Abstract
There are several methods of Pulse Width Modulation (PWM). For any method, the output of the pulse width modulator corresponding to a sinusoidal input consists of the various frequency components, depending on the frequencies of the input and the carrier. Generally speaking, some frequency components lower than the input frequency are mixed therein. When the ratio of the carrier frequency (fc) to the input frequency (fe) becomes small, the signal cannot be accurately transmitted, because these components become large. In communication, it is easy to make this ratio large enough. On the other hand, in control, the carrier frequency (fc) is limited by some function of the equipment in the systems, and it is required to broaden the bandwidth of the systems as far as possible. So it is important to use a method by which a frequency signal as high as possible can be transmitted on a constant (fc). For the above method it is necessary to clarify the limit of the ratio (fc/fe) from the viewpoint of accurate signal transmission.
In this paper, four typical modulators are shown. First their characteristics are analyzed theoretically. Second each modulator is compared from the viewpoints of the frequency characteristics and the so-called “effect of the removal of time independent nonlinearities” this is the significant advantage of the PWM. Finally as the result of the comparison, it is concluded that the method using both edges is the best one.
