| 摘要 |
An optical information tracking apparatus for reproducing information by applying light beam onto a track on a rotating record medium, sensing the diffracted light beam thus generated by means of a photodetector and transforming the diffracted light beam into electrical signals, wherein the origin of said photodetector is aligned with the light axis of the optical system, the X axis is placed in parallel with the direction of said track, the Y axis is placed perpendicular to said track. Electrical signals are taken out respectively from photodetector elements which exist respectively in the first, second, third and fourth quadrants. A difference signal representing the difference between a signal which is the sum of the output signal from the first quadrant and that from the third quadrant and a signal which is the sum of the output signal from the second quadrant and that from the fourth quadrant as well as a sum signal representing the sum of output signals from the first to fourth quadrants are calculated. The positive peak value and the negative peak value of said difference signal are held respectively in peak hold circuits, and occurrences of a positive peak and a negative peak of said sum signal fed from the quadrant photodetector are detected to reset said peak hold circuits when a peak of said sum signal having either positive or negative polarity occurs and to effect sample and hold function for a signal which represents the sum of outputs from said peak hold circuits when a peak of said sum signal having the polarity opposite to said polarity occurs so as to obtain the tracking signal.
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