JPS59193653A - Digital modulating system - Google Patents

Abstract

PURPOSE:To attain efficiently digital modulation by sectioning a data in the unit of 6-bit taking the rear ridge of a synchronizing signal as a reference, serial/parallel converting the data, giving the data as an address of 6-8 conversion ROM under the secific condition and obtaining its output as a modulation output of the specific condition. CONSTITUTION:The input is sampled, quantized and added with a correction code or the like, and further a synchronizing signal is added and the result is transmitted to a modulation circuit as a serial data. Then, the binary data is sectioned in the unit of 6-bit taking the rear edge of the synchronizing signal as a reference, serial/parallel converted 1 and given as an address to the 6-8 conversion ROM2 where 64-ways of 8-bit conversion word data satisfying specific conditions of SEM-1 and SEM-2 are written. An output of the ROM2 is parallel/series converted 3 and obtained as a modulation output of the SEM-1 or the SEM-2. In case of demodulation conversely, the synchronizing signal is extracted by the extraction of a specific bit pattern, the data is sectioned in the unit of 8-bit by taking the rear edge as a reference and the original data is obtained by the inverse procedure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital modulation system, and more particularly to a 6-8 conversion system for converting 6 data bits into an 8-bit code word.

Industrial Application FieldsRecently, research into digital magnetic recording, digital magneto-optical recording, and digital optical recording has become active. Disk files and the like are being commercialized. For example, among these devices, digital audio tape recorders and compact discs sample the music signal and then convert it into data, and then detect if the digital signal becomes erroneous due to dust or scratches on the recording medium. Generally, the data is recorded directly onto a recording medium after adding a redundant signal or applying other means for correction. In this case, the S/N of the reproduced signal,
Temporal variation (jitter), amplitude variation ω1 (dropout)
To prevent the leading and trailing edges of successive pulses from interfering with each other (code quantum f!Jc) when the pulse density is high, and to reliably extract digital codes. Digital modulation is performed so that The present invention relates to this digital modulation.

Conventional configurations and their problems In general, digital recording has the characteristics of being able to economically record a large amount of information and to store the information stably for a long period of time. The modulation method used for these is RZ (
Return to Zero), RB (Return to Zero)
t.

Bias), NRZ (Non-Return to
Zero), NRZI (Non-Return
Zero I), FM (Frequency Mod
lation), PE (PhaseEncoding)
, MFM (Mod:Lfied Frequency
Modulation).

M2FM (Modified MFM),
415 MNRZI (Modified NR
ZI).

3PM (3Po5ition Modulation)
, ZM (Zero Modulation).

There are M2, etc. These modulation methods are used by each device,
They are used selectively depending on the performance of the recording medium, etc. A typical example of these is MFM.

There is 3PM. These are the conditions (1) desired for the modulation method.
The detection window width Tw is wide (2) The minimum magnetization reversal interval Tm1n is large (3) The maximum magnetization reversal interval Tmax is small (4) Self-clocking is possible (5) Code error propagation during demodulation is small I'm reasonably satisfied with that. The MFM is characterized in that the detection window width Tw is 05T, where the data period is T, the minimum magnetization reversal interval Tm1n is T, the i-large magnetization reversal interval Tmax is 2T, and self-clocking is possible. For this h', 3PM is the detection window width Tw
is the same as MFM, but the minimum magnetization reversal interval Tm1
n is 1.5T, making it possible to achieve a recording density 15 times higher than that of MFM. However, since the maximum magnetization reversal interval Tmax is 6T, which is three times that of MFM, it has the disadvantage of being weak against time axis fluctuations. Therefore, if the device is a device with little time axis variation, its performance will be utilized. The present inventor has already improved this drawback and set the maximum magnetization reversal interval Tmax to 45T.
A conversion method and a 1-8 conversion method in which the maximum magnetization reversal interval Tmax is 4T are proposed.

In contrast to these modulation methods, rotary transformers used in digital VTRs cannot pass DC components, resulting in waveform distortion, or when recording and reproducing using a magnetic flux response type head and using a method called integral detection. However, DC regeneration is not possible, and QCF signal errors may occur depending on the modulation method used. Therefore, in such a case, a means called DC regeneration is used. However, as the number of channels or tracks for recording/reproduction increases, the circuit cost and circuit scale for this increase increase. For such purposes, it is preferable to use an original modulation method that does not itself generate direct current. As something like this,
There are several types, such as ZM and M2.

Of these, M2 is often used in digital VTRs. This method is the same as MFM in basic rR, but an algorithm has been added to prevent the generation of DC components. FIG. 1 shows the recording 'M' waveform of a typical conventional modulation method. Table 1 also shows a comparison of the main evaluation parameters. As is clear from these, the detection window width Tw of M2 is the same as 05T, MFM, 3PM, etc.

This may not be sufficient depending on the crosspiece used. In other words, many devices using disk devices or rotating heads have little time axis fluctuation and relatively good S/N, and it is relatively easy to keep the detection window width Tw within 05T. In general, those using a fixed headband, especially those using a compact cassette, are vulnerable to time axis fluctuations, and the same wave number characteristics of the recording medium used are also used near the high frequency limit, so the S/N is also compared. There is a tendency for the detection window width Tw to be wider, and a modulation method with a wider detection window width Tw is desired.

Purpose of the Invention With the recent release of digital records using compact discs and the digitalization of television signal sound by broadcasting systems in the near future, Hi-F will become popular for general users '7'.
We are living in an era where i audio and music sources are easily available. In response, research and development of compact cassette digital audio tape recorders using fixed heads has become active, with the aim of allowing anyone to record easily and inexpensively using compact cassettes.

Broadly speaking, two types of consumer digital audio recorders are considered.

4.1 KFIz sampling, 16-bit quantization, distribution recording method around 20 tracks, and 32 tracks.
It uses KHz sampling, 12-bit non-linear quantization, and 10-track distributed recording system.

The present invention provides a modulation method compatible with the latter.

As mentioned above, the one using the compact cassette is H Masuke Hen ui! Detection window 111! A modulation method with a wide liTw is desired. Next, no matter what type, 10~
Since the data is distributed over many tracks (approximately 20 trunks), if integral detection is to be performed using a magnetic flux differential response type head, a DC reproducing circuit is required for each track as mentioned above, which is difficult in terms of cost and space. I can't do inkstone anymore. Therefore, as the variable J1+i1 method, if it does not generate direct current, the cost and space for it are unnecessary. Third, when considered as a consumer device, recording and reproducing generally requires a recording head, a reproducing head, and an erasing head. However, erasing can achieve the same effect by recording new information over the old information, erasing the old information and leaving the new information (this is called overwriting). This makes it possible to omit the erasing head and its associated circuits and mechanical parts. This method of overwriting is very effective, but it is a phenomenon that is difficult to realize only under certain conditions. That is, it is known that the erasing effect (erasing rate) generally deteriorates as the recording wavelength becomes longer. Therefore, the smaller the maximum magnetization reversal interval Tmax, the easier it is to erase.

Furthermore, as mentioned above, in the multi-track system, a modulation circuit is required for each track, so it is obvious that the smaller the circuit scale for this purpose, the cheaper the cost.

Furthermore, when considering a modulation method, it is also important that code errors during reproduction do not propagate over multiple bits. That is, it is undesirable for a 1-bit error or a 1-word error to propagate over multiple bits or multiple words, since this will expand the information on the recording medium beyond the error itself.

The object of the present invention is to provide a modulation method that satisfies all of the above conditions.

Structure of the Invention The present invention divides sampled and quantized digital data bits into 6-bit units, and assigns 8-bit code words to 64 sets of 6-bit data (26=64). 6-8 conversion method (Sit.

Eight Modulation-SEM).

First of all, in order to have no DC component in the modulation method itself and to suppress the generation of DC components within an 8-bit code word, all 256 combinations (28
= 256), a combination in which the number of bits "1" and bits "O" are exactly half each, that is, four bits, is selected. This combination is. C4-70 types exist. Therefore, if we extract the previous 64 combinations from among these 70 combinations, the DC component -0, that is, DCFREE C0
It becomes DE. The choice is up to you. D in this case
Table 2 shows combinations of 8-bit code words that are valid as CFREE CODE. In this case, the magnetization reversal interval is 0.75T (=6/8・T) to 6T (=6/8・T) in the worst case.
8・T×8).

Next, in order to improve the overwriting characteristics, we will use a modulation method invented by shortening the maximum magnetization reversal interval Tmax = 6T to 3.75T (-6/8 T x 5) while suppressing the DC component as much as possible. Let's talk about.

From Table 2 above, the magnetization reversal interval is large (Tmax
=45T) Try to remove the conflict. In this case, the combinations are: First, among the chronologically old 8-bit codewords, all P4 to P7 are bits T or bits @, excluding the following chronologically new 8-bit codewords. Among the code words, Po-P5 are all beep) III or beep) "O" and P. - P2 is all from Pi 1 to A or bit 101 and P. -P2 is all bit I0
1 or bits excluding bit A, and secondly, among the chronologically older 8-bit codewords, P4 to P7 are all bin) '1' or pip).
'O', P5 to P7 are all bit 11 or bit Ow, and P5 to P7 are all 'O' or '1', and in the following chronological order Among the new 8-bit codewords, a combination in which P0 to P are all bits T or excluding bits 1 and 0 is considered, but in this case, the number of combinations is 60, and 4 Street shortage. For this, one of the 8-bit code words is ``1''.
2#1 out of 3 ``1''s, beep) 5. Suppose there are two sets of I'i from among these. Third
Table 4 shows effective combinations.

The case where Tmax=3.75T and ni1 (the first case) is called SEM-1, and the latter case (the second case) is called SEM-2.

Description of examples Specific examples of the present invention will be described below.

Here, the conversion algorithm is as described above.

First, the input is sampled and quantized, then subjected to interleaving techniques, error detection/correction codes, etc., a synchronization signal, and sent as serial data to the modulation circuit. Here, binary data is divided into 6-bit units based on the trailing edge of the synchronization signal, and serial-parallel conversion 't
? 64 types of 8-bit code word data (26 = 6
4) is written in the 6-8 conversion ROM (given as the address of 21.The output of ROM (2) is converted from parallel to serial by parallel 16 column conversion 'kg (3),
It is given as the modulated output of EM-1 or EM-2. This situation is shown in FIG.

Conversely, in the case of demodulation, a specific bit pattern (preferably, this is composed of n times 6 bits).

Therefore, after modulation, a synchronizing signal is extracted by extracting 8 bits (n times 8 bits), and the data is divided into 8-bit units based on this trailing edge, which is parallelized by a serial-to-parallel converter (4). , 6 corresponds to the 8-pitch mark ze one word in Table 2.
8-6 conversion R with 64 bit original data written
It is given as the address of OM (5). ROM (
The output of 5) is subjected to parallel-to-serial conversion by a serial converter (6) and demodulated to the original data.

Both SEM-1 and SEM-2 have the same circuit configuration, but the contents of the ROM are different. This situation is shown in FIG.

Effects of the Invention According to the present invention, the detection window width Tw is reduced by 25% (3PM 9MFM=0.5T, S
EM=0.75T=678-T) has also been improved, making the digital magnetic recording device j1f more resistant to time 'I'+b fluctuations, and eliminating the need for a DC playback circuit in the multi-track recording system, reducing costs. , space can be omitted, 111 large magnetization anti-hearsay interval 7) E 3.75
T and conventional 3PM Noro TK ratio g375% shorter, making it possible to overwrite in digital magnetic recording, and this also makes it possible to omit the erase head, its peripheral circuits, and expensive parts. Furthermore, 1
Table 1 Comparison of Main Evaluation Parameters Since the digital tape recorder, which uses 2 bits to convert JT to A1, has less code error propagation during demodulation and a very simple modulation/demodulation circuit, many benefits are expected.

[Brief explanation of the drawing]

Figure 1 is an example of the IE waveform recorded using the conventional modulation method.
The figure is an example diagram of a father modulation circuit of the present invention, and FIG. 3 is an example diagram of a demodulation circuit of the present invention. (υ(4)...Serial-parallel converter, (2)...6-8 conversion ROM, (31(6)...Parallel-serial converter, (5)...
...8-6 Conversion ROM 2nd table SEM-1, 5EM-2 8-bit code -; 3 words (combination table of 4 bits each for bit 11 and bit 10) DCFREE (6, 8) CONDITIONS :NtJMBEROF 0NES
=8/2 POPI 132 P3 P4 P5
P6 P7 S t-t SEM-2000
001111X X 100010111 X X20001
1011X 300011101 x 4.0O011110X 500100111 X6001010
11 7 0 (11,01101 800101110 900110011 1000110101 1,1 (10110110 1200111, OO1 1300111010 1400111), OO 1501000111X 16 0 1 0 0 1 0 1
117 0 1 0 0. 1 1. 0
118 0 1 0 0 1 1 1 0
19 0 1 0 1 0 0 1 120
0 1 0 1 0 1 0 12
1 0 1 0 1 0 1 1 022
0 1 0 1 1 0 0 12
30101101.0 24 0 1 0 1 1 1 0 025
0 1 1 0 0 0 1 12
6, 0 1. 1 0 0 1 0
127 0 1 1 0 0 1- 1 0
28 0 1 1 0 1 0 0 12
9 0 1 1 0 1 0 1 0×
: Unnecessary code word 3rd table DCFREE (6, 8) CONDITIONS: NUMBEROF 0NES=
8/2-12901011000 X 31 0 1 1 0 0 0 1
032 0 1 1 0 0 1 0
0330110'1000 X3
4 0 1 1 1 0 0 0 0
X X35 1 0 0 0
0 0 1 136 1 0 0
0 0 i 0 137 1 0
0 0 0 1 1 038 1 0
0 0 1 0 0 1-39 1
0 0 0 1 0 1 040 1
0 0 0 1 1 0 041 1
0 0 1 0 0 0 142
1 0 0 1 0 0 1 043
1 0 0 1 0 1 0 044
1 0 0 1 1 0 0 0
X45 1 0 1 0
0 0 0 146 1 0 1 0
0 0 1 047 1 0 1
0 0 1 0 0481C1101000X 49 1 0 1 1 0 0 0
0 X X50 1 1 0
0 0 0 0 151 1 1 0
0 0 0 1 052 1 1
0 0 0 1 0 053 1 1
0 0 1 0 0 0
X54 1 1 0 1 0 0
0 0 X X55 1
1 1 0 0 0 0 0 X
XX: Unnecessary code word 4 8-bit code word of Table SEM-1, 5EM-2 (bit '1
’ is a combination table of 5 digits and bit ``01'' is 3 digits)
DCFREE(6,8) CONDITIONS :NtJMBEROF 0NE
S = 8/2 + 1×: Unnecessary code word 2 ways selection procedure amendment from this code word (1 issue) June 72', 1980 Mr. Commissioner of the Patent Office 1, Indication of the case Showa 58 Lyrics Permission Request No. 674322 , Name of the invention Diginol modulation method 3 Relationship with the case of the person making the amendment Name of the patent applicant (582) 4th generation director of Matsushita Electric Industrial Co., Ltd. Address Address 1-6-17 Yumi Amano Building, Nishi-ku, Osaka 550 Telephone Osaka 06 (532) No. 4025 (Main)
Name (6808) Patent Attorney Yoshihiro Morimoto 5
Date (shipment date) 1939 Month, Day 6 Number of inventions increased by amendment 7 Detailed explanation of the invention in the detailed description layer subject to amendment (1.υ 8. Contents of amendment Column (1) Page 16, line 14 to page 17, line 1 [P4
〜P7 are all bits 111 or bits “0”, except for bits 111 or bits “0,” and the combination I5 is considered.” , among the chronologically new 8-bit code words that follow, Po-P5 are all bits "1", all bits are 101, and P.-P2 are all pinto "I" and all bits are 1
01, and secondly, conversely, excluding the chronologically old 8-bit codeword l) among the chronologically new 8-bit codewords. ~P5 is all bit l
110 and all bits of Ion are considered to be excluded,'' he corrected.

Claims (1)

[Claims] 1. In a digital modulation method that converts 6 data bits into an 8-bit code word, from all 256 combinations of 8-bit code words (28=256), the bits 1-1 ” and bit + (70 combinations where the number of pins is exactly half each, that is, 4 pieces (8C)
4 = 70), and from among them, choose the following 64 ways (2
6 = 6 mel), associate 6 data bits with 8 bit code words, and set the detection window width to 0.
By increasing the width to 75T and completing the variable hIM algorithm within 6 data bits, the recovery speed is 61T.
A digital modulation method that minimizes code error propagation at M time within a 6-bit unit and performs 6-8 conversion as DCFREE. 2. In a digital modulation method that converts 6 data bits into an 8-bit code word, out of all 256 combinations of 8-bit code words (28=256), the number of bits "11" and "bit lot" are exactly half each. ,
That is, 70 combinations of 4 each (8C4870) are selected, and from among these 70 combinations, the 8-bit code word (00001111) (00010111) (00011011) (00011101) (00011110) (11100001) (11100010) (11100100) (11101000) (11110000)
(00000111) (00001011) (00001101) (00001110) (00010011) (000], 0 1 0 1 ) (000101
10) (00011()0 1) (o o O1,10], O) (000111
00) (01110000) (1,0110000) (11,01,0000) Select 42 ways excluding (11,100000), and from among these, withstand any two ways of silk matching, and complete the above 60 ways. In addition to the combinations, there are 62 combinations, and from among the 56 combinations (8C5=56) where the number of bits lJ'' is 5 and the number of bits ``O'' is 3 (8C5 = 56), (000], 1111 ) (00101111) (0100111,t ) ('10001111) (11100011) (11100101) (1:t 1001.10 ) (11101001) (11101010) (11101100) (11110001) (1111001 0) (1111,0100) (11111000 Select 42 combinations excluding '), select 2 combinations of these 1 and 4 moi, and add them to the 623 IJl combinations above for a total of 64 combinations. By making the 6-bit take bit correspond to the 8-pin code word, and widening the detection 1'3 window width to 0.75T, the maximum magnetization resistance is set to 3.75T. And by completing the modulation algorithm within the unit of 6 take bits, the code error propagation at the time of decoding θ1v can be reduced to 6-8 conversion by using 6 bits, 11 bits, and DCFREE. Now digital modulation method. ;3. In a digital modulation method that converts 6 bits of take bits into 8 bits of code word, out of all 256 combinations (28-256) of 8 bits of code word,
Select 70 combinations (8C4-70) in which the number of bits T and 1010 bits are exactly half each, that is, 4 bits, and from among these 70 combinations, the 8-bit code word (0 (1 + 001111) (00010111) (00100111) (01000111) (01111000) (1,o o o O111) (10111000) (11011000) (11101000) (11110000) 60 combinations are extracted, and the number of bits 111 is 3. Big Katsu Pi) The number of “O” is 5
From among 56 combinations of 11001000) (11010000 ) (11100000), select any two combinations from these, make 62 combinations in addition to the 60 combinations above, and furthermore, if the number of bits "110" is 5 and Out of 56 combinations of 3 bits 10'', (00011111) (00101,111) (00110111) (01001,111) (01010111) (01100111) (10001111) (10010111) (10100111) (1,] , OOO111) (1,1110001) (11110010) (111,101,00) (11111000) Select 42 combinations excluding , OOO111) (1,1110001) (11110000), select any two combinations from among these, and in addition to the above 62 combinations, The detection window width was set to 0.75 by making 8-bit code words correspond to G-bit data bits.
While widening T, the maximum magnetization reversal interval is set to 3.75T,
In addition, by completing the modulation algorithm within a 6-bit unit of data bits, code error propagation during demodulation is minimized within a 6-bit unit, and I) CFREE is 6-8.
A digital modulation method that performs conversion.