CMFB in two stage folded cascode differential opamp

two stage cmfb

I am going to design a CMFB in two stage folded cascode differential opamp.

according to the , somebody said "we need to have two cmfb circuit in two stage."
is it correct that two cmfb circuit is needed in two stage folded cascode differential opamp?


this opamp is going to use in a S/H circuit of pipeline adc .
which type of cmfb is suitable for me ???
will somebody give me some reference (or paper) of CMFB?

two stage two separate cmfb

hi sj_helen,

in a two-stage amplifier, one method is to use two cmfb, and the other method is to use one cmfb with an inversion stage.

Re: CMFB in two stage

sj_helen said:

I am going to design a CMFB in two stage folded cascode differential opamp.

according to the , somebody said "we need to have two cmfb circuit in two stage."
is it correct that two cmfb circuit is needed in two stage folded cascode differential opamp?

Click to expand...

I think you can use one CMFB, but you must take care for the stability of the cmfb.
And I think using two CMFB is better because of less risk of stability.

Re: CMFB in two stage

didibabawu said:

sj_helen said:

I am going to design a CMFB in two stage folded cascode differential opamp.

according to the , somebody said "we need to have two cmfb circuit in two stage."
is it correct that two cmfb circuit is needed in two stage folded cascode differential opamp?

Click to expand...

I think you can use one CMFB, but you must take care for the stability of the cmfb.
And I think using two CMFB is better because of less risk of stability.

Click to expand...

this opamp is going to use in a S/H circuit of pipeline adc .
which type of cmfb is suitable for me ???
will somebody give me some reference (or paper) of CMFB?

CMFB in two stage

Most S/H circuit uses switch capacitor type of CMFB for its power saving and somewhat easier to implenment compared to continuous CMFB.

A.Abo's paper and thesis has mentioned about this (an excellent thesis for pipeline ADC). Paul Grey's book (4th. edition) has a chapater on this too.

Hope this helps!

Re: CMFB in two stage

Check chapter 8 "fully differential amplifiers" in "Analog Design Essentials" by Willy Sansen.
It is a very practical oriented book, and I recommend it highly.