# Effective resistance of a NMOS

How do we calculate effective resistance of a NMOS, operating in linear region across drain and source?

• I recall the formula Re = 1/GM with GM = K * W/L * Ve, where K = MU*Cox, and Ve = Vgs - Vt; this was long channel physics mode; – analogsystemsrf Jul 3 '19 at 1:34

$$\1/R_{ds}=g_m=\Delta I_{ds}/ \Delta V_{ds}\$$ @ Vgs