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| The bipolar junction transistor (BJT) relies on two types of charge: free
electrons and holes. This is why it is called bipolar: the prefix bi stands
for "two." This chapter discusses another kind of transistor called the
field-effect transistor (FET). This type of device is unipolar because its
operation depends on only one type of charge, either free electrons or
holes. In other words, an FET has majority carriers but not minority
carriers. For most linear applications, the BJT is the preferred device. But there are some linear applications in which the FET is better suited because of its high input impedance and other properties. Furthermore, the FET is the preferred device for most switching applications. Why? Because there are no minority carriers in an FET. As a result, it can switch off faster since no stored charge has to be removed from the junction area. There are two kinds of unipolar transistors: JFETs and MOSFETs. This chapter discusses the junction field-effect transistor (JFET) and its applications. In Chapter 14, we discuss the metal-oxide semiconductor FET (MOSFET) and its applications. |