1.1.2 The Ideal Op-Amp
To illustrate what an op-amp is, let's consider its ideal characteristics. A practical op-amp, of course, falls short of these ideal standards, but it is much easier to understand and analyze the device from an ideal point of view.
First, the ideal op-amp has infinite voltage gain and infinite bandwidth. Also, it has an
infinite input impedance (open) so that it does not load the driving source. Finally, it has a zero output impedance. These characteristics are illustrated in Figure 2(a). The input voltage, Vim appears between the two input terminals, and the output voltage is Av Vim as indicated by the internal voltage source symbol. The concept of infinite input impedance is a particularly valuable analysis tool for the various op-amp configurations.
Figure