Chapter 1 - The Op Amp

Abstract

This chapter discusses the basic operation of the op amp (operational amplifier), one of the most common linear design building blocks. In its classic form it consists of two input terminals—one of which inverts the phase of the signal, the other preserves the phase—and an output terminal. The basic operation of the op amp is discussed concentrating on the op amp from the black box point of view. There are a good many texts that describe the internal workings of an op amp, so in this work a more macro view is taken. The basic specifications are discussed. Some techniques to compensate for some of the op amps limitations are given. The various sections of the data sheet and how to interpret what is written are elaborated. How to select an op amp for a given application is also discussed. The classic model of the voltage feedback (VFB) op amp incorporates the following characteristics: infinite input impedance; infinite bandwidth; infinite gain; zero output impedance; and zero power consumption. There is a type of amplifiers that have several advantages over the standard VFB amplifier at high frequencies. They are called current feedback (CFB) or sometimes transimpedance amps. Most op amp specifications are largely topology independent. Although voltage feedback and current feedback op amps have similar error terms and specifications, the application of each part warrants discussing some of the specifications separately. In the following discussions, this will be done where significant differences exist.