| 摘要 |
PROBLEM TO BE SOLVED: To detect surely a MSK modulation mark from a wobble signal being MSK-modulated. SOLUTION: The wobble signal of an optical disk 10 is supplied to an address decoding circuit 28. The address decoding circuit 28 operates exclusive OR of binarized wobble signal and a reference clock signal generated by a PLL circuit from the wobble signal, and calculates a ratio in which the exclusive OR becomes 1 for each half period of the reference clock signal. When a prescribed number or more of sections in which the ratio becomes the prescribed threshold ratio or more exist, it is detected as the MSK modulation mark. A system controller 32 changes threshold ratio in accordance with cross talk from an adjacent track. COPYRIGHT: (C)2007,JPO&INPIT
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