SPICE Modeling

SPICE is the de facto standard for simulating circuit performance. Abundant libraries are available, but many of them were derived from data sheets. Data sheets seldom define the product, at best they offer minimum performance guarantees. Furthernore, the programs used to develop these faulty library models often employ default parameters that rightfully need to be-extracted.
The following table of SPICE parameters has been extracted from measurements-none have been derived from data sheets. Additionally, the parameters for each geometry have been verified by modeling, both as a sine-wave and pulse amplifier, with excellent precision.

The following table of parameters will input directly into a SPICE circuit file. Be aware that SPICE parameters for any semiconductor (JFETs included) are valid only for that manufacturer. Because of the variants in design, the product of one manufacturer seldom matches that of another. This is especially true for the critically-important parameters, RS and RD. InterFET makes no warranty, implied, expressed or otherwise, for the accuracy of these models. These models are offered only as a guide for use in circuit analysis. Once the SPICE  model is generated, the model outputs should be verified with actual measure values.  

JFET Output Graph

InterFET SPICE Models

SPICE modeling of JFETs can be tricky. Using typical values for parameters like Vto and Idss can sometimes be misleading. Use these models as a starting point and modify as needed. Once the model is generated you should verify the model outputs with actual measure values.

The InterFET SPICE models along with other JFET manufacturers models are summarized and sorted in the InterFET CTC-026 Standard.jft Models document below:

JFET LTspice Modeling

Links to JFET LTspice modeling recommendations and present JFET models in LTspice. LTspice is freeware computer software implementing a SPICE electronic circuit simulator, produced by semiconductor manufacturer Linear Technology, now part of Analog Devices. It is used in-house at Linear Technology for IC design, and the most widely distributed and used SPICE program in the industry.

The initial install of LTSpice comes with a limited set of JFET models stored in a filed called Standard.jft. This file is typically stored in location: C:\Users\YourUserName\Documents\LTspiceXVII\lib\cmp\standard.jft. InterFET recommends replacing this file with a more complete compilation of JFET models from a wide range of manufacturers. This compilation of JFET models is sorted by part numbers and lists the manufacturer in the part name with a “-” suffix. When the model manufacturer is unknown a “-GEN” is listed for Generic part. All of the models from the original LTSpice Standard.jft file are included in this newer file.

SPICE Modeling of a JFET from Datasheet

Not all JFET Models are going to be accurate and InterFET does not have JFET SPICE Models for all of their JFETS presently.  In that case you can Model a JFET based off of Datasheet information.