lecture14(20-3-11)

7/27/2019 Lecture14(20-3-11)

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EE 332

DEVICES AND CIRCUITS II

Lecture 14

Small-Signal Models

and Single Transistor Amplifier (6)

(CG Amplifier)

CG AMPLIFIER (NON-INVERTING)/SMALL SIGNAL MODEL

Small signal model

RI

vS

C1

R2

R1RD

RS

M1C2

VDD

RL

vo

vo

RG

RI

RD RL

r π

→∞

ro

gmvgs

vgs

vs

RS

CG AMPLIFIER (NON-INVERTING)/INPUT RESISTANCE

rs

Ri

vx

RG

vgs

/ /CG

i S s R R r

Input Resistance:

KCL at node S; 1

x m gs m x

x

s

x m

i g v g v

v r

i g

= − =

⇒ = =

vs

RGRD RLro

gmvgs

RS

ix

Lecture Goals

Understanding of concepts related to: CG Amplifier

• Small Signal Model

• Input Resistance

• Output Resistance

• Small Signal Analysis

• Small Signal Parameter

• Gain

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7/27/2019 Lecture14(20-3-11)


CG AMPLIFIER (NON-INVERTING)

/OUTPUT RESISTANCE

rd Ro

vs

RGRD RL

ro

gmvgs

vgs

RS

if then

if , then

0;

; (1 ) ( )

/ /

E c o

E B c o B

CB

o c C

R r r

R r R r r R r

R r R

π π

= =

>> = + + +

=

Output Resistance:Recall output resistance of CB

Common gate output resistance:The difference between small signal models of CB and CG is rπ→∞, then0;

/ /

S d o

CG

o d D

R r r

R r R

= =

=

CG AMPLIFIER (NON-INVERTING)/ SMALL SIGNAL ANALYSIS

Theveninizing LHS loop:

(2). RHS loop:

Assuming saturation:

1

1 2

2

(1).

(3). ( )

2(4).

th DD

DD DS D DS DS S

n

DS GS TN

S DS S

R V V

R R

V I R V I R

K I V V

V I R

=

+

= + +

= −

=

Substitute (4) into (3)

1. Solve for VS

2. Use (4) to solve for IDS

3. Use (2) to solve for VDS

4. Solve for VGS

R2

R1

RD

RS

M1

VDD

IDS

VDS

gm: small signal transconductance

rO: small signal output resistance=

CG AMPLIFIER (NON-INVERTING)/ SMALL SIGNAL PARAMETERS

2D

m

GS TN

I g

V V

=

−

2 1 2

( )

21

D

F m o

GS TN D GS TN

n

F

D

I g r

V V I V V

K

μλ λ

μ

= ≈ × =

− −

⇒ ≈

I

1 1DS

o

D D

V r

I I

λ

λ λ

+= ≈

vds

ro

gm

vgs

vgs

CG AMPLIFIER (NON-INVERTING)

/SMALL SIGNAL ANALYSIS

DC analysis

RI

vS

C1R

2

R1

RD

RS

M1C2

VDD

RL

vo

RI

C1

R2

R1

RD

RS

M1

C2

VDD

RL

vo

vS

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7/27/2019 Lecture14(20-3-11)


CG AMPLIFIER (NON-INVERTING)/GAIN

vo

vs

RG

RI

RD RL

ro

gmvgs

vgs

RS

( / / / / )CG

v m o L D A g r R R

Small Signal Equivalent Circuit

Common gate gain:The difference between small signal models of CB and CG is rπ→∞, which doesn’t affect the

result of

Terminal Voltage gain:Recall CB:

( / / / / )CB

v m o L C A g r R R

End of Lecture 14

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lecture14(20-3-11)

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