FOCUS CONTROL SIGNAL COMPENSATING DEVICE FOR OPTICAL RECORDING AND REPRODUCING DEVICE

摘要

PURPOSE:To compensate a minute extent of deviation of a bisected phtodetector at the attaching time by adding an electric compensating quantity proportional to the overall quantity of reflected light to the output of a subtracting circuit which includes a minute extent of mechanical deviation of the two-divided photodetector. CONSTITUTION:Outputs of areas (a) and (b) of the bisected photodetector 7 are denoted as Pa and Pb respectively and Pa+Pb is outputted by the first adder 2 and V0 of a DC reference power source 3 and Pa+Pb are multiplied by an multiplier 4 to obtain an electric compensating quantity P0. The output Pb-Pa of a subtractor 5 and the compensating quantity P0 are added by the second adder 5 to obtain a focus control signal S in accordance with S=(Pb-Pa)-(Pa+Pb).V0. Since the signal S includes an extent of mechanical deviation of the bisected photodetector 7, V0 is so set that S=0 is true in the in-focus state. This set value V0 functions similarly even when the quantity of reflected light is changed and the focus control signal S is obtained which is 0 in the in-focus state even if the quantity of reflected light is changed.