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JFETs (Junction FETs)

 National Instruments Corporation 4-17 Multisim Component Reference Guide

4.9 JFETs (Junction FETs)

The JFET is a unipolar, voltage-controlled transistor that uses an induced electrical field to

control current. The current through the transistor is controlled by the gate voltage. The more

negative the voltage, the smaller the current.

A JFET consists of a length of an n-type or p-type doped semiconductor material called a

channel. The ends of the channel are called the source and the drain. The terminal with the

arrowhead represents the gate.

In an n-channel JFET, the gate consists of p-type material surrounding the n-channel. In a p-

channel JFET, the gate consists of n-type material surrounding the p-channel.

4.9.1 DC Model

The DC model characteristic is determined by a nonlinear current source, I

Forward characteristics (

≥ 0):

Reverse characteristics (

< 0):

where:

= gate-source voltage, in volts

= drain-source voltage, in volts

= gate-drain voltage, in volts

210

for

()

()() ()

([( ) ]( ) ( )

IVV V VVV

VVVV V V VV

GS TO

D GSTO DS GSTO DS

DS GS TO DS DS DS GS TO

−≤

=− − + < − ≤

−− + <≤−

βλ

210

for

()