| 摘要 |
Noise generation is reduced further. Oscillation control circuit 11 generates a modulation signal modulating oscillation frequency of an oscillation signal generated by oscillation circuit 12 and outputs modulation signal to same. Preferably, the modulation signal fluctuates period of the oscillation signal sequentially. The oscillation circuit 12 is composed of a ring oscillator, for example, and the power supply voltage or power supply current of the ring oscillator is controlled to fluctuate sequentially by the modulation signal output from the oscillation circuit 11. Buffer 14 of charge pump circuit 13 generates signals/Phi and Phi by the oscillation signal and drives capacitors C 1 and C 2 for supplying a higher voltage than the voltage of the power supply Vcc to gate of N-channel MOSFET Q 1. |
