Analogue signals An analogue signal is a voltage or current that varies smoothly between two extremes. Consider the waveform shown in Fig. 5.1.
At any instant along the time axis, the voltage will have a certain value so it is easy to see that there is an infinite number of possible levels between OV and 9V! Many of the circuits considered have been analogue, e.g. amplifiers and power supplies. In everyday life analogue systems are all around us; the medical thermometer, car speedometer and fuel gauge. The natural world is also essentially analogue, for example the transition from day into night in terms of ambient light (Fig. 5.2).