Plural beam tracking servo including delay compensation

Abstract

A tracking servo circuit for controlling an optical pickup is used in a tracking error detecting device including an optical system for forming on an optical disc a main light spot for illuminating a pit on the optical disc and forward and backward sub-light spots. The forward and backward sub-light spots are disposed before and behind the main light spot in the moving direction of a track with a small distance between each of the sub-light spots and the main light spot and are shifted from the center line of the track, so that a half of each sub-light spot area is placed on the pits of the track. The tracking servo circuit includes photodetectors for detecting reflected light based upon the forward and backward sub-light spots, a tracking-error-signal detecting circuit for detecting a difference between output signals from the photodetectors, a tracking control circuit for controlling on the basis of an output signal from the tracking-error-signal detecting circuit an optical pickup for reading out a recorded signal which is recorded on a spiral track of the optical disc in the form of a row of pits, and a delay circuit for delaying the output signal from the photodetector. A difference between the output signal delayed by the delay circuit and the output signal from the photodetector is used as a tracking error signal.