Method and device for controlling an optical beam incident on a movable data carrier track, in particular a digital disk with a high rotation speed

摘要

Procedure using an optical receiver comprising four photo-detectors for four elementary signals. The signals are split into two secondary pairs of signals sampled and filtered by two low pass filters with a cut-off frequency equal to a quarter of the sampling frequency. The phase difference between the two signals is proportional to the positioning error of the laser beam. Determination of the phase difference involves selection of at least two samples (ECHM, ECHm) above or below a threshold amplitude plus or minus TH about a given level (SE). Hence two transitions (ECH12) of the secondary signals with respect to a threshold corresponding to crossing in the same direction of the threshold can be marked. The time scale between the two transitions can be found which then relates to the distance the laser light beam is from its correct path.