| 摘要 |
PURPOSE:To stabilize tracking control and to simplify a circuit for that by switching the gain of the tracking control according to a recording carrier and setting a loop gain constant. CONSTITUTION:A synthesizing circuit 29 adds four outputs of a photodetector 16 and sends the sum signal to dividers 32 and 37 through a gain switching circuit 43. The divider 32 outputs a signal corresponding to the value X1/Y of the output of a differential amplifier 20 over the output Y of a differential amplifier 30 and the divider 37 outputs a signal corresponding to the value X2/Y of the output X2 of a differential amplifier 31. The signal of a processing circuit 5 for the signal of a decision device 4 for the recording medium 1 is inputted to gain switching circuits 33, 38, and 43, which switch amplification factors according to the signal of the circuit 5. Consequently, the loop gain of focus control does not vary whatever recording carrier 1 is loaded, so the tracking control is stabilized and the tracking control circuit is simplified.
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