JPH0447394B2 - - Google Patents

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. For this purpose, the information signal modulation method is RZ (Return to Zero).
RB (Return to Bias), NRZ (Non-Return to
Zero), NRZI (Non-Return to Zero I), FM
(Frequency Modulation), PE (Phase
Encoding), MFM (Modified Frequency)
Various methods have been proposed, including M ² FM (Modified MFM) and M 2 FM (Modified MFM). On the other hand, recently, various new modulation methods other than these have been proposed. for example,
4/5MNRZ (Modified Non-Return to Zero
), 3PM (3 Position Modulation), ZM
(Zero Modulation) etc. Furthermore, in recent years, new modulation methods other than those mentioned above have been considered as higher density has progressed, but in digital magnetic recording, the detection window width Tw, the minimum magnetization reversal interval Tmin, or the ratio of the linear bit density to the maximum magnetization reversal density
It is said that a modulation method with a large DR (Density Ratio) is desirable. Furthermore, the ease of increasing the density is often expressed as the product of the minimum magnetization reversal interval Tmin and the detection window width Tw.

The present invention was made in view of these demands, and the minimum magnetization reversal interval Tmin is 1.5T and the same as the 3PM method, the maximum magnetization reversal interval Tmax is 5T and 3PM.
It is smaller than the 6T method, and the detection window width Tw is 0.5T.
As with the 3PM method, the product of the minimum magnetization reversal interval Tmin and the detection window width Tw is 0.75T, which is the same as ^{the 2} and 3PM methods.
In other words, the maximum magnetization reversal interval Tmax of the 3PM method is
This provides a self-clocking modulation method with 1T improvement.

The present invention will be described in detail below with reference to drawings of embodiments.

Figure 1 is a conversion table for the 3PM method.
The 3PM system converts 3-bit data into a 6-bit code word and modulates the code word sequence with NRZ. A code word is characterized by having at least two bits "0" between a bit "1" and the next bit "1", but the fifth bit _P5 of the chronologically older code word is " If a sequence of code words occurs in which the first bit _P1 of the following code word is “1”, the bit “1”
Since the condition that the minimum number of consecutive bits ``0'' between ``0'' and the next bit ``1'' is 2 is violated, in this case, the 5th bit _P5 of the old code word and the code following it are A special rule is provided for inverting the first bit _P1 of the word to bit "0" and inverting the sixth bit _P6 of the old code word to bit "1".
In other words, the 5th bit of a code word P ₅
is “1” and the 1st bit _P1 of the next code word is “1”
In the case of , the minimum reversal interval becomes T, so
In this case, both P ₅ and P ₁ are inverted to “0”,
The _6th bit P6, which is always "0", is inverted to "1" to maintain the inversion interval at 1.5T.
Furthermore, in this 3PM system, the maximum number of bits "0" that can be inserted between bits "1" in a code word sequence is limited to 11. Therefore, code words are selected so that the maximum inversion interval is 6T.

On the other hand, FIG. 2 shows the 4-8 conversion of the present invention.
This is a conversion table for FEM-3 (Four to Eight Modulation). This method converts 4-bit data into 8
Convert the bit codeword and convert the codeword series to
It modulates with NRZ. The code word consists of a bit “1” and the next bit “1” as shown in Figure 3a.
It is characterized by the fact that there is a restriction that at least two or more bits "0" can be present between the data and the number of bits is 9 or less, but as shown in Figure 3b, it is chronologically old. The 7th bit _P7 of the code word is “ ₁ ”,
Furthermore, the first bit _P1 of the code word that follows this is “1”
If a sequence of code words occurs, the conditions of this method are violated, so in this case, the 7th bit P ₇ of the old code word and the 1st bit P ₁ of the following code word are A special rule is provided to invert the 8th bit _P8 of the old code word to bit "1". However, among the combinations of time-series patterns of binary data words in FIG. 2, cases larger than 5T occur as shown in FIG. 3c. In other words, if No. 1 follows No. 5, the code word is If No.5 is followed by No.2, If No. 5 is followed by No. 3, If No. 1 continues after No. 4, If No.4 is followed by No.2, If No.3 is followed by No.1, If No.3 is followed by No.2, If No.9 is followed by No.1, If No.1 is followed by No.10, If No.10 is followed by No.2, If No.1 is followed by No.16, becomes. As a special case, after No. 2, No.
1 continues, then No.7 or No.10 or No.11
Or if No. 15 or No. 16 continues, 5T will occur. For example, in the case of No.2-No.1-No.7 Further, if No. 5 is followed by No. 1, and then No. 10, No. 11, No. 5, or No. 16, 7T occurs. For example, in the case of No.5-No.1-No.11, Therefore, a magnetization reversal interval of 7T to 5T occurs. The present invention shortens them, and the maximum magnetization reversal interval Tmax
is 5T. For this purpose, when the above codeword sequence occurs, the 8th bit _P8 of the chronologically older codeword is inverted to bit "1", and the 3rd bit _P3 of the following codeword is inverted. The bit is inverted to “1”. By doing so, No.5
If it follows If No.5 is followed by No.2, If No. 1 continues after No. 4, If No.4 is followed by No.2, If No.3 is followed by No.1, If No.3 is followed by No.2, If No.9 is followed by No.1, If No.1 is followed by No.10, If No.10 is followed by No.2, If No.1 is followed by No.16, becomes.

Also, No.5-No.1-No.10 (or No.11, No.15
，
No.16) becomes.

This allows a one-to-one correspondence between all data words and code words.

The maximum magnetization reversal interval Tmax of this method is code word No. 5
and No. 3 are consecutive, i.e. No.2, No.1 and No.7 (or No.10, No.11, No.15
，
No.16) is continuous, i.e. So it becomes 5T.

Figure 4 shows a comparison of recording current waveforms between the FEM-3 method and the conventional modulation method, where A is the data, B is the waveform by the NRZ method, C is the waveform by the FM method, and D is the MFM. Waveform by method, O is
The waveform is based on the 3PM method, and the waveform is based on the FEM-3 method. In the figure, T indicates the bit period.

In the case of the MFM method, which is currently most commonly used in large-capacity magnetic disk devices, there are three types of magnetization reversal intervals: T, 1.5T, and 2T, and the minimum magnetization reversal interval Tmin is T. For modulation methods other than MFM, NRZ is T and FM is Tmin.
It is 0.5T. In this way, most of the conventional modulation methods have a minimum magnetization reversal interval of T or less, and therefore
DR was 1 or less. On the other hand, 3PM and this method
In FEM3, the minimum magnetization reversal interval Tmin is 1.5T, and DR=1.5. Therefore, if the minimum magnetization reversal interval is the same as MEM, the line bit density can be reduced to 1.5.
Can be doubled.

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

As explained above, according to the present invention, the minimum magnetization reversal interval is 1.5T, the maximum magnetization reversal interval is 5T, and the detection window width is
Tw0.5T, minimum magnetization reversal interval Tmin and detection window width Tw
A self-clocking modulation scheme with a product of 0.75T ² can be provided.

[Brief explanation of the drawing]

Figure 1 is a conversion table diagram for the 3PM method, Figure 2 is a conversion table diagram for FEM-3 in the digital modulation method of the present invention, and Figure 3 is a case where the maximum magnetization reversal interval occurs in FEM-3 and application of special rules. FIG. 4 is a diagram for explaining an example, and FIG. 4 is a comparison diagram of recording current waveforms of FEM-3 and conventional modulation methods. FIG. 5 is a comparison diagram of various modulation methods.

Claims (1)

[Claims] 1. A digital modulation method for high-density recording, which divides data bits into 4-bit units,
8-bit code word (P ₁ P ₂ P ₃ P 4 P ₅ P ₆ P _{7 P 8 )} for 16 combinations of data bits in units of 4 bits
00000010 00000100 00010000 00100000 01000000 00010010 10010010 00100100 01000000 10010000 10000010 00100010 01000010 01000100 10000100 10001000, the data strings are made to correspond, and the codeword sequence pattern at the concatenation part of codewords is calculated in chronological order. The 7th bit P ₇ and the 8th bit P ₈ of the old code word and the 1st bit P ₁ of the chronologically new code word are 101.
In the case _{where the} code word is _followed by the code word or, When a code word is followed by a code word or , When a code word is followed by a code word or , When a code word is followed by a code word , When a code word is followed by a code word or ,
If a codeword follows a codeword, the 8th bit P8 of the chronologically older codeword is inverted to bit ₁ ", and the _3rd bit P3 of the chronologically newer codeword is inverted to bit 1". 1”, then NRZI
A digital modulation method characterized by modulation. 2. The scope of claims characterized in that the codeword sequence is configured such that at least two or more bits 0'' are included between bits 1'' and 1'', and no more than 9 bits are included at most. The digital modulation method according to item 1.