Figure 4-25.Harmonic composition of a square wave.
As shown in view (B), when the fifth harmonic (curve N with its decreased amplitude) is added, the
sides of the new resultant (curve P) are steeper than before. In view (C), the addition of the seventh
harmonic (curve Q), which is of even smaller amplitude, makes the sides of the composite waveform (R)
still steeper. The addition of more odd harmonics will bring the composite waveform nearer the shape of
the perfect square wave. A perfect square wave is, therefore, composed of an infinite number of odd
harmonics. In the composition of square waves, all the odd harmonics cross the reference line in phase
with the fundamental.
A sawtooth wave, shown in figure 4-26, is made up of both even and odd harmonics. Notice that
each higher harmonic is added in phase as it crosses the 0 reference in view (A), view (B), view (C), and
view (D). The resultant, shown in view (D), closely resembles a sawtooth waveform.