Disc recording medium and apparatus for reproducing data from disc recording medium

Abstract: A disc recording medium is provided for enhancing a capability of correcting a burst error caused by small dust left on the surface of a disc substrate. The data of two-dimensionally arrayed ECC blocks consisting of 172 words × 192 rows contains the PI parity and the PO parity added in the two error-correcting systems. The PI parity is intended for error correction for data arranged to go down by one row with advance of one word in the direction of a bit stream. The PI parity is intended for going back to the first row when the data being interleaved exceeds 192 rows. The PO parity is intended for error correction for data arranged to interleave the data perpendicularly to the bit stream.

Description: The present invention relates to a disc recording medium having a function of error-correcting data to be recorded on the medium and an apparatus for reproducing the data from the disc recording medium. In a case that a recording medium such as an optical disc contains defects or dust adhering to a recording plane of the disc, an error takes place on the data to be reproduced from the recording medium. This error makes the servo operation unstable and thereby brings about a further data error. In general, the data recorded on the optical disc is recorded together with parity bits used for error correction. For example, consider an optical disc such as a digital video disc whose recording capacity is on the several giga bytes level. This kind of optical disc is arranged to perform error correction about each unit data of 32 KB. This error correction unit is referred to as an ECC block. Fig.1 is a model view showing a format of an ECC block of the optical disc. This ECC block is composed of a two-dimensional array consisting of 172 words × 192 rows and contains parity bits added in two error-correcting systems. The format of this ECC block is arranged to add parity bits for ten words of 172 words in the direction of the bit stream of the data, that is, the direction of C1 shown in Fig.1. (These parity bits in the C1 direction are referred to as a PI parity.) The format of this ECC block is arranged to range 192 rows each of which is composed of 172 words and the PI parities corresponding to ten words and add parity bits for 16 words in the direction perpendicular to the bit stream, that is, in the C2 direction shown in Fig.1. (These parity bits in the C2 direction are referred to as a PO parity.) These PI and PO parities are used when the data is error-corrected by a RSPC (Reed Solomon Product Code). On the other hand, in recent days, an optical disc is now being required for enhancing its density, for the purpose of recording a larger capacity of data than the digital video disc. In order to enhance the density of the optical disc, it is necessary to keep a spot size of a laser beam to be projected onto the recording medium smaller than the conventional size. The spot size of the laser beam has a radius R expressed as shown in the following expression (1). R = 0.32 λ / NA where NA denotes a numeric aperture and λ denotes a wavelength of the laser beam. As represented in this expression (1), for reducing the radius R of the spot size of the laser beam in size, it is necessary to shorten the wavelength λ of the laser beam or enlarge the numeric aperture NA of an objective lens. When the numeric aperture NA of the objective lens is made larger, however, the aberration is made so large that the signal cannot be recorded or reproduced from the recording medium. As one of the solving methods, it is known that the disc substrate is made so thin that the aberration becomes lower. If the thickness of the disc substrate is made thinner, as mentioned above, the aberration is lower. However, small dust left on the surface of the disc substrate brings about data error though such small dust conventionally has no influence on the recording and reproduction of the optical disc. Fig.2 is a graph showing an error propagation of an error against a diameter of dust left on the surface of the disc substrate as the thickness of disc substrate is changing. In this graph, an axis of abscissa denotes a diameter of dust left on the surface of the disc substrate, while an axis of ordinates denotes a propagating distance of error, in which the unit is a micrometer order. The error propagating length is calculated on the assumption that an error takes place when an amplitude of a RF signal output from a photo detector to which the reflected laser beam is applied is 55 % or less. It is grasped from the graph shown in Fig.2 that no error takes place if a dust diameter is about 300 micrometer or less when the thickness of the disc substrate is 1.2 mm. This thickness corresponds to the thickness of the so-called compact disc. Further, it is also grasped from the graph of Fig. 2 that no error takes place if the dust diameter is about 150 micrometer or less when the thickness of the disc substrate is 0.6 mm. This thickness corresponds to the thickness of the so-called digital video disc. Further, when the thickness of the disc substrate is 0.3 mm, the error propagating length is 200 micrometer when the dust diameter is about 100 micrometer. When the thickness of the disc substrate is 0.15 mm, the error propagating length is 60 micrometer when the dust diameter is about 20 micrometer. Further, when the thickness of the disc substrate is 0.02 mm, the error propagating length is several tens micrometer when the dust diameter is about several micrometers. As mentioned above, this graph has indicated that even dust of such a diameter as giving no influence when the disc substrate has a conventional thickness such as 1.2 mm or 1.6mm is likely to have influence on the data recording or reproduction. Hence, even small dust left on the surface of the disc brings about a data error even though it does not conventionally have any influence on the data recording and reproduction. US Patent Application No. US-A-4 680 764 discloses a method and apparatus for transmitting digital data in which codes are used to reduce the error rate of data reproduced from a disc. In one embodiment two Reed-Solomon codes are used, the two codes being interleaved in different directions to each other and to the recording or reproducing direction. The parities obtained from the two different codes are recorded subsequent to one another at the end of the data array. "The Digital Versatile Disc (DVD): System Requirements and Channel Coding" by Schouhamer Immink in SMPTE Journal, August 1996 discloses a DVD having a storage capacity several times higher than a CD. The substrate thickness of the DVD is 0.6mm and, in a variant in accordance with the pre-characterising part of claim 1 hereof, the error correction code used is a RS-PC error correction code. This document also discusses the use of a CIRC interleaving technique, which was specifically designed for very long, non-blocked data segments, such as digital audio or video The present invention seeks to address the above problems and to provide a disc recording medium which provides a higher capability of correcting a burst error against small dust left on the surface of the disc substrate and an apparatus for recording and reproducing data from the disc recording medium. According to a first aspect of the invention there is provided an optical disc on which is recorded blocked data containing parity bits added by performing interleaving in the direction of a bit stream and generated from a two-dimensional data array using first and second Reed Solomon error-correcting codes, said parity bits of the first error-correcting code being added to the end of the columns of said two-dimensional array, said parity bits of the second error-correcting code being added to the end of the rows of said two-dimensional array, said parity bits being generated on error-correcting blocks each comprising 16 sectors each in turn comprising 2KB of data, and frame synch data being recorded at each group of 91 bytes in each error-correcting block; characterised in that: said second error-correcting code is arranged to interleave in a slanted direction that is different both from the direction of blocked data for adding said parity bits, and from the direction of the first error-correcting code, and when said data being interleaved exceeds the total number of rows in said two-dimensional array, said second error-correcting code goes back to the first row and then advances the interleave again; and the thickness of a substrate of the disc is 0.3 mm or less. According to a second aspect the invention there is provided a reproducing apparatus for an optical disc as set forth above, the apparatus comprising: reproducing means for reproducing the blocked data from the optical disc; a memory; means for supplying blocks of the reproduced data to the memory; first error correcting means for de-interleaving and error-correcting the blocks in accordance with the parity bits of the first error-correcting code; and second error correcting means for de-interleaving and error correcting the blocks in accordance with the parity bits of the second error-correcting code. In operation, the reproducing apparatus error-corrects an error resulting from dust on the recording plane if it takes place in the reproduced data, based on the parity bits interleaved in the two error-correcting codes directed differently from the direction of the data. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig.1 is an explanatory view showing a format of an ECC block contained in a conventional optical disc; Fig.2 is a graph showing an error propagating length against a diameter of dust left on the surface of a disc substrate as the thickness of the disc substrate is changing; Fig.3 is an explanatory view showing a sector of an optical disc according to one embodiment of the present invention; Fig.4 is an explanatory view showing a format of an ECC block contained in the optical disc according to one embodiment of the present invention; Fig.5 is a view showing the interleaving direction of parity bits to be added to the ECC block; Fig.6 is an explanatory view showing a frame synchronization to be added to the ECC block; Fig.7 is a block diagram showing a recording apparatus for an optical disc for recording data from an optical disc according to one embodiment of the present invention; and Fig.8 is a block diagram showing a reproducing apparatus for an optical disc for reproducing data from an optical disc according to one embodiment of the present invention. Hereafter, an embodiment of the invention will be described with reference to the appended drawings. The optical disc according to the embodiment of the invention has a larger storage capacity than the digital video disc and has a thickness of 0.3 mm or less, for example. This optical disc contains a data block of 32 KB as one unit. A parity bit is added to each data block. The format of the data of this optical disc will be described below. The data recorded on the optical disc according to the invention is made up of sectors each of which is composed of data of 2 KB. As shown in Fig.3, concretely, this sector is composed of data of 2048 bytes, a sector address (ADR) of 16 bytes and an error-detecting code (EDC). The data recorded on this optical disc is error-corrected at a 16-sector unit. The error-correcting unit is referred to as an ECC block. As shown in Fig.4, the format of this ECC block is arranged so that 172 words of each block are ranged in the direction of bit stream, that is, the C1 director shown in Fig.4. The 192 rows each of which is composed of 172 words are ranged in the direction perpendicular to the bit stream, that is, the C2 direction shown in Fig.4. The two-dimensionally arranged data consisting of 172 words × 192 rows contains parity bits to be added in two error-correcting systems. These two kinds of error-correcting system parity bits are given by error-correcting the data with the RSPC (Reed Solomon Product Code). One kind of parity bits is called PI parity and the other kind of parity bits is called PO parity. The PI parity is added to the data block of 172 words and is compose of ten words. The PO parity is added to the data block of 192 words and is composed of 16 words. These PI and PO parities are added by doing the interleaving operation in the direction of the bit stream. As shown in an arrow A of Fig.5, the PI parity is given to the data arranged to go down by one row as it goes by one word in the direction of a bit stream. The PI parity is given to the data interleaved downward in the right slanting direction against the bit stream as viewed in Fig.5. When the data being interleaved exceeds 192 rows, as shown by an arrow B of Fig.5, the PI parity goes back to the first row and then advances the interleave again. As shown by an arrow C of Fig.5, the PO parity is given to the data being interleaved in the direction perpendicular to the bit stream. The ECC block contains a frame sync added at each group of 91 words as shown in Fig.6. This ECC block is recorded on the track. Hence, the optical disc according to this embodiment of the invention is arranged so that the two error-correcting systems of the ECC block have the corresponding interleave length directed in different ways against the recording direction. Hence, if a frequency of a short burst error is increased, the error can be randomized in different ways so that the error correction is made stronger accordingly. In turn, the description will be oriented to an optical disc recording apparatus for recording data on the foregoing optical disc and an optical disc reproducing apparatus for reproducing data from this optical disc. As shown in Fig.7, the optical disc recording apparatus 10 provides a PI encoder 12, a PO encoder 14 and a modulator 17 on a data bus as well as a PI address counter 13, a PO address counter 15 and an ECC out counter 16 on an address bus. Further, a random access memory 11 is also provided so that the memory 11 is connected to the data bus and the address bus. The PI encoder 12 is inputted with video data to be recorded on the optical disc from an external device. The PI encoder 12 operates to divide the inputted data into 32-KB blocks and then sequentially put the blocks into the random access memory 11. The 32-KB block is the error-correcting unit. When the random access memory 11 stores data of ECC blocks each consisting of 32 KB, the PI encoder 12 operates to count an address of the ECC block stored in the random access memory 11 and then supply the data of the counted address to the PI encoder 12. In the counting operation, the PI address counter 13 operates to interleave the two-dimensionally arrayed ECC blocks downward in the right slanting direction. The PI encoder 12 operates to perform an operation of a given error-correcting code (PI parity) with respect to the supplied data and then supply this PI parity to the random access memory 11. When all PI parities are obtained about the data of ECC blocks, the PO address counter 15 operates to count the addresses of the ECC blocks stored in the random access memory 11 and then supply the data of the counted address to the PO encoder 14. In the counting operation, the PO address counter 15 operates to interleave the two-dimensionally arrayed ECC blocks perpendicularly to the bit stream. The PO encoder 14 operates to perform an operation of a given error-correcting code (PO parity) with respect to the supplied data and then supply the PO parity to the random access memory 11. The PO encoder 14 operates to perform an operation of the PO parity about the PI parity obtained by the PI encoder 12 and then put it into the random access memory 11. When all PO parities are obtained about the data of ECC blocks, the ECC out counter 16 operates to add the address to the ECC block having the PI parity and the PO parity added thereto. Then, the ECC out counter 16 operates to supply the data from the random access memory 11 to the modulator 17 at an ECC block unit. The modulator 17 operates to add a frame synchronization to the ECC block data containing the address added thereto, perform a given modulation with respect to the resulting data and then supply it to a recording circuit such as a light pickup unit. The recording circuit operates to record the data on the optical disc. Hence, the optical disc recording apparatus 10 operates to add parity bits having interleave lengths directed in the two error-correcting systems differently from the recording direction when recording the data on the optical disc. As such, the optical disc recording apparatus 10 operates to randomize the error if a frequency of a short burst error is increased, for the purpose of implementing a strong error correction. On the other hand, as shown in Fig.8, the optical disc reproducing apparatus 20 provides a PI decoder 22, a PO decoder 24 and a demodulator 27 on a data bus and an PI address counter 23, a PO address counter 25 and an ECC in counter 26 on an address bus. A random access memory 21 is further connected to the data bus and the address bus. The demodulator 27 is inputted with a reproduction signal of the optical disc from a reproducing circuit such as a light pickup unit. The demodulator 27 operates to demodulate the reproduction signal from the light pickup unit in a predetermined modulating system and remove the frame synch added to the reproduction signal. The ECC in counter 26 operates to count the data demodulated by the demodulator 27 at an ECC block unit and sequentially supply the ECC block data to the random access memory 21. The random access memory 21 stores the data supplied from the demodulator 27. The data stored in the random access memory 21 contains the PI parity and the PO parity added thereto. When the random access memory 21 stores all data of ECC blocks each consisting of 32 KB, the PO address counter 25 operates to count the address of the ECC block stored in the random access memory 21 and supply the data block of the counted address and the PO parity corresponding to the data block to the PO decoder 24. The PO address counter 25 operates to de-interleave the two-dimensionally arrayed ECC blocks perpendicularly to the bit stream when counting the address. The PO decoder 24 operates to error-correct the supplied data based on the PO parity. The PO decoder 24 operates to supply the data to the random access memory 21 when the correct data is obtained by the error correction. The PO decoder 24 operates to obtain the correct data about the PI parity obtained by the PI encoder 12 and then supply it to the random access memory 21. When the PO decoder 24 obtains all ECC blocks, the PI address counter 23 operates to count the address of the ECC block stored in the random access memory 21 and supply to the PI decoder 22 the data of the counted address and the PI parity corresponding to the data. The PI address counter 23 operates to de-interleave the two-dimensionally arrayed ECC blocks downward in the right slanting direction when counting the address. The PI decoder 22 operates to error-correct the data based on the PI parity. After the correct data is obtained by the error correction, the PI decoder 22 operates to supply this correct data to the external device such as a reproducing device for video data. Hence, the optical disc reproducing apparatus 20 operates to de-interleave the data of the ECC blocks having different interleave lengths from the recording direction of the optical disc according to the present invention when reproducing the data. The optical disc reproducing apparatus 20 operates to randomize the error if a frequency of a short burst error is increased in the data reproduced from the optical disc, for the purpose of implementing the stronger error correction. The disc recording medium according to the invention is arranged to interleave the data in the two error-correcting systems that are different from each other and error-correct an error of the reproduced data caused by dust on the recording plane in the two error-correcting systems. Hence, the disc recording medium operates to enhance the correcting capability of a burst error caused by small dust left on the surface of the disc substrate. The reproducing apparatus for the disc recording medium according to the present invention is arranged to de-interleave the data in the two error-correcting systems that are directed differently from the data stream for the purpose of error-correcting the data and error-correct the error of the reproduced data caused by the dust left on the recording plane in the two error-correcting systems. The reproducing apparatus enables to enhance the correcting capability of a burst error caused by small dust left on the surface of the disc substrate and thereby reduce the error of the reproduced data. Many widely different embodiments of the present invention may be constructed without departing from the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification except as defined in the appended claims.

Claims: An optical disc on which is recorded blocked data containing parity bits added by performing interleaving in the direction of a bit stream and generated from a two-dimensional data array using first and second Reed Solomon error-correcting codes, said parity bits of the first error-correcting code being added to the end of the columns of said two-dimensional array, said parity bits of the second error-correcting code being added to the end of the rows of said two-dimensional array, said parity bits being generated on error-correcting blocks each comprising 16 sectors each in turn comprising 2KB of data, and frame synch data being recorded at each group of 91 bytes in each error-correcting block; characterised in that : said second error-correcting code is arranged to interleave in a slanted direction that is different both from the direction of blocked data for adding said parity bits, and from the direction of the first error-correcting code, and when said data being interleaved exceeds the total number of rows in said two-dimensional array, said second error-correcting code goes back to the first row and then advances the interleave again; and the thickness of a substrate of the disc is 0.3 mm or less. An optical disc according to claim 1, in which each said sector comprises 2048 bytes of data, a sector address (ADR) and an error detecting code. An optical disc according to claim 2, in which said sector address comprises 16 bytes. An optical disc according to any one of the preceding claims, in which the extent of each said sector comprises 172 bytes in the direction of data and 12 bytes in a direction orthogonal to the direction of data, and the extent of each said error-correcting block comprises 172 bytes in the direction of data and 192 bytes in the direction orthogonal to the direction of data. A reproducing apparatus capable of reproducing an optical disc according to any one of the preceding claims, the apparatus comprising: reproducing means for reproducing the blocked data from the optical disc; a memory (21); means (26,27) for supplying blocks of the reproduced data to the memory (21); first error correcting means (24,25) for de-interleaving and error-correcting the blocks in accordance with the parity bits of the first error-correcting code; and second error correcting means (22,23) for de-interleaving and error-correcting the blocks in accordance with the parity bits of the second error-correcting code.

Inventors: KOBAYASHI SHOEI, KOBAYASHI, SHOEI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1997
Main classification: G11B20
IPC codes: G11B20, G11B7