| 摘要 |
A mark detecting circuit that stably and reliably detects the marks for address information from an optical disk having tracks formed in a spiral shape and having waviness with a fixed period. In the land pre-pit signal extracting portion 12, by means of first bottom envelope circuit 32 with a high tracking speed, first bottom envelope signal Sbtm1 that represents at high sensitivity the bottom envelope of push-pull signal (SA+SB)-(SC+SD) is generated; and, by means of second bottom envelope circuit 34 with a low tracking speed, second bottom envelope signal Sbtm2 that represents at low sensitivity the bottom envelope waveform of push-pull signal (SA+SB)-(SC+SD) is generated. Then, with the signal, obtained by level shift treatment of said second bottom envelope signal Sbtm2 using offset circuit 36, used as threshold signal Sref, first bottom envelope signal Sbtm1 is converted to a binary form. And land pre-pit signal SLPP is extracted from push-pull signal (SA+SB)-(SC+SD).
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