Patent ID: 7102405

Claim:
A pulse-width modulation circuit connected to a power amplifying circuit including a plurality of switches operated to vary duration of power application to a load, the modulation circuit convening an input signal into a pulse signal to be supplied to the power amplifying circuit, the modulation circuit comprising: a comparison signal generator that generates a comparison signal having a prescribed period; an amplitude controller that controls an amplitude of the comparison signal in accordance with a volume control signal differing from power voltage; and a comparator that compares the comparison signal and the input signal after the amplitude of the comparison signal is controlled; and a noise remover for removing noise from the input signal; wherein the comparator outputs a signal having a level inverted in accordance with a relative level of the input signal with respect to the comparison signal, the outputted signal being supplied to the power amplifying circuit; and wherein the noise remover includes an integrating circuit that performs integration on the input signal and a sample hold circuit that performs sample-holding on the integrated input signal.