| 摘要 |
PURPOSE:To produce a tracking error signal which is free from offset by using a waveform processing means which deletes the parts higher than the prescribed levels of each output of four light receiving areas. CONSTITUTION:A tracking error signal generator performs the waveform processing to delete the parts higher than the prescribed levels of four element outputs of a 4-split photodetector 1 and then adds together the output of two pairs of elements which are symmetrical to the intersecting point of two straight lines that divide the four elements for the production of a signal corresponding to the phase difference of two signals in the form of a tracking error signal. Therefore the output amplitudes of those four elements are kept constant despite the displacement of a light spot formed on the light receiving surface of the element 1. Then the phase difference of said two signals is never changed. Thus it is possible to prevent the offset of the tracking error signal.
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