Coded data generation or conversion – Digital code to digital code converters – To or from minimum d.c. level codes
Reexamination Certificate
1999-08-20
2002-01-22
Wamsley, Patrick (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from minimum d.c. level codes
C341S059000, C341S067000
Reexamination Certificate
active
06340938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a demodulating device, a demodulating method and supply medium and more particularly to a demodulating device, a demodulating method and supply medium for reproducing data by demodulating data modulated suitably for data transmission or recording on a record medium.
2. Description of Related Art
When data is transmitted on a predetermined transmission path or recorded on a record medium such as a magnetic disk, an optical disk, a magneto-optic disc or the like, data is modulated to be suitable for transmission or recording. As one of such modulation methods, block coding is known. According to the block coding, a data string is blocked in a unit comprising m×i bits (hereinafter, simply referred to as data word) and the data word is converted into a data word comprising n×i bits in accordance with a pertinent code rule. Further, a code becomes a fixed length code when “i” is equal to 1 and becomes a variable length code when a plurality of “i”'s can be selected, that is, when the code is converted by selecting a predetermined one of “i ” in a range of “i”'s of 1 through imax (maximum“i”). The block-coded code is represented as a variable length code (d,k;m,n;r).
In this case, “i” is referred to as a constraint length and imax is referred to as a maximum constraint length “r”. Further, a minimum run “d” indicates a minimum number of consecutive “0”'s put between consecutive “1”'s in a code series and a maximum run “k” indicates a maximum number of consecutive “0”'s put between consecutive “1”'s in a code series.
In a compact disk, a mini disk or the like, there is carried out NRZI (Non Return to Zero Inverted) modulation in which the variable length code provided as described above is inverted with “1” and is not inverted with “0” and a variable length code which has been subjected to NRZI modulation (hereinafter, NRZI-modulated variable length code is referred to as level code) is recorded.
Further, when there is carried out inverse NRZI modulation in which the level code is set to “1” when the level code is inverted from “1” to “0” or from “0” to “1”, that is, when the level code constitutes an edge, a code string the same as original EFM code or RLL (1-7) code can be provided. The inverse NRZI code string is referred to as edge code.
When a minimum inversion interval of the level code is designated by notation Tmin and a maximum inversion interval thereof is designated by notation Tmax, in order to carry out high density recording in a linear velocity direction, the longer the minimum inversion interval Tmin, that is, the larger the minimum run d, the better, further, in view of reproducing clocks, the shorter the maximum inversion interval Tmax, that is, the smaller the maximum run k, the more preferable and various modulation methods have been proposed.
Specifically, there is provided RLL (Run Length Limited Code) (2-7) as a modulation system used in, for example, a magnetic disk, a magnet-optical disk or the like. Parameters of the modulation system is (2,7;1,2;4). When a bit interval of the level code is designated by notation T, the minimum inversion interval Tmin calculated by (d+1)T becomes 3T from (2+1)T. When a bit interval of the data string is designated by notation Tdata, the minimum inversion interval Tmin becomes 1.5Tdata from (m
)×Tmin=(½)×3. Further, the maximum inversion interval Tmax calculated by (k+1)T becomes 8(=7+1)T((=(m
)×Tmax)Tdata=(½)×8Tdata=4.0Tdata). Further, a detection window width Tw calculated by (m
)T becomes 0.5(=½)Tdata.
Otherwise, for example, there is RLL(1-7) as a modulation system used in recording of a magnetic disk, a magneto-optic disc or the like. Parameters of the modulation system are (1,7;2,3;2) and the minimum inversion interval Tmin becomes 2(=1+1)T(=⅔×2Tdata=1.33Tdata). Further, the maximum inversion interval Tmax becomes 8(=7+1)T(=⅔×8Tdata=5.33Tdata). Further, the detection window width Tw becomes 0.67(=⅔)Tdata.
When RLL(2-7) is compared with RLL(1-7), for example, in a magnetic disk system or a magnet-optical disk system, in order to increase a record density in the linear velocity direction, RLL(2-7) having the minimum inversion interval Tmin of 1.5Tdata is more preferably than RLL(1-7) having the minimum inversion interval Tmin of 1.33 Tdata. However, actually, RLL(1-7) having larger detection window width Tw and having a large allowance amount in respect of jitter is used more frequently than RLL(2-7).
The conversion table of RLL(1-7) code is, for example, a table shown by Table 1.
TABLE 1
RLL(1,7; 2,3; 2)
Data
Code
i=1
11
00x
10
010
01
10x
i=2
0011
000 00x
0010
000 010
0001
100 00x
0000
100 010
A symbol “x” in the conversion table is given “1” when a subsequent channel bit is “0” and given “0” when the subsequent channel bit is “1”. The maximum constraint length “r” is 2.
Further, the conversion table of RLL(2-7) code having the minimum run “d” of 2 and the maximum inversion interval Tmax of 8T (maximum run 7) is, for example, a table shown by
TABLE 2
RLL(2,7; 1,2; 4)
Data
Code
i=2
11
1000
10
0100
i=3
011
001000
010
100100
000
000100
i=4
0011
00001000
0010
00100100
The maximum constraint length “r” is 4.
Meanwhile, according to a channel bit string modulated by RLL(1-7), the occurrence frequency of 2T which is Tmin is the largest and followed by 3T and 4T. When much of edge information such as 2T or 3T is produced at early periods, it is preferable for reproducing clocks, however, when 2T's continue, a distortion is liable to cause in the record waveform (waveform output of 2T is small and susceptible to influence by defocusing or tangential tilt). Further, recording with high line density where minimum marks continue, is suspectible to influence of disturbance such as noise or the like and data reproduction error is liable to cause.
Hence, the applicant has proposed to restrict Tmin's from continuing by a predetermined number of times or more in Japanese Patent Application No. 9-133379 and the conversion table of the code is, for example, a table shown by Table 3.
TABLE 3
RML (1,7;2,3;3)
Data
Code
i=1
11
00x
10
010
01
10x
i=2
0011
000 00x
0010
000 010
0001
100 00x
0000
100 010
i=3
100110
100 000 010
The symbol “x” in the conversion table is given “1” when a subsequent channel bit is “0” and is given “0” when the subsequent channel bit is “1”. The maximum constraint length “r” is 3.
According to the conversion used in Table 3, in the case in which the data string becomes “10”, when subsequent 4 data are referred and the total 6 data string becomes “100110”, a code “100 000 010” for restricting repetition of the minimum run “d” is given. A number of the repetition of the minimum run “d” of the code provided by the conversion is 5 at maximum.
When the conversion using Table 3 is compared with RLL (1-7) of Table 1, although the minimum run “d”, the maximum run “k”, the basic data length “m” and the basic code length “n” remain the same, the constraint length “r” is increased from 2 to 3. This indicates that a maximum size of the table is increased and indicates that there is a possibility of increasing demodulation error propagation when, for example, bit shift error is caused in demodulation.
The bit shift error is an error in which “1” representing an edge in a code string is shifted forwardly or rearwardly by 1 bit. The error propagation is represented by, for example, a number of bits from start of error to finish of error of demodulation error which is caused when a code string in which an error is caused at one location thereof by the bit shift error is decoded as it is.
The bit shift error is a mode of error which is most frequently caused in reproducing data in an actual recording/reproducing device. Further, it has been confi
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