design of cmfb circuit...

hi i am desinging the CMFB circuit for folded cascode fully differential amplifier ...
i want to know the desining of CMFB circuit ..
is it necessary to have suffiecent gain and icmr of cmfb circuit..
if yes then what should be the gain of cmfb and icmr of that circuit ..
regards
manish

you can see paul gray " Analysis and Design of Analog Integrated Circuits ", where maybe have your answer.

Hi.
The most important thing in designing a CMFB circuit is its gain and speed. In some applications the speed is more important, but if it is not, usually after a short transient response your CMFB would work properly. However there are two main types of CMFB : Continuous-Time and Discrete-Time CMFBs. Chosing one of these depends on your application. In folded cascode structure, gain is not very important often, but don't forget! it really depends on your closed-form structure, for closed-loop part will act as a positive feedback for CM signal. So the CMFB loop should have a larger gain than this positive feedback loop in order to compensate it. There are lots of good and simple CMFB structures in electronic books. But I recommend Johns and Martin's book and Razavi's book about Analog IC design.
Good luck.

Regards,
EZT