| 摘要 |
PURPOSE:To enable to make accurate drawing of focus servo at all times by changing reference potantial that determines timing of drawing of focus servo automatically corresponding to intensity of a light soruce, reflection factor, transmission factor etc. of an irradiated body instead of fixing the reference potential. CONSTITUTION:The peak value of a focus error signal F transmitted through a switch 11 is held by a peak hole circuit 12, and at the same time, arrival of the (negative) peak vlue is detected by a peak detecting circuit 13. An adder 14 adds the peak held value and specified fixed voltage V1 outputted by a voltage generator 15. An analog switch 16 outputs either of fixed voltage V2 outputted by a voltage generator 17 or output of the adder 14 to a comparator 7 alternatively. A monostable multivibrator 18 is triggered by output of the peak detecting circuit 13, and outputs pulse of specified time width. These and an inverter 19 constitute a reference potential generator 6.
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