EP0138275A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Apparatus for reproducing information from an optically readable record carrier
Assignee: Koninklijke Philips NV
•
Filing: 1984-10-10
•
Granted: —
•
Expires: 2004-10-10
Abstract
Abstract An apparatus is described for reading an optical record carrier. Tracking errors are detected by comparing the signal obtained during read out of the pits with the signal obtained during read out of the areas between the pits. In particular, the signal read is sampled in synchronism with the bit frequency and is processed digitally.
Inventors
- 👤 Martinus Petrus Maria Bierhoff
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 15:14
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/08; G11B7/085; G11B20/00; G11B20/10; G11B20/18; G11B27/00; G11B27/36; G11B5/00; G11B5/012; G11B7/004; G11B7/005
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
164 words
An apparatus for reproducing information from an optically readable record carrier on which the information is stored in the form of a track of optically detectable areas which alternate with intermediate areas, which apparatus comprises: an optical system for projecting a light beam on the record carrier, an optical detector for detecting the light beam modulated by the record carrier and generating a detection signal which is determined by said modulation, and track-loss detection means for generating a track-loss signal which is an indication of a condition in which the spot produced by the light beam is positioned off the track to a specific extent, characterized in that the track-loss detection means effect a comparison between a first signal supplied by the detector during scanning of the optically detectable areas and a second signal supplied by the detector during scanning of the intermediate areas, and the track-loss signal is generated when the first signal is larger than a predetermined fraction of the second signal.
Claim 2
Independent Claim
164 words
An apparatus for reproducing information from an optically readable record carrier on which the information is stored in the form of a track of optically detectable areas which alternate with intermediate areas, which apparatus comprises: an optical system for projecting a light beam on the record carrier, an optical detector for detecting the light beam modulated by the record carrier and generating a detection signal which is determined by said modulation, and track-loss detection means for generating a track-loss signal which is an indication of a condition in which the spot produced by the light beam is positioned off the track to a specific extent, characterized in that the track-loss detection means effect a comparison between a first signal supplied by the detector during scanning of the optically detectable areas and a second signal supplied by the detector during scanning of the intermediate areas, and the track-loss signal is generated when the first signal is larger than a predetermined fraction of the second signal.
Claim 3
Dependent Claim
55 words
An apparatus as claimed in Claim 1, characterized in that the apparatus comprises detection means for detecting signal drop-outs which are identified by the first signal being substantially identical to the second signal, the track-loss detection means being adapted to inhibit the generation of a track-loss signal during the occurrence of such a signal drop-out.
Claim 4
Dependent Claim
37 words
An apparatus as claimed in Claim 1 or 2, characterized in that said fraction comprises a modulation factor which is determined by the average strength of the first signal and the average strength of the second signal.
Claim 5
Dependent Claim
106 words
An apparatus as claimed in Claim 1, 2 or 3, characterized in that the apparatus comprises: oscillator means for supplying a clock signal, an analog-to-digital converter which is clocked by the oscillator means for sampling a detection signal detected by the detector both during scanning of the optically detectable areas and during scanning of the intermediate areas, detection means for identifying samples as originating either from an optically detectable area or from an intermediate area, and signal-separating means for separating, under command of the detection means, the samples taken during scanning of the optically detectable areas and the samples taken during scanning of the intermediate areas.
Claim 6
Dependent Claim
49 words
An apparatus as claimed in Claim 4, characterized in that the detection means are adapted to detect one sample per optically detectable area and one sample per intermediate area, the clock frequency being equal to or being a multiple of the bit frequency of the digital information being read.
Claim 7
Dependent Claim
41 words
An apparatus as claimed in Claim 5, characterized in that the detection means are adapted to detect said one sample only when the optically detectable areas and intermediate areas are longer than the predetermined number of periods of the bit frequency.
Claim 8
Dependent Claim
78 words
An apparatus as claimed in Claim 6, characterized in that the signal-separating means comprise: first and second storage means to which the samples are applied, the first storage means are switched on by th.;: detection means only upon detection of said one sample if this sample originates from intermediate area and the second storage means are switched on by the detection means only upon detection of said one sample if this sample originates from an optically detectable area.
Claim 9
Dependent Claim
108 words
An apparatus as claimed in Claim 7, characterized in that the detection means comprise counting means which are started upon every transition between an optically detectable area and an intermediate area and which are arranged to count in the rhythm of the clock signal of bit frequency and to generate a control signal for the first storage means when a predetermined count is reached while scanning an intermediate area and a control signal for the second storage circuit when said predetermined count is reached while scanning an optically detectable area, the samples being applied to the storage means with a delay of a predetermined number of clock periods.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.