| 摘要 |
PROBLEM TO BE SOLVED: To provide a prepit detecting device capable of detecting prepits correctly even when there is fluctuation in the amplitude of a radial push-pull signal. SOLUTION: In a prepit detecting device in which prepit detecting circuits 600, 700 which correspond respectively to a mark-period beam intensity and a space-period beam intensity are provided in parallel at the output side of a push-pull circuit for generating a pre-information signal 500 and which finally outputs the logical OR of outputs of both prepit detecting circuits as a prepit detection signal (1), AGC circuits making the maximum amplitude of a radial puss-pull signal which is to be obtained from the push-pull circuit 500 coincide with a reference value are provided at front stages of comparators for detecting prepits which are in both prepit detecting circuits.
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