Apparatus for demodulating digital FM signal in an optical disc device
AssigneeSony Corporation
InventorYoshiro Joichi
Life of this patent
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Abstract
A frequency modulated signal, which is expected to have level inversions at data bit boundaries, and which is produced by the reflection of a laser beam from a wobbled spiral groove on a disk-shaped recording medium is detected. The frequency modulated signal is demodulated and its signal level at the location just after the absence of a level inversion is corrected. The position of a movable recording/reproducing head is determined in response to the demodulated FM signal; and data is recorded on or reproduced from the recording medium at the determined position.
Claims18
Apparatus for recording or reproducing data on a disc-shaped recording medium having a wobbled spiral groove thereon, comprising:
- means for emitting a laser beam to impinge on said recording medium;
- means for receiving said laser beam reflected from said recording medium;
- means for detecting a frequency modulated signal produced by the reflection of said laser beam from said spiral groove and which is expected to have level inversions at data bit boundaries of said frequency modulated (FM) signal;
- means for demodulating said FM signal, said means for demodulating includes means for correcting a signal level of said FM signal just after said means for detecting senses the absence of a level inversion at a respective one of said data bit boundaries;
- a recording or reproducing head moveable in respect to said recording medium;
- means for determining a position of said recording or reproducing head on said recording medium in response to said demodulated FM signal;
- and
- means for recording data on or reproducing data from said determined position on the recording medium by means of said head.
Apparatus for recording or reproducing data on a disc-shaped recording medium having a wobbled spiral groove thereon, comprising:
- means for emitting a laser beam to impinge on said recording medium;
- means for receiving said laser beam reflected from said recording medium;
- means for detecting a FM signal produced by the reflection of said laser beam from said spiral groove and which contains error correcting code and is expected to have level inversions at data bit boundaries of said FM signal;
- means for demodulating said FM signal, said means for demodulating includes means for modifying a signal level of said FM signal just before and just after said means for detecting senses the absence of a level inversion at a respective one of said data bit boundaries to provide first and second modified FM signals, respectively;
- means for evaluating said first and second modified FM signals using said error detecting code included in said FM signal so as to determine which of said first and second modified FM signals corrects said uninverted data bit boundary in said FM signal;
- means for selecting said modified FM signal which corrects said uninverted data bit boundary;
- means for correcting said FM signal in accordance with said modified FM signal selected by said selecting means to provide a corrected FM signal;
- a recording or reproducing head movable in respect to said recording medium;
- means for determining a position of said recording or reproducing head on said recording medium in response to said corrected FM signal;
- and
- means for recording data on or reproducing data from said determined position on the recording medium by means of said head.
A method of recording or reproducing data on a disc-shaped recording medium having a wobble spiral groove thereon, comprising the steps of
- emitting a laser beam to impinge on said recording medium;
- receiving said laser beam reflected from said recording medium;
- detecting a FM signal produced by the reflection of said laser beam from said spiral groove and which contains error correcting code and is expected to have level inversions at data bit boundaries of said FM signal;
- demodulating said detected FM signal by modifying a signal level of said FM signal just before and just after a data bit boundary at which a signal level inversion is nonexistent so as to provide first and second modified FM signals, respectively, evaluating said first and second modified FM signals using said error detecting code included in said detected FM signal so as to determine which of said first and second modified FM signals corrects said uninverted data bit boundary in said detected FM signal, selecting said modified digital FM signal which corrects said uninverted data bit boundary, and correcting said detected FM signal in accordance with the selected modified digital FM signal to provide a corrected FM signal;
- determining a position of a recording or reproducing head on said recording medium in response to said corrected FM signal;
- and
- recording data on or reproducing data from said determined position on the recording medium.
Dependencies are inferred from the claim text.