| 摘要 |
PURPOSE:To previously prevent the out-of-tracking phenomenon, by foreseeing the disturbance of error signal of a tracking servo circuit caused by a defect produced during the production of a disk or the damage caused during the handling of the disk and then stopping the following of the servo system for a short time. CONSTITUTION:The laser beams reflected by a disk 1 are amplified by a preamplifier 8. One of these beams is changed into a video signal after the demodulation 9, and the other beam receives a tracking error detection 10 to be compared with the reference voltage given from a reference voltage generator 11 through a differential amplifier 12. Then a tracking mirror 5 is made movable via a drive amplifier 13. In this case, if a reduction of amplitude is caused to the output signal of the amplifier 8 due to a dropout, the pulse signal of a certain width is produced from a monostable multivibrator 16 by the trigger signal of an envelope wave detector 15 that constitutes a preholding circuit 14. Thus an analog gate 17 is turned off. Then the error signal is preheld by a holding capacitor 18 to eliminate the noise. |
