50 Adaline and Madaline
2.1 Review of Signal Processing 51
which describes a typical square wave.
As illustrated in Figure 2.5, if we algebraically add together the first three sinusoidal components of this Fourier series, we produce a signal that already strongly resembles the square wave. However, we should notice that the resul-tant signal also exhibits ripples in both active regions. These ripples will remain to some extent, unless we complete the infinite series. Since that is obviously not practical, we must eventually truncate the series and settle for some amount of ripple in the resulting signal.