1. Frequency modulation ratio mf. The Fourier series of the PWM output
voltage has a fundamental frequency which is the same as the reference
signal. Harmonic frequencies exist at and around multiples of the switching
frequency. The magnitudes of some harmonics are quite large, sometimes
larger than the fundamental. However, because these harmonics are located
at high frequencies, a simple low-pass filter can be quite effective in
removing them. Details of the harmonics in PWM are given in the next
section. The frequency modulation ratio mf is defined as the ratio of the
frequencies of the carrier and reference signals,