| 摘要 |
PURPOSE:To facilitate focus adjustment by providing a focus servo circuit with a means of adjusting the distance between a disk and an objective lens finely and by making the fine adjustment while monitoring the level of a reproduced signal. CONSTITUTION:A signal detected by a photodetector 6 is amplified by a head amplifier 7 and an amplifier 13, and a DC voltage which corresponds to the level of the reproduced signal is supplied from a rectifying circuit 14 to a monitoring device 12. As this monitoring device 12, a display device, etc., such as a voltmeter, performing step display corresponding to the lighting states of light emitting diodes is used. Even if the influence of secular change, etc., shifts the optical axis of a laser beam and temperature fluctuations, etc., vary the characteristics of circuit elements, focusing circuit is adjusted without using a special measuring instrument, while the monitoring device 12 is viewed, so that the level of the reproduced signal reaches its peak or exceeds a prescribed level. |
