Symbol Names: NJF, PJF
Syntax: Jxxx D G S <model> [area] [off] [IC=Vds, Vgs]
[temp=T]
Examples:
J1 0 in out MyJFETmodel
.model MyJFETmodel NJF(Lambda=.001)
J2 0 in out MyPJFETmodel
.model MyPJFETmodel PJF(Lambda=.001)
A JFET transistor requires a .model card to specify its characteristics. Note that the model card keywords NJF and PJF specify the polarity of the transistor. The area factor determines the number of equivalent parallel devices of a specified model.
The JFET model is derived from the FET model of Shichman and Hodges extended to include Gate junction recombination current and impact ionization. The DC characteristics are defined by the parameters VTO and BETA, which determine the variation of drain current with gate voltage; LAMBDA, which determines the output conductance; and Is, the saturation current of the two gate junctions. Two ohmic resistances, Rd and Rs, are included. Charge storage is modeled by nonlinear depletion layer capacitances for both gate junctions; which vary as the 1/2 power of junction voltage and are defined by the parameters Cgs, Cgd, and PB. A fitting parameter B has been added. See A. E. Parker and D. J. Skellern, An Improved FET Model for Computer Simulators, IEEE Trans CAD, vol. 9, no. 5, pp. 551553, May 1990.
Name 
Description 
Units 
Default 
Example 
Vto 
Threshold voltage 
V 
2.0 
2.0 
Beta 
Transconductance parameter 
A/V/V 
1e4 
1e3 
Lambda 
Channellength modulation parameter 
1/V 
0 
1e4 
Rd 
Drain ohmic resistance 
W 
0. 
100 
Rs 
Source ohmic resistance 
W 
0. 
100 
Cgs 
Zerobias GS junction capacitance 
F 
0. 
5p 
Cgd 
Zerobias GD junction capacitance 
F 
0. 
1p 
Pb 
Gate junction potential 
V 
1. 
0.6 
Is 
Gate junction saturation current 
A 
1e14 
1e14 
B 
Doping tail parameter 
 
1 
1.1 
KF 
Flicker noise coefficient 
 
0 

AF 
Flicker noise exponent 
 
1 

Fc 
Coefficient for forwarddepletion capacitance 
 
.5 

Tnom 
Parameter measurement temperature 
ºC 
27 
50 
BetaTce 
Transconductance parameter exponential temperature coefficient 
%/ºC 
0 

VtoTc 
Threshold voltage temperature coefficient 
V/ºC 
0 

N 
Gate junction emission coefficient 
 
1. 

Isr 
Gate junction recombination current parameter 
A 
0. 

Nr 
Emission coefficient for Isr 
 
2 

alpha 
Ionization coefficient 
1/V 
0 

Vk 
Ionization knee voltage 
V 
0 

Xti 
Saturation current temperature coefficient 
 
3 
