The operational amplifier, or op amp, is a fundamental building block of analog circuit design. The name “operational amplifier” originates from the use of this type of amplifier to perform specific electronic circuit functions or operations, such as scaling, summation, and integration, in analog computers.

Integrated circuit operational amplifiers evolved rapidly following development of the first bipolar integrated circuit processes in the 1960s. Although early IC amplifier designs offer little if any performance improvements over tube-type designs and discrete semiconductor realizations and were somewhat “delicate,” they offered significant advantages in physical size, cost, and power consumption. The μA709, introduced by Fairchild Semiconductor in 1965, was one of the first widely used general-purpose IC operational amplifiers. IC op amp circuits improved quickly, and the now-classic Fairchild μA741 amplifier design, which appeared in the late 1960s, is a robust amplifier with excellent characteristics for general-purpose applications. The internal circuit design of these op amps used 20 to 50 bipolar transistors. Later designs improved performance in most specification areas. Today there is an almost overwhelming array of operational amplifiers from which to choose.

This chapter introduces the important performance specifications of operational amplifiers and provides a general overview to help users choose an amplifier from among the array of available components. The chapter begins by exploring the characteristics of the ideal operational amplifier. A number of basic circuit applications are discussed, including inverting and noninverting amplifiers, the summing and instrumentation amplifiers, the integrator, and a basic low-pass filter. Limitations caused by the nonideal behavior of the operational amplifier are also discussed. These limitations include finite gain, bandwidth, input and output resistances, common-mode rejection, offset voltage, and bias current.

The frequency response of circuits containing operational amplifiers is analyzed, including both single-stage and cascaded amplifiers. A multistage design example is explored using computer analysis via a spreadsheet. The chapter concludes with presentation of macro models that are used in the simulation of op amp circuits, and large-signal response limitations, including slew rate considerations and full-power bandwidth, are discussed.