[Help] Two stage fully differential opamp

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I want design a two stages fully diff-opamp. But in many textbooks，each stage needs a cmfb circuit for balancing.

maybe there are some two stage fully diff-opamp just using only one cmfb~!!

who has any information about it ?

thanks in advance~!!
 

you can check it out in allen's book...
 

batistuta said:
you can check it out in allen's book...
Click to expand...

In Allen's book ,for example,(fig7.3-12) the first stage doesn't utilize cmfb, but
I don't know whether it can work well


Anything wrong?
 


Yes, u can use a single CMFB for the two stage fully diff-opamp by sensing the common mode of the second stage and controlling the tail current source of the first stage
 

generally, the second stage doesnot need cmfb, or the outputs of the second are used the inputs of cmfb
 

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