FET Parameters

A basic, low-frequency hybrid-pi model for the MOSFET is displayed in figure. The several parameters are as follows.

is the transconductance in siemens that evaluated in the Shichman-Hodges model in terms of the Q-point drain current I_D by:

                                                     Figure: Simplified, low-frequency hybrid-piMOSFET model.

g_m = 2I_D /V_GS = V_th ,

In which:

I_D stands for the quiescent drain current (also called the drain bias or DC drain current)

V_th stands for the threshold voltage and

V_GS stands for gate-to-source voltage.

The combination:

V_oU = (V_GS - V_th)

Often is called the overdrive voltage.

is the output resistance because of channel length modulation, calculated by using the Shichman-Hodges model as

r_o = (1/ λ + V_DS) / I_D ≈ V_EL / I_D ,

By using the approximation for the channel length modulation parameter λ:

λ = 1/V_EL

Where V_E is a technology-related parameter (about 4 V/μm for the 65 nm technology node) and L is the length of the source-to-drain separation.

The reciprocal of the output (o/p) resistance is named the drain conductance

g_ds = 1/r_o .