| 摘要 |
PURPOSE:To adjust the mounting position of an optical head with high accuracy, by obtaining a phase difference between the output signals of a photodetector which receives reflected light from two tracking spots, and setting the polarity of a phase difference output signal at a constant level in spite of the decentering of an optical disk. CONSTITUTION:In a state where a tracking control loop is opened, the phase difference between the output voltages of photodiodes 1 and 2 which receive the reflected light from the tracking spot is detected by a phase detector 8. Also, the phase difference between the output signal of a photodiode 3 which receives the reflected light from a main spot and the tracking error voltage obtained from the output voltages of the photodiodes 1 and 2, is detected, then, a direction in which a track crosses two tracking spots is detected. Therefore, it is possible to obtain a phase difference output voltage having a constant polarity even when the phase difference of the output voltages outputted from the photodiodes 1 and 2 is set at an arbitrary value without limiting it at 180 deg.. In such a way, the position adjustment of the optical head can be performed easily by referring to the phase difference output voltage.
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