Patent ID: 6900676

Claim:
A clock generator comprising: a clock generating circuit having a function for varying a clock phase in accordance with a control signal; a phase difference detection circuit comparing the clock phase output from said clock generating circuit with a phase of a reference waveform, and detecting a phase difference therebetween; and a control signal generating circuit generating the control signal for controlling the clock phase of said clock generating circuit, wherein: said phase difference detection circuit comprises a plurality of phase detection units; at least one of said plurality of phase detection units carries out a direct phase detection in which a phase of the clock is directly compared with the phase of the reference waveform; and at least one of the other of said plurality of phase detection units carries out an indirect phase detection using a phase-synchronized waveform generating circuit generating a waveform synchronized in phase with the reference waveform or an output of said clock generating circuit and a phase information extracting circuit extracting phase information from the phase-synchronized waveform, wherein the control signal is generated based on phase difference detection information from at least one of said plurality of phase detection units and at least one of the other of said plurality of phase detection units.