Patent ID: 7570570

Claim:
An optical disk drive for demodulating a wobble signal modulated by a modulation scheme which expresses a data value by means of a first phase and a second phase out of phase with the first phase by 180 degrees, the drive comprising: reproduction means for reproducing the wobble signal; binarization means for binarizing the wobble signal; computation means for computing an exclusive-OR result from the binarized wobble signal and a reference clock signal; determination means for determining whether or not the wobble signal is of the first phase or the second phase every period of the reference clock signal by means of comparing a ratio, at which the exclusive-OR result assumes a value of one, with a predetermined threshold ratio in a half period of the reference clock signal; and control means for changing the predetermined threshold ratio when crosstalk originating from an adjacent track is superimposed on the wobble signal.