Image Number 13 for United States Patent #5451900.
To suppress electromagnetic radiation without exerting any harmful influence upon both S/N ratio and dynamic range, a pulse width modulation circuit includes an integrating circuit for integrating an input signal applied to an input terminal with respect to time, a comparing circuit connected to the integrating circuit and having hysteresis characteristics, a feedback circuit for feeding back the output of the comparing circuit to an input of the integrating circuit, and an amplitude modulation circuit, provided in a loop including the integrating circuit and the comparing circuit, for implementing amplitude modulation to modulate a frequency of the output of the comparing circuit. Further, the output of the comparing circuit can be fed-back to the integrating circuit via an amplitude modulation circuit. Alternatively, the amplitude of the output of the integrating circuit is first modulated by the amplitude modulation circuit, before being applied to the comparing circuit. A dither signal is applied to the amplitude modulation circuit or, alternatively, a signal for maintaining frequency of the pulse modulated signal may be applied.