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.

.MODEL <model name> NJF [model parameters]
.MODEL <model name> PJF [model parameters]


Parameter Description Default Units Area
VTO Threshold voltage (VTO) -2.0 V  
BETA Transconductance parameter (B) 10-4 A/V2 *
LAMBDA Channel-length modulation parameter (λ) 0.0 1/V  
RD Drain ohmic resistance 0 Ω *
RS Source ohmic resistance 0 Ω *
CGS Zero-bias G-S junction capacitance (Cgs) 0 F *
CGD Zero-bias G-D junction capacitance (Cgd) 0 F *
PB Gate junction potentiale 1 V  
IS Gate junction saturation current (IS) 10-14 A *
B Doping tail parameter 1    
KF Flicker noise coefficient 0    
AF Flicker noise exponent 1    
FC Coefficient for forward-bias depletion capacitance formula 0.5    
TNOM Temperature at which the model parameters were measured. If this value is specified overrides the nominal TNOM value which is set in the options.   °C  
TABS Specifies the temperature at which the component operates. This value, if specified, takes precedence over the analysis temperature.    °C  
TREL Device temperature relative to current temperature. If this parameter is specified but not the parameter TABS then the current temperature of the component is equal to the current temperature plus TREL.    °C  


.MODEL JMOD PJF ( VTO=-3 RD=20 RS=20  )

See also