Microwave and Wireless Communications Technology

Field-Effect Transistors 239

12-5 FIELD-EFFECT TRANSISTORS

The field-effect transistor (FET) operates by varying the conductivity of a semi-

conductor channel by varying the electric field in the channel. Two elementary

types are found:

junction field-effect transistors

(JFET) and

metal oxide semiconductor

field-effect transistors

(MOSFET), also sometimes called

insulated gate field-effect tran-

sistors

(IGFET). In the microwave world, a number of devices are modifications of

these basic types.

Figure 12-6A shows the structure of a generic JFET device that works on the de-

pletion principle. The channel in this case is