OPTICAL DISK DEVICE AND ITS FOCUS CONTROL METHOD

摘要

PROBLEM TO BE SOLVED: To provide an optical disk device capable of stable focus servo pull-in operation even for an optical disk having the thickness of a substrate largely different from a standard value, and its focus control method. SOLUTION: The optical disk device comprises: a motor driving part 10 for moving an objective lens 14 to the optical disk 1; a split photodetector 18 for inputting reflection signals from the optical disk 1; an addition part 24 for generating focus error signals for performing the focus control of the objective lens on the basis of the reflection signals; a filter 25 for advancing a phase near a gain crossover frequency in the open loop characteristics of a focus servo by an amount indicated by a prescribed setting value; and a controller 13 for advancing the phase near the gain crossover frequency by changing the prescribed setting value according to the difference or ratio of a first absolute value from the reference value to the maximum value of the amplitude waveform of the focus error signals and a second absolute value from the reference value to the minimum value of the amplitude waveform of the focus error signals. COPYRIGHT: (C)2007,JPO&INPIT