The first stage is a common gate , the second is common drain. The AC current converted to a voltage at the source of M2 and amplified by CG stage. CD stage performs many function (like lowering output impedance, current amplification, level shifting, whatever)  except voltage amplification. If ro_M1 >> Rd, the input impedance without feedback 1/gm1. Applying feedback, the impedance decreases even more by amount of Loop Gain. This is desirable since, the input source is current.

hello all,
i agree with  that feedback stuff, basically it is not -ve feedback, did you observed that?

Thanks,
Raj.

hello praveen,
Here Vb indicates bias, they are not equal. Imagine entire circuit is an open loop amp and rf is feedback resister, look at the impedance without Rf, it will be 1/gm. With feedback it will lower just because resister draws some current which is not the case in without res.

Thanks,
Raj.

RCG means?

Thanks,
raj.

Lex wrote on Feb 19^th, 2013, 2:19am:


yeah, you need an inversion somewhere. Perhaps M3 was supposed to be a PMOS.

RobG wrote on Feb 23^rd, 2013, 1:25pm:


I think it's quite difficult to say if this is a good or bad circuit without knowledge about the application where it is used. And the function it implements. Probably, it can be stable if loop gain < 1. Ya, of course this circuit can be only a textbook example =)

RobG wrote on Feb 23^rd, 2013, 3:51pm:


I agree =)