| 摘要 |
A position-error-signal calculation circuit (105) calculates a relative position error between a laser-focused-beam spot (103) and an information recording layer (102), and generates a focus error signal (106). A filter (108) amplifies and passes therethrough a signal component in the vicinity of the natural resonance frequency of at least one mode among the natural vibration modes of the optical disc medium (101). A drive amplifier receives through a stabilizing compensator (109) and a D/A converter (110) the focus error signal (106) passed by the filter (108), to drive an objective lens (113), thereby allowing the laser-focused-beam spot (103) to track the information recording layer (102).
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