| 摘要 |
PURPOSE:To prevent effectively track jumps by dividing the band of a tracking error signal at appropriate frequencies and using the signal whose high band component is cut off in accordance with a drop detecting signal as an error signal for control of a tracking error. CONSTITUTION:A peak holding circuit 53 has a sufficiently large discharge time constant compared with a peak holding circuit 52. A voltage comparator 55 detects that the output of the circuit 52 is lower than the output voltage of a split resistance 54 which is defined as a threshold level and outputs a signal showing the drop of the pickup output due to the stains or soil on the disk surface. Both an LPF 56 and 57 have the same time constant and usually add the high range component of a tracking error signal with its low range component to output them. If the pickup output signal drops, the high range component is cut off by a switch circuit 58. Thus, the tracking actions are never disturbed by the stains or soil on the surface of an optical disk.
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