Patent ID: 8040192

Claim:
A power supply voltage output circuit comprising: a power supply voltage generation unit generating a power supply voltage to be supplied into a ring oscillator; a reference clock oscillator oscillating a reference clock with respect to a clock oscillated by the ring oscillator; a phase difference detection unit detecting a phase difference between the clock from the ring oscillator and the reference clock from the reference clock oscillator; a filter unit smoothing an output of the phase difference detection unit; and a Pulse Width Modulation (PWM) signal generation unit generating a PWM signal based on an output of the filter unit; and a control unit adjusting at least one of the output of the phase difference detection unit, the output of the filter unit, and an output of the PWM signal generation unit to an output so that a certain power supply voltage is output from the power supply voltage generation unit within a prescribed period of time after the ring oscillator is activated, the control unit being formed of a digital circuit.