Help me with doing a CMFB for an OTA

[safwatonline]

CMFB

hello,
i want to do a CMFB for a simple OTA , do i have to use two resistance to sense the CMFB from the OTA , or is there another methode for CM sensing , also in CMFB do i have to compare to a certain refrence or is there another way?
thnx and regards
a.safwat

 

[avlsi]

Re: CMFB

Please refer Paul Gray for reference(chapter 16),he suggests to use two other techniques.

If u really want something state-of-art,use switched capacitor circuit to sense the output common mode volatage and set it to desired value.But I think,this is tedious.

You have also a reference circuit in Jonhs and martin.you can find a CMFB circuit in Advanced current mirrors and opamps chapter(pg no. around 256).

 

[eng_Semi]

Re: CMFB

U can use two capacitors rather than the two resistors, u can check Razavi reference for this technique.