# GaAsFET

In this topic:

## Netlist Entry

Zxxxx drain gate source modelname [area] [OFF] [IC=vds, vgs]
 drain Drain node gate Gate node source Source node modelname Name of model defined in a .model statement. Must begin with a letter but can contain any character except whitespace and period '.' . area Area multiplying factor. Area scales up the device. E.g. an area of 3 would make the device behave like 3 transistors in parallel. Default is one. OFF Instructs simulator to calculate operating point analysis with device initially off. This is used in latching circuits such as thyristors and bistables to induce a particular state. See .OP for more details. vds,vgs Initial conditions for drain-source and gate-source junctions respectively. These only have an effect if the UIC parameter is specified on the .TRAN statement.

## GaAsFET Model Syntax

.model modelname NMF ( parameters )

## GaAsFET Model Parameters

The symbols '$\times$' and '$\div$' in the Area column means that parameter should be multiplied or divided by the area factor respectively.

 Name Description Units Default Area VTO Pinch-off Voltage V -2.0 BETA Transconductance parameter A/V$^2$ 2.5e-3 $\times$ B Doping tail extending parameter 1/V 0.3 ALPHA Saturation voltage parameter 1/V 2 LAMBDA Channel length modulation parameter 1/V 0 RD Drain ohmic resistance $\Omega$ 0 $\div$ RS Source ohmic resistance $\Omega$ 0 $\div$ CGS Zero bias gate source capacitance F 0 $\times$ CGD Zero bias gate drain capacitance F 0 $\times$ PB Gate junction potential V 1 IS Gate p-n saturation current A 1e-14 $\times$ FC Forward bias depletion capacitance coefficient 0.5 KF Flicker noise coefficient 0 AF Flicker noise exponent 1
 Notes The GaAsFET model is derived from the model developed by Statz. The DC characteristics are defined by 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. IS determines the gate-source and gate-drain dc characteristics. Two ohmic resistances are included. Charge storage is modelled by total gate charge as a function of gate-drain and gate-source voltages and is defined by the parameters CGS, CGD and PB.