As mentioned in Chapter 11, the op amp is used in an extremely wide variety of circuits, and nowthat we understand the basic operation and limitations of the operational amplifier itself, we are in a position to explore a number of these applications. The variety of possibilities is almost endless. In fact, there are a large number of texts that focus just on the op amp and its application (see [1–7], for example). Here we will focus on six different application areas.

Filters employing op amps, referred to as active filters, are an extremely useful class of circuits, and we first explore examples of continuous-time low-pass, high-pass, and band-pass filters. This is followed by an introduction to switched-capacitor techniques, which are widely used to implement filters in digital signal processing ICs.

Digital-to-analog (D/A) and analog-to-digital (A/D) converters provide the important interface between the analog and digital signal domains and are standard components in mixed-signal designs. A basic introduction to D/A and A/D converter circuits follows the section on switched capacitor circuits. Most D/A and A/D converters require op amps in their implementations.

The majority of the applications that we study are in linear circuits, but the op amp is also useful in many nonlinear applications. We introduce nonlinear applications with implementation of precision rectifiers using op amps. The chapter then concludes with an introduction to multivibrator circuits that represents our first use of positive feedback to perform circuit functions.