4 ; β =100; VBE = 0.7V.
Assumptions: Small-signal operating conditions.
Analysis: For C-E Amplifier,
Chap 1 - 21
(Example 1)




Problem: Find overall voltage gain.
Given data: Q-point values and values for RI, R1, R2, R3, R7 ,for both
BJT and FET as well as values for RE and RS .
Assumptions: Small-signal operating conditions.
Analysis: For C-E Amplifier,
I  0.245mA;V
 3.39V
C
CE
Chap 1 - 22
Inverting Amplifiers: Voltage Gain Calculations
(Example 1)
Fig 14.7
Chap 1 - 23
Inverting Amplifiers: Voltage Gain Calculations
(Example 1)




Problem: Find overall voltage gain.
Given data: Q-point values and values for RI, R1, R2, R3, R7 ,for both
BJT and FET as well as values for RE and RS .
Assumptions: Small-signal operating conditions.
Analysis: For C-E Amplifier,
I
 0.245mA; V
 3.39V
CE
C
g m  40 I
C

r 
Jaeger/Blalock
7/1/03
o 
gm
 40x0.245mA  9.8mS
100
9.8mS
 10.2 K
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 24
Inverting Amplifiers: Voltage Gain Calculations
(Example 1)




Problem: Find overall voltage gain.
Given data: Q-point values and values for RI, R1, R2, R3, R7 ,for both
BJT and FET as well as values for RE and RS .
Assumptions: Small-signal operating conditions.
Analysis: For C-E Amplifier,
R  R R 160kΩ 300kΩ 104kΩ
B
1 2
RiB  r  (o 1) RE 10kΩ  (101) 3kΩ   313kΩ
R  R R  22kΩ 100kΩ 18kΩ
L
C 3
 R
CE   o L  100(18kΩ)  5.75
Avt
313kΩ
RiB
Jaeger/Blalock
7/1/03
CE
Av 

CE 
Avt
R
 I
Microelectronic Circuit Design
McGraw-Hill

R RiB 
B
  5.61


  R RiB  
 B

Chap 14 - 25
Inverting Amplifiers: Common-Emitter and
Common-Source Circuits
AC equivalent for C-E Amplifier
Jaeger/Blalock
7/1/03
AC equivalent for C-S Amplifier
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 26
Inverting Amplifiers: Voltage Gain Calculations
(Example contd.)

Analysis: For C-S Amplifier,
R  R R  1.5MΩ 2.2 MΩ  892kΩ
G
1 2
R  R R  22kΩ 100kΩ  18kΩ
L
D 7
g R
m L   (0.491mS)(18kΩ)  4.46
1 (0.491mS)(2kΩ)
1 g R
m S
CS
Avt  
CS
Av 
Jaeger/Blalock
7/1/03
 R

CS 
G   4.45
Avt 
R  R 
G
 I
Microelectronic Circuit Design
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Chap 14 - 27
Inverting Amplifiers: Output Resistance
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 28
Inverting Amplifiers: Output Resistance
vx  vr  ve  (ix  oi)ro  ve



ve  ix   R  r  R 
 E
  th
R
E
i  ix
R  R  r
E th


o R


E

R  ro 1


iC
R

R

r

E th  

Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
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Chap 14 - 29
Inverting Amplifiers: Output Resistance (contd.)
o R






E
R  ro 1
iC
R  R  r
E th






Assuming (r  RE )  R and ro  RE , with o  gmr
th


R  ro 1 gm (r R )   ro   (r R )
iC
f
E 
E


R   (r R )
iC
f
E
…….for gm (r RE )  1
Finite current gain of BJT places an upper limit on size of output
resistance. r appears in parallel with RE if Rth is neglected. If we let RE be
infinite, maximum value of output resistance is RiC  (o 1)ro
Output resistance of C-S amplifier is given by,
R  ro 1 gm R 
S
iD

Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
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Chap 14 - 30
Current gain and Power gain of CE amplifier with RE
R
L
in
Av  

1 g m R
R R
E
I
in
gmR
Current gain
vo
R R
R
i
v R  Rin
3  o I
I in
A  o 

A
v
v
i
i
i
v
R
R
i
i
3
3
R R
in
I
Power gain
Ap  Av A
i
31
Current gain and Power gain of CS amplifier with RS
R
G
L
Av  

1 g m R R  R
I
S
G
gmR
Current gain
vo
i
A  o 
i
i
i
R R
R
v R R
G A I
G
3  o I
v
v
v
R
R
i
i
3
3
R R
I
G
Power gain
A p  Av A
i
32
Exercise
Chap13
33
Chap 1 --33
Inverting Amplifiers: Common-Emitter
Fig 14.7
Chap 1 - 34
Solution
Chap13
35
Chap 1 --35
Solution
Chap13
36
Chap 1 --36
Inverting Amplifiers: Summary






C-E and C-S amplifiers have similar voltage gains.
C-S amplifier provides extremely high input resistance but that of C-E is also
substantial due to the f RE term.
Output resistance of C-E amplifier is much higher than that of C-S amplifier as
f is much larger for BJT than for FET.
Input signal range of C-E amplifier is also higher than that of C-S amplifier.
Current gains of both are identical to those of individual transistors.
Following transformation is used to simplify circuit analysis by absorbing RE
(or RS ) into the transistor (For FET, current gain and input resistance are
infinite).
gm
r '  r (1 gm R ) ro '  ro (1 gm R )
gm ' 
E
E
1 g m R
E
 '  gm' ro'  
o'  gm' r '  o
f
f
Jaeger/Blalock
7/1/03
Microelectronic Circuit Design
McGraw-Hill
Chap 14 - 37
End of Lecture 3
Chap 1 - 39