APPARATUS AND DETECTION UNIT FOR SCANNING OPTICALLY READABLE RECORD CARRIER

摘要

PURPOSE: An apparatus and a detection unit are provided to scan a record carrier generating a tracking error signal which is more reliable. CONSTITUTION: A light beam modulated by information marks in a track on the record carrier is projected onto a detection unit(15) comprising four detectors. A reliable tracking error signal based on time differences between detector signals is obtained by comparing digitized signals of the detectors with a delayed signal Td when high-density is recorded. The time differences between the detector signals is the length differences between pulses having a nominal length of Td in the compared signals A and B. The compared signals A and B are low-pass filtered and combined to generate the tracking error signal TE.