MESFETs

General form

ZXXXXXXX ND NG NS MNAME <AREA> <OFF> <IC=VDS, VGS>

Examples

Z1 7 2 3 ZM1 OFF

ND, NG, and NS are the drain, gate, and source nodes, respectively. MNAME is the model name, AREA is the area factor, and OFF indicates an (optional) initial condition on the device for dc analysis. If the area factor is omitted, a value of 1.0 is assumed. The (optional) initial condition specification, using IC=VDS, VGS is intended for use with the UIC option on the .TRAN control line, when a transient analysis is desired starting from other than the quiescent operating point. See the .IC control line for a better way to set initial conditions.

Parameters: GaAs MESFET

MESFET Models (NMF/PMF)

The MESFET model is derived from the GaAs FET model of Statz et al. as described in [11]. 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 formulas are:

\begin{array}{l} I_{d} = \frac{β {(V_{gs} - V_{T})}^{2}}{1 + b (V_{gs} - V_{T})} [1 - {(1 - α \frac{V_{ds}}{3})}^{3}] (1 + λ V_{ds}) & for 0 < V_{ds} < \frac{3}{α} \\ I_{d} = \frac{β {(V_{gs} - V_{T})}^{2}}{1 + b (V_{gs} - V_{T})} (1 + λ V_{ds}) & for V_{ds} \geq \frac{3}{α} \end{array}

where β is BETA, b is B, α is ALPHA and λ is LAMBDA.

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.

name	parameter	units	default	example	area
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	Ω	0	100	*
RS	source ohmic resistance	Ω	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

Parameters: GaAs MESFET