Servo circuit, digital PLL circuit and optical disk device

An optical disk device comprising:

• a digital demodulation circuit for receiving a signal which is obtained as a result of reproducing from an optical disk and converting into a two-level signal, on which optical disk a digital modulated signal was previously recorded, said digital demodulation circuit performing digital demodulation on the received signal;
• a digital phase-locked loop circuit for generating a clock signal which is in phase synchronization with a demodulated signal output by said digital demodulation circuit;
• and
• a digital servo circuit for performing rotation control of said optical disk so as to correct a frequency error and a phase error between said clock signal and a reference clock signal;
• wherein said digital servo circuit comprises:
• speed error detecting means for detecting a speed error which is a frequency difference between a reproduced clock signal which is reproduced from the optical disk and a reference clock signal;
• phase error detecting means for detecting a phase error which is a phase difference between the reproduced clock signal and the reference clock signal;
• and
• servo signal generating means for generating a servo signal which is used for eliminating the speed error and phase error,
• wherein said phase error detecting means comprises:
• first and second frequency dividing means for performing frequency dividing on the reproduced clock signal and the reference clock signal, respectively, a frequency dividing ratio being changed according to a change of a speed error gain of said speed error detecting means;
• and
• phase comparing means for detecting a phase error between the frequency-divided reproduced clock signal and the frequency-divided reference clock signal.