A TECHNIQUE FOR CONTROLLING TRACKING IN AN OPTICAL DISC APPARATUS

In a method for detecting a tracking error of a light spot with respect to a track recorded spirally or concentrically on an optical video or audio disc on which a light beam emitted from a laser light source is to be focused as a light spot by an objective lens, a light flux reflected by the disc is made incident upon a photo-detector having four light receiving regions divided in orthogonal directions to generate four output signals, two output signals from two pairs of diagonally arranged regions are summed to produce first and second sum signals, and a tracking error signal is derived by detecting a phase difference between the first and second sum signals. In order to detect the phase difference, the first and second sum signals are supplied to first and second band pass filters, respectively and first and second limiter circuits, respectively to produce first and second zero cross signals and a phase difference between the first and second zero cross signals is detected by a phase comparator. It is possible to effect the tracking control in a stable manner without being affected by amplitude variation of the first and second sum signals and by frequency modulated components included in the first and second sum signals.