Transistors

Abstract

Abstract The most important active devices presently available are transistors. They can be used as switches in digital circuits or amplifiers in analogue circuits. There are two main basic types of transistors: The operational principles of these two types differ considerably. In bipolar transistors both carrier types (electrons and holes) are involved in the operation, whereas in field-effect transistors only one type is important (with the exception of second-order effects). Therefore the field-effect transistors are examples of unipolar transistors. Another difference is that bipolar transistors are current-controlled devices whereas field-effect transistors are voltage controlled. Bipolar transistors are three-terminal active devices consisting of p-n-p or n-p-n structures (Fig. 2.1). The operation is based on minority carrier injection (see Section 1.4.4). The three terminals are emitter (E), base (B), and collector (C).