| 摘要 |
PROBLEM TO BE SOLVED: To provide a focus servo circuit capable of correctly setting an optimum focus bias value in a short time without increasing the manufacturing cost. SOLUTION: This focus servo circuit is provided with a jitter value measurement circuit 16 for successively measuring prescribed pieces of jitter values corresponding to prescribed focus bias values and a controller 22 for calculating the mean value of prescribed pieces of jitter values to obtain the optimum jitter value, calculating the optimum jitter values corresponding to at least three points of focus bias values and setting the optimum focus bias value FBz based on the optimum jitter values. The controller 22 measures successively prescribed pieces of jitter values within a prescribed period corresponding to the prescribed focus bias values before calculating the optimum jitter value corresponding to respective focus bias values, and makes the mean value of these prescribed pieces of jitter values a reference jitter value Jsa, and decides whether or not the jitter values measured by the jitter value measurement circuit 16 are a defective jitter value based on the reference jitter value Jsa.
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