Pulse and Digital Circuits

1.11 FIELD-EFFECT TRANSISTORS

A junction field-effect transistor (JFET), also called a field-effect transistor (FET), is a voltage-controlled three-terminal device in which the current flow is essentially due to the majority carriers—either holes or electrons. Hence, this device is a unipolar device whereas a transistor is a bipolar device where the current is due to both the majority and minority carriers. The major advantage of an FET over a BJT is that it has a large input resistance. JFETs are again of two types, an n-channel FET and a p-channel FET, schematically represented in Figs. 1.53(a) and (b), respectively.

In an n-channel FET, the gate is made negative with respect to the source whereas in a p-channel FET the gate is positive with ...