| 摘要 |
PURPOSE:To obtain a focus control circuit which has an assured actuation with a simple constitution by using a charging/discharging circuit which holds the level of the output signal sent from a circuit which detects the position of an objective lens and a set/reset flip-flop circuit. CONSTITUTION:When an objective lens 17 gets close to its focused position, the photodetecting quantity of a photodetector 16 increases to produce the pit signal. The voltage signal Vs is delivered from a level comparator IC10 when the peak voltage of the pit signal exceeds the reference voltage V11. Then the polarity of the signal Vs is first inverted, an S-R.FF circuit 241 is set to lock the focus servo to an ON state. The signal Vs is held by a time constant circuit 242, and the voltage Vc is discharged when a reproduction working, for example, is over. Then the signal VR rises from the negative polarity to the positive polarity when the voltage Vc is less than the threshold level on an inverter IC11. Thus the circuit 241 is reset to turn off the focus servo. |
