| 摘要 |
PURPOSE:To increase a range of the tracking servo control by providing the polarity to the pulse signal obtained from a phase difference detecting means in response to the phase relation between output signals of two elements set at the same column position against the tracking direction of a 4-split photodetecting element. CONSTITUTION:The output signals of elements 1a and 1d or 1b and 1c of a 4-split photodetecting element 1 are compared with the threshold value and converted into the binary signals. Then EXOR gates 4 and 5 secure the exclusive OR of said binary signals for each value between those diagonal elements 1a and 1d or 1b and 1c of the element 1. Then a pulse signal X is produced with polarity corresponding to the phase relation between the output signals of the elements 1a and 1d or 1b and 1c set at the same column position to the track direction with the pulse width equivalent to the phase difference between output signals P and Q of both gates 4 and 5. Then a tracking error signal is obtained by integrating the signal X. In such a way, a range of the tracking servo control can be increased.
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