The JFET characteristic curves can be described by an equation of the form

where the function varies with the particular transistor. This expression yields the AC relationship

where the AC currents and voltages are complex but the partial derivatives evaluate to real numbers. In the pinch-off region the curves of constant are essential flat ( ) and allow the equation to be written as

where is the transconductance.

Tue Jul 13 16:55:15 EDT 1999