CS Amplifier with Source Degeneration and Ohmic Load in the Presence - - PowerPoint PPT Presentation

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Aug 23, 2022 139 likes •220 views

4 4 CS Amplifier with Source Degeneration and Ohmic Load in the Presence of Body Effect and CLM r = o G g ( ) + + + m m r R g g r R o S m mb o S IIT-Bombay Lecture 8

SLIDE 1

4

IIT-Bombay Lecture 8 M. Shojaei Baghini

4

CS Amplifier with Source Degeneration and Ohmic Load in the Presence of Body Effect and CLM

( )

m S

R r g g R r r g G + + + × =

SLIDE 2

5

IIT-Bombay Lecture 8 M. Shojaei Baghini

5

s mb m s mb s mb m m v

R g g R g R g g g A || 1 1 || 1 1 + = + + = ⇒

m mb

g g = η

Source Follower

SLIDE 3

6

IIT-Bombay Lecture 8 M. Shojaei Baghini

6

gs in

V V V − =

Level shift and headroom reduction by one Vgs drop
Drain current considerably changes with the input

voltage due to Rs ⇒ nonlinearity (Note: Most of the change in the input voltage drops across Rs). So current source biasing is preferred.

Source Follower (cont’d)

SLIDE 4

7

IIT-Bombay Lecture 8 M. Shojaei Baghini

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W/L of M2 should be large enough to remain in active region (as a current source).

Source Follower with Current Source Biasing

SLIDE 5

IIT-Bombay Lecture 8 M. Shojaei Baghini

8

Example: Current Source Design

VDD M2 Vb Vout Vin M1 Vss

W/L of M2 should be large enough to remain in saturation (i.e. as a current source).

( ) ( ) ( )

15 2 . 14 200 75 . 50 2 1 75 . 6 . 65 . 1 3 3 65 . 1 6 . 25 . 2 25 . 2 200 6 . 2 . 1 40 50 2 1 2 . 1 200 | | 2 1

min 2 2 2 2 2 2 2 2 2 1 1 1

max max max

⇒ = ⇒ = × × = − − = ⇒ = = − > ⇒ = ⇒ = − − × × × ⇒ = = = − − = L W A L W V V V V V V V V A V V V A I V V V L W C I

SGT DD b

in D THP in

µ µ µ µ

V Vin L W V V V A C A I V V

p bias DD

2 . 1 40 6 . , 50 200 , 3

max 1 1 2

= = − = = = = µ µ µ

VDD scaling  Increase in W2/L2 and hence more capacitive loading

SLIDE 6

9

IIT-Bombay Lecture 8 M. Shojaei Baghini

9

1 2 |

|

TH GS DD in

V V V V + − <

1 2 3

| |

TH GS DD GS in

V V V V V + − + <

SF and CS

SLIDE 7

10

IIT-Bombay Lecture 8 M. Shojaei Baghini

10 10

mb m in m mb D m D mb m v

g g R g g R g R g g A + = = + = + = 1 ) 1 ( ) ( η η

Relatively low!

Common-Gate Stage

SLIDE 8

11

IIT-Bombay Lecture 8 M. Shojaei Baghini

11 11

Example

Requirement: 50 Ω input impedance at the end of the line provided by RD1 (in the first case)

r Rin of CG stage (in

4

4

CS Amplifier with Source Degeneration and Ohmic Load in the Presence of Body Effect and CLM

( )

R r g g R r r g G + + + × =

5

5

R g g R g R g g g A || 1 1 || 1 1 + = + + = ⇒

g g = η

Source Follower

6

6

V V V − =

voltage due to Rs ⇒ nonlinearity (Note: Most of the change in the input voltage drops across Rs). So current source biasing is preferred.

Source Follower (cont’d)

7

7

W/L of M2 should be large enough to remain in active region (as a current source).

Source Follower with Current Source Biasing

8

Example: Current Source Design

VDD M2 Vb Vout Vin M1 Vss

W/L of M2 should be large enough to remain in saturation (i.e. as a current source).

( ) ( ) ( )

15 2 . 14 200 75 . 50 2 1 75 . 6 . 65 . 1 3 3 65 . 1 6 . 25 . 2 25 . 2 200 6 . 2 . 1 40 50 2 1 2 . 1 200 | | 2 1

⇒ = ⇒ = × × = − − = ⇒ = = − > ⇒ = ⇒ = − − × × × ⇒ = = = − − = L W A L W V V V V V V V V A V V V A I V V V L W C I

µ µ µ µ

V Vin L W V V V A C A I V V

2 . 1 40 6 . , 50 200 , 3

= = − = = = = µ µ µ

VDD scaling  Increase in W2/L2 and hence more capacitive loading

9

9

|

V V V V + − <

| |

V V V V V + − + <

SF and CS

10

10 10

g g R g g R g R g g A + = = + = + = 1 ) 1 ( ) ( η η

Relatively low!

Common-Gate Stage

11

11 11

Example

Requirement: 50 Ω input impedance at the end of the line provided by RD1 (in the first case)

the second case). However RD2 can be more than RD1 ⇒ more gain for the line driver with CG stage at the Rx.

Common-Gate Stage as Current Buffer

1 2