APPARATUS FOR OPTICALLY SCANNING A DISC-SHAPED RECORD CARRIER

摘要

An apparatus for optically scanning a disc-shaped record carrier, which apparatus comprises a radial tracking control system which employs a radial error signal obtained by comparing two signals supplied by two radially adjacent detectors. In order to correct tracking errors caused by deviations between the signals supplied by the two detectors the correlation between the radial error signal and the amplitude of the information signal being read is measured. The control signal obtained by means of this correlation measurement controls a balancing amplifier-circuit for balancing the two signals supplied by the detectors. Suitably a signal of predetermined frequency is injected into the control loop to cause the scanning beam to oscillate relative to the track so as to improve the correlation measurement. This injected signal may also be used for stabilizing the loop gain in the radial tracking control loop.