JP2728094B2 - Magnetic recording / reproducing device - Google Patents

Description

The present invention relates to a magnetic recording / reproducing apparatus that reproduces reproduction signals from a plurality of adjacent recording tracks by using a Viterbi decoding method, and to a plurality of recording tracks on which signals are recorded adjacently. The purpose of the present invention is to perform accurate Viterbi decoding in consideration of the influence of crosstalk between tracks when reproducing from a magnetic recording medium, and a magnetic recording medium has a plurality of recording tracks on which signals are recorded adjacently. In a magnetic recording / reproducing apparatus which reproduces a signal recorded in a plurality of heads using a plurality of heads and decodes the reproduced signal using a Viterbi decoder provided for each head, a crosstalk from one track to another track is reproduced. And a signal from the crosstalk memory and a signal from the path memory of the Viterbi decoder. A crosstalk circuit for calculating the cross talk amount imparted to the Viterbi decoder for each track, while predicting the crosstalk from other tracks for each track, configured to perform the Viterbi decoding the reproduction signal of each track.

[Industrial applications]

The present invention relates to a magnetic recording / reproducing apparatus, and more particularly to a magnetic recording / reproducing apparatus that reproduces reproduction signals from a plurality of adjacent recording tracks by using a Viterbi decoding method.

In recent years, with an increase in the amount of information to be recorded, a considerable amount of information is recorded at a high density on a recording medium such as one magnetic disk. When reproducing a signal recorded on such a high-density magnetic disk, for example, a floppy disk or a hard disk, in addition to noise from a recording medium, a reproducing head, a reproducing circuit, and the like, crosstalk between recording tracks of the magnetic disk may occur. However, deterioration of signal quality is inevitable. Such deterioration of the signal quality is a problem because the reliability of the recorded information is significantly impaired. Therefore, a magnetic recording / reproducing apparatus which can obtain a high reliability of a reproduced signal even if there is crosstalk between recording tracks is desired.

[Conventional technology]

Hitherto, as a means for obtaining high reliability even at a low S / N ratio, application of a Viterbi decoding method to a magnetic recording signal reproducing circuit has been considered.

This Viterbi decoding method is one of decoding methods of a convolutional code, and when all possible information is generated with equal probability,
This is an optimal decoding method in the sense of minimizing the signal error rate.

FIG. 6 is a block diagram showing a configuration of a conventional Viterbi decoder when waveform interference in a reproduced signal from a magnetic recording device is regarded as a convolutional code.

In the figure, 10 is an A / D converter, 20 is an isolated waveform detection circuit, 30 is a branch metric calculation circuit, 40 is an ACS (Add
Compare Selector), 50 is an isolated waveform memory, 60 is an interference amount calculation circuit, 70 is a path memory, and 80 is a path selector. A long period (isolated waveform) is recorded at the beginning of data to be recorded in the magnetic recording device, and a waveform (isolated waveform) free from waveform interference is obtained during reproduction.

In this conventional Viterbi decoder, a reproduction signal from a magnetic recording device is sampled by an A / D converter 10 and input to an isolated waveform detection circuit 20. A clock signal synchronized with the reproduction signal is used, and the isolated waveform detection circuit 20 is given in advance which clock of this clock signal is an isolated waveform and which data clock is a data signal.

If an isolated waveform is determined by the isolated waveform detection circuit 20 based on this clock signal, the sample value is taken into the isolated waveform memory 50 and stored. If the isolated waveform detection circuit 20 determines that the reproduced signal is a data signal, the sample value is used as a branch metric calculation circuit.
Entered in 30.

The sample values stored in the isolated waveform memory 50 are input to the interference amount calculation circuit 60, and the interference amount calculation circuit 60 assumes all combinations and overlaps with the data input from the isolated waveform memory 50. And calculate the amount of interference for all expected data. In the branch metric calculation circuit 30, the input sample value and the interference amount calculation circuit 60
A branch metric, which is an error between an expected value and an actual input value, is calculated based on the waveform interference amount predicted by.
The branch metric calculated by the branch metric calculation circuit 30 is input to the ACS 40, where the calculation and comparison of the path metric are performed, and the surviving path is selected.
Then, the selected surviving path is stored in the path memory 70.

Further, the path selector 80 selects the maximum likelihood path (the path having the minimum path metric value) at this time based on the surviving path stored in the path memory 70 and the branch metric having the smallest error from the ACS 40, and reproduces the reproduced data. Is output.

FIG. 7 shows an expected value obtained by superposition calculation of a sample value (each point on a solid line) of an actual signal waveform and an isolated waveform (each point on a broken line) by the Viterbi decoder configured as shown in FIG. (Each point on the dashed line). As can be seen from the figure, in the Viterbi decoder, the path having the highest expected value for the actual sample value is selected. The error between the sample value of the actual signal waveform and the expected value obtained by the superposition calculation of the isolated waveform is an error due to noise, and this error can be rescued by a Viterbi decoder. That is, when the error between the sample value and the expected value of the correct path is noise according to the Gaussian distribution, the original function of the Viterbi decoder can be exhibited.

[Problems to be solved by the invention]

However, due to the remarkable improvement in recording density seen in recent years of magnetic recording devices, crosstalk from a neighboring track to a signal recorded on a certain track may cause the recorded signal to interfere with the signal, thereby distorting the signal. In such a case, there is a problem that a reproduced waveform cannot be correctly decoded because a wrong selection is made in the conventional Viterbi decoder.

FIG. 8 shows an example in which a sample value of an actual signal is interfered by a signal waveform A recorded on an adjacent track and becomes a waveform B. From this figure, it can be seen that the waveform C, which is the expected value of the correct path by the Viterbi decoder, is significantly different from the waveform B of the sample value of the actual signal. in this way,
If there is crosstalk from adjacent tracks,
Since the actual sample value is far from the expected value of the correct path due to crosstalk noise (which is not a Gaussian distribution), the wrong path is selected and the original function of the Viterbi decoder is not performed. . Therefore, when there is crosstalk noise, there remains a problem that the reliability of recorded information is significantly impaired even if a conventional Viterbi decoder is used.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and even if there is crosstalk between magnetically recorded tracks, the effect of crosstalk does not appear in a reproduced signal, and the reliability of recorded information can be improved. It is an object of the present invention to provide a magnetic recording / reproducing apparatus capable of decoding a reproduced signal without deteriorating performance.

[Means for solving the problem]

In the magnetic recording and reproducing apparatus of the present invention which achieves the above object, as shown by a principle block in FIG. 1, a magnetic recording medium has a plurality of recording tracks on which signals are recorded adjacent to each other. The reproduced signal is reproduced by a plurality of heads, and the reproduced signal is decoded by using a Viterbi decoder provided for each head, a plurality of recording tracks at the same time, Records an isolated waveform so that a single isolated waveform is not reproduced by a plurality of heads, and the Viterbi decoder 100 of each track stores a sample value of crosstalk to another track from another track. A crosstalk memory 1, a signal from the crosstalk memory 1, and a Viterbi decoder 100
And a crosstalk circuit 2 for calculating the amount of crosstalk from another track according to the signal from the path memory of each track. It is characterized in that decoding is performed.

(Operation)

According to the magnetic recording / reproducing apparatus of the present invention, a predetermined portion of a plurality of recording tracks of a magnetic recording medium reproduces a crosstalk to another track by an isolated waveform recorded so as not to be adjacent to each other. By doing so, it is detected in advance and stored for each track, and decoding is performed in a Viterbi decoder in consideration of the influence of this crosstalk during data reproduction.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a circuit diagram showing the configuration of one embodiment of the magnetic recording / reproducing apparatus of the present invention. The circuit shown in FIG. 2 is a wide non-recording track on the magnetic disk D on which data is concentrically recorded as shown in FIG. Using a guard band, the recording area is divided into a plurality of recording areas, and N high-density tracks are provided concentrically in each recording area, and reproduction signals from each track are extracted by the same number of magnetic heads as the number of tracks. This is used for a device that decrypts data.

Therefore, the circuit of FIG. 2 requires N Viterbi decoders corresponding to N tracks of the storage area in the magnetic disk D, but FIG. Including the i-th track, the i-th track, and the i + of the N Viterbi decoders, including the 70 and the path selector 80.
Only the track No. 1 is shown.

In the figure, 10 _i−1 , 10 _i , 10 _{i + 1} are A / D converters, 20 _i−1 , 20 _i
i , 20 _{i + 1} are isolated waveform detection circuits, 30 _i-1 , 30 _i , 30 _{i + 1} are branch metric calculation circuits, 50 _i-1 , 50 _i , 50 _{i + 1} are isolated waveform memories, 60 _{i- 1} , 60 _i and 60 _{i + 1} indicate interference calculation circuits, and the suffixes “ _i−1 ”, “ _i ” and “ _{i + 1} ” attached to the respective codes indicate that they are i−1 Track, track i or i
This indicates that the track is for the + 1st track. A / D
Converters 10 _i-1 , 10 _i , 10 _{i + 1} , isolated waveform detection circuits 20 _i-1 , 20 _i , 20
_{i + 1} , branch metric calculation circuit 30 _i-1 , 30 _i , 30 _{i + 1} , isolated waveform memory 50 _i-1 , 50 _i , 50 _{i + 1} , interference amount calculation circuit 60 _i-1 , 60 _i ,
The operation of 60 _{i + 1} is the same as the conventional one.

Further, in this embodiment, as shown in the circuit of the i-th track, the crosstalk memories 1 _i (1) to 1- _{th to} ( _i− 1) -th tracks are _{supplied to} the output of the isolated waveform detection circuit 20 _i.
1 _i (i−1) and crosstalk memories 1 _i (i + 1) to 1 _i (N) from track i + 1 to track N are connected, and these crosstalk memories 1 _i (1) to 1 _i (N) are connected.
1 _i (i−1) and 1 _i (i + 1) to 1 _i (N) are crosstalk calculation circuits 2 _i (1) to 2 _i (i−1) for calculating crosstalk from the corresponding tracks, respectively. , And 2i
(I + 1) to 2 _i (N) are connected. The crosstalk calculation circuits 2 _i (1) to 2 _i (i−1) and 2 _i (i + 1)
The outputs of .about.2 _i (N) are input to the branch metric calculation circuit 30 _i together with the output of the interference amount calculation circuit 60 _i , and the crosstalk calculation circuits 2 _i (1) to.
Path memories 70 ₁ to 70 _N are connected to inputs of 2 _i (i−1) and 2 _i (i + 1) to 2 _i (N).

As described above, the Viterbi decoder of each track is provided with the crosstalk memory and the clock talk calculation circuit from other tracks other than the own track. Such a crosstalk memory and a crosstalk calculation circuit from another track are collectively indicated by a code of 1 _i-1 in the Viterbi decoder of the (i-1) th track, and are represented by a code of 1 _i-1 in the Viterbi decoder of the (i + 1) th track. They are collectively indicated by the code _{1i + 1} .
Furthermore, so that the output from the branch metric calculating circuit 30 ₁ to 30 _N of each track is input to the ACS40.

When performing Viterbi decoding using the above circuit,
On the magnetic disk D whose recording area is divided as shown in FIG. 3, recording as shown in FIG. 4 is executed in advance.
That is, in N recording tracks in a certain recording area, isolated waveforms are recorded in parallel and stepwise with a time difference on each track so that the isolated waveforms do not overlap in the radial direction of the magnetic disk. When this will be described specifically three tracks from i-1 th track to the i + 1 th track, from time t ₀ to time t ₁ i-1
The isolated waveform recorded in th track, the time t ₂ from time t ₁
Until the isolated waveform is recorded in the i-th track, from time t ₂ to time t ₃ it comes to record the isolated waveform to the (i + 1) th track.

As a result, an isolated waveform is recorded only on one of the N tracks at the same time, and a reproduced signal detected from a magnetic head other than the magnetic head reproducing the isolated waveform at the same time is This can be regarded as crosstalk from the track on which this isolated waveform is recorded. To describe this in Figure 4, the Takashi Namikata X of isolated waveform of i-th track from the time t ₁ at time t _2, the in i-1 th track and (i + 1) -th track, the waveform Y and waveform Z The crosstalk indicated by occurs.

Note that such an isolated waveform recording area recorded in a staircase is recorded at the beginning of the data portion, and the sample value of the isolated waveform and the sample value of the crosstalk are stored in each memory before the data is reproduced. It shall be stored.

Next, the operation of the circuit of FIG. 2 will be described. i−1, i, i +
The signal from the first track is A / D converter 10 _i-1 , 1
0 _i , 10 _{i + 1} sampled and isolated waveform detection circuit 20
_i-1 , 20 _i , and 20 _{i + 1} are input. Isolated waveform detection circuit 20 _i-1 , 2
0 _i and 20 _{i + 1} detect the isolated waveform and the sample value of the crosstalk shown in FIG. 4 while measuring the timing with a clock signal (not shown).
_i-1 , 50 _i , 50 _{i + 1} and the crosstalk signal is determined while determining which track caused the isolated waveform.
The signal is stored in a crosstalk memory corresponding to the track number that caused the crosstalk.

The storage of the crosstalk signal will be described for the i-th track. When the isolated waveform is recorded on the first track, the reproduction output of the i-th track is stored in the crosstalk memory 1.
_i (1), and the reproduced output of the i-th track when the isolated waveform is recorded on the (i-1) -th track is stored in the crosstalk memory 1 _i (1-1). The sample values of the reproduced signal at that time are stored in the crosstalk memories 1 _i to 1 _N corresponding to the track numbers 1 to N in which the waveforms are recorded.

In this way, when the reproduction of the isolated waveform recording area is completed and the crosstalk amount of each track from another track is stored in the crosstalk memories 1 _i to 1 _N of each track, the next data is recorded. Move to reproduction of the recorded area. All the reproduced signals of the data from each track are output from the isolated waveform detection circuits 20 _{i to} 20 _N by the branch metric calculation circuit 30.
_i to 30 _N. And isolated waveform memory
Waveform interference amount of each track is calculated in 50 _i to 50 using the value of _N and assuming path interference amount calculating circuit of each Viterbi decoder 60 ₁ to 60 _N. When signal lines from the path memories 70 ₁ to 70 _N are connected, the value of the path memory 70 is also taken into consideration, and the circuit from the path memory 70 functions as a path feedback circuit. Also,
The crosstalk is calculated in each crosstalk calculation circuit using the crosstalk from each track and the value of the assumed path. That is, in the i-th Viterbi decoder, first, the crosstalk is calculated by the crosstalk calculation circuit 2 _i (1) using the crosstalk from the first track and the value of the assumed path, and similarly, the i-th track is affected. 2 to i-1, i + 1 to
Crosstalk from the Nth track is calculated by the crosstalk calculation circuits 2 _i (2) to 2 _i (i−1) and 2 _i (i + 1) to 2 _i (N).

The branch metric calculation circuit calculates the error between the sample value shown in the equation and the expected value.

Here, the crosstalk from the n-th track and a _i sample values of the i-th track, b _i is the predicted value of the waveform interference amount of the i-th track is determined, c _i (n) is affecting the i-th track Where c _i (i) = 0.

The ACS 40 selects a path that is the smallest of the sum of the metric value of the surviving path one cycle before and the branch metric value obtained therefrom. This is stored in the path memory 70 that becomes the surviving path. Further, the path selector 80 sequentially decodes and outputs the value of the path that is the smallest of all the metric values.

As described above, in the circuit shown in FIG. 2, when a certain track is reproduced, the reproduced signal is decoded in consideration of the influence of crosstalk from the other track to that track. Is only a noise component according to the Gaussian distribution, and the original function as a Viterbi decoder can be exhibited. Therefore, it can be considered that the signal decoded by the circuit of this embodiment is hardly affected by the crosstalk from other tracks.

FIG. 5 is a state transition diagram in the circuit of FIG.
Here, in order to simplify the description, a case where the constraint length K in the bit direction is 3 and the number of tracks N in one recording area is 2 will be described.

There are 16 internal states, α _{11 to} α ₄₄ . In general, there are (2 ^N ) ^K-1 internal states. The combination of inputs is I
A four ₁ ~I _4, usually the number will be 2 ^N pieces. Accordingly, 16 × 4 branch metrics are input to the ACS 40 of FIG. 2, and one path is selected from 2 ^N there.
As a result, (2 ^N ) ^K-1 surviving paths are obtained. This is sent to the path selector 80, and finally N pieces of reproduction data are obtained.

In the above-described embodiment, the magnetic recording medium has been described as a disk-shaped one such as a floppy disk, but a magnetic recording medium having a plurality of recording tracks may be a band-shaped magnetic tape. However, when the recording density in the track direction increases, it is expected that the tracking (servo) signal deteriorates due to the decrease in the track width, and that tracking becomes difficult. However, by keeping the thermal expansion coefficient in the track direction of the continuous heads (N consecutive tracks) and the thermal expansion coefficient of the recording medium substrate the same, the N continuous heads are regarded as one head from the tracking side. Therefore, the above problem is eliminated because N tracks of data can be used for one tracking.

〔The invention's effect〕

As described above, according to the present invention, when recording is performed by providing a plurality of tracks on a magnetic recording medium, not only the waveform interference between the magnetic recording directions of the magnetic recording medium but also the crosstalk between the tracks is considered. Then, Viterbi decoding is performed, so that it can be considered that there is apparently no influence of crosstalk in the reproduced signal. Accordingly, it is possible to perform high-density recording by reducing the non-recording portion between the tracks, and it is possible to greatly improve the recording density.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the principle of a magnetic recording / reproducing apparatus according to the present invention;
FIG. 2 is a circuit diagram showing the configuration of an embodiment of the magnetic recording / reproducing apparatus of the present invention, FIG. 3 is a configuration diagram of a magnetic recording medium to which the circuit of FIG. 2 is applied, and FIG. FIG. 5 is a waveform diagram showing a recording state of an isolated waveform recorded on a recording medium, FIG. 5 is a state transition diagram in the circuit of the present invention, FIG. 6 is a block diagram showing a configuration of a conventional Viterbi decoder, and FIG. FIG. 8 is a waveform diagram showing a sample value of an actual signal waveform and an expected value obtained by superimposing an isolated waveform in a Viterbi decoder. FIG. 8 is a waveform diagram showing a sample value in a case where there is a crosstalk from an adjacent track and an expected value of a correct path. It is. 10: A / D converter, 20: Isolated waveform detection circuit, 30: Branch metric calculation circuit, 40: ACS, 50: Isolated waveform memory, 60: Interference amount calculation circuit, 70: Path memory , 80... Path selector, 11 ₁ to 1 _N , 1 _i (1) to 1 _i (i−1), 1 _i (i + 1) to 1
_i (N) ...... crosstalk _{memory, 2 1 ~2 N, 2 i} (1) ~2 i (i-1), 2 i (i + 1) ~2
_i (N): Crosstalk calculation circuit.

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location G11B 20/18 576 G11B 20/18 576A (72) Inventor Hiroshi Muto 1015 Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Incorporated (72) Inventor Shinya Kawaguchi 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) References JP-A-58-12110 (JP, A)

Claims (1)

(57) [Claims] A magnetic recording medium has a plurality of recording tracks on which signals are recorded adjacent to each other, and reproduces signals recorded on the tracks by a plurality of heads, and reproduces the reproduced signals for each of the heads. A magnetic recording / reproducing apparatus for decoding by using a provided Viterbi decoder, wherein an isolated waveform is provided on the plurality of recording tracks so that a single isolated waveform is not reproduced by the plurality of heads at the same time. Are stored in the Viterbi decoder (100) of each track, a crosstalk memory (1) for storing a sample value of crosstalk from one track to another track, and a crosstalk memory (1). ) And a signal from the path memory of the Viterbi decoder (100), and a crosstalk circuit (2) for calculating a crosstalk amount from another track. A magnetic recording / reproducing apparatus, wherein Viterbi decoding of a reproduction signal of each track is performed while predicting crosstalk to each track from another track.