CG Configuration = + C C C Assumption: r o is large. 1 1 D - - PowerPoint PPT Presentation

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Apr 09, 2023 48 likes •139 views

4 CG Configuration = + C C C Assumption: r o is large. 1 1 D DG DB isolation between input and output nodes 1 ( ) = + || RC C C R + 1 1 in GS SB s g g 1 1 m mb ( )( )

SLIDE 1

4

IIT-Bombay Lecture 24 M. Shojaei Baghini

CG Configuration

( ) ( )( )

D DB DG

mb m s SB GS in

R C C RC g g R C C RC

1 1 1 1 1 1

1 || + =         + + =

Assumption: ro is large. ⇒ isolation between input and

utput nodes

1 1 DB DG D

C C C + =

( )( )

in mb m S D in

sRC sRC g g R R s v s v s H + + + + = = ⇒ 1 1 1 1 ) ( ) ( ) (

SLIDE 2

5

IIT-Bombay Lecture 24 M. Shojaei Baghini

Precise H(s): CG Configuration (If ro is not negligible but RL is negligible)

( ) ( ) ( )

[ ]

1 1 ) ( ) (

+ + + + + + + + = s R C C R r g g R r s C C r R r g g s v s v

s in L s

m s

m in

SLIDE 3

6

IIT-Bombay Lecture 24 M. Shojaei Baghini

CG Configuration (If ro is not negligible)

( ) ( )

        + + + ≈ + + + =

m L mb m in

in in

r g g Z g g sC r g g r Z sC Z 1 || 1 1 || 1

in in s in M s

v Z R Z v + =

RL

Pole estimation at the input

SLIDE 4

7

IIT-Bombay Lecture 24 M. Shojaei Baghini

Interesting Approximation for the Second Pole

f CG Configuration

( ) ( ) ( )

[ ]

( ) ( )

mb m in L s

m in L

L s

m s in L s

m s

m in

g g C C R r g g C C r R C R r g g If s R C C R r g g R r s C C r R r g g s v s v + = + ≈ ⇒ + ≈ + + + + + + + + =

2 1 2

: 1 1 ) ( ) ( τ τ

Simple isolated time constant at the input (pole assigned to the input node) and τ1 >> τ2

SLIDE 5

8

IIT-Bombay Lecture 24 M. Shojaei Baghini

Very difficult to use direct calculation! We use property of CG configuration, given in the previous slide.

Frequency Response of Cascode Amplifier

SLIDE 6

9

IIT-Bombay Lecture 24 M. Shojaei Baghini

Approximation in the Frequency Response of Cascode Amplifier ( )

eq in s in GD mb m m GS eq in mb m m A X L GD BD eq

C R C g g g C C A g g g s v s v C C C C C R R

, 1 2 2 1 1 , 2 2 1 2 2 , ,

1 ) ( ) ( || ≈ ⇒         + + + = ⇒ − = + − ≈ + + = ≈ τ τ

What about the pole

at node X?

Worst case estimation

SLIDE 7

4

IIT-Bombay Lecture 25 M. Shojaei Baghini

Related to the assignment (approximations and validity of time constant method)

SLIDE 8

5

IIT-Bombay Lecture 25 M. Shojaei Baghini

DM Frequency Response of Differential Amplifier Differential-mode half circuit

SLIDE 9

6

IIT-Bombay Lecture 25 M. Shojaei Baghini

CM Frequency Response of Differential Amplifier

Impact of mismatch
Tradeoff between

4

CG Configuration

( ) ( )( )

R C C RC g g R C C RC

1 || + =         + + =

Assumption: ro is large. ⇒ isolation between input and

C C C + =

( )( )

sRC sRC g g R R s v s v s H + + + + = = ⇒ 1 1 1 1 ) ( ) ( ) (

5

Precise H(s): CG Configuration (If ro is not negligible but RL is negligible)

( ) ( ) ( )

[ ]

1 1 ) ( ) (

+ + + + + + + + = s R C C R r g g R r s C C r R r g g s v s v

6

CG Configuration (If ro is not negligible)

( ) ( )

        + + + ≈ + + + =

r g g Z g g sC r g g r Z sC Z 1 || 1 1 || 1

v Z R Z v + =

RL

Pole estimation at the input

7

Interesting Approximation for the Second Pole

( ) ( ) ( )

[ ]

( ) ( )

g g C C R r g g C C r R C R r g g If s R C C R r g g R r s C C r R r g g s v s v + = + ≈ ⇒ + ≈ + + + + + + + + =

: 1 1 ) ( ) ( τ τ

Simple isolated time constant at the input (pole assigned to the input node) and τ1 >> τ2

8

Very difficult to use direct calculation! We use property of CG configuration, given in the previous slide.

Frequency Response of Cascode Amplifier

9

Approximation in the Frequency Response of Cascode Amplifier ( )

C R C g g g C C A g g g s v s v C C C C C R R

1 ) ( ) ( || ≈ ⇒         + + + = ⇒ − = + − ≈ + + = ≈ τ τ

at node X?

4

Related to the assignment (approximations and validity of time constant method)

5

DM Frequency Response of Differential Amplifier Differential-mode half circuit

6

CM Frequency Response of Differential Amplifier

voltage headroom and CM frequency response

1 2 1 2