Feedback

Abstract

Feedback occurs in one form or other in every amplifier. It can take the form of desired feedback, such as the negative feedback described in this chapter or the positive feedback described in chapter 6, or undesired feedback, such as that due to stray capacitance. Negative feedback is often introduced into an amplifier, since this gives improved bandwidth and stability as well as reducing noise and distortion. Positive feedback produces oscillations in a normal amplifier; sometimes these occur as unwanted signals, such as in the power amplifier of section 2.7 where parasitic oscillations required suppression, or they may be controlled for use in an oscillator circuit of chapter 6. This chapter introduces general feedback principles, which may be positive or negative, and then concentrates on the applications of negative feedback to amplifier design and performance, including applications of the high-gain operational amplifier whose current availability and low cost has revolutionised circuit design.