Patent ID: 7289399
Filing Date: 2007-10-30
Classification: G11B

Abstract:
1. A tracking error detection apparatus comprising: a photodetector comprising four photoreceptor elements which are partitioned along a tangential direction and a perpendicular direction with respect to an information track that is recorded as an information pit line on an optical disc to be played; zerocross detection circuits for detecting zerocross points at which two digital signals intersect center levels of the respective digital signals, each of said two digital signals being obtained by adding output signals from the two photoreceptor elements positioned on a diagonal line, among four signals that are generated according to the amounts of light received by the respective photoreceptor elements and are outputted from the photodetector; a phase difference detection circuit for performing phase comparison based on a distance between the zerocross points of the two digital signals, and limiting a result of phase comparison to a value under a first predetermined value when the result of phase comparison is larger than the first predetermined value; and a low-pass filter for performing band restriction to a signal outputted from the phase difference detection circuit to obtain a tracking error signal, wherein, the first predetermined value is a maximum value of the tracking error signal, the maximum value being based on a relationship between a shortest pit length and a track pitch of the optical disc to be played.