JPH05205409A - Digital signal recording and reproducing device - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce data identification errors when using a vertically oriented tape. [Structure] The output of the equalizer circuit 3 is connected in cascade to a delay circuit 4.
Delayed by ~ 6, the signals at the three identification points and the midpoint are obtained. The discrimination circuits 9 to 12 discriminate the signals at the respective discrimination points,
The identification circuit 13 detects the inversion part of the code string by obtaining bn-an. The AND circuit 21 performs an AND operation on the data of the identification circuits 10 to 13, detects an identification error at the rising portion of the reproduction signal, and outputs an error flag to the error correction circuit 23. Also, the AND circuit 22 is the identification circuit 10-
A logical product operation is performed on the data of 13 to detect an identification error at the falling portion of the reproduction signal and output an error flag to the error correction circuit 23. When the error flag is input, the error correction circuit 23 corrects the identification data and outputs it. This reduces identification errors even when the isolated reproduction waveform has an asymmetrical positive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal recording / reproducing device, and more particularly to a digital signal recording / reproducing device suitable for a vertically oriented recording medium.

[0002]

2. Description of the Related Art Conventionally, when a digital signal is recorded / reproduced on / from a medium such as a magnetic tape, longitudinal recording for forming a magnetization pattern parallel to the recording medium.
Has been adopted. Now, assume that a digital signal that changes stepwise is recorded on a magnetic tape. Even in this case, the magnetization reversal of the tape does not have an ideal step shape. Therefore, the pulse waveform of the reproduced digital signal becomes a mountain-shaped pulse waveform with a widened skirt as shown in FIG.

This reproduced waveform is called an isolated reproduced waveform, which is considered to be almost symmetrical in the case of longitudinal recording, and can be approximated by the Lorentz function shown in the following equation (1).

[0004] Here, t represents time, a represents a pulse width coefficient, and is represented by a = W50 / 2T. However, T is a bit interval, and W50 is a pulse half width.

Generally, in digital recording, the conditions that enable identification of data strings are that there is no intersymbol interference,
That is, the amplitude of the isolated reproduction waveform at the identification point of another code is "0". For this reason, an equalization circuit for equalizing the isolated reproduction waveform is adopted to remove the interference of the adjacent pulses at the discrimination point.

FIG. 6 is a waveform diagram showing an equalized waveform from the equalizer circuit. FIG. 6A shows an equalized waveform in the NRZ code, and FIG. 6B shows a mirror square modulation (hereinafter referred to as M2 modulation). () Means the equalized waveform in the code.

As shown in FIG. 6A, the equalizer circuit is configured to output an output waveform h (nT) satisfying the following expression (2) at time nT, where T is the bit interval. There is.

H (nT) = 0 | n | ≧ 1 h (0) = 1n = 0 (2) By the way, the 8-14 modulation method and the D2 digital VTR are used.
In a modulation method such as the M2 modulation method adopted in (1) or (2), the minimum consecutive number of "1" or "0" (hereinafter referred to as the minimum run length) is 2. Therefore, as shown in FIG. 6B, assuming that the isolated reproduction waveform has the maximum value at time t = 0, at the time ± T (T is a bit interval) adjacent to time t = 0, the inter-symbol Interference can be tolerated. Therefore, in this case, the technical report of the Institute of Television Engineers
Vol.13 No.59 VIR89-20 As described in “Simple automatic equalizer for digital VTR” in detail, if the intersymbol interference values are μ and ν, the output waveform h (nT ) May satisfy the following expression (3).

H (nT) = 0 | n | ≧ 2 h (−T) = μ ≧ 0 h (T) = ν ≧ 0 h (0) = 1 (3) When μ = ν, Nyquist By satisfying the ideal frequency characteristic of, it is possible to obtain the equalization characteristic of the narrowest band. In this case, the frequency band is 1/2 of that when the Nyquist first condition shown in the above equation (2) is satisfied,
High-density recording is possible.

By the way, it is considered that high density recording will be further advanced in the future. However, in longitudinal recording that has been conventionally adopted, if the recording frequency is increased for high density recording, self-demagnetization becomes large and recording becomes difficult. Further, since the bit interval T becomes smaller due to the high density recording, the pulse width coefficient a becomes larger, and as a result, the spread of the tail of the isolated reproduction waveform becomes wider and the S / N deterioration due to equalization becomes larger. For these reasons, longitudinal recording is not suitable for high density recording.

On the other hand, if perpendicular recording is adopted, high density recording is possible. In perpendicular recording, a magnetization pattern having a constant length is formed on the medium surface, and the demagnetizing field decreases as the recording wavelength decreases, and the recording state stabilizes. That is, a large reproduction output can be obtained in high density recording.

By the way, in order to perform perpendicular recording, it is necessary to employ a head which produces a perpendicular magnetic field distribution which is strong and changes sharply. Even a ring head used in a VTR or the like has a strong vertical magnetic field component at the gap edge, and if the recording medium has a vertical alignment characteristic, almost perpendicular recording is possible. This is called quasi-perpendicular recording, and cobalt-chromium, barium-ferrite, etc. are used as the recording medium. In particular, barium-ferrite is expected as a high-density recording medium because the conventional coating technique can be directly adopted and the degree of vertical orientation can be easily controlled.

As described above, in order to perform vertical recording using the ring head, it is necessary to use a recording medium having a high degree of vertical alignment. PEAK SHIFT CHARACTERISTICS FOR BAR
IUMFERRITE FLEXIBLE DISK DRIVE "(1987 DIJEST OF
As described in THE "INTERMAG CONFERENCE" AB-04) (Reference 1) and the like, as the degree of vertical orientation of the recording medium increases, the asymmetry of the isolated reproduction waveform also increases, and μ in the above equation (3) = Ν will not hold.

In equalization and signal detection, assuming that the isolated reproduction waveform is substantially symmetrical, the waveform is equalized so as to be "0" at the adjacent discrimination point. Cannot be completely equalized by an amplitude equalization circuit such as a cosine equalizer, and asymmetry remains in the waveform after equalization, which easily causes a bit error.

FIG. 7 is an explanatory diagram for explaining this problem. Further, FIG. 8 is a waveform diagram showing an equalized waveform of a modulation method in which the minimum run length is 2, and FIG.
8 shows the case where ν holds, and FIG. 8B shows the case where μ ≠ ν.

In the modulation method such as 8-14 modulation or M2 modulation, as shown in FIG. 8A, it is not necessary to set the amplitudes at the adjacent discrimination points −T and T to “0” at the time of equalization, and It suffices to satisfy the second condition of Nyquist in the equation (3).

Even when the code value is "0", the amplitude at the identification point is
It is one of 0, μ, and ν, and the code value is "1".
Is one of 1 + μ, 1 + ν, and 1 + μ + ν. For example, as shown in FIG. 7, the code string “001”
The amplitude of the code value "0" at the center of the symbol becomes .mu. Due to the intersymbol interference of the last code value "1". Also, the code string "100"
The amplitude of the code value "0" at the center of the signal becomes ν due to the inter-code interference of the first code value "1". In addition, the code string “011”
The amplitude of the code value "1" at the center of 1 becomes 1 + μ due to the inter-code interference of the last code value "1", and similarly, the code string "1"
The amplitude of the code value "1" at the center of 10 "and" 111 "is 1 + ν and 1 + μ + ν, respectively. The threshold value for code identification is the intermediate value (0..0) between the minimum value (0) and the maximum value (1 + μ + ν) of the amplitude.
5+ (μ + ν) / 2), and the absolute value of the difference between each amplitude and the threshold value (distance from the threshold value) is as shown in FIG.

When the isolated reproduction waveform is substantially symmetrical as in the case of longitudinal recording, μ≈ν as shown in FIG. 8A, and the distance from the threshold is always 0.5 or more. Therefore, high discrimination ability can be obtained. However, μ ≠ ν
In this case, the distance from the threshold may be 0.5 or less. When a recording medium having vertical orientation is adopted, the isolated reproduction waveform becomes asymmetric as shown in FIG.
> Ν, and the distance from the threshold value 0.5+ (μ−ν) / 2 becomes 0.5 or less. As the degree of vertical alignment increases, the difference between μ and ν increases, the distance from the threshold decreases, and errors easily occur. In this case, as shown in FIG. 7, there is a high possibility that a bit error will occur in the shaded portion, that is, in the first 1 bit of the switching between "0" and "1".

[0019]

As described above, conventionally, when vertical recording is performed by a ring type head using a vertically aligned recording medium for high density digital recording, the isolated reproduction waveform becomes asymmetrical, There is a problem that it is extremely difficult to identify the reproduced waveform.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a digital signal recording / reproducing apparatus capable of identifying a reproduced waveform even when a vertically aligned recording medium is adopted. To aim.

[0021]

A digital signal recording / reproducing apparatus according to the present invention has a waveform for removing intersymbol interference with a reproduced signal from a recording medium on which a modulated signal having a minimum run length of 2 is recorded. Equalizing means for performing equalization, and data identification for identifying each data and outputting identification data at a predetermined three consecutive identification points and an intermediate point between the first two identification points in the output signal of the equalizing means Means, an inversion part detecting means for detecting an inversion part of the code string by comparing the amplitude of the intermediate point and the amplitude of the first discrimination point, and based on the regularity of the code string of the digital signal, 3 error detection means for detecting an error from the identification data of the identification point and the intermediate point and the output of the inversion part detection means, and an error correction means for correcting the data of the first identification point based on the output of this error detection means It is those provided with the door.

[0022]

In the present invention, the data identification means is composed of three consecutive data.
In addition to the identification point, the data of the intermediate point is also identified. Since the modulation signal having the minimum run length of 2 does not invert with the same code having only one bit, the amplitude of the intermediate point is larger than the amplitude of the first discrimination point at the rising portion or the falling portion of the reproduction signal. Therefore, the identification error can be reduced by using the identification data of the intermediate point. The error detection means detects an identification error from the output of the inversion part detection means and the output of the data identification means based on the regularity of the code string. The error correction means corrects the data of the first discrimination point by the output of the error detection means.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a digital signal recording / reproducing apparatus according to the present invention. The present embodiment is applied to recording / reproducing of a modulation code having a minimum run length of 2.

First, the principle of this embodiment will be described with reference to FIG. 2A and 2B are waveform diagrams when a vertically oriented tape is adopted. FIG. 2A shows a recording signal and FIG. 2B shows a reproduction waveform.

As shown in FIG. 2A, the data string "00"
011000 ", ie, a 2T (T is the bit interval) pulse having the highest frequency of the modulated signal with a minimum run length of 2. When recorded on a vertically oriented tape, the reproduced waveform is shown in FIG. 2 (b). As shown, the amplitude of the discrimination point an having the first code value "1" is smaller than the amplitude of the discrimination point an + 1 of the code value "1" one bit after, that is, the threshold Th at the discrimination point an. The distance from is small and errors are likely to occur.

Now, let bn be the midpoint between the discrimination point an and the discrimination point an + 1. Since the minimum run length is 2 and data of the same code is not inverted by 1 bit, at the time when the data changes from "0" to "1", that is, at the rising edge of the reproduced waveform, the discrimination point an The amplitude of the intermediate point bn is larger than the amplitude. Therefore, instead of the identification point an, the data of the identification point bn may be used for identification, which can reduce errors.

As described above, in this embodiment, the value of the intermediate point bn between the discrimination points is used to correct the code string to improve the error rate. That is, in the rising portion of the code, the discrimination point an + 1 next to the discrimination point an and the intermediate point bn between the discrimination points an and an + 1 are "1", indicating that the waveform is the rising portion (bn -An) (bn,
If an is the positive value of the identification points bn and an, respectively, the data of the identification point an is corrected to "1". The same applies to the processing of the falling portion, and if the data at the discrimination point an + 1 and the intermediate point bn is "0" and (bn-an) is negative, the data at the discrimination point an is set to "0".

However, at the time of high density recording, S /
When N is reduced, the reproduced waveform is easily affected by noise, and the originally falling portion may become the rising portion. In such a case, if the correction is performed only with the above-mentioned determination condition, an error will occur.
Therefore, in this embodiment, the amplitude variation is likely to occur due to the influence of space loss and the like, and only the 2T pulse having the highest frequency with the highest probability of error occurrence is corrected. To determine the 2T pulse, the amplitude value of the discrimination point an + 2 is also referred to. That is, a code string (0,0,1,0) having an error in the rising portion is determined from the fact that the data at the identification point an + 2 is "0", and a code having an error in the falling portion is also detected. The column (1, 1, 0, 1) is determined from the fact that the data of the identification point an + 2 is "1". In this way, these code strings are respectively converted into code strings (0, 1, 1,
0) and the code string (1, 0, 0, 1).

In FIG. 1, the magnetic head 2 reproduces the digital signal recorded on the vertically oriented magnetic tape 1 and outputs it to the equalizing circuit 3. The equalizing circuit 3 shapes the reproduced waveform so as to remove the waveform distortion generated during recording and reproduction. The output of the equalization circuit 3 is output to the delay circuit 4 and the discrimination circuit 12 as the value of the discrimination point an + 2.

The delay circuit 4 delays the output of the equalization circuit 3 by a bit interval T and outputs it to the delay circuit 5 and the discrimination circuit 11 as the value of the discrimination point an + 1. The delay circuit 5 is the delay circuit 4
Is delayed by T / 2 and output to the delay circuit 6, the discrimination circuit 10 and the sample hold circuit 8 as the value of the intermediate point bn. The delay circuit 6 delays the output of the delay circuit 5 by T / 2 and outputs it as the value of the discrimination point an to the discrimination circuit 9 and the sample hold circuit 7.

The discrimination circuits 9 to 12 discriminate whether each input signal is "1" or "0" depending on whether or not the input signal exceeds a predetermined threshold value Th.
The identification data of the identification points an, the intermediate point bn, and the identification points an + 1, an + 2 are latched by the identification circuits 9 to 12 respectively.
Is output to. On the other hand, the sample and hold circuits 7 and 8 hold the input signal and output it to the analog subtractor 14. The analog subtractor 14 differentially amplifies the outputs of the sample and hold circuits 7 and 8 to obtain (bn-an) and outputs it to the discrimination circuit 13. The identification circuit 13 compares the input signal with a predetermined value and latches positive or negative data into the latch circuit 19
It is designed to output to.

A PLL (Phase Locked Loop) 20 extracts a clock from the output of the identification circuit 9 and latches the circuits 15 to 19.
Give to. The latch circuits 16 to 19 are supplied with a clock from the PLL 20, and output the outputs of the identification circuits 10 to 13 to the AND circuits 21 and 22 at the same time. AND circuit 21 is a latch circuit
The logical product of the inverted output of 18 and the outputs of the latch circuits 16, 17, and 19 is obtained and output to the error correction circuit 23 as an error flag at the rising edge of the reproduced waveform. That is, the AND circuit 21
Is the data of the intermediate point bn and the discrimination point an + 1 is "1",
(Bn-an) is positive and the data at the identification point an + 2 is "0".
If so, a positive error flag is output. The AND circuit 22 obtains a logical product of the output of the latch circuit 18 and the inverted outputs of the latch circuits 16, 17, and 19 to obtain an error correction circuit 23 as an error flag when the reproduced waveform falls.
Output to. That is, the AND circuit 22 is positive only when the data of the intermediate point bn and the discrimination point an + 1 is "0", (bn-an) is negative, and the data of the discrimination point an + 2 is "1". It is designed to output an error flag.

The data of the identification point an from the latch circuit 15 is given to the error correction circuit 23. When the positive error flag is input, the error correction circuit 23 inverts the output of the latch circuit 15 and outputs it to a digital signal processing unit (not shown).

Next, an embodiment having such a configuration will be described with reference to the waveform diagrams of FIGS. 3 and 4. FIG. 3 shows a case where noise is not mixed, and FIG. 4 shows a case where noise is mixed. FIG. 3A shows a recording signal,
3B shows a reproduction waveform when longitudinal recording is adopted, FIG. 3C shows a reproduction waveform from the vertically oriented magnetic tape 1, and FIG. 3D shows identification data from the identification circuit 9. 3 (e) shows the corrected data when the data of the identification point an + 2 is not used, and FIG. 3 (f) shows the corrected data from the error correction circuit 23. FIGS. 4A to 4F correspond to FIGS. 3A to 3F, respectively. In the figure, white circles represent identification points, and black circles represent intermediate points.

It is assumed that the recording signal train "... 00111000110 ..." As shown in FIG. 3A is recorded on the vertically oriented magnetic tape 1. The reproduction signal from the magnetic head 2 is waveform-equalized and then cascaded to form delay circuits 4, 5, 6
Given to. As shown in FIG. 3B, when longitudinal recording is adopted, each value of the identification points indicated by white circles corresponds to the recording signal when identified by the threshold Th. On the other hand, the reproduced waveform from the vertically oriented magnetic tape 1 is the reproduced waveform corresponding to the recorded data "1" at the rising edge from "0" to "1", as shown by the white circle in FIG. 3 (c). It is lower than the threshold Th.

The delay circuits 4, 5 and 6 delay the input signals by T, T / 2 and T / 2 respectively, and the equalizing circuit 3
And the delay circuits 4, 5 and 6 from the identification points an + 2 and an +, respectively.
1, the values of the intermediate point bn and the discrimination point an are output. The values of the discrimination point an, the intermediate point bn, and the discrimination points an + 1 and an + 2 are given to the discrimination circuits 9 to 12 and compared with the threshold Th shown in FIG. The identification data from the identification circuits 10 to 12 are given to the AND circuits 21 and 22 via the latches 16 to 18, respectively. As shown by the shaded area in FIG. 3D, the identification data from the identification circuit 9 has an error when rising from "0" to "1".

The values of the intermediate point bn and the discrimination point an from the delay circuits 5 and 6 are given to the analog subtractor 14 via the sample hold circuits 7 and 8 and subtracted, and the discrimination circuit 13 outputs (bn-an). Is given. The discrimination circuit 13 has bn> an
In the case of, a positive output is given to the AND circuits 21 and 22, and bn <
In the case of an, a negative output is given to the AND circuits 21 and 22.
Thus, the error flag from the AND circuit 21 is used when the reproduced waveform rises, and the error flag from the AND circuit 22 is used when the reproduced waveform falls.

The AND circuit 21 obtains the logical product of the inverted output of the latch circuit 18 and the outputs of the latch circuits 16, 17, 19 and outputs the error flag at the rising edge of the reproduced waveform to the error correction circuit 23. Further, the AND circuit 22 obtains the logical product of the output of the latch circuit 18 and the inverted outputs of the latch circuits 16, 17, 19 and outputs the error flag at the falling edge of the reproduced waveform to the error correction circuit 23. That is, when the reproduced waveform rises, the values of the discrimination points ann + 1 and the intermediate point bn are positive and the discrimination point an + 2 is "0", that is, the data of the discrimination points an-1 to an + 2. The AND circuit 21 outputs a positive error flag only when is (0010). Also, at the fall of the reproduced waveform, when the values of the discrimination point an + 1 and the intermediate point bn are negative and the discrimination point an + 2 is "1", that is, the discrimination point an-
Only when the data of 1 to an + 2 is (1101), the AND circuit 21 outputs a positive error flag to the error correction circuit 23. When the positive error flag is input, the error correction circuit 23 inverts the data of the identification point an from the latch circuit 15 and outputs it.

As described above, when the influence of noise is not considered, when the data at the discrimination point an + 1 and the data at the intermediate point bn are "1" and (bn-an) is positive, "1". Correct to. That is, in this case, the output of the identification circuit 12 is not applied to the AND circuits 21 and 22, and FIG.
As shown in, the positive error flag is generated at the transition point from "0" to "1" and the data is corrected from "0" to "1". In this embodiment, the influence of noise is taken into consideration, the 2T pulse of the highest frequency is detected by using the data of the identification point an + 2, and only the data of the 2T pulse is corrected. That is, as shown in FIG. 3F, no error flag is generated at the first change point from "0" to "1", and the identification data at the identification point an is not corrected.

Here, as shown by the white circles in FIGS. 4B and 4C, when a vertically oriented tape is adopted, the recording signal is switched from "0" to "1" due to the inclusion of noise. It is assumed that the amplitude of the discrimination point corresponding to “0” at time increases and the distance from the threshold Th decreases. Even in this case, no error occurs in the identification data of the identification point an from the identification circuit 9 as shown in FIGS. 4 (a) and 4 (d). However, when the discrimination is made only by the data of the discrimination point an + 1 and the intermediate point bn and the positive / negative of (bn-an), as shown by the diagonal lines in FIG. , "0" is erroneously corrected to "1". On the other hand, in this embodiment, the 2T pulse is detected and corrected using the data of the discrimination point an + 2. At each timing when the hatched portion in FIG. 4E is the identification point an, the identification point an + 2 is "1". Therefore,
A positive error flag is not output from the AND circuit 21, and no erroneous correction is performed as shown in FIG.

After all, the correction method in this embodiment is shown in Table 1 below. In Table 1, identification point an and intermediate point bn
And the data of the identification points an + 1 and an + 2 are shown as (1110) for the rising portion of the reproduced waveform.

[0042]

[Table 1] At the rising edge of the reproduced waveform, only when the data at the discrimination point an and the intermediate point bn are "1", (bn-an) is positive, and further, the data at the discrimination point an + 2 is "0". The data at the identification point an is corrected to the same code value as the data at the identification point an + 1. For example, as shown in the column of error 1 in Table 1, when the data at the identification point an is identified as "0" due to the asymmetry of the reproduced waveform, the data at the identification point an is corrected to "1". To be done. Further, as shown in the column of error 2 in Table 1, if it is discriminated that an = bn = 0, there is a possibility that the error is due to noise mixing and therefore it is not corrected. Further, as shown in the columns of errors 3 and 4 in Table 1, when the data of the intermediate point bn or the identification point an is "0", the correction is not performed.

The polarity of Table 1 may be reversed for the falling portion. That is, the identification point an + 1 and the intermediate point b
Only when the data of n is "0", (bn-an) is negative, and the data of the discrimination point an + 2 is "1", the discrimination point an
Data is corrected to the same code value as the data at the identification point an + 1.

As described above, in the present embodiment, for the 2T pulse, the code string is corrected using the value of the intermediate point between the identification points, and the code error is corrected without erroneous correction. Reproduction output from the asymmetric vertical orientation tape can be reliably identified.

[0045]

As described above, according to the present invention, it is possible to identify the reproduced waveform even when the vertically aligned recording medium is adopted.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a digital signal recording / reproducing apparatus according to the present invention.

FIG. 2 is an explanatory diagram for explaining the principle of the embodiment.

FIG. 3 is a waveform chart for explaining the operation of the embodiment.

FIG. 4 is a waveform diagram for explaining the operation of the embodiment.

FIG. 5 is a waveform diagram showing an isolated reproduction waveform.

FIG. 6 is a waveform diagram showing an equalized waveform of an isolated reproduction waveform.

FIG. 7 is an explanatory diagram for explaining problems of the conventional example.

FIG. 8 is a waveform diagram showing equalized waveforms of a modulation method in which the minimum run length is 2.

[Explanation of symbols]

1 ... Magnetic tape, 2 ... Magnetic head, 3 ... Equalization circuit, 4 ...
6 ... Delay circuit, 9-13 ... Identification circuit, 21, 22 ... AND circuit, 23 ... Error correction circuit

Claims (1)

[Claims] 1. An equalizing means for performing waveform equalization on a reproduced signal from a recording medium on which a modulated signal having a minimum run length of 2 is recorded, and an output of the equalizing means. Data identification means for identifying each data and outputting identification data at predetermined intermediate three identification points of the signal and an intermediate point between the first two identification points, and an amplitude of the intermediate point and the first identification point. Inversion part detecting means for detecting the inversion part of the code string by comparing with the amplitude, and identification data of the three identification points and the intermediate point and the inversion part detecting means based on the regularity of the code string of the digital signal. A digital signal recording / reproducing apparatus comprising: an error detecting means for detecting an error from the output of the error detection means; and an error correcting means for correcting the data of the first discrimination point based on the output of the error detecting means. .