Complete Electronics Self-Teaching Guide with Projects

Chapter 8

Transistor Amplifiers

Many of the AC signals you'll work with in electronics are small. For example, the signal that an optical detector reads from a DVD disk cannot drive a speaker, and the signal from a microphone's output is too weak to send out as a radio signal. In cases such as these, you must use an amplifier to boost the signal.

The best way to demonstrate the basics of amplifying a weak signal to a usable level is by starting with a one-transistor amplifier. When you understand a one-transistor amplifier, you can grasp the building block that makes up amplifier circuits used in electronic devices such as cellphones, MP3 players, and home entertainment centers.

Many amplifier circuit configurations are possible. The simplest and most basic of amplifying circuits are used in this chapter to demonstrate how a transistor amplifies a signal. You can also see the steps to design an amplifier.

The emphasis in this chapter is on the bipolar junction transistor (BJT), just as it was in Chapter 3, “Introduction to the Transistor,” and Chapter 4, “The Transistor Switch,” which dealt primarily with the application of transistors in switching circuits. Two other types of devices used as amplifiers are also examined: the junction field effect transistor (JFET) (introduced in Chapters 3 and 4), and an integrated circuit called the operational amplifier (op-amp).

When you complete this chapter, you will be able to do the following:

• Calculate the voltage gain for an amplifier. ...