Current mirror - Transconductance parameters

Discussion in 'Homework Help' started by soon86, Nov 17, 2007.

  1. soon86

    Thread Starter New Member

    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!