| 摘要 |
PROBLEM TO BE SOLVED: To detect a pre-pit reliably in an optical disk device which performs recording and reproducing to an optical disk, such as a DVD-R with the pre-pit formed thereon. SOLUTION: After gain adjustment of signals of quadripartite photodetector A-D is carried out by AGCs 26c, 26d, the difference between them is calculated by a differential amplifier 26e and is binarized through a binary circuit 26f, and pre-pit information in a mark period is detected. Besides the upper limits of signals from AGCs 26c, 26d are limited to a constant value by limiter amplifiers 26g, 26h, and a noise in the mark period is thereby removed. Then, the difference between two signals is calculated in a differential amplifier 26i and binarized thought a binary circuit 26j, and pre-pit information in a space period is detected. OR operation of both signals is carried out by an OR operation unit 26k, and they are output to a controller 20 as pre-pit information.
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