The open-loop voltage gain of an op-amp is the ratio of the change in output voltage to a change in the input voltage without feedback. The actual op-amp has a finite voltage gain that decreases as the frequency increases (we explore this in detail in the next chapter). The ideal op-amp has a voltage gain that approaches infinity. The most significant difference between ideal and actual op-amps is in the voltage gain. As the various parameters are defined in the following sections, reference should be made to Table 9.1 in order to find typical values. We use μA741 operational amplifiers in many of the examples and end-of-chapter problems for the following reasons: (1) they have been fabricated by many IC manufacturers, (2) they are found in great quantities throughout the electronics industry, and (3) they are general-purpose internally-compensated op-amps, and their properties can be used as a reference for comparison purposes when dealing with other op-amp types. Table 1 lists the parameter values for three particular op-amps, one of the three being the μA741. These parameters are specified in listings on data sheets supplied by the op-amp manufacturer. We begin by defining the parameters used to describe practical op-amps. Our goal is to develop a detailed model of the practical op-amp – a model that takes into account the most significant characteristics of the non-ideal device. It is important for the circuit designer to understand the differences between actual op-amps and ideal op-amps, since these differences can adversely affect circuit performance. Practical Op-amps approximate their ideal counterparts but differ in some important respects.