| 摘要 |
PURPOSE:To detect a mirror surface without an influence due to the difference of a disc upon the size of a signal by making a comparator detect that the level of a bit surface is higher than a level obtained by dividing the output of the mirror surface level at its voltage. CONSTITUTION:When a motor 2 is rotated and a track servo following the signal track of the disc 1 is not actuated, an output obtained by converting an optical output from an optical type pickup 3 from light to voltage by a photoelectric converter 4 is supplied as a signal (a) at the information recording surface of the disc 1 and as a signal (b) at the mirror surface. The output of the converter 4 is inputted to a level detectors 5, 6 to obtain the maximum and minimum levels of the signal. The level detectors 5, 6 detect the maximum and minimum levels of the input signal respectively. The output of the level detector 5 is inputted to a voltage divider 7 and the voltage-divided output is 0.7 times the output of the detector 5, so that the output of the detector 6 is higher than the output of the voltage divider 7 at the input port of a comparator 8. Consequently, an outut 9 is turned to ''L'' and the mirror surface can be detected. |
