How to size the cap of a sc cmfb?

[didibabawu]

I have read something about the sc cmfb in the book--'analog integrated circuit design'. there are four cap in the circuit. two of them are bigger and two smaller.
It says that the value of the smaller might be between 1/4~1/10 of the biger. I don't know why.Can anyone tell me? Thank you.

 

[hanm]

I guess you have known about continous time RC cmfb. In fact the sc cmfb do the same thing. Just look the sc as a resistor, and another capacitor serve as a filter. The size of the caps is up to your clock and amp's output impedance and also the frequency your amp works.

hanm

 

[hr_rezaee]

Hi
I Think this paper can help you:
H. Recoules, R. Bouchakour, and P. Loumeau, “A comparative study of two SC-CMFB networks used in fully differential OTA,” in Proc. IEEE Int. Conf. Electronic Circuits Systems, vol. 2, Sept. 1998, pp. 291–294.

Regards

 

[ch1k0]

Read this, it's useful,


Ojas Choksi and L.Richard Carley, Analysis of Switched-Capacitor Common-Mode
Feedback Circuit, IEEE Transactions on Circuits and Systems II, 2003.