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 the 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, the discrete-component circuit construction is favored only when power dissipation levels are too high for integrated circuits to handle.