| 摘要 |
PURPOSE:To easily adjust a device, by providing a band-pass filter having a specific central frequency, a rectifier circuit to rectify the output of the filter, a generation circuit for a prescribed reference voltage, and a comparator to compare the output of the rectifier circuit and the reference voltage. CONSTITUTION:A tracking error signal generated from a difference between received two sub spot light 12 and 13 is inputted to the band-pass filters 56 and 57. The band-pass filters 56 and 57, assuming the interval of the sub spot light 12 and 13 as P and the linear velocity of a recording medium as S, extracts a frequency component of S/P. The outputs of the band-pass filters 56 and 57 are rectified and smoothed by the rectifier circuits 58 and 59, and are inputted to the comparator 61, and the comparator 61 compares the outputs of the rectifier circuits 58 and 59 with the reference voltage outputted by the generation circuit. In such a way, a grating is rotated as monitoring the output of the comparator 61, and it is enough only to rotate the grating from the present position to a position where the level of the tracking error signal goes to the minimum level when the level reaches a high level, thereby, adjusting work can be simplified.
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