Fully differential complementary output amplifier without CMFB

[Junus2012]

Hello

I have a basic question regarding complementary fully differential output like the one I have attached to this email, it is basically a modified version of the folded amplifier referred as recycled folded OTA, indeed my question is about the fully-differential scheme used in this circuit, as you can see , the circuit has two complementary output stage, in each, there is a mirror just like of the single-ended OTA, so I am not understanding if this circuit needs a common mode feedback circuit (CMFB) or not and why even need it.

I found the circuit from this link:

https://www.researchgate.net/publication/329573274_Design_and_simulation_of_high_precision_second-order_sigma-delta_modulator_for_bluetooth_applications

Also, I have made little research to see the original of this topology, and I found this US patent

US5146179A - Fully differential operational amplifier having frequency dependent impedance division - Google Patents

A fully differential operational amplifier includes first and second frequency dependent impedance dividers, preferably frequency dependent current dividers, each of which has an input, a noninverting output and an inverting output. A respective input is coupled to a differential input signal...

patents.google.com

I do appreciate your kind help

Thank you very much in advance

Best Regards

 

[jjx]

( Might be stating the obvious here, but the M14 source should connect to C1 rather than C2. Just a typo in the figure. )

My guess would be that - regardless - a CMFB would be nice to fix the levels at a desired point. Cannot see that it would automagically stabilize at vdd/2 assuming pure capacitive feedback. And with that said, is vdd/2 what you want for next stage, etc.