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_{D}S) / I_{D} ≈ V_{E}L / I_{D}_{ },
By using the approximation for the channel length modulation parameter λ:
λ = 1/V_{E}L
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 }.