| 摘要 |
PURPOSE:To maintain the accuracy of control at a fixed level even if the reflectivity of the recording surface of a disk and light emitting power of a laser fluctuate, by adding the outputs of plural photodetectors to each other and using the sum of the outputs as the reference voltage of an AD converter. CONSTITUTION:Increases of the reflectivity of the recording surface of a disk and light emitting power of a laser proportional to the sum of outputs of photodetectors 1 and 2 calculated by an adder 7 and, as they increase, the reference voltage of an AD converter 5 increases and acts to compensate the increases of the reflectivity and light emitting power. Therefore, the digital signal inputted to a signal processing section 8 represents an actual out-of-focus quantity.
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