JPS58220214A - Digital modulating method - Google Patents

Abstract

PURPOSE:To realize self-clocking, by dividing the data bits to every 4 bits to convert them into codes words of 8 bits to 16 combinations of the data bits and then applying NRZI modulation to the series of code words. CONSTITUTION:The data bits are divided to every 4 bits and then converted into codes words P1-P8 of 8 bits to 16 combinations of data bits as shown in a table. Then NRZI modulation is applied to the series of code words. At least >=2 bits 0 are included between the bit 1 and 1 of the code series, and the number of bits 0 are reduced down to <=10 at most. Thus the conventional minimum magnetization inverting interval is set as Tmin=1.5T compared with the conventional interval T along with the maximum magnetization inverting interval Tmax=5.5T and the detecting window width Tw=0.5T respectively. This process increases the linear bit density and realizes the self-clocking.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital modulation method, and more particularly to a digital modulation method based on a 4-8 conversion method for converting 4 data bits into an 8-bit code word.

In general, digital magnetic recording has the characteristics of being able to economically record a large amount of information and to store it stably for a long period of time. The information signal modulation method for this purpose is RZ (Return to Zero).

RB (Return to Bias), N RZ
(Won-Raturn to Zero), NRZ
X (Non-Return to Zero I).

F M (Frequency Modulation
), PIC (PhaseICncoding),
MFM (Modified Frequency
Modulation), M2FM (Modification)
Various proposals have been made, including ed MFM). On the other hand, recently, various new modulation methods other than these have been proposed.

For example, 415 MNRZI (Modified Non
-Return.

Zero I), 3PM (3Po5ition Mo
duration).

ZM (Zero Modulation), etc. Furthermore, recently, with increasing density, new modulation methods other than those described above are being considered, but in digital magnetic recording, the detection window width Tw and the minimum magnetization reversal interval Twin.

Or the ratio D of the linear bit density to the maximum magnetization reversal density
It is said that a modulation method with a large R (Devsity Ratio) is desirable. Further, the ease of increasing the density is often expressed as the product of the minimum magnetization reversal interval Tm1n and the detection window width 'rw.

The present invention was made in view of these demands, and has a minimum magnetization reversal interval T min of 1.5T, which is the same as the 3PM method, and a maximum magnetization reversal interval T max of 5.5T, which is smaller than 6T of the 3PM method. Detection window width Tw is 0.5T and 3
As with the PM method, the product of the minimum magnetization reversal interval Twin and the detection window width Tw is also 0.75 T2, which is the same as the 3PM method, that is, the maximum magnetization reversal interval Th+ax of the 3PM method is set to 0.75.
This provides a 5T improved self-clocking modulation scheme.

Details 57. of the present invention are given below along with drawings of embodiments.・ Explain.

FIG. 1 is a conversion table for the aPM method. The SPM method converts 3-bit data into a 6-bit code word,
This code word sequence is modulated with NRZI. The codeword is characterized by having at least two bits “0” between bit 111 I+ and the next bit “1′°, but the fifth bit P5 of the chronologically older codeword is “1”. ″
Then, the 1st bit Pl of the following word is “1”
If a sequence of code words occurs, bit “1′
Since the condition that the minimum number of consecutive bits “0” between ° and the next bit “・1” is 2 is violated, in this case, the 5th bit P5 of the old code word and the following A special rule is provided in which the first bit P1 of the code word is inverted to bit "0" and the sixth bit P6 of the old code word is inverted to bit 1n. Furthermore, 6 of a certain code word
If the first bit P5 of the next code word is "1" and the first bit P1 of the next code word is "1", the minimum inversion interval is T.
In this case, both Ps and P1 are inverted to 0"' and always 6 pes.

The 6th bit P6, which is "'0", is inverted to 1'' to maintain the inversion interval at 1.5T. moreover,
In this 3PM system, the maximum number of bits "0" that can be inserted between bits "1" and "1" in the codeword sequence is 11.
is limited to. Therefore, the code words are selected so that the maximum inversion interval is 6T.

On the other hand, FIG. 2 shows the 4-8 conversion FEM-2 (
Four to Eight Modulation)
This is the conversion table. This method Fi converts 4-bit data into an 8-bit code word and converts the code word sequence into NR
It is modulated by ZI. As shown in Figure 3a, the code word is limited so that at least two or more bits ``0'' are inserted between bit ``1'' and the next bit ``1'', and there are no more than 10 bits at most. is added, but as shown in Figure 3, the 7th bit P7 of the chronologically older codeword is "'1", and the 1st bit of the following codeword is If a sequence of code words in which P1 is "1" occurs, the conditions of this method are violated, so in this case, the 7th bit P7 of the old code word and the 7 bit
- Invert the 1st bit P1 of the following code word to pit 0'',
A special rule is provided to invert the 8th bit P8 of the old codeword to bit "1". However, if N011 follows the binary data word No. 5 in FIG. 2, the code word becomes , and the maximum magnetization reversal interval Tmax=eT
occurs.

Therefore, in this case, as shown in FIG. 3C, the 8th bit P8 of the code word N005 is set to bit "1", and the 3rd bit P3 of the code word N011 is set to bit "1".
to be reversed. The code string in this case is as follows.

The code word for N091 in this case is N018 in Figure 2.
becomes the same as However, in this case FIK M-
2 demodulation is performed using the 8th bit P8 of the chronologically older code word.
- and the 3rd bit P3 of the following code word are in focus at the same time "
'1' is detected, and the 8th bit P of the old code word is
It is clear that this becomes possible if the third bit of the code word following 8 is inverted to bit "O". In other words, when code word N008 is used as a subsequent code word, both the first bit Pl and the second bit P2 of the code word are bit “O”.
”, the 8th bit P8 of the old code word does not become bit “1” in the input field. Therefore, if the 8th bit P8 of the old code word is bit "1"' and code word No. and a follow next, it can be distinguished as a case where a special rule is applied. That is, the 8th bit P8 of the code word is XXXX
XX10111 If the condition of this method that at least two or more bits “0” are included between bit “1” and bit “1” of XXXXXXXX is not satisfied, convert xxxxxxxollloxxxxxxxx and use it as a flag bit to satisfy the condition. It is used as a flag bit to improve the maximum magnetization reversal interval Tmax=6T, which occurs when the code word N015 and No.1 are consecutive, to 6.6T. The maximum magnetization reversal interval T max9 of this method of 5.6T occurs when the words N006 and N002 are consecutive, and when N084 and No. 1 are consecutive.

That is, Figure 4 is a diagram showing a comparison of recording current waveforms between the FEM-2 method and the conventional modulation method, where A is data and B is N.
The waveform is based on the RZI method, the waveform is based on the FM method, the waveform is obtained using the MFM method, the waveform is obtained using the SPM method, and the waveform is obtained using the FEM-2 method. In addition, in the figure,
It shows the Tu bit period.

In the case of the MFM method, which is currently most commonly used in large-capacity magnetic disk drives, the magnetization reversal interval is T, 1.5T.
, 2T, and the minimum magnetization reversal interval Tm1n is T
It is. For modulation methods other than MFM, Twi
As n, NRZI is 'r, and FM is 0.5T. In this way, in most of the conventional modulation methods, the minimum magnetization reversal interval is T or less, and therefore D
R was 1 or less. On the other hand, the F E of 3PM and this method
In M-2, the minimum magnetization reversal interval Tm1n is 1.5T, and DR=1.5. Therefore, if the minimum magnetization reversal interval is made the same as that of MFM, the linear bit density can be increased by 1.5 times.

FIG. 5 shows a comparison of various modulation methods for reference.

As explained above, according to the present invention, the minimum magnetization reversal interval 1
．． 5T, maximum magnetization reversal interval 5.5T, detection window width Tw
o, 5Tt A self-clockable modulation system with a product of the minimum magnetization reversal interval Tm1n and the detection window width TW of 0.75 T2 can be provided.

[Brief explanation of drawings]

Fig. 1 is a conversion table diagram of the aPM method, Fig. 2 is a conversion table diagram of FEM-2 in the digital modulation method of the present invention, and Fig. 3 is a case where the maximum magnetization reversal interval occurs in FICM-2 and application of special rules. A diagram for explaining an example, FIG. 4 is a comparison diagram of recording current waveforms of FEN-2 and conventional modulation method, and FIG. Name of agent: Patent attorney Masao Nakao, 1st person
Figure 2 Figure 3 4T/8 x 12 = 6T Old.

Claims (2)

[Claims] (1) A digital modulation method for high-density recording, in which data bits are divided into 4-bit units, and 16 combinations of data bits in 4-bit units are combined with -8-bit code words (PIF2P3P4 PS P6). P7 p
s) and the data time series group as ■ 00000100 ■ ○oo○10oO ■ 00010000 ■ 00100oO0 ■ 01000000 ■ 00010010 ■ 1 o○10o10 ■ 00100100 ■ 01001000 @ 10Q10000 2be, 010000010 0001oo01゜Ooloooolo Q 011000100 o 10000100 ■ 100o10o. Then, the data strings are made to correspond, and the 7th bit P7 and the 8th bit P8 of the chronologically old codeword and the 1st bit of the chronologically new codeword of the codeword sequence pattern at the concatenation part of the codeword and codeword are If the bit P1 is 101, the above 8
The bit P8 is inverted to "1", the seventh bit P7 and the first bit Pi are inverted to bit "0", and if the code word ■ follows the code word ■, the code word ■
A digital modulation method characterized by inverting the Q8th bit P8 to bit "1", further inverting the third bit P3 of code word (2) to bit "1", and then modulating with NRZI. (2) At least two or more bits “0” are included between the bit 1” and the bit “1” of the codeword sequence, and 3-:
The digital modulation method according to claim 1, characterized in that the number of modulation signals is at most 10 or less.