APPARATUS AND DETECTION UNIT FOR SCANNING AN OPTICALLY READABLE RECORD CARRIER

摘要

An apparatus for scanning an optically readable record carrier 1, in which a light beam modulated by the information marks in a track on the record carrier is incident on a detection unit with four detectors. A reliable tracking error signal based on time differences between detector signals, is obtained for high-density recording by comparing digitized signals of the detectors with a delayed signal Td generated by a delay unit and based on the digitized signals. The time differences between the detector signals result in length differences between pulses in the comparing signals A and B, which pulses have a nominal length of Td. The comparing signals A and B are low-pass filtered and combined to generate the tracking error signal TE.