Source Followers (Common Drain)

Copyright  2004 by Oxford University Press, Inc.

Microelectronic Circuits - Fifth Edition Sedra/Smith 1

Source Followers (Common Drain)

Fundamentals of Microelectronics Behzad Razavi Copyright 2009 by John Wiley & Sons, Inc

' 1

L L o

mb

R R r

  ^װ  ^װ g

' o g m gs R L

  

gs i o

    

Copyright  2004 by Oxford University Press, Inc.

Microelectronic Circuits - Fifth Edition Sedra/Smith

1

o o

m mb

R r

g g

  

 

1 1

o m

R      g  

 

1

m o o

m mb o

A g r

g g r

 

 

'

1 '

o m L

i m L

A g R

 g R



  



1 1

m o

m mb

A g

g g

 ^  ^  

װ

< 1

g _mb /g _m

gd sig

R  R

'

1 '

sig L

gs

m L

R R

R g R

 



C

L o

R  R  ^װ R

 

1 1 2

2

H gd sig gs gs L C

H

f  C R C R C R

    

저항 감소 효과

R_o가 작은 값이므로 저항이 작음 (g_mV_x-I_x)R_L’ + V_x = I_xR_sig

V

x

g

V

Copyright  2004 by Oxford University Press, Inc.

Microelectronic Circuits - Fifth Edition Sedra/Smith 5

CD-CS Configuration

- CS 대비 다소 작은 전압 이득

- CS 대비 우수한 주파수 특성

CS Amplifier w/ source degeneration

Copyright  2004 by Oxford University Press, Inc.

Microelectronic Circuits - Fifth Edition Sedra/Smith 7

CS Amplifier w/ source degeneration

 

out o 1 m mb o s

R   r    g  g r   R

 

out o 1 m mb s

R  r    g  g R  

 Output resistance

R_S ~ 0 인 경우 대비 증가 !

CS Amplifier w/ source degeneration

 Open circuit voltage gain & short circuit transconductance

m gs

i  g 

o ir o g r m o gs g r m o i

        

o m o 0

A _   g r   A

 

1

o m o

m

out o m mb s

A g r

G R r g g R

  

   

 

 

1

m m

m mb s

G g

g g R

  

Same w/ the CS Amp. w/ R_S = 0

R_S ~ 0 인 경우 대비 감소 !

Copyright  2004 by Oxford University Press, Inc.

Microelectronic Circuits - Fifth Edition Sedra/Smith 9

CS Amplifier w/ source degeneration

 Voltage gain w/ load resistance

L o

L out

A A R

R R

   



CS Amplifier w/ source degeneration

 Frequency Response

Copyright  2004 by Oxford University Press, Inc.

Microelectronic Circuits - Fifth Edition Sedra/Smith 11

 ^{1 '}  ^'

gd sig m L L

R  R  G R  R

'

L L out

R  R  R

'

C

L out L

R  R  R  R

 

1

sig s

gs

o

m mb s

o L

R R

R r

g g R

r R

 

 

      

װ

װ

CS Amplifier w/ source degeneration

1 2

H

gd gd

f ^  C R

H C R gs gs C R gd gd C R L C

   

H C R gd gd

 

'

gd m L sig M sig

R  G R R  A R

1 2

H

gd sig M

f ^  C R A

Gain-bandwidth product, ^{f  A f  1}

CS Amplifier w/ source degeneration

R_sig 이 큰 경우,

R_S 의 크기에 의한 이득과 bandwidth의 trade-off 가능 R_S의 함수

단, 곱은 일정

Differential and Multistage Amplifier

Microelectronic Circuits - Fifth Edition Sedra/Smith Copyright 2004 by Oxford University Press, Inc Fundamentals of Microelectronics Behzad Razavi Copyright 2009 by John Wiley & Sons, Inc

ꞏ2