| 摘要 |
PURPOSE:To detect a focus error without fail regardless of the sample-hold timing of a focus error signal and to speedily transfer to returning operation by providing a mean to monitor whether its own focus error signal is changed beyond a certain level range or not excepting for a loop in a focusing controller equipped with the focusing control loop. CONSTITUTION:Difference between the focus error signal being applied with sample-hold at the timing of a mirror surface and a target value, is passed through a phase compensating circuit 2 and afterwards, an actuartor 4 is driven by an actuator driver 3. Then, a servo loop is formed for focusing control. For the high frequency noise area of an output from a focus error detector 5, a high frequency component modulated by a pit is removed by an lowpass filter LFP 6. In such a case, when the focus eroor is generated, the output of the LPF 6 is inputted to an window comparator 7. Thus, the focus error is detected even in a held state and following processing can be suitably execut ed. |
