| 摘要 |
An optical disk apparatus with a focus bias circuit including a focus servo device for an optical pickup, wherein a return light beam from an optical disk is received by a photo detector, then a focus error signal is detected from the outputs of divided sensors of the photo detector, and focus servo control is executed by applying a focus bias from a focus bias generator circuit to the focus error signal. The apparatus comprises an extractor for extracting a traverse level of a tracking error signal computed on the basis of the outputs of the sensors while changing the focus bias in an off-state of the tracking servo; a computer circuit for obtaining a focus bias corresponding to the maximum value of the traverse level extracted by the extractor; and a controller for controlling the focus bias generator circuit in such a manner as to attain a coincidence between the output thereof and the focus bias obtained from the computer circuit. In this apparatus, the focus bias can always be adjusted to an optimal value thereof and the production cost is reducible with a simplified structure.
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