How can we, understanding only sources and resistors, hope to comprehend the performance
of the op-amp? The answer lies in modeling. When the bells and whistles are
removed, an op-amp is just a really good voltage amplifier. In other words, the output voltage
is a scaled replica of the input voltage. Modern op-amps are such good amplifiers that
it is easy to create an accurate, first-order model. As mentioned earlier, the op-amp is very
popular and is used extensively in circuit design at all levels. We should not be surprised
to find that op-amps are available for every application—low voltage, high voltage, micropower,
high speed, high current, and so forth. Fortunately, the topology of our model is
independent of these issues.