chapter  1

Feedback Amplifier Theory

WithJohn Choma

The use of negative feedback is fundamental to the design of reliable and reproducible analog electronic networks. This chapter examines the salient features of the theory that underlies the efficient analysis and design of commonly used feedback networks. Intentional degenerative feedback applied around an analog network produces four circuit performance benefits. First, negative feedback desensitizes the gain of an open-loop amplifier with respect to variations in circuit element and active device model parameters. The chapter aims to formulate systematic feedback circuit analysis procedures and ultimately, and to demonstrate their applicability to six specific types of commonly used feedback architectures. Four of these feedback types, the series-shunt, shunt-series, shunt-shunt, and series-series configurations are singleloop architectures, while the remaining two types are: the series-series/shunt-shunt and series-shunt/shunt-series dual-loop configurations. Several standard techniques are used for analyzing linear feedback circuits. The most straightforward of these entails writing the Kirchhoff equilibrium equations for the small-signal model of the entire feedback system.