Abstract: A device according to the invention for scanning a rotating information carrier (2) comprises a transducer (10) and controller (20, 22) for controlling a scanning parameter of the transducer (10), such as the radial position and the setting of a focus. The controller comprise difference signal generator (20) for generating a difference signal (RE) which is indicative of a difference between a current value and a desired value of the scanning parameter, and correction signal generator (22) for generating a correction signal (SC) in response to the difference signal. The correction signal generator (22) comprise a delay loop (25) having first in first out memory (36) for generating a delayed signal (SDL1) and feedback filter (38) for filtering the delayed signal (SDL1).

Abstract: A device according to the invention for scanning a rotating information carrier (2) comprises a transducer (10) and control means (20, 22) for controlling a scanning parameter of the transducer (10), such as the radial position and the setting of a focus. The control means comprise difference signal generating means (20) for generating a difference signal (RE) which is indicative of a difference between a current value and a desired value of the scanning parameter, and correction signal generating means (22) for generating a correction signal (SC) in response to the difference signal. The correction signal generating means (22) comprise a delay loop (25) having first in first out memory means (36) for generating a delayed signal (SDL1) and feedback filter means (38) for filtering the delayed signal (SDL1).

Abstract: 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.

Abstract: A device for scanning a record carrier having essentially parallel tracks produces detection signals (AS, . . . , FS) which depend on the location of the scanning point relative to the tracks and from which are derived a tracking error signal (RE) and a track position signal (TP). A comparator (7) detects whether the track position signal intersects a first threshold (D1), and a comparator (6) detects whether the tracking error signal is located within an amplitude window established by a second positive threshold (D2) and a third negative threshold (D3). A signal processor (8) derives a track loss signal from the results of the detections performed by the comparators (6, 7), which track loss signal signifies that the scanning point no longer follows the track.