Positioning control system utilizing optical beam having servo-error

Abstract

A positioning control system for performing recording/reproducing operations by irradiating an optical beam to predertermined position on an optically recording medium, e.g., magneto-optical disk, includes a photo-detector constituted by at least two-divisional units; and a servo-error signal generating circuit which can generate at least one servo-error signal in accordance with a difference between the detection currents. Preferably, servo-error signal generating circuit includes at least one division circuit that has two pairs of transistors, two emitters in each pair of transistors being connected together into a common emitter, bias voltages of direct current type being applied to the respective bases of transistors on one side, the respective collectors of the transistors on one side being connected to a common connecting portion via resistors, the common connecting portion being connected to a power supply, the respective bases of transistors on the other side being connected together into a common base; and an integrating capacitor which is connected to the common base of transistors on the other side, and which integrates a difference between the current flowing through the common connecting portion and the reference current, to apply the thus integrated difference to the common base of transistors on the other side. Further, preferably, the photo-detector is connected to the common emitters in the respective pairs of transistors, so that the detection currents can flow through the common emitters.