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Influence of Body Effect on small signal gain

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mvj

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Dear All,

If we do the small signal analysis of
1. CS stage with source degeneration ( ie. additional resistor at the source terminal)
2. Source follower
3. Common gate stage

all the three have their source voltages varying as the input voltage varies, hence all of them would have influence of body effect. However, in the case of the first two cofigurations the small signal gain is decreased due to body effect and in the last case gain is increased.

May I know why this difference occurs when influence of body effect in all the circuits is the same i.e. to decrease the drain current.

Thanks a lot in advance!!
M.
 

Dear All,

If we do the small signal analysis of
1. CS stage with source degeneration ( ie. additional resistor at the source terminal)
2. Source follower
3. Common gate stage

all the three have their source voltages varying as the input voltage varies, hence all of them would have influence of body effect. However, in the case of the first two cofigurations the small signal gain is decreased due to body effect and in the last case gain is increased.

May I know why this difference occurs when influence of body effect in all the circuits is the same i.e. to decrease the drain current.

Thanks a lot in advance!!
M.
As the signal at the input and output are out of phase for CS, gmb1 is in the oppoiste direction to that of gm1, in contrast to CG.
 
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