Technique for controlling tracking in an optical disc apparatus

Claim 1

In a tracking control method for correcting the tracking error of a beam spot projecting upon a rotating optical disc having information recorded in the form of pits forming tracks, to correct deviation of the beam spot with respect to said tracks in a radial direction of said disc, wherein the method includes the steps of receiving a light beam modulated by the pits of said disc by a plurality of photoelectric detectors, producing a plurality of output signals representing a two-dimensional pattern of the light beam impinging upon said detectors in response to deviation of said beam spot from said tracks causing a tracking error, processing said signals to produce a tracking error signal, and correcting the tracking error of said beam spot in response to said tracking error signal, wherein the improvement in said receiving, producing and processing steps comprise: receiving the light beam by four photodetector regions divided in mutually orthogonal directions, one direction extending in the radial direction of the disc and the other direction extending perpendicular to said one direction; producing a first sum signal from the output signals of a first pair of said photodetector regions diagonally positioned with respect to one another and a second sum signal from the output signals of a second pair of said photodetector regions diagonally positioned with respect to one another; processing said first and second sum signals to etect a phase difference between said first and second sum signals to produce a phase difference signal representing the direction and magnitude of the tracking error; and deriving said tracking error signal from said phase difference signal.