#### andover

##### Newbie level 4

When I was reading razavi's book about feedback, I got a question about the attached circuit. (chapter 8 Fig8.3, 8.6).

From KCL, It's straight forward to get Vout/Vin=-C1/C2, and it's not hard to get Y/X=A/(1+BA)=1/B * (1-1/BA) as a general equation for feedback. However, when he applies loop break method (break at right side of C2)to calculate the open loop gain, he gets BA=C2/(C1+C2)gm1r01, where B feedback factor equals to C2/(C1+C2). My question is, when you apply this B back to Y/X, you will get (1+C1/C2) instead of (-C1/C2).

I am just wondering did I miss something in the deduction? I really appreciate if you can help to explain this.

Thanks