Optical information reproduction device and signal processing circuit used therein

• US 6,320,830 B1
• Filed: 01/29/1999
• Issued: 11/20/2001
• Est. Priority Date: 02/02/1998
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Goto, Kenji, Umeyama, Takehiko, Tsukamoto, Manabu, Shimamoto, Masayoshi, Inoue, Yoshiji
• Primary Examiner(s): Hudspeth, David
• Assistant Examiner(s): CHU, KIM KWOK
• Application Number:
  US09/239,857
• Time in Patent Office: 1,026 Days
• Field of Search: 369/32, 369/275.2, 369/44.26, 369/275.4, 369/47.19, 369/44.28, 369/44.25, 369/44.29, 369/44.35
• US Class Current: 369/47.19
• CPC Class Codes: G11B 7/0053 Reproducing non-user data, e.g. wobbled address, prepits, BCA
• CPC Class Codes: G11B 7/0948 specially adapted for detection and avoidance or compensation of imperfections on the carrier, e.g. dust, scratches, dropouts G11B7/095 takes precedence

Abstract

In an optical information reproduction device for reproducing information from an optical disk medium on which an identification information area including first identification information shifted radially outward with respect to the center of a recording track by a specified distance and second identification information shifted radially inward with respect to the center of a recording track by a specified distance, and a user information area disposed along the center of a recording track are disposed, information is reproduced using a sum signal and a difference signal of the outputs from a split photodetector having at least two light-receiving parts disposed on opposite sides of a track tangential line. The first or second identification information signal is inverted and the direct-current component in the identification information signal and the user information signal are removed.

Claims

1. An optical information reproduction device for reproducing information from an optical disk medium on which an identification information area including first identification information shifted radially outward with respect to the center of a recording track by a specified distance and second identification information shifted radially inward with respect to the center of a recording track by a specified distance, and a user information area disposed along the center of a recording track are disposed in concentric or spiral form, said optical information reproduction device comprising:

an optical head illuminating the optical disk medium with a light beam, and including a split photodetector having at least two light-receiving parts disposed on opposite side of a track tangential line in the far field of the optical disk medium and receiving light reflected from the optical disk medium,

an adding means for adding the outputs of said optical head;

a subtracting means which obtains a difference between the outputs of said optical head;

a difference signal processing means which makes the output of said subtracting means similar to the output signal of said adding means in waveform pattern;

a signal selecting means which selectively outputs the output of said adding means and the output of said difference signal processing means; and

a waveform shaping means which detects the information recorded on said disk medium from the output signal of said signal selecting means;

said signal selecting means being set to select the output of said difference signal processing means or the output of said adding means when said identification information area is being scanned and to select the output of said adding means when said user Information area Is being scanned.

2. A signal processing circuit of an optical information reproduction device for reproducing information from an optical disk medium on which an identification information area including first identification information shifted radially outward with respect to the center of a recording track by a specified distance and second identification information shifted radially inward with respect to the center of a recording track by a specified distance, and a user information area disposed along the center of a recording track are disposed in concentric or spiral form, and including an optical head illuminating the optical disk medium with a light beam, and including a split photodetector having at least two light-receiving parts disposed on opposite side of a track tangential line in the far field of the optical disk medium and receiving light reflected from the optical disk medium, said signal processing circuit comprising:

an adder adding the outputs of the split photodetector;

a subtracter which obtains a difference between the outputs of the split photodetector;

a difference signal processor which makes the output of said subtracter similar to the output signal of said adder in waveform pattern;

a signal selecter which selectively outputs the output of said adder and the output of said difference signal processor; and

a waveform shaper which detects the information recorded on said disk medium from the output signal of said signal selecter;

said signal selecter selecting the output of said difference signal processor or the output of said adder when said identification information area is being scanned and selecting the output of said adder when said user information area is being scanned.

3. The signal processing circuit according to claim 2, wherein said difference signal processor comprises:

a polarity inverter inverting the polarity of the output of the subtracter;

a selector selectively outputting the output of the subtracter and the output of the polarity inverter; and

a polarity switching signal generator generating a switching timing for said selecter.

4. The signal processing circuit according to claim 3, wherein said polarity switching signal generator comprises:

a first gate generator generating a first gate signal indicating the position at which the first identification information appears;

a second gate generator generating a second gate signal indicating the position at which the second identification information appears; and

a polarity judger for judging the polarity of the waveform of the output of the subtracter.

5. The signal processing circuit according to claim 4, wherein said user information area includes user information and wherein said waveform shaper comprises:

a direct-current component rejecter removing the direct-current component of the output of the signal selecting means with a first time constant;

a third gate generator generating a gate signal indicating the position at which the user information appears;

a fourth gate generator generating a gate signal indicating the position of a defect;

a boost gate generator generating a first boost gate signal changing the first time constant of the direct-current component rejecter in accordance with the outputs of said first gate generator, said second gate generator, said third gate generator, and said fourth gate generator; and

a signal slicer binarizing the output of the direct-current component rejecter;

said direct-current component rejecter reducing said first time constant for a predetermined period after the beginning of the first identification information, the beginning of the second identification information, the beginning of the user information, and the end of the defect.

6. The signal processing circuit according to claim 5, wherein said signal slicer comprises:

a first binarizing circuit binarizing the output of the direct-current component rejecter at a slice level;

a slice level controller controlling the slice level to an optimum value with a second time constant based on the output of said first binarization means;

a slice level adjuster applying an offset to the slice level set by said slice level controller; and

a second binarizating circuit binarizing the output of the direct-current component rejecter at the output of said slice level adjuster.

7. The signal processing circuit according claim 6, wherein said slice level adjuster sets the offset values separately for the first identification information, the second information, and the user information.

8. The signal processing circuit according to claim 6, wherein said slice level adjuster generates a second boost gate signal in accordance with the outputs of the first to fourth gate generators, and reduces the time constant for control of the slice level, for the period of said second boost gate signal.

9. The signal processing circuit according to claim 8, wherein said first boost gate generator and the slice level adjuster set the duration of the boost gate signal separately from each other.

10. The signal processing circuit according to claim 8, wherein said boost gate generator and the slice level adjuster vary the duration of the boost gate signal according to the reproduction speed.

11. The signal processing circuit according to claim 6, wherein said direct-current component rejecter, and said slice level controller vary said time constants according to the reproduction speed.

12. The signal processing circuit according to claim 6, wherein said recording tracks comprise groove tracks in concentric or spiral form on the optical disk medium, and land tracks formed between groove tracks, and said slice level adjuster sets the offset separately for the first identification information, the identification offset information, and the user information of the groove tracks and land tracks.

13. An device reproducing information from an optical disk medium being scanned, said device comprising:

an adding circuit having at least two inputs, each of said at least two inputs being operatively connected to one of at least two outputs of an optical head, said adding circuit having as an output a first signal related to the sum of the at least two outputs of the optical head;

a subtracting circuit having at least two inputs, each of said at least two inputs being operatively connected to one of said at least two outputs of the optical head, said subtracting circuit having as an output a second signal related to the difference between the at least two outputs of the optical head;

a signal processing circuit having at least one input operatively connected to said output of said subtracting circuit, said signal processing circuit having as an output a third signal that is either related to the second signal or that is related to the selectively modified second signal, said processing circuit ensuring that said third signal is similar in waveform pattern to said first signal;

a signal selecting circuit having at least two inputs, one of said at least two selecting circuit inputs operatively connected to said output of said adding circuit and the other of said at least two selecting circuit inputs operatively connected to said output of said signal processing circuit, said signal selecting circuit having as an output a fourth signal selectively related to said first signal or selectively related to said third signal; and

a waveform shaping circuit having at least one input operatively connected to said output of said signal selecting circuit, said waveform shaping circuit at least obtaining information recorded on the disk medium from said fourth signal.

14. The device according to claim 13 further comprising the optical head, said optical head illuminating the optical disk medium with a light beam, and said optical head including a split photodetector having at least two light-receiving parts disposed on opposite side of a track tangential line in the far field of the optical disk medium and receiving light reflected from the optical disk medium.

15. The device according to claim 13, wherein the optical disk medium has a user information area and an identification information area including at least first identification information and second identification information, wherein said signal selecting circuit selects said first signal or said third signal when the identification information area is being scanned, and wherein said selecting circuit selects said first signal when the user information area is being scanned.

16. The device according to claim 15, wherein said signal processing circuit comprises:

a polarity inverting circuit outputting a fifth signal related to the second signal having an inverted polarity;

a timing signal generating circuit generating a switching timing signal; and

a second selecting circuit having an input operatively connected to receive said switching timing signal and outputting a sixth signal selectively related to the second signal or the fifth signal.

17. The device according to claim 16, wherein said polarity inverting circuit comprises:

a first circuit generating a first gate signal indicating the position at which the first identification information appears;

a second circuit generating a second gate signal indicating the position at which the second identification information appears; and

a polarity judging circuit judging the polarity of the waveform of said second signal.

18. The device according to claim 17, wherein said waveform shaping circuit comprises:

a third circuit generating a third gate signal indicating the position at which the user information appears;

a fourth circuit generating a fourth gate signal indicating the position of a defect;

a direct-current rejection circuit having an input operatively connected to said signal selecting circuit and outputting, at a first time constant a seventh signal related to said fourth signal but with the direct-current component being removed;

a boost circuit generating a first boost gate signal changing said first time constant depending on said first gate signal, said second gate signal, said third gate signal, and said fourth gate signal; and

a signal slicing circuit having an input operatively connected to said direct-current rejection circuit and having as output an eighth signal related to the binarization of said sixth signal;

wherein said direct-current rejection circuit reduces said first time constant for a first period after the beginning of the first identification information, the beginning of the second identification information, the beginning of the user information, and the end of the defect.

19. The device according to claim 18, wherein said signal slicing circuit comprises:

a first binarization circuit binarizing said seventh signal at a slice level;

slice level control circuit controlling said slice level to an optimum value with a second time constant based on the output of said first binarization circuit;

slice level adjustment circuit applying an offset value to said slice level set by said slice level control circuit; and

a second binarization circuit binarizing said seventh signal at the output of said slice level adjustment circuit.

20. The device according claim 19, wherein said slice level adjustment circuit sets the offset value depending on the first identification information, the second information, and the user information.

21. The device according to claim 19, wherein said slice level adjustment circuit generates a second boost gate signal according to said first, second, third, and fourth circuits, and wherein said slice level adjustment circuit reduces said second time constant for the duration of said second boost gate signal.

22. The device according to claim 21, wherein said boost circuit and said slice level adjustment circuit independently set the durations of said first boost gate signal and said second boost gate signal, respectively.

23. The device according to claim 21, wherein said boost circuit and the slice level adjustment circuit vary the durations of said first boost gate signal and said second boost gate signal, respectively, according to a reproduction speed.

24. The device according to claim 19, wherein said direct-current rejection circuit and said slice level control circuit vary said first and said second time constants, respectively, according to a reproduction speed.

25. The device according to claim 19, wherein and said slice level adjuster sets the offset separately for the first identification information, the identification offset information, and the user information of the groove tracks and land tracks.