| 摘要 |
PURPOSE:To stably and exactly execute leading-in of servo by setting a servo- loop to a closed state by detecting zero-crossing immediately after detecting a focus error signal. CONSTITUTION:When a comparison output (h) of a high level is generated from a comparator 18, and also, a comparison output (g) of a low level is generated from a peak comparator 16, a gate circuit 17 supplies an enable signal (j) of a high level to a switch controlling circuit 12. Subsequently, when a focus error signal (b) ascends after passing through a peak level and becomes a zero level, its face is detected by a zero crossing comparator 15, this detection output (j) responds to a rise edge and the switch controlling circuit 12 outputs a close command signal (k) of a high level to a change over switch 8, so that switch 8 becomes a loop close state for selecting an output of an equalizer circuit 7. By said consecutive operations, leading-in of a focus servo-loop can be executed. In such a way, leading-in of servo can be stably and exactly executed.
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