JPH0485766A - Data detecting method - Google Patents

Abstract

PURPOSE:To improve the data detecting accuracy by providing the reproduction transmission characteristic which grants (n) pieces of inter-code interference, comparing a signal pattern corresponding to the detection data with plural prescribed patterns, and referring to a selected approximation pattern at the subsequent comparison of both patterns. CONSTITUTION:A data conversion circuit ROM 13 of a recording system 10 applies the 2-4 conversion to the source data, and the inter-code interference number to be granted in response to the transmission characteristic is referred to (n). Then continuous (n) pieces of inter-code interference are weighted among those codes of the data replaced with the conversion data. The conversion data having a code distance obtained by adding three codes together and larger than the reference weighting value by twice or more is selected, and a code pattern proper to each conversion data is obtained at the output of a waveform equalizing circuit 22. A minimum value selection circuit 36 selects an approximation pattern of the smallest distance out of the outputs of the pattern distance computing circuits 35a - 35m and sends the pattern to an output terminal 30omicron. Then the approximation pattern is fed back to the reference value ROM 34a - 34m via a delay circuit 37 for reference. Thus the subsequent input patterns are detected. Then the detection accuracy is improved for the conversion data recorded in high density.

Description

[Detailed description of the invention] The invention will be explained in the following order.

A. Industrial field of application B0 Summary of the invention C1 Prior art 1 Problems to be solved by the invention 81 Means for solving the problems F1 Effects G. Example 61 - Structure of the example (Fig. 1, FIG. 2) G2 Operation of one embodiment (FIGS. 1 to 8) H1 Effects of the invention A, Industrial application field This invention relates to a data detection method suitable for high-density recording.

B6 Summary of the Invention This invention provides a data detection method for detecting converted data from a reproduced signal of a medium on which converted data in units of N bits is recorded, in which the reproduction system of the medium is adjusted to allow n intersymbol interferences. In addition to setting the transmission characteristics, the data to be detected is set in units of N bits, and the pattern of the reproduced signal corresponding to the data to be detected is compared with the code pattern group corresponding to each converted data to select an approximate pattern. At the same time, by referring to this selected approximate pattern when comparing the signal pattern of the subsequent reproduced signal with a plurality of predetermined patterns, the error rate at the time of detection can be reduced and the current medium and recording/playback device can be improved. This makes it possible to reliably detect converted data recorded at an extremely high density.

C1 Prior Art Conventionally, in digital magnetic recording, the binary values of the digital signal -1, ``O'', ``+'' are basically associated with the polarity of magnetization or the presence or absence of magnetization reversal. , 2 by encoding according to various modulation (writing) methods such as NRZ, FM, MFMccR (8-10 conversion), etc., depending on the physical characteristics of the recording medium and the transmission band of the system.
The base value and the magnetization are made to correspond appropriately on a bit-by-bit basis.

In general, these modulation methods require a large minimum magnetization reversal interval (Tmin) and a large maximum magnetization reversal interval (Tmin).
max) is small, local changes in recording density are small, and the direct current component is small.

Further, during demodulation (reading), differential detection or integral detection is used depending on the amount of DC component of the modulation code, and data is demodulated by detection in units of 1 bit.

Conventional digital magnetic recording as described above is based on the assumption that there is no intersymbol interference, and requires that the level of the reproduced signal in the high frequency range be 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 Tm1n of various modulation codes.

As shown in FIG. 9, the current maximum repetition frequency f max is set at a portion where a high S/N can be obtained in a decreasing region of the reproduction level-frequency characteristic. In this descending region, the level of the reproduced signal decreases at a gradient of, for example, 12 dB10 ct due to various losses during recording and reproduction.

Further, an ideal transmission characteristic (frequency spectrum) as shown in FIG. 10A is required, and a sinusoidal descending equalization characteristic satisfying Nyquist's first criterion as shown in FIG. 10A is used.

In addition, in the same figure, the frequency fO is Tm1 of the modulation code.
This corresponds to n.

Further, Nyquist's first criterion is a condition in which when a waveform is sampled at regular intervals on the receiving side, sampled values other than the center become 0.

For example, the current digital audio recorder (D
In the case of the 8-10 conversion adopted in AT), the relative speed between the coated metal (MP) tape and the magnetic head is 3 m.
/s, and the maximum repetition frequency f max is 4.7 Mt.
lz, the gap length is 0.25 μm, and the recording wavelength is 0.67 μm. In this case, the track pitch is 10 to 15 μm, and the linear recording density is approximately 60 to gQ kbpi.

D1 Problem to be solved by the invention By the way, when recording at high density, the maximum repetition frequency f
It is possible to increase max.

However, if you try to double the recording density, for example,
At a repetition frequency of 2 (max), as is clear from Figure 9 above, there is a problem in that the level of the reproduced signal decreases, the S/N ratio deteriorates significantly, and it becomes impossible to detect data. Ta.

As mentioned above, current magnetic systems use recording media and conversion devices at their limits, so it is possible to reduce various losses during recording and playback and significantly improve the level of playback signals in high frequencies. It is extremely difficult to do so.

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

When one magnetization reversal exists in isolation on a magnetic medium,
As a reproduction signal, a pulse-like voltage waveform (isolated pulse) as shown in FIG. 11 is obtained. The waveform of an isolated pulse, that is, an impulse response, is approximated to a Lawrence type waveform, for example, as shown in the following equation (1), and its spread on the time axis (pulse width) depends on the recording system/playback system used. It is determined by the overall transmission characteristics of the magnetic medium and the peak value.
It is represented by the half-value width Wh1 at a level of 0% or the width wb at a base level of substantially 0%.

f(t)-1/ (1 し(t/lo)')...(1
) When multiple magnetization reversals exist consecutively at regular intervals,
If the recording density is coarse, there will be no interference between adjacent pulses during reproduction, and the reproduced signal will consist of a series of alternately inverted isolated pulses as described above.

The recording density has become considerably high, as shown in Figure 12.
Pulse width wb when the interval between adjacent pulses is at the base level
When the width is narrowed to 172, the tails of adjacent pulses overlap, and the waveform of the reproduced signal becomes quite different from that of an isolated pulse.

As is clear from the figure, at this stage, information on the peak value of each pulse is preserved without any loss, and although there is interference between waveforms, no intersymbol interference occurs.

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

As the recording density further increases, for example, as shown in FIG. 13, when the interval between adjacent pulses narrows to 1/4 of the pulse width wb at the base level, the reproduced waveform of the pulses becomes close to a sine wave. The wave height value also decreases significantly. In this case as well, intersymbol interference occurs that destroys information on the peak value of each pulse.

By the way, as a method that utilizes intersymbol interference, a partial response (Partial Response) method% type% is used.In this method, for example, the first
As shown in FIG. 4, 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 partial response class 4 (modified duobinary) and are expressed as in the following equation (2).

P r (1, O4-1) −s i n (2yr
f / fo) -12) However, since the various modulation codes mentioned above do not themselves assume intersymbol interference, there is a problem that even if the partial response method is applied, its advantages cannot be fully utilized. there were.

Further, in some types of modulation codes, Tmax becomes infinite, and even if a partial response method is applied, there is a problem that functions necessary for system configuration such as override or clock regeneration cannot be realized.

In view of this, an object of the present invention is to reduce the error rate during detection and reliably detect converted data recorded at high density while using current recording media and recording/reproducing devices. The goal is to provide a method for detecting data that can be used to detect data.

81 Means for Solving the Problems This invention provides 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, in which the medium is configured to allow n intersymbol interference. At the same time, the data to be detected is set in units of N bits, and the signal pattern of the reproduced signal corresponding to the data to be detected is compared with a plurality of predetermined patterns limited by the conversion data. , selects an approximate pattern that approximates the plurality of predetermined signal patterns, and detects data by referring to the selected approximate pattern when comparing the signal pattern of the subsequent reproduced signal with the plurality of predetermined patterns. This is a method for detecting data.

F1 Effect According to the present invention, the error rate at the time of detection is reduced, and converted data recorded at high density can be reliably detected while using current recording media and recording/reproducing devices.

G. Examples below, 15th! An embodiment of the data detection method according to the present invention will be described with reference to FIGS.

Structure of G1 Embodiment FIG. 1 shows the overall structure of a magnetic system to which an embodiment of the present invention is applied, and FIG. 2 shows the structure of its main parts.

In FIG. 1, (10) is a recording system, and the terminal IN
Analog signals such as audio signals and video signals from the
2), and recording data conforming to the system format is generated. (13) is a data conversion circuit, which is an RO in which a conversion code as shown in Table 1 below is stored.
Equipped with M table. The output of the generation circuit (12) is supplied to a data conversion circuit (ROM> (13)), and the symbol data output from this conversion circuit (13) is sent to the magnetic head (1) via a recording amplifier (14). supplied to,
Recorded directly on magnetic tape MT.

(20) is a reproduction system, in which the signal (differential waveform) reproduced from the magnetic tape MT by the magnetic head (2) is processed through a reproduction amplifier (21) and subjected to waveform equalization consisting of an integrator and a low-pass filter. It is supplied to the circuit (22). This equalization circuit (
22) is supplied to the A-D converter (23), where it is converted into, for example, 8-bit data, and is also supplied to the PLL circuit (24). The output of the PLL circuit (24) is supplied as a signal.

(30) is a data detection circuit, the detailed configuration of which will be described later. The data detection circuit (30) is supplied with the output of the A-D converter (23), and the detected symbol data is supplied to the decoding circuit (24), where it is decoded into original data and output to the output terminal OUT. be done.

In FIG. 2, the input terminal (
30i), a series of pattern data is directly supplied to the synchronization detection circuit (31), and Hanwha (32)
The signal is commonly supplied to a plurality of subtracters (33a) to (33m) through the subtracters (33a) to (33m). (34a) to (34m) are reference value ROMs
The waveform values of each code pattern selected as a reference are stored. The output of the synchronization detection circuit (31) is commonly supplied to each ROM (34a) to (34m), and the output of the cono ROM (34a) to (34m) is supplied to the corresponding subtractor (33a) to (33m), respectively. be done.

(35a) to (35m) are pattern distance calculation circuits, (3
6) is a minimum value selection circuit, which includes arithmetic circuits (35a) to
(35m) is supplied with the outputs of the subtracters (33a) to (33m), respectively, and each arithmetic circuit (35a) to (35m)
The output is supplied to a minimum value selection circuit 36), and pattern data having the shortest distance to the waveform value of each code pattern is derived to an output terminal (30o).

Further, in this embodiment, the output of the minimum value selection circuit (36) is sent to each reference value ROM (34) via a delay circuit (37).
Feedback is provided to a) to (34m).

Note that the code pattern and pattern distance will be explained in detail in the next section.

G2 Operation of the first embodiment Next, the operation of the second embodiment of the invention will be described with reference to FIGS. 3 to 8.

In this embodiment, for vector encoding as described later, the relationship between the highest recording repetition frequency f○ and the pulse width wb at the base level of the isolated pulse is set as shown in the following equation (3), and the pulse width wb is equal to four times the sampling period, and three sampling points are included within the pulse width wb of each isolated pulse, as shown in FIGS. 3 and 4.

Wb = 1/4 ・fo -43) In this specification, the above-mentioned state is called a state in which three intersymbol interferences are allowed, and n samplings are allowed within the pulse width wb of each isolated pulse. The state in which the points are included will be referred to as the state in which n intersymbol interferences are allowed.

In this embodiment, the data conversion circuit (R
OM) (13), as shown in Table 1 below, 2
A 2-4 conversion is performed to convert original data in units of bits into converted data (modulation code) in units of 4 bits.

Table 1 The conversion data in Table 1 has the same number of "0" and "1" among the 16 normal 4-bit data patterns, and [3
/41. [01, and is selected as follows.

First, let n be the number of intersymbol interferences allowed according to the characteristics of the transmission path, and prepare coefficients for weighting that is distributed linearly decreasing from the center as shown in Table 2 and Figure 5 below. be done.

Next, this weighting is performed using coefficients for each successive n code among the N codes of the replacement data in which 〇2 is replaced with r-I J, respectively, in Table 1. Weighting is done.

The weighting as shown in Table 2 and FIG. 5 is done by the coefficient w31.
w32. Using w33 (w31=w33),
1 in Table 1. Each of the four codes bil to bi4 . bjl〜bj
4, each consecutive three codes are weighted.

These three weighted codes are added as shown in the following equation (4), and the result is 1.2 of the 1st and 3rd intermediate series in Table 1.
th code U+1. U+2: UJI, UF
4 are formed respectively.

Ui1=w31bi1+w32bi2+w33bi3
) As is clear from Table 1, the intermediate sequences are different, and the code distance vIJ, which represents the degree of dissimilarity, is
It is defined as the following equation (5) as the sum of the absolute values of the differences between the signs of each of a pair of intermediate sequences Ui and Uj.

Vij= l 0il-Ujl l +i Ui2-U
j2ΣI[Jik −Ujk l...
(5) In this embodiment, conversion data such that the code distance V1 is more than twice the weighting reference value is selected as the modulation code in Table 1. This reference value corresponds to the peak value of the impulse response according to the overall transmission characteristics of the recording system (10) and the reproduction system (20).

On the other hand, in the reproduction system (20), in order to cope with the three intersymbol interferences, the equalization characteristics of the waveform equalization circuit (22) are set to the following (6) 2 and 2, which correspond to partial response class 2. The one shown in FIG. 6 is selected.

Pr (1, 2, 1) = co s' (yr f
/fo) - (6) This allows the waveform equalization circuit (
22), the number of levels of the reproduced signal is five, as is well known. Then, a reproduced waveform (code pattern) unique to the data pattern of each converted data in Table 1 is obtained. This code pattern is as shown in Figure 3 above when used alone, and when it is continuous as shown in Figure 4 above, where A is the level of isolated pulses at the sampling point. At each sampling point within the detection period T[] where pulses coexist, [2A
], JAl, [O], [-A].

E-2A] can take on five different values.

In addition, the pattern distance Dpq representing the degree of dissimilarity between the code patterns P, Q...
The following (
7) It is defined as in Eq.

D9q=Σl 5pk-5(lk l...(7
) Of the two consecutive code patterns illustrated in Figure 4, the solid line 1100/1100 code pattern has the same preceding code and different subsequent codes within the detection period Td,
In the broken line 1100-0011 code pattern, the pattern distance of the subsequent code is expressed as D=nl (lkl).

As shown in FIG. 7, in this embodiment, the pattern distances between the four code patterns corresponding to the conversion data in Table 1 are the same for the recording system (10) and the reproduction system (20).
2-1 of the peak value A of the impulse response of the transmission line consisting of
It becomes more than M times.

In the data detection circuit (30) of FIG. 2, the code pattern corresponding to each conversion data as described above is selected as a reference, and each reference value ROM (34a) to
> Stored in In the subtracters (33a) to (33m), these TTI (=4> code patterns) are compared with the 4-bit position input cover pattern from the buffer (32).Based on this comparison output, the arithmetic circuit In (35a) to (35m), the pattern distance between the human cover turn and each code pattern is calculated according to the above equation (7).

In the minimum value selection circuit (36), each calculation circuit (35
During the output of a) to (35 m), one pattern data located at the shortest distance Dmin from any of the m code patterns is selected, and the maximum likelihood (Maximum Likely)
hood) detection data, ie, the most likely detection data, is led out to the output terminal (300).

In this embodiment, the detected data of the preceding and <turns that have already been determined is sent to each reference value ROM (34a) to ( 34m), and the subsequent incoming cover turn is detected by referring to this preceding pattern.

As illustrated in FIG. 4 above, in the continuous playback waveform, the solid line 1100/1100 code pattern and the chain line 00
When the preceding codes are different, as in the case of the code pattern 11.1100, the level of the subsequent code pattern varies greatly depending on the preceding code pattern even if the subsequent code within the detection period Td is the same.

In this embodiment, by referring to the preceding code pattern during the process of detecting the subsequent input covert pattern, it is possible to remove the influence of level fluctuations as described above, and to reliably detect the subsequent code pattern. error rate is reduced.

In this embodiment, for example, 1
At a recording density of 20kbJ)i, the symbol error rate is approximately 5Xl0-', and as shown by the chain line in the figure, the current DAT (8-10 conversion) has the same error rate at a recording density of just over 7Qkbpi. Compared to this, the error rate at high recording density is significantly improved.

H1 Effects of the Invention As detailed above, according to the present invention, in a data detection method for detecting converted data from a reproduced signal of a medium on which converted data in units of N bits are recorded, it is possible to eliminate n intersymbol interferences. In addition to setting the transmission characteristics of the reproduction system of the medium so as to allow the data to be detected, the data to be detected is set in units of N bits, and the pattern of the reproduction signal corresponding to this data to be detected and the code pattern group corresponding to each converted data are set. In addition, this selected approximate pattern is referred to when comparing the signal pattern of the subsequent reproduced signal with a plurality of predetermined patterns, thereby reducing the error rate at the time of detection. Thus, a data detection method can be obtained that can reliably detect converted data recorded at a much higher density while using current media and recording/reproducing devices.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the data conversion and detection method according to the present invention, FIG. 2 is a block diagram showing the configuration of the main part of an embodiment of the present invention, and FIG. 4 is a waveform diagram for explaining the operation of an embodiment of the present invention, FIG. 5 is a line diagram for explaining the operation of an embodiment of the invention, and FIG. 6 is an embodiment of the invention. Fig. 7 is a line diagram showing the characteristics of other important parts, Fig. 7 is a route diagram for explaining the operation of an embodiment of this invention, and Fig. 8 is a line diagram for explaining the effects of an embodiment of this invention. Fig. 9 is a diagram for explaining the conventional digital magnetic recording, Fig. 10 is a diagram showing the characteristics of the conventional example, and Figs. 11, 12, and 13 are for explaining the present invention. FIG. 14 is a diagram showing the characteristics of another conventional example. (10) is the recording system, (13) is the data conversion circuit (ROM
), (20) is the reproduction system, (22) is the waveform equalization circuit, (3
0) is a data detection circuit, (34a) to (34m) are reference value ROMs, (36) is a minimum value selection circuit, and (37) is a delay circuit. Agent Hidemori Matsukuma Diagram O Zhou Jian Diagram Q

Claims (1)

[Claims] In a data detection method for detecting the converted data from a reproduced signal of a medium on which N bits of converted data are recorded, the reproduction system of the medium is configured to allow n intersymbol interferences. In addition to setting the transmission characteristics, the data to be detected is set in units of N bits, and the signal pattern of the reproduced signal corresponding to the data to be detected is compared with a plurality of predetermined patterns limited by the conversion data. Selecting an approximate pattern that approximates the signal pattern from a plurality of predetermined patterns, and detecting data by referring to the selected approximate pattern when comparing the subsequent signal pattern of the reproduced signal with the plurality of predetermined patterns. A data detection method characterized by: