gm and ro in a NewFET

Discussion in 'General Electronics Chat' started by kbcheong, Apr 7, 2012.

  1. kbcheong

    Thread Starter New Member

    Mar 24, 2012
    5
    0
    How to derive gm and ro in a small signal models in term of large model parameters K, VT and bias voltages VGS and VDS, given that in a bias region iD = K(VGS-VT)(VDS^2)

    [​IMG]
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,006
    3,232
    Sounds like homework. If so it should be in that section.
     
  3. Vahe

    Member

    Mar 3, 2011
    75
    9
    Take the partial derivative of the drain current with respect to the drain-source voltage and invert it to find the output resistance.
     r_o = \left( \frac{\partial i_d}{\partial v_{ds} \right) ^{-1}

    Take the partial derivative of the drain current with respect to the gate-source voltage to find the transconductance.
     g_m = \frac{\partial i_d}{\partial v_{gs}

    All partial derivatives should be evaluated at the operating point -- that is, you should plug in the dc voltage/current values to evaluate the output resistance and the transconductance.
     
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