| 摘要 |
PROBLEM TO BE SOLVED: To detect stably and surely a mark for address information from an optical disk in which a track having undulation of a fixed period is formed spirally. SOLUTION: In a land pre-pit signal extracting part 12, a first bottom envelope signal S<SB>btm1</SB>indicating a bottom envelope waveform of a push-pull signal (S<SB>A</SB>+S<SB>B</SB>)-(S<SB>C</SB>+S<SB>D</SB>) with high sensitivity is generated by a first bottom envelope circuit 32 having high tracking speed, and a second bottom envelope signal S<SB>btm2</SB>indicating a bottom envelope waveform of a push-pull signal (S<SB>A</SB>+S<SB>B</SB>)-(S<SB>C</SB>+S<SB>D</SB>) with low sensitivity is generated by a second bottom envelope circuit 34 having a low tracking speed, And the second bottom envelope signal S<SB>btm2</SB>level-shifted by an offset circuit 36 is made a threshold signal S<SB>ref</SB>and the first bottom envelope signal S<SB>btm1</SB>is binarized, and a land pre-pit signal S<SB>LPP</SB>is extracted from the push-pull signal (S<SB>A</SB>+S<SB>B</SB>)-(S<SB>C</SB>+S<SB>D</SB>). COPYRIGHT: (C)2004,JPO&NCIPI
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