ugb of single ended differential amplifier used as CMFB of main opamp

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pankaj jha

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hello everyone...
is it necessary to have the UGB of single ended differential amplifier used as CMFB of main opamp to be equal to the UGB of the main opamp ????
Is there any specific crieteria???
 

The common mode gain of an amp stage across frequencies depends on the ugb of the cmfb loop of that stage. In two stage amps, the differential loop forms a positive feed back for common mode signals. Hence it is essential to ensure that the common mode gain of your open loop amp is less than one across frequencies, which means that the cmfb should have enough bandwidth. It is not necessary that the ugbs should be same.
 

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