| 摘要 |
PURPOSE:To quicken the pull-in of a focus servo by detecting whether a focus error signal deviates from a window which is set around the center of the zero cross point of the focus error signal or not. CONSTITUTION:After initializing an S/H-FES generation circuit 54, the pull-in of the focus servo is turned ON. An analog switch 63 is turned ON by making -FON from a controller 61 an L-level, and simultaneously, Int. is made the L-level, and R/-S is made the L-level, and the pull-in of the focus servo is started. When an objective lens is positioned at a position distant from a focusing point, and deviates from the window, S/H-FES becomes constant voltage whose polarity is equal to FES. On the contrary, when it is positioned at a near position, and deviates from the window, S/H-FES becomes the constant voltage whose polarity is equal to FES. Thus, by generating S/H-FES from FES by using the window, the focus servo is retracted. Thus, the pull-in of the focus servo can be quickened. |
