| 摘要 |
PROBLEM TO BE SOLVED: To enable speedy and sure refocus servo to defects by changing a generation balance of focus error signals when focus control is executed. SOLUTION: An output of each of cells A, B, C and D of a light receiving element 8a is inputted to a servo amplifier 8 and supplied to a first and a second addition amplifiers 8c and 8d via an LPF 8b. The first addition amplifier 8c generates a signal of the cells B+D, and the second addition amplifier 8d generates a signal of the cells A+C. The output of the second addition amplifier 8d is supplied to a gain variable amplifier 8e. An output of the gain variable amplifier 8e and the output of the first addition amplifier 8c are supplied to a differential amplifier 8f, whereby an output voltage is controlled to be constant. Outputs of the first and second addition amplifiers 8c and 8d are supplied to a third addition amplifier 8h and, a pull-in signal P1 as a sum signal of the A+B+C+D is outputted.
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