JP3187528B2 - Encoding device and decoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoding apparatus and a coding apparatus suitable for digitally recording data on a recording medium.
And a decoding device .

[0002]

2. Description of the Related Art In a magnetic recording system, for example, the frequency characteristic of a signal is generally a differential characteristic, and there is a deterioration in a high frequency band. This is due to, for example, a loss due to a head gap, a loss due to a space between head media, a loss due to a medium thickness, a low-frequency loss due to a rotary transformer, and the like. Furthermore, noise such as crosstalk noise from an adjacent track, noise from a medium, and overwrite noise causes random errors. Despite such loss and noise, in order to accurately record and reproduce data, it is better to record digital information on a recording medium after modulating the digital information so as to be compatible with the recording system. Can be stably accommodated. For this reason, data is converted into a recording code (channel code) according to a predetermined rule.

[0003] Among such recording codes, there is a block code. In this block code, a data sequence is divided into m × i bits, and this data word is converted into an n × i channel bit recording code according to an appropriate code rule. When i = 1, the code is a fixed length code. When i is greater than 1 and the constraint length r is greater than 1, the code is a variable length code. Block codes are also referred to as (d, k; m, n; r) codes. Here, d indicates the minimum continuous number of the same symbol (for example, 0), and k indicates the maximum continuous number of the same symbol (0).

For example, (2,7; 1,2; 4) (2-7RLL) is used in an optical disk or a magnetic disk. The minimum inversion interval Tmin of this code is 1.5T
(T is the interval of digital data).

[0005]

The conventional code has a problem that the minimum inversion interval Tmin is small. Generally, in a recording medium, particularly an optical recording medium, the reproduction output in a high frequency band is greatly deteriorated, and it is desired to increase the minimum inversion interval in order to perform high-density recording.

The present invention has been made in view of such a situation, and aims to make the minimum inversion interval larger.

[0007]

[Means for Solving the Problems]

The encoding apparatus according to the present invention is an encoding apparatus for encoding digital data into a variable-length code, wherein the digital data is represented by a minimum inversion interval Tmin of 2.0 T or more, where T is the interval between the digital data. A ROM 4 as storage means for storing a plurality of tables for converting into a variable-length code in which the same symbol (for example, 0) has a minimum continuous length d of 4 or more, and a constraint length r of digital data. It is characterized by comprising an encoder 2 as a judging means and a selector 3 as a selecting means for selecting any one of a plurality of tables in the ROM 4 according to the judgment result of the encoder 2.

Also, the decoding device of the present invention is a
In the decoding apparatus for decoding the digital data into the original digital data, when the interval of the digital data is T, the minimum inversion interval Tmin is 2.0T or more, and the continuous minimum length of the same symbol (for example, 0) ROM 23 as storage means for storing a plurality of tables for converting a variable length code whose d is 4 or more into digital data, a conversion length determination circuit 21 as determination means for determining the conversion length of the variable length code, According to the determination result of the conversion length determination circuit 21, R
The selector 22 is characterized by including a selector 22 as a selecting means for selecting any one of the plurality of tables of the OM 23.

[0010]

[Action]

In the encoding apparatus according to the present invention , the digital data is converted into a variable length code having a minimum inversion interval Tmin of 2.0T and a minimum length d of continuous 0s of 4 being 4. The conversion table is stored in the ROM 4. Therefore, the digital data can be quickly and easily converted to a predetermined code by referring to this table.

Further, in the decoding device of the present invention,
In the ROM 23, the minimum inversion interval Tmin is 2.0T,
A conversion table for converting a variable-length code in which the minimum continuous length d of 0s is 4 into digital data is RO.
It is stored in M23. Therefore, the code can be efficiently decoded into the original digital data.

[0013]

Next, a variable length code (4, 2
2; 2, 5; 5) will be described.

That is, in this embodiment, a data word having a basic data length of 2 bits is converted into a code word having a basic code length of 5 bits. Six basic codes shown in Table 1 are used as basic codes for this purpose. That is,
By combining these six types of basic codes, digital data is converted into variable-length code words.

[0015]

[Table 1]

Table 2 shows the number of effective codes obtained using this basic code. That is, when the constraint length r is 1, 2, 3,
As the number is increased sequentially to 4,5, the required number N of codewords changes to 4,8,16,28,32. On the contrary,
The number M of codewords that can be actually adopted is 2, 4,
9, 20, and 34. Therefore, the difference D (= N−
M) changes to 2, 4, 7, 8, and -2. That is, by using a code word until the constraint length r becomes 5, the original digital data can be converted into a code word without excess or deficiency.

[0017]

[Table 2]

Tables 3 and 4 show specific examples of tables for converting digital data into code words using the basic codes shown in Table 1. As shown in Tables 3 and 4, digital data having a basic data length of 2 bits is converted into a code word having a basic code length of 5 bits. For example, data '11' is converted to code '00000' and data '1'
"0" is converted to code "10000". Then, similarly, the data of each bit length of 4, 6, 8, and 10 is converted into a code word having a code length of 10, 15, 20, and 25.

[0019]

[Table 3]

[0020]

[Table 4]

As shown in Table 3, the digital data is “1”.
When it is 1, the codeword is '00000'. Therefore, when no special rule is set, if logic 1 (symbol) of digital data is continuous, logic 0 is continuous as a code word. In this case, the codeword is (4,
∞; 2, 5; 5), and the number N of codewords obtained when the constraint length r is changed changes as shown in Table 5.
If the logic 0 continues indefinitely, it becomes difficult to detect the self-clock. Therefore, in this embodiment, when the logic of the digital data is 1 continuously for 6 bits, the code is converted to '00000010000100000'.

[0022]

[Table 5]

The minimum inversion interval Tmin (= (m / n) (d + 1) T), the maximum inversion interval Tmax (= (m / n) (k + 1) T) of the codewords shown in Tables 3 and 4, data detection The window width Tw (= (m / n) T), the product of Tmin and Tw, and the ratio of Tmax to Tmin are as shown in the column of 4Z in Table 6. Here, T is an interval between digital data. Table 6
In addition, when the value of d is set to 3 (3Z), and E
The values for FM are also shown. As is apparent from comparison with these values, in the present embodiment, the minimum inversion interval T
It can be seen that min is 2.0T, which is larger than in the case of 3Z and EFM.

[0024]

[Table 6]

FIG. 1 shows MTF and normalized spatial frequency (NA).
/ Λ). As shown in the figure, it can be seen that the MTF decreases as the normalized spatial frequency increases (frequency increases). And in FIG.
It shows the range of the normalized spatial frequency when codes are recorded at the same density according to the EFM, 3Z and 4Z methods. In the case of EFM, the normalized spatial frequency ranges from 0.43 to 1.57, whereas in the case of 4Z,
It is in the range of 0.24 to 1.1. Therefore, in order to achieve the same recording density, a lower frequency is required in the case of 4Z as compared with the EFM. In other words, higher-density recording becomes possible. The magnification (3.0 times) shown in parentheses in FIG. 1 is a magnification with respect to the linear density of a normal CD (compact disc).

FIG. 2 is a block diagram showing the configuration of an embodiment of the encoding apparatus according to the present invention. In the shift register 1,
Digital data is sequentially input in synchronization with a data clock. In this example, 10
Bit digital data is stored in the shift register 1. The data output from the shift register 1 is supplied to the encoder 2, where the constraint length r is determined. The encoder 2 outputs the digital data supplied from the shift register 1 to the selector 3.

The selector 3 converts the digital data supplied from the shift register 1 via the encoder 2 into an RO according to the determination result of the constraint length r output from the encoder 2.
M4-1 to 4-6. The ROM 4-1 stores a table for converting the 2-bit data shown in Table 3 into a 5-bit code. Similarly, the ROMs 4-2 to 4-5 include
A table for converting digital data having a data length of 4, 6, 8, or 10 bits into codewords having a code length of 10, 15, 20, or 25 is stored. Further R
The logic of the input digital data is OM4-6.
The conversion table in the case where the bit is 1 continuously is stored.

The multiplexer 5 includes ROMs 4-1 to 4
The output of −6 is synthesized and output to the buffer 6. The data read from the buffer 6 is further supplied to the formatter 7. The clock generation circuit 8 generates a channel clock synchronized with the data clock and supplies the channel clock to the buffer 6.

Next, the operation will be described. The encoder 2 determines the constraint length r from the 10-bit data stored in the shift register 1. Then, the selector 3 is controlled in accordance with the determination result, and the input digital data is supplied to one of the ROMs 4-1 to 4-6. When it is determined that the constraint length r is 1, the 2-bit data is supplied to the ROM 4-1. This data is '11' or '10'. The digital data '11' is converted into the code '0000' according to the table stored in the ROM 4-1, and the digital data '10' is converted into the code '10000'.

For example, when the input is digital data '0111', the constraint length r is determined to be 2, and
This data is supplied to the ROM 4-2. And, corresponding to the table stored therein, the code '0100
000000 '.

In the same manner, the digital data shown in Tables 3 and 4 are converted into corresponding codes.

FIG. 3 shows an example of this conversion. Now
The input digital data is represented by hexadecimal number 18D2
(FIG. 3A), the binary data (FIG.
(B)) is '0001100011010010'. The encoder 2 determines the constraint length r of the input binary data as follows. Data corresponding to the first two bits '00' does not exist in Table 3. Therefore, it is determined whether or not a total of 4-bit data '0001' to which the subsequent 2-bit data is added exists in the table. As shown in Table 3, this data also does not exist in the table.

Therefore, it is further increased by 2 bits to determine whether or not 6-bit data '000110' exists in the table. Since this data does not exist in the table shown in Table 3, 2-bit data is further added. The 8-bit data '00011000' is data existing in the table of Table 3 with the constraint length r = 4. Therefore, it is determined that r = 4, and the selector 3 outputs the data '0
0011000 'is supplied to the ROM 4-4. And
This digital data is stored in a codeword '01010000000000 according to a table stored in the ROM 4-4.
0100000 '(FIG. 3 (c)).

Since the following 2-bit data '11' is determined as data having a constraint length r = 1 shown in Table 3, RO
It is supplied to M4-1 and converted into a code word '00000' (FIG. 3 (c)).

Further, the following 2-bit data '0
Since 1 'does not exist in Table 3, 2-bit data is further added. Since the data '0100' is detected as data with the constraint length r = 2 in Table 3, the ROM 4-2
Supplied to And the codeword '00000010000
It is converted to 0 '(FIG. 3 (c)).

Since the subsequent data '10' is detected as the constraint length r = 1, it is supplied to the ROM 4-1 and converted into a code word '10000' (FIG. 3 (c)).

The code words converted by the ROMs 4-1 to 4-6 in this way are supplied to the multiplexer 5, where they are synthesized as continuous codes. As mentioned above,
This code word delimiter exists in the first 20 bits, the next 5 bits, the subsequent 10 bits, and the subsequent 5 bits (FIG. 3D).

The codeword synthesized by the multiplexer 5 is supplied to the buffer 6 in synchronization with the channel clock (FIG. 3 (f)) and stored. Then, it is read therefrom and supplied to the formatter 7. Formatter 7
Interleave the code word supplied from the buffer 6 and add an error correction code and a synchronization signal to make the code conform to a predetermined format. Then, this code is output to a recording circuit (not shown). As a result, a recording signal (FIG. 3E) whose level is inverted every time a logic 1 is generated is generated. This recording signal is recorded on a recording medium such as a magnetic disk and a magneto-optical disk.

FIG. 4 is a block diagram showing the configuration of an embodiment of the decoding apparatus of the present invention. The codeword reproduced from the recording medium is supplied to the selector 22. The conversion length determining circuit 21 determines the conversion length of the code word and controls the selector 22. The selector 22 converts the input code word into a ROM 23-
1 to 23-6. ROM23-1
Tables 23 to 6 store tables reverse to the tables shown in Tables 3 and 4. That is, Table 3 and Table 4
Are stored in order to decode the codeword shown in (1) into the original digital data.

The multiplexer 24 combines the data read from the ROMs 23-1 to 23-6 and outputs the combined data to the buffer 25. The data read from the buffer 25 is supplied to a deformatter 26, and after being reformatted, supplied to a circuit (not shown).

The reference clock generation circuit 27 generates a reference clock synchronized with the input code word, and
To the synchronization detection circuit 28. Synchronization detection circuit 28
Detects the position of the code word synchronization signal with reference to the reference clock supplied from the reference clock generation circuit 27. Then, the detection signal is supplied to the ROM 23.

Next, the operation will be described. The conversion length determination circuit 21 determines the conversion length of the input codeword,
The selector 22 is controlled according to the determination result. As a result, a code word having a basic code length of 5 bits is stored in the ROM 23-
1 and the 10-bit codeword is supplied to the ROM 23-2. Similarly, code words having a basic code length of 15, 20, or 25 bits are supplied to the ROMs 23-3 to 23-5, respectively. In the case where the input code word has a code length of 15 bits of “00000010000100000”, the ROM 2
3-6.

The ROMs 23-1 to 23-6 decode the input codewords into the original digital data according to the stored table. The digital data decoded by the ROMs 23-1 to 23-6 is
And written into the buffer 25. Then, the data read from the buffer 25 is supplied to a deformatter 26, subjected to processing such as error correction, deinterleaving, and separation of a synchronization signal, and then supplied to a circuit (not shown).

[0044]

【The invention's effect】

According to the encoding apparatus of the present invention , a variable length code having a minimum inversion interval of 2.0 T or more and a minimum continuous length of the same symbol of 4 or more is stored in a plurality of tables, Since any one of the plurality of tables is selected according to the constraint length of the data, it is possible to obtain a code capable of high-density recording quickly with a simple configuration.

Further, according to the decoding apparatus of the present invention, a plurality of variable-length codes for converting a variable length code having a minimum inversion interval of 2.0 T or more and a minimum continuous length of the same symbol of 4 or more into digital data are provided. Since the tables are stored and any one of a plurality of tables is selected according to the conversion length of the variable length code, it is possible to decode data recorded at high density quickly with a simple configuration. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram comparing an encoding system of the present invention with a conventional encoding system.

FIG. 2 is a block diagram illustrating a configuration of an embodiment of an encoding device according to the present invention.

FIG. 3 is a timing chart for explaining the operation of the embodiment of FIG. 2;

FIG. 4 is a block diagram showing a configuration of an embodiment of a decoding device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shift register 2 Encoder 3 Selector 4 ROM 5 Multiplexer 6 Buffer 7 Formatter 8 Clock generation circuit 21 Conversion length judgment circuit 22 Selector 23 ROM 24 Multiplexer 25 Buffer 26 Deformatter

Continuation of the front page (72) Inventor Toshiyuki Nakagawa 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (56) References JP-B 53-21257 (JP, B2) IBM Journal of search and developmentment Vol. 14, No. 4, July 1970, pp 376-383, p. A. Franaszek, "Sequence-state Methods for Run-length-limited d Coding" (58) Fields investigated (Int. Cl. ⁷ , DB name) H03M 7/14

Claims (2)

(57) [Claims] 1. An encoding device for encoding digital data into a variable length code, wherein the digital data is represented by an interval T
Storage means for storing a plurality of tables for converting into the variable-length code in which the minimum inversion interval Tmin is 2.0T or more and the minimum continuous length d of the same symbol is 4 or more; Determining means for determining the constraint length r of the digital data; and selecting means for selecting any one of the plurality of tables in the storage means in accordance with a result of the determination by the determining means. Device. 2. A decoding apparatus for decoding a variable-length code into original digital data, wherein when the interval of the digital data is T, the minimum inversion interval Tmin is 2.0T or more and the same symbol Storage means for storing a plurality of tables for converting the variable-length code having a minimum continuous length d of 4 or more into the digital data; determining means for determining a conversion length of the variable-length code; A selection unit for selecting one of the plurality of tables in the storage unit in accordance with the determination result of the unit.