| 摘要 |
PURPOSE:To improve the reliability with a simple constitution by electrically detecting the operation abnormality of a phase lock oscillation (PLO) circuit with the input voltage of a voltage controlled oscillator (VCO) in this circuit to cope with abnormality of the PLO circuit without a time delay. CONSTITUTION:The input voltage of the VCO in a PLO circuit 10 operated synchronously with the reference clock component of a servo signal has correlations to the operation state of the PLO circuit 10. This input voltage of the VCO and a prescribed reference voltage are compared with each other by a monitor circuit 13 to monitor the operation state of the PLO circuit 10, and the operation of a driving control circuit 12 of a voice coil motor 6 is continued or stopped in accordance with the monitor result. Thus, the abnormality is momently detected if the operation abnormality of the PLO circuit occurs, and runaway of the voice coil motor which cannot be controlled is prevented.
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