| 摘要 |
PURPOSE:To detect accurately a track shift by correcting electrically the electric output signal given from a photodetector which detects the reflected light sent from two secondary spots through an electric circuit. CONSTITUTION:Averaging circuits 18a and 18b are provided at the following stages of photodetectors 8 and 10 which detect the reflected light sent from two secondary spots for a track tracing device. At the same time, an amplifier 17 is added at the side which receives the effect of a recording pit 16. The band of a track tracing servo is set extremely lower than about 1MHz of the band of the recording signal, that is, about 10kHz. As a result, the average value outputs of the circuits 18a and 18b are set approximately constant as shown by solid lines (a) and (b) within a servo band. The (a) is sent from a secondary spot B1 which receives no effect of the pit 16; while the (b) is sent from a secondary spot B2 which receives the effect of the pit 16. The maximum level of light intensity is shown by the broken lines and equal between (a) and (b). However the minimum level of the (b) is smaller than the (a) at the area which receives the effect of the pit 16. |
