9.1 Introduction to Negative Feedback

As we saw in the last chapter, op amps are very useful devices. However, in many applications, the device’s gain is simply too large and its bandwidth too narrow, for effective use. In this chapter we will explore the concept of negative feedback. This concept is realized by feeding a portion of the output signal back to the input of the system. The proper use of negative feedback will allow us to exercise fine control over the performance of electronic circuits. As a matter of fact, negative feedback is so useful to us that we will seldom use op amps without it. Negative feedback is not tied solely to op amps though, as almost any electronic circuit may benefit from its application. As with most things, there are disadvantages as well. A successful design will minimize the disadvantages and capitalize on the positive aspects. We will begin with the basic concepts of what negative feedback is and does, and then fine-tune our viewing by examining its four specific variants. We will look at specific examples of how negative feedback is applied to op amps, and finish off with a discussion of its practical limits.