biasing circuit question from berkeley ee240

[jszair]

Hi all,

I'm simulating intrinsic gain of a mos fet using ckt suggested in berkeley ee240 course. (ckt in the attachment)

But I don't understand why using opamp here (vcvs in spice) could set the bias voltage correct..Similar bias ckt is used in another cs amplifier example (also attached).

Please help~

 

[icfans]

Use an opamp can make the vds of M1 equal to the voltage of V0.

Notice the circuit use negative feedback, so the opamp will help to set the quiesent point.

 

[amwygah]

I agree with you.