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CMFB in two stage differential CMOS amp.

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yanivh

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cmos cmfb

I was wondering why analog design books dont
present common mode feedback circuits for single ended two-stages op-amp.
Can someone propose a CMFB circuit for design of single ended differential CMOS op-amp?
Thanks.
 

only the fully differential opamp need the cmfb
 

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    yanivh

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xusoso said:
only the fully differential opamp need the cmfb
Click to expand...

I saw as well that the CMFB is necessary only for fully differential opamps. Can you, pls, elaborate on that?
 

yes, CMFB is only for full differental op, that is to say your structure do not need CMFB circuits.
 

I know that cmfb is only for full-diff OPA, but can u give some tips for cmfb?
 

Re: cmos cmfb

yanivh said:
I was wondering why analog design books dont
present common mode feedback circuits for single ended two-stages op-amp.
Can someone propose a CMFB circuit for design of single ended differential CMOS op-amp?
Thanks.
Click to expand...
opamp is always used in negtive feedback, so the output of single-ended will be settled in Vcm.

feifang
 

In fully differential amplifiers, what you see is a current source feeding the current sink.
It is impossible to have both currents exactly the same, and whoever "wins" will likely push the other one out of saturation.
The CMFB essentially makes one of the them adaptive to the output voltage, such that both operate in saturation.

A single-ended amplifier only has one current source (or sink) calling the shots. The other just mirrors the current, so no contention there.

- - - Updated - - -

Just realized this thread is 4 years old.
Bummers.
 
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