CHAPTER 5 – Practical Amplifier Circuits

The objective of this chapter is to master the components that compose a multistage, high-gain amplifier, as well as the characteristics of such an amplifier. The characteristics of ideal amplifiers such as infinite input resistance, zero output resistance, very large but constant gain are frequently used as design goals for practical amplifiers. When a numerical value for the gain of an amplifier is given, it is understood to be applicable only for a frequency range called the midband. In integrated circuits capacitors are avoided as they take up too much space. It is possible to design direct-coupled amplifiers in which the collector potential of one stage is equal to the base potential of the succeeding stage. After a signal is sufficiently amplified in voltage, which frequently is the end goal in some applications, power capabilities must be also added to the signal. This is achieved by feeding the amplified signal into a power amplifier, which typically is a current amplifier. A radio receiver presents a good example of applications of analog circuitry. High-power receivers are more modular, with the receiving section as one module, the power supply as another, and the audio section as one chip, usually mounted on a heat sink.