| 摘要 |
PURPOSE:To enter quickly an optical spot at a track position by providing a circuit detecting that tracking is deviated, turning on/off the limit action of a limiter circuit with the aid of the detecting output, or changing a limited voltage level. CONSTITUTION:An absolute value circuit 12 takes the absolute value of a tracking error signal (a), and a comparator 13 compares the signal with a reference voltage. When the output (e) of the circuit 12 exceeds the reference voltage value, the output (f) of the comparator 13 is raised at a high level so as to detect that the optical spot is deviated from the track position. Thus the detection positions are not changed not only when the optical spot is deviated in the inner peripheral direction of the track but also when it is deviated in the outer peripheral direction. The output (f) of the comparator 13 is inputted as a limiter switching signal (d) to a limiter circuit 4 through an AND circuit 14 and a re-triggerable monostable multiplexer 15. Then the circuit 4 turns on/off the limiter action or changes the limited voltage level with the aid of the signal (d). Thus a signal with a large amplitude is not applied to the actuator.
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