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6.1. FIELD-EFFECT TRANSISTORS (FET), Chaf, Field Effect Transistors, The field effect transistor (FET) is a three terminal semiconductor device in, chich current is controlled by an applied electric field. It is also called a unipolar, ensistor because in it the current is carried by one type of carriers, specially the, majority carriers., There are two main categories of field effect transistors :, (i) Junction field effect transistor (JFET), (ii) Insulated gate field effect transistor (IGFET), It is also called metal-oxide semiconductor field effect transistor, (MOSFET). In brief, it is also written as MOST. It has a much greater commercial, importance than a JFET., A MOSFET is further subdivided into two types :, (i) Depletion MOSFET, (ii) Enhancement MOSFET, 6.2. ADVANTAGES OF FET OVER TRANSISTOR, The important characteristics in which the field effect transistor differs from, the bipolar junction transistor are :, 1. The FET is 'a unipolar device depending upon the flow of majority carriers, only (either electron in the N-type or holes in the P-type). The conventional, transistor (BJT) is a bipolar device relying upon both types of charge carriers, the, electrons and the holes i.e., the majority and minority carriers., 2. The FET exhibits a high input resistance, typically in the order of 100, mega ohm for a JFET and 1040 to 101º ohms for the MOSFET. Thus, the FET is a, voltage controlled device, like a vacuum tube, and not current-controlled, like BJT., 3. The FET exhibits a high degree of isolation between input and output., 4. The EFT is simpler to fabricate and occupies less space in integrated form., 5. The FET is less noisy than a BJT., 6. FET has a better thermal stability., The main disadvantage of the FET is its relatively low gain-bandwidth, product in comparison with what can be obtained with a conventional, (193), Scanned with CamScanner