JPS6459639A - Servo device for optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To detect a focusing error and a tracking error with high accuracy by adding outputs of a photodetector so as to obtain the total reflection luminous quantity, attenuating it to a voltage corresponding to the output offset, subtracting the attenuator output from the detector output and applying D/A conversion to the result. CONSTITUTION:Detectors 4, 5 apply photoelectric conversion to an output of an optical system 3 to generate a focus error signal and a tracking error signal. Signals are added by an adder 7 and the result is attenuated to a voltage corresponding to the offset by an attenuator 8. The output of the attenuator 8 is subtracted from the output of the detectors 4, 5 subject to time division multiplex by the switch 6 by a subtractor 9 and the result is converted by an A/D converter 10. An arithmetic circuit 11 subtracts the signal subject to A/D conversion 10 from the output of the detectors 4, 5 to obtain a focus error and a tracking error, they are subject to phase compensation and gain control and the focusing and tracking drive signal is outputted in time division. The result is given to actuators 14, 15 via a D/A converter 12 and a time division switch 13 to apply focusing and tracking servo. Through the constitution above, the error is detected with high accuracy in the dynamic range at D/A conversion.