Stepping motor systems in which, in order to reduce electromagnetic interference (EMI) noise that is generated by controlling H-bridge field effect transistors (FETs), the frequency of a carrier signal (hereinafter referred to as a carrier frequency) used in pulse-width modulation (PWM) control is changed with time are known. In such systems, since the carrier frequency is changed sinusoidally with time, spectrum components having noise at high levels generated at an nth harmonic frequency of a predetermined carrier frequency are spread over an nth-order frequency range (for example, n·5 kHz to n·20 kHz) of a frequency range (for example, 5 kHz to 20 kHz) in which the carrier frequency is changed with time. Thus, the levels of the noise generated at the nth harmonic frequency can be reduced. Accordingly, interference with radio reception and other electronic apparatuses can be reduced. One example of such a system is shown in Japanese Unexamined Patent Application Publication No. 7-99795.
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