Patent ID: 7136340

Claim:
A semiconductor integrated circuit comprising: a time-constant variable bandpass filter which extracts a signal attributable to wobble from a signal outputted from a pickup circuit for scanning a surface of a recording medium formed with a track having in a surface thereof the wobble to thereby read a signal; a digitizing circuit which digitizes a wobble signal having passed through the bandpass filter; and a filter frequency control circuit which generates a control signal for controlling a frequency characteristic of the bandpass filter in accordance with the frequency of the wobble signal having passed through the bandpass filter, wherein the filter frequency control circuit includes, a lowpass filter for eliminating harmonic components of a signal outputted from the digitizing circuit, a dummy filter identical in configuration to the bandpass filter, a phase comparator which detects a difference in phase between a signal having passed through the dummy filter and a signal having not passed therethrough, and a control signal generator which generates a frequency control signal for controlling an intermediate frequency of the bandpass filter according to the phase difference on the basis of a signal outputted from the phase comparator, and wherein the intermediate frequency of the dummy filter and the cutoff frequency of the lowpass filter are controlled in conjunction with the intermediate frequency of the bandpass filter on the basis of the frequency control signal.