Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal gain processing
Patent
1997-10-03
2000-08-29
Tran, Thang V.
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal gain processing
369 48, 369124, G11B 700
Patent
active
061118338
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a data decoding apparatus adapted for decoding, on the basis of at least one comparison level, a reproduction RF signal which has been read out from a recording medium on which information are recorded by using RLL (Run Length Limited) codes to output channel bit data, and more particularly to a data decoding apparatus such that in the case where any portion which does not satisfy the condition of the minimum run length or the maximum run length of the same symbols exists in channel bit data, bit of high probability considered to be bit error is selected on the basis of reproduction RF signal level when level judgment is carried out to correct the selected bit to output channel bit data which satisfies the conditions of the minimum run length and the maximum run length of the same symbols.
BACKGROUND ART
In transmitting data, or recording data onto a recording medium, e.g., magnetic disc, optical disc or magneto-optical disc, etc., modulation of data is carried out so as to become in conformity with transmission or recording. Block encoding is known as one of such modulation systems. This block encoding is adapted to block data train into units consisting of m.times.i bits (hereinafter referred to as data words) to convert such data words into code words consisting of n.times.i bits in accordance with the suitable code rule. In this case, when i is equal to 1, this code word is caused to be fixed length code, while when plural values can be selected as i, i.e., i is equal to 2 or more and conversion is made by i max=r which is the maximum i, that code word is caused to be variable length code. This block encoded code is generally represented as variable length code (d, k; m, n; r). In this expression, i is constraint length and r is the maximum constraint length. In addition, d and k respectively denote the minimum successive number of "0" and the maximum successive number of "0" falling (assigned) between successive "1" within the code series.
The modulation system used in the Compact Disc (CD) system as a more practical example will now be explained. In the compact disc system, EFM (Eight to Fourteen Modulation) system is used. Data words of 8 bits are subjected to pattern conversion into code words (channel bit data) of 14 bits thereafter to add respective margin bits of 3 bits for the purpose of reducing d.c. component (DSV) after undergone EFM to record, onto the disc, code words to which the margin bits are respectively added after undergone NRZI modulation. In this case, in order to satisfy the condition where the minimum successive number of logic "0" levels is 2 and the maximum successive number of logic "0" level is 10, conversion from 8 bits into 14 bits and addition of margin bits are carried out. Accordingly, the parameter of this modulation system is (2, 10; 8, 17; 1). When bit interval of the channel bit data train (recording waveform train) is assumed to be T, the minimum inverting (inversion) interval T.sub.min is 3(=2+1)T. Further, the maximum inverting interval T.sub.max is 11(=10+1)T. In addition, the detection window width T.sub.w is expressed as (m
)xT, and its value is 0.47 (=8/17) T in the above-mentioned example.
Moreover, the minimum run length d' of the same symbols after undergone NRZI modulation is 3(=d+1=2+1), and the maximum run length k' of the same symbols is 11(=k+1=10+1).
In the above-described compact disc system, if pits on the optical disc are reduced in the linear velocity direction, the recording density can be caused to be high. In this case, the minimum pit length corresponding to the minimum inverting interval T.sub.min is reduced. When this minimum pit length is too smaller than the spot size of laser beam, detection of pits becomes difficult. This constitutes the cause of occurrence of error.
Further, in reproduction of the disc, when skew is applied to the reproduction surface of the disc, the error rate is deteriorated. The skew (angle) of the disc is gradient (inclined angle) that the disc and the optical axis fo
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Ino Hiroyuki
Kai Shinichi
Nakagawa Toshiyuki
Yoshimura Shunji
Frommer William S.
Sony Corporation
Tran Thang V.
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