| 摘要 |
PURPOSE:To prevent a track jump phenomenon due to soil on the surface of a disk by comparing the peak value of a reproduced RF signal with its level fluctuation through a comparator to detect flaws and also feeding the output of another detector back to a level fluctuation detector. CONSTITUTION:The reproduced RF signal obtain via an optical pickup 3 and a current/voltage converter 4 is supplied to a peak detector 5 having a large discharge time constant as well as to a level detector 6 having a small discharge time constant respectively. Thus outputs eM and eP are delivered. The level of the output eP is increased by a TR26 by an amount equal to the base-emitter threshold voltage VF and then compared with the level of the output eM. This comparison output is supplied to a time constant circuit 9. When the difference VF is produced between both outputs eM and eP, a current (i) is supplied to a capacitor 19 of the detector 6 to make the eP follow the eM. Then these eM and eP are compared with each other through a comparator 7 to obtain a flow detection signal eS. The track error signal is held at its preceding level by the signal eS in order to keep the actuator voltage at a fixed level. This prevents a track jump phenomenon. |
