MESFET Models (both N and P Channel)

Type Names: nmf, pmf

The MESFET model is derived from the GaAs FET model of Statz et al. as described in[10]. The dc characteristics are defined by the parameters vto, b, and beta, which determine the variation of drain current with gate voltage, alpha, which determines saturation voltage, and lambda, which determines the output conductance. The formula are given by

Id = $${\frac{{\beta(V_{gs}-V_T)^2}}{{1+b(V_{gs}-V_T)}}}$$$$\left(\vphantom{1-\left(1-\alpha \frac{V_{ds}}{3}\right)^3}\right.$$1 - $$\left(\vphantom{1-\alpha \frac{V_{ds}}{3}}\right.$$1 - $$\alpha$$$${\frac{{V_{ds}}}{{3}}}$$$$\left.\vphantom{1-\alpha \frac{V_{ds}}{3}}\right)^{3}_{}$$$$\left.\vphantom{1-\left(1-\alpha \frac{V_{ds}}{3}\right)^3}\right)$$(1 + $$\lambda$$V_ds)    for    0 < V_ds < 3/$$\alpha$$

Id = $${\frac{{\beta(V_{gs}-V_T)^2}}{{1+b(V_{gs}-V_T)}}}$$(1 + $$\lambda$$V_ds)    for    V_ds > 3/$$\alpha$$

Two ohmic resistances, rd and rs, are included. Charge storage is modeled by total gate charge as a function of gate-drain and gate-source voltages and is defined by the parameters cgs, cgd, and pb.

The parameters marked with an asterisk in the area column scale with the area parameter given in the device line.

MES Model Parameters
name	area	parameter	units	default	example
vto		pinch-off voltage	V	-2.0	-2.0
beta	*	transconductance parameter	A/V2	1.0e-4	1.0e-3
b	*	doping tail extending parameter	1/V	0.3	0.3
alpha	*	saturation voltage parameter	1/V	2	2
lambda		channel length modulation parameter	1/V	0	1.0e-4
rd	*	drain ohmic resistance	$\Omega$	0	100
rs	*	source ohmic resistance	$\Omega$	0	100
cgs	*	zero-bias G-S junction capacitance	F	0	5pf
cgd	*	zero-bias G-D junction capacitance	F	0	1pf
pb		gate junction potential	V	1	0.6
kf		flicker noise coefficient	-	0	-
af		flicker noise exponent	-	1	-
fc		coefficient for forward-bias depletion capacitance formula	-	0.5	-