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 ID by:
Figure: Simplified, low-frequency hybrid-piMOSFET model.
gm = 2ID /VGS = Vth ,
In which:
ID stands for the quiescent drain current (also called the drain bias or DC drain current)
Vth stands for the threshold voltage and
VGS stands for gate-to-source voltage.
The combination:
VoU = (VGS - Vth)
Often is called the overdrive voltage.
is the output resistance because of channel length modulation, calculated by using the Shichman-Hodges model as
ro = (1/ λ + VDS) / ID ≈ VEL / ID ,
By using the approximation for the channel length modulation parameter λ:
λ = 1/VEL
Where VE 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
gds = 1/ro .