SPICE modeling of a JFET from Datasheet

In this article we’ ll see how to find the parameters used to describe the mathematical behaviour of JFET (Junction Field Effect Transistors).The syntax for the N-channel model is:

model ModelName NJF( par1=a par2=b………parn=x)

while for the P-channel model is:

model ModelName PJF( par1=a par2=b………parn=x)

Where par1 par2… parn are the parameters that allow us to model the equations of the JFET transistor.

The main parameters for modeling the JFET are listed below in this table:


ParametersDescriptionUnitsDefault Value
AFFlicker noise exponentno unit dimension1.0
ALPHAIonization coefficient1/V1e-006
BETATransconductance coefficientA/V^20.0001
BETATCEBETA exponential temperature coefficient%/°C-0.5
CGDZero-bias gate-drain p-n capacitanceF1e-012
CGSZero-bias gate-source p-n capacitanceF1e-012
FCForward-bias depletion capacitance coefficientno unit dimension0.5
ISGate p-n saturation currentA1e-014
ISRGate p-n recombination current parameterA0
KFFlicker noise coefficientno unit dimension1e-018
LAMBDAChannel-length modulation1/V1e-006
MGate p-n grading coefficientno unit dimension0.5
NGate p-n emission coefficientno unit dimension1.0
NREmission coefficient for ISRno unit dimension2.0
PBGate p-n potentialV1.0
RDDrain ohmic resistanceOhm1.0
RSSource ohmic resistanceOhm1.0
VKIonization knee voltageV1.0
VTOThresold voltageV-2.0
VTOTCVTO temperature coefficientV/°C-0.0025
XTIIS temperature coefficientno unit dimension3.0