| 摘要 |
PURPOSE:To reduce the tracking offset with respect to the slippage of an optical axis and the inclination of a disc by separating the differential signal between output signals from two light receiving areas of a photodetector into the signal of a bit center part and the signal of a land center part and detecting a signal of the offset from the latter signal to correct the former signal. CONSTITUTION:Outputs from two light receiving areas of a photodetector 11 which receives the reflected light of a light spot from the disc pass a summing amplifier 17, a differentiator 18, and a comparator 19 with zero level as the reference and are inputted to a 1st pulse generator 20, which generates a pulse by the rise of a signal, and a 2nd pulse generator 21 which generates a pulse by the fall of the signal. Two outputs of the photodetector 11 are inputted to a differential amplifier 12, and the differential output is sampled and held by 1st and 2nd sample holders 22 and 23 in accordance with pulses corresponding to light spots in the bit center and the land center from pulse generators 20 and 21, and the differential signal between the output of the sample holder 22 and the output of the sample holder 23, which passes a level adjuster 24, from a differential amplifier 25 passes an LPF16 to go to a tracking signal which does not include the offset signal. |
