JFET Models (NJF/PJF)

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JFET Models (NJF/PJF)

The JFET model is derived from the FET model of Shichman and Hodges. 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.

Note that in Spice3f and later, a fitting parameter B has been added. For details, see [9].

name

parameter

units

default

example

area

VTO

threshold voltage (VT0)

V

-2.0

-2.0

 

BETA

transconductance parameter (Beta)

A/V2

1.0e-4

1.0e-3

*

LAMBDA

channel-length modulation parameter ( )

1/V

0

1.0e-4

 

RD

drain ohmic resistance

Ohm

0

100

*

RS

source ohmic resistance

Ohm

0

100

*

CGS

zero-bias G-S junction capacitance (Cgs)

F

0

5pF

*

CGD

zero-bias G-D junction capacitance (Cgs)

F

0

1pF

*

PB

gate junction potential

V

1

0.6

 

IS

gate junction saturation current (IS)

A

1.0e-14

1.0E-14

*

B

doping tail parameter

-

1

 

 

KF

flicker noise coefficient

-

0

 

 

AF

flicker noise exponent

-

1

 

 

FC

coefficient for forward-bias

-

0.5

 

 

TNOM

parameter measurement temperature

ºC

 

50