| 摘要 |
PURPOSE:To always keep the stability of a servo circuit high by providing an amplifying means whose gain is controlled in response to the amplitude of a tracking error signal into a tracking servo loop, and setting previously the gain of said amplifying means when the tracking servo loop is opened. CONSTITUTION:An amplifying circuit 30 detects the amplitude of a tracking error signal and then varies the amplification degree of the error signal in accordance with the result of amplitude detection. This circuit 30 is set between a differential amplifier 12 and a variable resistor 14. Thus the error signal, i.e., the output of the amplifier 12 is supplied to a comparator 32 consisting of plural level comparators. Then each level comparison output is applied to a memory 33 and stored there. The contents of the memory 33 are replaced with a control signal supplied from an external control circuit when a tracking servo loop switch S1 is open. The output of the memory 33 controls the gain of a variable gain amplifier VCA31. Thus the amplification degree of the error signal is controlled. |
