| 摘要 |
<p>PROBLEM TO BE SOLVED: To keep a servo control gain constant even when the light quantity to be detected is changed reducing the change of the gain responsing to the change of the light quantity by providing an arithmetic part, a dividing part and a focus control part. SOLUTION: A current-voltage conversion part 3 inputs output currents of a first photodetector part 101 and a second photodetector part 102 and converts them into voltage signals. An arithmetic part 104 outputs a focus error signal. An LPF 105 reduces the high frequency noise of the focus error signal to be inputted. A multiplying part 107 amplifies the focus error signal subjected to a gain adjustment 106. A dividing part 108 divides the amplified focus error signal by a sum signal. A phase compensation part 109 inputs the output of the dividing part 108 and performs a phase compensation for securing a stable frequency area to the characteristic of a focusing actuator 113. A focus search control part 110 turns a focus control routine ON in order to perform the minute control of a focusing.</p> |
