Optical information reproducing apparatus

Abstract: In reproduction of data from one of the N-frame sectors of an optical disk, data marks representing the front ends of their respective frames of a desired sector are detected and counted. When the number of the data marks is more than a predetermined value of M (1<M≦N), the data reproduced is accepted. Hence, the effectiveness of data can highly be ensured and the operating reliability of a data reproducing apparatus can be improved.

Description: The present invention relates to an optical information reproducing apparatus for reproduction of data recorded in sectors of a recording medium. Fig.1 is an external front view of a known optical disk. The optical disk denoted by the numeral 1 is provided with guide tracks 2 formed thereon in a spiral or concentric arrangement for optical detection and for serving as a guiding path(s), so that the recording tracks are arranged at high density and discrete writing and erasing of fragments of data can be ensured. The recording is thus made by forming pits or providing variations in reflectivity or transmittance with a beam of laser of less than 1 µm in diameter directed to a recording layer provided on the guide track 2. For recording a variable length digital information data, the track is separated into a plurality of sectors to enhance the recording efficiency, allowing the data to be recorded and reproduced on a sector by sector basis. Fig.2 shows a graphic representation of a sector. Each sector comprises an ID field 4 containing information of both track and sector addresses and a data field 5 for recording and reproducing data. A format of data in the data field 5 is shown in Fig. 3. The data field 5 comprises a pull-in signal 6 for pulling in with a phase locked loop, marks 7 for identification of the leading ends of data (which will be referred to as data marks hereinafter), and segments of data 8. For demodulation of the data, one of the data marks 7 is detected from a reproduced signal to produce an enable signal which announces the presence or absence of data. The enable signal is then examined as to whether it is active or non-active for determining that the data has been demodulated or not and also, for verifying the end of demodulation. On the other hand, if there is any flaw, dirt, or injury on the substrate, recording layer, or protective layer of the optical disk, the reproduced signal induces drop-out. Because both the size of each recording pit and the length of track pitch on the optical disk are as small as about 1 µm, the rate of actual operational error is practically not less than a range between 10⁻⁴ and 10⁻⁵ and also, the drop-out of the reproduction signal will occur at random or in an extensive burst-like form. Additionally, the recording layer of the optical disk is intended to involve a limited number of recording operations and the actual error rate will gradually be increased until finally demodulation becomes impossible. When determining whether a given sector is recorded or not or when retrieving an unrecorded sector, the leader of the data needs to be detected. When it is found out that a corresponding demodulation circuit remains inactivated, the sector is judged unrecorded. However, if a data mark of a data block in a sector is lost due to a drop-out and the data in the data block contains the same bit pattern as the data mark bit pattern, such bit pattern in the data would be erroneously detected as a data mark. Also, if a drop-out exits near a data mark in a sector in an adjacent track, the data mark in the adjacent track would be erroneously detected due to crosstalk. Such erroneous data mark detection will cause the corresponding demodulation circuit to be activated to inadvertently demodulate the data in the second defected due to drop out. It is also understood that a known rewritable optical disk becomes increased in operational error due to the fatigue of its recording layer after a particular number of recording operations. Although a corresponding demodulation circuit identifies a demodulation error such as bias demodulation, it cannot detect any sign of deterioration in the data. Accordingly, failure data will be demodulated for reproduction or the error cannot be corrected when surpassing its limit. European Patent Application EP-A-0282036 discloses an apparatus for recording data on an optical medium on which a plurality of blocks are provided in correspondence with a plurality of positions, each block having a header and a data recording area, the header including a plurality of block numbers each indicating the corresponding one of said positions, and said data recording area recording data; reproducing means for reproducing the block numbers from the header of said recording medium; recording means for recording the data into the recording medium; and inhibiting means for inhibiting recording of the data on the data recording area when at least two of said block numbers are not reproduced by the reproducing means. German Patent Application DE-A-3 704 898 discloses an optical disk apparatus for recording and reproducing information on and from an optical disk medium, which has formed thereon a plurality of tracks each divided into a plurality of sectors. The apparatus records data by "RAW" (read-after-write), whereby the data recorded into the sectors is immediately reproduced and verified in order to ascertain whether or not the data has been correctly written. It is a primary object of the present invention to provide an optical information reproducing apparatus adapted to improve its operational reliability and ensure the effectiveness of data to be demodulated by determining whether a corresponding circuit is turned on according to a normal procedure or a detection fault while detecting a data mark of the data. According to the present invention, there is provided an optical information reproducing apparatus for reproducing data recorded on an optical recording medium, the optical recording medium having formed thereon a plurality of tracks each being divided into a plurality of sectors each having N data blocks in which data are recorded, where N ≧ 2, each of the N data blocks having a data mark located at the leading portion thereof, said apparatus comprising: reproducing means for reproducing the data recorded on the recording medium to obtain reproduced data; data mark detecting means for detecting each data mark of the reproduced data; and demodulating means for demodulating the reproduced data to obtain a demodulated data, characterized by further comprising: counting means for counting the number of data marks detected by said data mark detecting means, said counting means having a count value in accordance with the number of data marks thus counted; and means responsive to the count value of said counting means for invalidating the demodulated data when the count value obtained from the reproduced data for each sector is smaller than a predetermined value M, where l < M ≦ N. The value of value of M may arbitrarily be determined for presetting, depending on the number and state of drop-out failures on an optical disk to be detected. In the operation of reproducing recorded data from a given sector and particularly, retrieving a non-recorded sector having N of the blocks, which will also be referred to as frames, if an error data mark is detected due to the effect of drop-out existing on an optical disk causing a corresponding reproduction circuit to start operating, the number of the data marks provided in the front ends of their respective frames is read and counted. When the number is greater than M (l<M≦N), the data in data fields of the sector is accepted. This allows determining whether the demodulation circuit is normally activated or not, whereby the effectiveness of data will be ensured and the operating reliability of the apparatus will be improved. Fig.1 is an external front view of an optical disk; Fig.2 is a diagram showing a sector on the optical disk; Fig.3 is a diagram showing a recording format of the sector composed of frames; Fig.4 is a block diagram showing an embodiment of the present invention in the form of an optical information reproducing apparatus; and Fig.5 is a timing chart of demodulation of data. A preferred embodiment of the present invention will be described in detail referring to the accompanying drawings. Fig.4 is a block diagram showing an optical information reproducing apparatus according to the present invention, in which represented by the numeral 9 is an optical detector for reproduction of data from an optical disk 1, 11 is an amplifier for amplifying a reproduced signal 10, 12 is a waveform equalizer, 13 is a binary comparator for binarizing or digitizing the reproduced signal, 15 is an address reproduction circuit for read-out of the address of an ID field section, 17 is a central processing unit (CPU), 18 is a clock reproduction circuit for read-out of a reproduced signal 14 which has been binarized, 20 is a shift register for shifting the binarized reproduced signal 14 from serial to parallel form, 21 is a parallel data output produced by the shift register 20, 22 is a data mark detection circuit for detection of a data mark pattern, 24 is a timing gate generation circuit for control on the execution of demodulation, 27 is a demodulation circuit for demodulating the reproduced signal, 30 is a data mark counting circuit for counting the number of data marks detected from the reproduced signal, 33 is a presetting circuit for setting a specific number of data marks, and 35 is a determining circuit for comparing a presetting value with an output from the data mark count circuit 30. Data recorded in one of sectors 3 along a guide track 2 of the optical disk 1 is read by the optical detector 9 for reproduction. A reproduced signal 10 of the data which is minimal is amplified by the amplifier 11 and shaped in waveform with the waveform equalizer 12. The reproduced signal passed through the waveform equalizer 12 is then binarized by the binary comparator 13 to turn to a binarized, or digital, reproduced signal 14. Meanwhile, the address of an ID field section of the sector is read by the address reproduction circuit 15 for output of an address reproduction signal 16 of the sector. For retrieval of data from a desired sector, the CPU 17 supplies a demodulation instruction signal 25 to the timing gate generation circuit 24 upon receiving such an address reproduction signal 16 for the desired sector. Also, the shift register 20 performs shift operation in sequence according to a clock signal 19 extracted from the binarized reproduction signal 14 by the clock reproduction circuit 18. The binarized reproduction signal 14 is thus shifted by the shift register 20 from serial to parallel form, i.e to a parallel data output 21 which is in turn transmitted to the data mark detection circuit 22. The data mark detection circuit 22, when detecting the data mark bit pattern from the parallel data output 21, generates a data mark detection signal 23. In response to the data mark detection signal 23, the timing gate generation circuit 24 outputs a demodulation gate signal 26 to the demodulation circuit 27. Then, the demodulation circuit 27 commences demodulation of the binarized reproduction signal 14 to produce a demodulated data output 28 which will be transmitted further to a data processing unit 40. In addition, a presetting datum of M is given by the CPU 17 to a preset circuit 33 which in turn transfers the value of M to the determining circuit 35. On the other hand, the number of data marks in the data mark detection signal 23 detected by the data mark detection circuit 22 is counted by the data mark counting circuit 30 and a resultant value of m is sent to the determining circuit 35. The two values of M and m are then compared in the determining circuit 35. As the result of comparison, when m calculated from the counting of the data mark detection signal 23 with the data mark counting circuit 30 is equal to or greater than M of presetting, a data demodulation validation signal 36 is delivered to the CPU 17 which acts as a controller, informing that the desired sector is furnished with recorded data and also, demodulation of the data is normally being carried out. The CPU 17 then controls the data processing unit 40 according to the determination whether demodulation is normally executed or not. Fig.5 is a timing chart showing the demodulation of data. When the address information of a sector mark 4 preformated is identified, the CPU 17 transmits a demodulation instruction signal 25 to the timing gate generating circuit 24. Also, upon detecting the data mark, the data mark detection circuit 22 outputs a data mark detection signal 23. Then, the timing gate generating circuit 24 produces a demodulation gate signal 26 to enable the demodulation circuit 27. Only when the demodulation data signal 26 is active, the demodulation circuit 27 performs demodulation to produce a demodulated data output 28. The timing data generating circuit 27 transmits a demodulation completion signal 29 to the CPU 17 when having finished the demodulation of data of the final frame through counting the number of frames with a counter. The CPU 17 upon receiving the demodulation completion signal 29 shifts the demodulation instruction signal to non-active for terminating the demodulation. Also, during the demodulation, data marks are detected from the binarized reproduction signal by the data mark detection circuit 22 and the number of data mark patterns is counted by the data mark counting circuit 30. A resultant number of m is then compared with the presetting value of M. If m≧M, a data demodulation validation signal 36 is generated for output. As shown in Fig.5, the number of the frames in the sector is 8, i.e. N=8, while the presetting of M is 6. Hence, when the number of detected data marks is more than 6, i.e. m>6, the demodulation validation signal 36 becomes active. M may be determined according to the number of frames and the capability of error correction.

Claims: An optical information reproducing apparatus for reproducing data recorded on an optical recording medium (1), the optical recording medium having formed thereon a plurality of tracks each being divided into a plurality of sectors each having N data blocks in which data are recorded, where N ≧ 2, each of the N data blocks having a data mark located at the leading portion thereof, said apparatus comprising: reproducing means (9) for reproducing the data recorded on the recording medium to obtain reproduced data; data mark detecting means (22) for detecting each data mark of the reproduced data; and demodulating means (27) for demodulating the reproduced data to obtain a demodulated data, characterized by further comprising: counting means (30) for counting the number of data marks detected by said data mark detecting means, said counting means having a count value in accordance with the number of data marks thus counted; and means (35,17,40) responsive to the count value of said counting means for invalidating the demodulated data when the count value obtained from the reproduced data for each sector is smaller than a predetermined value M, where 1 < M ≦ N. An apparatus according to claim 1, further comprising means (33) for changing said predetermined value M.

Inventors: HIROYOSHI JUN, KUROKI YUZURU, SATOH ISAO, HIROYOSHI, JUN, KUROKI, YUZURU, SATOH, ISAO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G11B20
IPC codes: G11B27, G11B20