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Analog circuits are circuits dealing
with signals free to vary from zero to full power supply
voltage. This stands in contrast to digital circuits,
which almost exclusively employ "all or nothing" signals:
voltages restricted to values of zero and full supply
voltage, with no valid state in between those extreme
limits. Analog circuits are often referred to as linear
circuits to emphasize the valid continuity of signal range
forbidden in digital circuits, but this label is
unfortunately misleading. Just because a voltage or current
signal is allowed to vary smoothly between the extremes of
zero and full power supply limits does not necessarily mean
that all mathematical relationships between these signals
are linear in the "straight-line" or "proportional" sense of
the word. As you will see in this chapter, many so-called
"linear" circuits are quite nonlinear in their
behavior, either by necessity of physics or by design.
The circuits in this chapter make use of
IC, or integrated circuit, components. Such
components are actually networks of interconnected
components manufactured on a single wafer of semiconducting
material. Integrated circuits providing a multitude of
pre-engineered functions are available at very low cost,
benefitting students, hobbyists and professional circuit
designers alike. Most integrated circuits provide the same
functionality as "discrete" semiconductor circuits at higher
levels of reliability and at a fraction of the cost.
Usually, discrete-component circuit construction is favored
only when power dissipation levels are too high for
integrated circuits to handle.
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