| 摘要 |
PROBLEM TO BE SOLVED: To considerably reduce the circuit scale of a rough servo circuit to reduce the cost and the power consumption and to improve the reliability of a system. SOLUTION: With respect to a rotation servo circuit, the frequency in inversion of an inputted EFM signal is detected (21 and 22). The circuit is so constituted that this frequency may be compared with a prescribed reference value (23) by a means (24) to generate a rotation servo signal as rough servo. The reference value is determined on the basis of an average frequency in inversion of all generated patterns of the EFM signal.
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