| 摘要 |
PROBLEM TO BE SOLVED: To obtain a stable servo operation even if the frequency band of the photodetecting signals of sub-beams are insufficient when the track servo operation is performed by a differential push-pull method. SOLUTION: The reflected light from an optical disk is received by respective photodetectors 1a to (h and is converted into the photodetecting signals meeting the quantities of the received light in I/V converters 2a to 2h. SHs 3a to 3d respectively hold the photodetecting signals from the I/V converters 2a to (2d) in periods for irradiation with the recording power during recording and sample and output the signals in periods for irradiation with non-recording power. LPFs 4e to 4h respectively extract the DC components of the photodetecting signals from the I/V converters 2e to 2h. A variable amplifier 12 amplifies the DC components at the amplification factor meeting the ratio of the average power for the irradiation and the non-recording power in recording and outputs the same without amplification in reproducing. A differential amplifier 14 forms the servo error signals in accordance with the respectively outputted signals.
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