| 摘要 |
PROBLEM TO BE SOLVED: To regulate focus balance without rotating a disk with a disk player. SOLUTION: This disk player forms a first addition signal by adding the outputs of two photodetectors of an optical pickup 2, forms a second addition signal by adding the outputs of another two photodetectors, supplies both addition signals to both input ends of a differential amplifier 93 and forms a focus error signal. The disk player simultaneously forms an RF signal by obtaining the sum of both addition signals. This disk player has a switching circuit 35 for mutually substituting the first addition signal and second addition signal to be inputted to both input ends of the differential amplifier 93, gain regulators 33 and 34 for changing the level ratios of the first addition signal and second addition signal to be inputted to the switching circuit 35, and gain regulators 31 and 32 for changing the level ratio of the first and second addition signal to be added to each other in order to form the RF signal.
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