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

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

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 -


next up previous contents index
Next: MOSFETs Up: Semiconductor Devices Previous: MESFETs   Contents   Index
Stephen R. Whiteley 2017-03-28