1. The problem statement, all variables and given/known data Calculate the impedance Zin 2. Relevant equations 3. The attempt at a solution I cut VDD and the DC current source at the top. Put in test DC voltage VTest - 10* ITest = VGS (because voltage "after" the resistor = the voltage at the gate and the drain, and source is to ground. times gm to find current trough NMOS: gm [VTest - 10* ITest ]= gm VGS This equals VTest / 10 (current through resistor would be the same as current through NMOS rearranging VTest / I Test = 10*gm / (gm - 1/10) = Zin Zin = 101.01 k Ohm ? This is probably wrong.