Junction field-effect transistors

Junction Field-Effect Transistors (JFETs)

General form

JXXXXXXX ND NG NS MNAME <AREA> <OFF> <IC=VDS, VGS> <TEMP=T>

Examples

J1 7 2 3 JM1 OFF

ND, NG, and NS are the drain, gate, and source nodes, respectively. MNAME is the model name, AREA is the area factor, and OFF indicates an (optional) initial condition on the device for dc analysis. If the area factor is omitted, a value of 1.0 is assumed. The (optional) initial condition specification, using IC=VDS, VGS is intended for use with the UIC option on the .TRAN control line, when a transient analysis is desired starting from other than the quiescent operating point. See the .IC control line for a better way to set initial conditions. The (optional) TEMP value is the temperature at which this device is to operate, and overrides the temperature specification on the .OPTION control line.

Parameters: JFET level 1 (Shichman-Hodges), JFET level 2 (Parker-Skellern)

JFET Models (NJF/PJF)

Spice3f5 provides two JFET device models. The variable LEVEL on the .MODEL line specifies the model to be used:

LEVEL	model	parameters
1	Shichman-Hodges, with the doping tail parameter B of [9]	JFET level 1
2	Parker-Skellern, for JFETs and GaAs MESFETs	JFET level 2

If LEVEL is not given, level 1 is used. Any other level gives the error Only JFET device levels 1-2 are supported in this binary.

Level 1

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
LEVEL	model index	-	1
VTO	threshold voltage (V_TO)	V	-2.0	-2.0
BETA	transconductance parameter (B)	A/V²	1.0e-4	1.0e-3	*
LAMBDA	channel-length modulation parameter (λ)	1/V	0	1.0e-4
RD	drain ohmic resistance	Ω	0	100	*
RS	source ohmic resistance	Ω	0	100	*
CGS	zero-bias G-S junction capacitance (C_gs)	F	0	5pF	*
CGD	zero-bias G-D junction capacitance (C_gd)	F	0	1pF	*
PB	gate junction potential	V	1	0.6
IS	gate junction saturation current (I_S)	A	1.0e-14	1.0e-14	*
B	doping tail parameter	-	1	1.1
KF	flicker noise coefficient	-	0
AF	flicker noise exponent	-	1
FC	coefficient for forward-bias depletion capacitance formula	-	0.5
TNOM	parameter measurement temperature	C	27	50

Level 2 (Parker-Skellern)

The level 2 model is the Parker-Skellern (PS) model of JFETs and GaAs MESFETs, by A. E. Parker and D. J. Skellern of Macquarie University, described in A Realistic Large-Signal MESFET Model for SPICE, IEEE Trans. Microwave Theory Tech., vol. 45, no. 9, pp. 1563-1571, Sept. 1997. It keeps the level 1 parameters VTO, BETA, LAMBDA, RD, RS, CGS, CGD, PB, IS, FC, KF, AF and TNOM, with the same meanings and defaults, but not B. It adds power laws for the triode and saturated regions (P and Q), velocity saturation (XI and Z), subthreshold conduction (VST and MVST), drain feedback that depends on frequency (LFGAM, HFGAM, TAUG), a reduction of current with dissipated power (DELTA, TAUD), gate junction breakdown (IBD and VBD), a gate capacitance that reduces at pinch-off (XC), and a drain-source capacitance (CDS). VT0 may be written for VTO and VBI for PB.

.model mesfet njf level=2 vto=-2 beta=1e-3 lambda=0.01 p=2 q=2
J1 d g s mesfet

The level 2 model has no pole-zero or distortion analysis code, so a level 2 JFET takes no part in .PZ or .DISTO. Its full parameter list is under JFET level 2.

Parameters: JFET level 1 (Shichman-Hodges), JFET level 2 (Parker-Skellern)