Current mirror - Transconductance parameters

Thread Starter


Joined Nov 17, 2007
Hi, Need help on finding the the design equations for transconductance parameters, gm of both Ma and Mb.
What are the assumptions to be made?
And also what is the purpose of that circuit in the middle? If let's say i replace that portion with a simple line, the whole circuit would look like a simple current mirror.

Also the input resistance is 1/gm (gm of M1) right? If of course i assume that it is just simple current mirror.

I got two equations though not sure about them
Gm of Mb = Ib/(Vg(Ma) - Vs(Mb))
Gm of Ma = (Vdd - Vg(Ma))/RVs(Mb)

Please advise. Thanks!