| 摘要 |
PURPOSE:To prevent surely a track jump phenomenon by extracting an envelope signal by an envelope wave detecting circuit in response to the output of an optical pickup and giving the variable control to the open loop gain of the tracking servo. CONSTITUTION:When a transparent substrate has some flaws, the component of an RF signal is omitted when the flaw part is reproduced. Then the level of an envelope signal S19 is lowered less then the reference voltage Vref1. Thus the 2nd level comparator 20 detects that a disc has a flaw and delivers the 2nd detection signal S20. Here a tracking error signal TE has a large amplitude. Then the signal S20 drives with control an analog switch SW via an OR gate circuit 28 to reduce the open loop gain of the tracking servo of a flaw reproduction part. Thus this gain is attenuated by an attenuating circuit 15 and led to an actuator coil 19. In other words, the open loop gain of the tracking servo is reduced when the flaw part is reproduced. In such a way, the track jump scarcely occurs.
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