Hi, This is not a homework question. I need to calculate input impedance for a LNA and this is part of it. How do you calculate input impedance, Zin, for the circuit below? I tried by applying an input voltage, V1, and calculate Iin. Input impedance will be V1/Iin. However, the expression still contains V1 and I can't figure out how to make it independent on V1. There is another method that I am not sure. Input impedance will be equal to the impedance as all independent sources are turned off. This means that Zin in the picture will be equal to s(Lg + Ls) + 1/(gg + sCgs) gg is a conductance.