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EE 332

DEVICES AND CIRCUITS II

Lecture 11

Small-Signal Models

and Single Transistor Amplifier (3)

(CB Amplifier)

CB AMPLIFIER (NONINVERTING)/INPUT RESISTANCE

vx

ix

re

RB

r gmvbe

vbe

Ri

RE

vb

ve

Inputresistance:/ /

C B

i E eR R r

KCL at node E:

b e b e

Bb e x x x

B B

x

m b e x

B

m x

x x

B B

x B

e

v v v

rRv v v v

1x m

R r R r

vg v i

R r

g r vv i

R r R r

v R rr

i g r

= = = + +

+ = + + =+ +

+ = = +

re

CB AMPLIFIER (NONINVERTING)/OUTPUT RESISTANCE

vx

ic

rc

RB r

gmvbe

vbe

Ro

RE

vb

ve

Outputresistance:/ /

CB

o c CR r R

RecallCEamplifieroutputresistance,rc RC

ro

if then

if , then

0;

; (1 ) ( )

E c o

E th c o th

R r r

R r R r r R r

= =>> = + + +

TheCBoutputresistancewouldbe:if then

if , then

0;

; (1 ) ( )

E c o

E B c o B

R r r

R r R r r R r

= =>> = + + +

Rth =RB inthiscaseVerylargeresistance

CB AMPLIFIER (NONINVERTING)/SMALL SIGNAL MODEL

Smallsignalmodel

Rs

vS

C1R2

R1 RC

RE

Q1

C2

VCC

RL

voIgnorerosinceitislarge

vo

vs

R2R1 RC RLr

gmvbe

vbe

Rs RE

vo

vs

R2R1 RC RLr

gmvbe

vbe

Rs RE

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CB AMPLIFIER (NONINVERTING)/GAIN

ANSWER

ANSWER Step2:SmallSignalParameters:1

4025

100 2.540

104.67105

1

C

m

T

m

A CE

o

C

I mAg mS

V mV

r kg mS

V V Vr k

I mA

= = == = =

+= = =

CB AMPLIFIER (NONINVERTING)/GAIN

ANSWER

ANSWER

[ / / / / ]

[ / / ]

[ / / ]

[ / / ]

CB o

v

e

o m be c C L

Current

m be C L

be b e e

B

CB o m be C L

v

Bebe

m

C L

B

vA

v

v g v r R R

g v R R

rv v v v

R r

v g v R R A

R rvv

r

g rR R

R r

==

= = + = = +

= +

40 2.5[5.1 / /1.0 ] 8.36

7.5 2.5

m kk k

k k

= =+

123

vo

vs

R2 RC RLr

gmvbe

vbe

Rs

R1

rc

{

RB

vb

ve

rc//RC//RLRC//RLsincerc >>RC,RL

CB AMPLIFIER (NONINVERTING)/GAIN

ANSWER

ANSWER

vo

vs

R2 RC RLr

gmvbe

vbe

Rs

R1 [ / / ]

[ / / ] 100

7.5 2.5100

1 101

95

CB o o e

vs

s e s

ie s

i s

e E e

s E e

B

e

CB

v v vA

v v v

Rv vR R

v R r

v R r

R r k kr

= =

= + = +

+ +

8.36 4.07

195

vsA

= = = +

Sourcesignalgain

= =

CB AMPLIFIER (NONINVERTING)/GAIN

ANSWER

ANSWER

Rs

vS

C1

R2

R1

RC

RE

Q1

C2

VCC

RL

vo

vo

vs

R2R1RC RL

r

gmvbe

vbe

Rs

vo

vs

R2R1RC

RLr

gmvbe

vbe

Rs

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CB AMPLIFIER (NONINVERTING)/GAIN

ANSWERANSWER

vo

vs

R2 RC RLr

gmvbe

vbe

Rs

R1

( )( )( )1

0.792

CB o e c o

i

i i e c

CE

E e C L

i i i i A

i i i i

RR

R r R R

= = = + + +

=,

958.36 0.792

1000

i L v i

i

i v

L

Use

A R A R

RA A

R

= == =

Currentgain

End of lecture 11

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