JP3235096B2 - Data conversion and detection methods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A. Industrial application fields B. Summary of the invention C. Conventional technology D. Problems to be solved by the invention E. Means to solve the problems F. Function G. Example G1 Configuration of one example (No. (Figs. 1 to 3) G2 Operation of one embodiment (Figs. 1 to 8) H. Effects of the invention A. Industrial application field This invention is suitable for high-density recording, and converts and detects data. About the method.

B. Summary of the Invention A first aspect of the present invention relates to a data conversion method for converting M-bit unit original data to be recorded on a medium into N (> M) -bit unit conversion data. Medium, when the n consecutive codes of the allowable number of inter-symbol interferences of the transmission path are weighted by a distribution linearly decreasing from the center, and the n consecutive codes are sequentially added to form an intermediate sequence. As a code of the conversion data, a code having a sum of absolute values of differences between codes between intermediate sequences (modulation code distance) that is equal to or more than a predetermined multiple of a criterion value for weighting is selected. By switching a plurality of code groups formed with different correspondences according to the frequency of predetermined original data, the pattern distance between code patterns is increased, and the current medium and the recording / reproducing device are used. The recording density with remarkably improved, is obtained so as to improve the data detection accuracy at the time of reproduction.

According to a second aspect of the present invention, in a data detection method for detecting converted data from a reproduced signal of a medium in which converted data of N bits is recorded, a transmission system of a medium reproducing system allows n inter-symbol interferences. In addition to setting the characteristics, the data to be detected is set in N-bit units. When detecting the converted data, a predetermined zero-cross point among a plurality of zero-cross points of all patterns of the reproduction signal corresponding to the data to be detected is set as a synchronization position. By selecting, by obtaining more accurate information of the data detection position, it is possible to reliably detect the converted data recorded at a remarkably high density with a low error rate while using the current medium and the recording / reproducing device. Is made possible.

C. Prior Art Conventionally, in digital magnetic recording, basically, binary values "1" and "0" of a digital signal correspond to the polarity of magnetization or the presence or absence of magnetization reversal. Then, according to the physical characteristics of the recording medium, the transmission band of the system, etc., binary coding is performed according to various modulation (writing) methods such as NRZ, FM, MFM, and GCR (8-10 conversion). Value and magnetization are 1
Correspondence is made appropriately in bit units.

In general, for these modulation methods, the minimum magnetization reversal interval (Tmin) is large and the maximum magnetization reversal interval (Tmax) is large.
It is required that the recording density is small, the change in the local recording density is small, and the DC component is small.

At the time of demodulation (reading), differential detection or integration detection is used in accordance with the DC component of the modulation code, and data is demodulated by detection in units of 1 bit.

In the conventional digital magnetic recording as described above, it is assumed that there is no intersymbol interference, and it is necessary that the level of a reproduced signal in a high frequency band is sufficiently high. In other words, the maximum repetition frequency of the recording signal and the density of the recording information are determined by the S / N of the high-frequency reproduction signal corresponding to Tmin of various modulation codes.

For this reason, as shown in FIG. 9, the current maximum repetition frequency f max is in the falling region of the reproduction level-frequency characteristic,
It is set in the area where high S / N can be obtained. In the descending region, the level of the reproduced signal decreases at a gradient of, for example, 12 dB / oct due to various losses during recording and reproduction.

Further, an ideal transmission characteristic (frequency spectrum) as shown in FIG. 10A is required, and a sine-sloping equalization characteristic satisfying the first Nyquist criterion as shown in FIG. 10B is used.

In the figure, the frequency fo corresponds to the modulation code Tmin.

Also, the Nyquist's first criterion is that on the receiving side,
This is a condition that, when the waveform is sampled at regular intervals, sample values other than the center become 0.

For example, in the case of 8-10 conversion used in current digital audio tape recorders (DATs), the conversion efficiency of encoding is [8/10], and the coating type metal (MP)
The relative speed between the tape and the magnetic head is just over 3m / s, the maximum repetition frequency f max is set to 4.7MHz, and the gap length is 0.25
μm, and the recording wavelength is 0.67 μm. In this case, the track pitch is about 10 to 15 μm, and the linear recording density is about 60 to 80 kbpi.

D. Problems to be solved by the invention By the way, when recording at high density, the maximum repetition frequency
It is conceivable to increase f max.

However, if the recording density is to be increased, for example, by a factor of two, at a repetition frequency of 2f max, the level of the reproduced signal decreases as shown in FIG. There is a problem that it becomes impossible to detect an image.

As described above, current magnetic systems generally use recording media and conversion devices at their limits, reducing various losses during recording and playback, and significantly improving the level of playback signals in high frequencies. It is extremely difficult to do so.

On the other hand, when the recording density is increased, the following problem of intersymbol interference occurs in the reproduced waveform.

When one magnetization reversal exists in isolation on the magnetic medium, a pulse-like voltage waveform (isolated pulse) as shown in FIG. 11 is obtained as a reproduction signal. This isolated pulse, that is, the waveform of the impulse response is approximated to, for example, a lawrence type waveform as shown in the following equation (1), and the spread (pulse width) on the time axis is determined by the recording system / reproducing system used. Is determined by the total transmission characteristics of the
It is represented by a half-width Wh at the 50% level or a width Wb at the base level of substantially 0%.

f (t) = 1 / {1+ (t / to) ² } (1) When a plurality of magnetization reversals are continuously present at a constant interval,
If the recording density is low, there is no interference between adjacent pulses at the time of reproduction, and the reproduction signal is simply a series of the above-described isolated pulses alternately inverted.

The recording density has increased considerably, as shown in FIG.
The interval between adjacent pulses is equal to the pulse width Wb at the base level.
When the width is reduced to 1/2, the skirts of the pulses adjacent to each other overlap, and the waveform of the reproduced signal is considerably different from the isolated pulse.

As is clear from the figure, at this stage, the information of the peak value of each pulse is stored without any loss,
Although there is inter-waveform interference, no intersymbol interference has occurred.

When the recording density is higher than the state shown in FIG. 12, the peak value of the reproduced signal decreases and nonlinear intersymbol interference (peak shift) occurs in which the interval between peak positions increases.

When the recording density further increases, for example, as shown in FIG. 13, when the interval between adjacent pulses is reduced to 1/4 of the pulse width Wb at the base level, the reproduced waveform of the pulse becomes closer to a sine wave, The peak value also drops significantly. Also in this case, intersymbol interference occurs that impairs the information of the peak value of each pulse.

Incidentally, a partial response (Partial Response) method is known as one that utilizes intersymbol interference.

In this system, for example,
As shown in FIG. 14, there is an advantage that the frequency spectrum is limited to the Nyquist bandwidth and high frequency components are not required.

The characteristics shown in FIG. 14 correspond to the class 4 of the partial response (modified duobinary).
It is expressed as the following equation (2).

Pr (1,0, −1) = sin (2πf / fo) ‥‥ (2) However, since the above-described various modulation codes themselves do not assume intersymbol interference, even if the partial response method is applied. However, there is a problem that the advantage cannot be fully utilized.

Further, with a certain type of modulation code, Tmax becomes infinite, and even if the partial response method is applied, there is a problem that functions necessary for a system configuration such as overwriting or clock reproduction cannot be realized.

In addition, when data is detected in units of a plurality of bits by applying the partial response method while allowing intersymbol interference, clock recovery can be performed by synchronizing sampling points, but sufficient synchronization information for data detection is sufficient. There was a problem that was not.

In view of the above, an object of the present invention is to improve the recording density while using the current recording medium and recording / reproducing device, and to improve the data detection accuracy at the time of reproducing. It is intended to provide a conversion and detection method.

E. Means for Solving the Problems A first aspect of the present invention is a data conversion method for converting M-bit original data to be recorded on a medium into N (> M) -bit conversion data. Among the N codes, n consecutive codes equal to the number of intersymbol interferences allowed according to the characteristics of the transmission path are weighted so as to linearly decrease from the reference value of the distribution center, and the weighting is performed. N consecutive codes are sequentially added to obtain N-n + 1
When forming an intermediate sequence in bit units, as the code of the converted data, select a code in which the sum of absolute values of the differences between the codes between the intermediate sequences is equal to or more than a predetermined multiple of the standard value of the weight,
This is a data conversion method in which a plurality of code groups are formed by making the correspondence between the selected code and the original data different, and the plurality of code groups are switched in accordance with a predetermined frequency of the original data. .

According to a second aspect of the present invention, in a data detection method for detecting converted data from a reproduced signal of a medium in which converted data of N bits is recorded, a transmission system of a medium reproducing system allows n inter-symbol interferences. In addition to setting the characteristics, the data to be detected is set in N-bit units, and when detecting the converted data, a predetermined zero-cross point among a plurality of zero-cross points of all signal patterns of the reproduction signal corresponding to the data to be detected is set to the synchronization position. This is a method of detecting data which is selected as “1”.

E. Function According to the present invention, while using the current recording medium and the recording / reproducing device, the recording density is remarkably improved, and the data detection accuracy at the time of reproducing is improved.

G. Embodiment An embodiment of the data conversion and detection method according to the present invention will be described below with reference to FIGS.

G1 Configuration of One Embodiment FIG. 1 shows the overall configuration of a magnetic system to which one embodiment of the present invention is applied, and FIG. 2 and FIG. 3 show the configuration of main parts thereof.

In FIG. 1, reference numeral (10) denotes a recording system in which an analog signal such as an audio signal and a video signal from a terminal IN is
The data is supplied to a data generation circuit (12) via an A / D converter (11), and recording data conforming to a system format is generated. The output of the generation circuit (12) is supplied to a data conversion circuit (13), and the symbol data output from the conversion circuit (13) is supplied to a magnetic head (1) via a recording amplifier (14). , Recorded directly on the magnetic tape MT.

As shown in FIG. 2, the data conversion circuit (13)
It has ROM tables (13a) and (13b), and stores a pair of conversion codes having different correspondences with the original data as shown in Tables 1 and 2 below. ROM table (13
The converted codes (symbol data) read from (a) and (13b) are alternatively derived via a switch (13s) controlled by a frequency detection circuit (13c).

Reference numeral (20) denotes a reproducing system, in which a signal (differential waveform) reproduced from the magnetic tape MT by the magnetic head (2) is equalized by an integrator and a low-pass filter via a reproducing amplifier (21). It is supplied to the circuit (22). The output of the equalizing circuit (22) is supplied to an A / D converter (23), where the output is converted into, for example, 8-bit data. ) Is supplied with the output of the PLL circuit (24) as a clock synchronization signal.

(30) is a data detection circuit, the detailed configuration of which will be described later. The output of the A / D converter (23) is supplied to the data detection circuit (30), and the detected symbol data is supplied to the decoding circuit (25), decoded into the original data, and derived to the output terminal OUT. Is done.

In FIG. 3, a series of pattern data is supplied from an input terminal (30i) of the data detection circuit (30) to the synchronization detection circuit (3).
The signal is directly supplied to 1), and is commonly supplied to a plurality of subtracters (33a) to (33m) via a buffer (32). Reference numerals (34a) to (34m) denote reference value ROMs in which the waveform values of the respective code patterns selected as the reference are stored. The output of the synchronization detection circuit (31) is output from each ROM (34a) to
(34m), and the outputs of the ROMs (34a) to (34m) are supplied to the corresponding subtracters (33a) to (33m).

(35a) to (35m) are pattern distance calculation circuits, and (36) is a minimum value selection circuit. The outputs of subtracters (33a) to (33m) are supplied to the calculation circuits (35a) to (35m), respectively. And
The outputs of the arithmetic circuits (35a) to (35m) are supplied to the minimum value selection circuit (36), and the pattern data of the shortest distance to the waveform value of each code pattern is derived to the output terminal (30o).

For code patterns and pattern distances,
This will be described in detail in the next section.

Operation of G2 Embodiment Next, the operation of the embodiment of the present invention will be described with reference to FIGS.

In this embodiment, the equalization characteristic of the waveform equalization circuit (22) of the reproduction system (20) is
The following equation (3) and the one shown in FIG. 4 corresponding to the class 2 of the partial response are selected.

Pr (1,2,1) = cos ² (πf / fo) ‥‥ (3) The relationship between the maximum recording repetition frequency fo and the pulse width Wb at the base level of the isolated pulse is expressed by the following equation (4). Thus, the pulse width Wb becomes equal to four times the sampling period, and as shown in FIG. 5, three sampling points are included in the pulse width Wb of each isolated pulse.

Wb = 1/4 · fo ‥‥ (4) In this specification, the above-mentioned state is referred to as a state where three intersymbol interferences are allowed, and n number of pulses are included in the pulse width Wb of each isolated pulse. Is referred to as a state in which n intersymbol interferences are allowed.

In this embodiment, the data conversion circuit (1) of the recording system (10) is used.
In 3), as shown in Tables 1 and 2 below,
2-4 conversion is performed to convert original data in bit units into converted data (modulation code) in 4 bit units.

The conversion data in Tables 1 and 2 are data in which “0” and “1” are the same in each of 16 normal 4-bit data patterns and the DC component is [0]. The correspondence relationship with the original data is different for each of the two.

In this embodiment, in the frequency detection circuit (13c) (see FIG. 2) of the data conversion circuit (13), the sum of each frequency of 00 and 01 and the sum of each frequency of 10 and 11 in the original data block are calculated. Are compared, and based on this, both modulation code groups in Tables 1 and 2 are appropriately switched in the data block.

In this case, when the modulation code group shown in Table 1 is used, “1111
By using the code "0000" and the code "00001111" together as a block synchronization code when using the modulation code group shown in Table 2, the reproducing side recognizes which of the two modulation code groups is used. be able to.

Then, each modulation code in Tables 1 and 2 is selected as follows.

First, assuming that the number of intersymbol interferences allowed according to the characteristics of the transmission path is n, weighting coefficients distributed linearly from the center as shown in Table 3 below are prepared.

Next, using this weighting coefficient, weighting is performed on n consecutive codes among the N codes of the replacement data in which each conversion data “0” in Table 1 is replaced with “−1”. Done.

Weighting coefficients w31, w32, w33 (w31 =
w33), four codes bi1 to bi4, bj1 to bj of the replacement data respectively corresponding to the ith and jth conversion data in Table 1.
In 4, the continuous three codes are weighted.

The three weighted codes are added as in the following equation (5), and the first and second codes Ui1, Ui2; Uj1, Uj2 of the i, j-th intermediate sequence in Table 1 are respectively obtained. It is formed.

As is clear from Tables 1 and 2, the intermediate sequences are different from each other, and the code distance Vi indicating the degree of dissimilarity is different.
j is defined as the following equation (6) as the sum of the absolute values of the differences between the k-th codes of the pair of intermediate sequences Ui and Uj.

In this embodiment, conversion data in which the code distance Vij is equal to or more than twice the reference value for weighting is selected as the modulation codes in Tables 1 and 2. The reference value corresponds to the peak value of the impulse response according to the total transmission characteristics of the recording system (10) and the reproduction system (20).

On the other hand, in the reproduction system (20), as is well known, the reproduction signal is output at the output of the waveform equalization circuit (22) by selecting the characteristics shown in the above equation (3) and FIG. Has 5 levels. Then, a reproduction waveform (code pattern) unique to the data pattern of each conversion data common to Tables 1 and 2 is obtained. This code pattern is as shown in FIG. 5 alone, and as shown in FIGS. 6 and 7 in succession. When the level of an isolated pulse at a sampling point is A, four code patterns are obtained. At each sampling point within the detection period Td where isolated pulses coexist, [2
[A], [A], [0], [−A], and [−2A].

The pattern distance Dpq representing the degree of dissimilarity between the code patterns P and Q ‥‥ represents the reproduction output level at the sampling point corresponding to each k-th code of the pair of patterns P and Q by Spk and Sqk, respectively. Is defined as the following equation (7).

In the two consecutive code patterns illustrated in FIG. 6, the code patterns of 1100 and 1100 indicated by a solid line and 1100 indicated by a broken line indicate that the preceding code is the same and the succeeding codes in the detection period Td are different.
・ In the code pattern of 0011, the pattern distance of the subsequent code is It is represented by

In this embodiment, the pattern distance D between the four code patterns respectively corresponding to the conversion data in Table 1 and Table 2 is determined by the impulse response of the transmission line including the recording system (10) and the reproduction system (20). Of the peak value A More than double.

In the data detection circuit (30) of FIG. 3, the code pattern corresponding to each of the conversion data as described above is selected as a reference and stored in each of the reference value ROMs (34a) to (34m). In the subtracters (33a) to (33m), this m (=
The 4) code patterns are compared with 4-bit input patterns from the buffer (32). On the basis of this comparison output, in the arithmetic circuits (35a) to (35m), the pattern distance between the input pattern and each code pattern is calculated in accordance with the above equation (7).

In the minimum value selection circuit (36), each arithmetic circuit (35
During the output of a) to (35m), one of the m code patterns and one pattern data at the shortest distance Dmin are selected, and the maximum likelihood (Maximum Likelyhood) detection data, that is,
It is led to the output terminal (30o) as the most likely detection data.

In this embodiment, in the synchronization detection circuit (31), zero cross point detection processing is performed for all the signal patterns of the reproduced signal as shown in FIG.

As illustrated in FIG. 6 above, in the continuous reproduction waveform, the solid line code pattern of 1100/1100 and the chain line 0011/1100
The detection period depends on whether the preceding code is different, as in the case of the code pattern of 1100, or the code pattern of 1100, 1100 in the solid line and the code pattern of 1100, 0011 in the dashed line. Each subsequent code pattern in Td changes in various ways.

In this embodiment, as shown in FIG. 7 and the following Table 4, by combining the preceding code and the succeeding code, 16 types of code patterns can appear in the detection period Td, and four zero-crossing points can be obtained. There are C1, C2, C3, C4.

In Table 4, the passing of the zero-cross points C1 to C4 is indicated by “1”. As is clear from this, the probability that each code pattern passes is higher than that of the first to third zero-cross points C1 to C3. It is much larger at the zero crossing point C4 of 4. Further, the code pattern passing through the zero cross point C4 includes 1100
Code or 0011 code exists.

Therefore, in this embodiment, as described above, the recording system (1
0) in the data conversion circuit (13) (see FIG. 2)
The ROM tables (13a) and (13
By switching b) appropriately, it is guaranteed that the frequency of the 1100 code and the 0011 code will be 1/2 or more.

Thereby, as shown in FIG. 8A, in the case of a random pattern, each code pattern is changed to the fourth zero-cross point.
The probability that the code pattern passes through C4 is remarkably large. For example, in the case of a fixed pattern in which 1100 codes are repeated, the probability that the code pattern passes through the second and fourth zero-cross points C2 and C4 as shown in FIG. Becomes larger. Note that FIG. 8 shows the accumulation of passing zero cross points during the detection period Td, assuming that there are N patterns in one signal block.

In any case, the signal passes through the fourth zero-cross point C4 most frequently, and the S / N of the signal passing through the zero-cross point C4 is also good. Therefore, the accumulation of the zero-cross points at the C4 point or the zero-cross itself is used for data detection. By using synchronization information, accurate detection synchronization information that follows the time axis fluctuation such as jitter can be obtained relatively easily, and the reproduced data can be reliably detected, and data detection at high recording density Accuracy is significantly improved.

H. Effects of the Invention As described in detail above, according to the first aspect of the present invention, a data conversion method for converting M-bit original data to be recorded on a medium into N (> M) -bit converted data , Weighting is applied to n continuous codes of the allowable number of inter-symbol interferences of the transmission path in a distribution linearly decreasing from the center among the N codes of the converted data, and the weighted n continuous codes are sequentially added. When the intermediate sequence is formed, at least the code of the leading part of the converted data is selected so that the sum of the absolute values of the differences between the codes between the intermediate sequences is equal to or more than a predetermined multiple of the reference value of the weight. Since a plurality of code groups formed by changing the correspondence between the selected code and the original data are switched according to the frequency of the predetermined original data, the pattern distance between the code patterns can be increased. ,current While using the body and the recording and playback device,
A data conversion method that can significantly improve the recording density and improve the data detection accuracy during reproduction can be obtained.

According to the second aspect of the present invention, in a data detection method for detecting conversion data from a reproduction signal of a medium on which conversion data in N bits is recorded, the medium is configured to allow n inter-symbol interferences. In addition to setting the transmission characteristics of the reproduction system, the data to be detected is set in N-bit units, and when detecting the converted data, a predetermined zero-cross point among a plurality of zero-cross points of all patterns of the reproduction signal corresponding to the data to be detected Is selected as the synchronization position, so that more accurate information of the data detection position can be obtained, and the conversion data recorded at a remarkably high density can be obtained while using the current medium and the recording / reproducing device. A data detection method that can be reliably detected at a low error rate is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an entire configuration of an embodiment of a data conversion and detection method according to the present invention, FIG. 2 is a block diagram showing a configuration of a main part of an embodiment of the present invention, and FIG. FIG. 4 is a block diagram showing the configuration of another main part of one embodiment of the present invention, FIG. 4 is a diagram showing characteristics of still another main part of one embodiment of the present invention, and FIGS. FIG. 8 is a waveform chart for explaining the operation of one embodiment of the present invention, FIG. 8 is a diagram for explaining the operation of one embodiment of the present invention, and FIG. 9 is a line for explaining conventional digital magnetic recording. FIG. 10 is a diagram showing characteristics of a conventional example, FIGS. 11 to 13 are waveform diagrams for explaining the present invention, and FIG. 14 is a diagram showing characteristics of another conventional example. (10) is a recording system, (13) is a data conversion circuit, (13a),
(13b) is a ROM table, (13c) is a frequency detection circuit, (2
0) is a reproduction system, (22) is a waveform equalization circuit, (30) is a data detection circuit, (31) is a synchronization detection circuit, (34a) to (34m) are reference value ROMs, and (36) is a minimum value selection. Circuit.

Continuation of the front page (56) References JP-A-62-243447 (JP, A) JP-A-54-9717 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 20 / 10 G11B 20/14 H03M 3/00-11/00

Claims (2)

(57) [Claims] 1. A data conversion method for converting original data in M bits to be recorded on a medium into converted data in N (> M) bits, comprising: Is weighted so that n consecutive codes equal to the number of inter-symbol interferences allowed according to are linearly reduced from the reference value at the center of distribution, and the weighted n consecutive codes are When an intermediate sequence of N-n + 1 bits is formed by sequentially adding, the sum of the absolute values of the differences between the codes between the intermediate sequences is equal to or more than a predetermined multiple of the reference value of the weight as the code of the converted data. And forming a plurality of code groups by changing the correspondence between the selected code and the original data, and cutting the plurality of code groups according to a predetermined frequency of the original data. The method of converting data, characterized in that the obtaining manner. 2. A data detection method for detecting converted data from a reproduced signal of a medium in which converted data in units of N bits is recorded, wherein the transmission of the reproducing system of the medium so as to allow n inter-symbol interferences. In addition to setting the characteristics, the data to be detected is set in the N-bit unit. When detecting the converted data, a predetermined zero-crossing point among a plurality of zero-crossing points of all signal patterns of the reproduction signal corresponding to the data to be detected is set. A method for detecting data, wherein a point is selected as a synchronization position.