| 摘要 |
PURPOSE:To prevent the disturbance of tracking due to flaws and dirt of a disc by cutting off transmission of a tracking signal for a prescribed time including the time, when the level of the AM detection output of a read information signal exceeds a prescribed level, and holding the level of the tracking signal just before cutting-off. CONSTITUTION:An AM detecting circuit 7 performs AM detection of the output of an information signal amplifying circuit 2 to extract amplitude components of the information signal. A high-pass filter HPF8 permits only signal components having frequencies higher than a prescribed cut-off frequency in the output of the AM detecting circuit 7 to pass through, and thereby, signal components due to flaws and dirt of the disc are taken out. A loop cut-off control signal generating circuit 9 outputs a control signal which turns off the switch of a loop cutting-off circuit 10 while the output level of the high-pass filter 8 exceeds a certain level. The input signal to an actuator driving circuit 5 in the time, when this switch is turned off, is held in the signal level just before turning-off and is supplied. |
