JPH0729320A - Detecting device for digital information - Google Patents

Abstract

PURPOSE:To obtain a detecting device for digital information in which code error rate is not degraded even if characteristics of a transmitting medium, a recording medium or the like are varied. CONSTITUTION:Interference between codes is given to a signal reproduced from a transmitting medium or a recording medium by a variable partial response equalizing circuit 10, an original digital information is detected by a viterbi decoder 11. At the time, noise information included in the reproduced signal is detected by a noise detecting circuit 8, and low code error rate can be obtained by controlling quantity of interference between codes of the variable partial response equalizing circuit 10 and the viterbi decoder from noise information using a control circuit 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital information detecting device for detecting original digital information from a signal reproduced from an information transmission line or a recording medium.

[0002]

2. Description of the Related Art In recent years, as a method of detecting digital information from a signal reproduced from a transmission or recording medium, Viterbi decoding for estimating the state transition by maximum likelihood after performing partial response equalization so as to cause a specific intersymbol interference. The detection method used has been developed. This method can detect with a lower code error rate than the equalization method that suppresses intersymbol interference, especially in the case of large intersymbol interference such as magnetic recording.

A conventional digital information detecting device will be described below. FIG. 5 shows a digital information detecting device using a partial response equalization circuit having a specific intersymbol interference and a Viterbi decoder in the conventional digital magnetic reproducing device.

In FIG. 5, the signal recorded on the magnetic medium is reproduced by the magnetic head 1. The reproduced signal is amplified by the head amplifier 2 and is equalized by the equalizing circuit 3 so that the impulse response from recording to the output of the equalizing circuit 3 has a specific intersymbol interference. This particular intersymbol interference is (1,0,
The coefficients such as -1) are limited to 1, 0, -1, and the amount of intersymbol interference is fixed when equalization is performed.

Now, the equalized signal is input to the Viterbi decoder 4. The Viterbi decoder performs maximum likelihood estimation of the state transition determined by partial response equalization with specific inter-code interference, and outputs the original digital information.

As described above, the original digital information is detected from the partial response equalized signal. From this point of view, as an example in which this method is applied to a digital magnetic reproducing apparatus, Tasaki and Osawa: "Signal processing method in digital recording", Journal of Television Society, VOL42, N.
O4, pp. 330-337 (Sho 63-04).

[0007]

However, in the above-mentioned conventional configuration, the intersymbol interference in the partial response equalization is limited to a specific sequence, so that the intersymbol interference suitable for the magnetic recording characteristics, the recording wavelength, and the like can be prevented. It is necessary to select in advance. Therefore, the amount of intersymbol interference is fixed, information cannot always be detected in an optimal state according to changes in the characteristics of the tape and the head, and this leads to a deterioration of the code error rate. Had.

Therefore, in order to solve the above problems, the present invention is not limited to a specific intersymbol interference, but always detects information in an optimum state according to a change in the characteristics of a tape or a head and causes a code error. It is an object of the present invention to provide a digital information detection device that does not deteriorate the rate.

Another object of the present invention is to provide a digital information detecting device capable of detecting information with a lower code error rate than the conventional method even when the characteristics of the tape, head, etc. are not changed.

[0010]

In order to achieve the above object, a digital information detecting apparatus of the present invention is a partial information processing apparatus, in which a signal reproduced from a transmission or recording medium is optimally controlled in accordance with noise information to control an intersymbol interference amount. -Variable partial response equalization means for response equalization, Viterbi decoding means for maximum likelihood estimation of the state transition of the original digital signal from the output of the variable partial response equalization means, and reproduction from the transmission or recording medium Noise detecting means for detecting noise included in the signal, and control means for controlling the intersymbol interference amount of the variable partial response equalizing means and the Viterbi decoding means based on the noise information obtained by the noise detecting means. It is equipped with and.

Furthermore, the digital information detecting apparatus of the present invention comprises equalizing means for equalizing a signal reproduced from a transmission or recording medium so as to suppress intersymbol interference, and intersymbol interference at the output of the equalizing means. , A Viterbi decoding means for estimating the state transition of the original digital signal from the output of the variable partial response equalization means, and a noise included in the output of the equalization means. Noise detecting means, and the variable partial circuit based on the noise information obtained by the noise detecting means.
It may be provided with a control means for controlling the inter-code interference amount of the response equalization means and the Viterbi decoding means.

[0012]

According to the present invention, with the above-described configuration, the variable partial response equalization for optimally controlling the intersymbol interference amount according to the noise information contained in the signal reproduced from the transmission or recording medium is performed. It is possible to always achieve a low code error rate even if the characteristics of the above change.

Furthermore, since the amount of intersymbol interference is set so that the code error rate becomes low from the noise characteristic of the input signal, a code error rate lower than that of the conventional method can be obtained even when the characteristics of the tape, head, etc. do not change. Can be realized.

[0014]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment in which the digital information detecting device of the present invention is applied to a digital magnetic reproducing device.

In FIG. 1, the signal reproduced by the magnetic head 1 is amplified by the head amplifier 2 and input to the noise detection circuit 8 and the variable partial response equalization circuit 10. The noise detection circuit 8 is composed of an equalization circuit 5, a comparator 6 and a subtractor 7. The output of the head amplifier 2 is input to the equalization circuit 5 and equalized so as to suppress intersymbol interference. The frequency characteristic E (f) of the equalization circuit 5 is the frequency characteristic of the system from recording to the output of the head amplifier 2 which is H.
When the frequency characteristic of the roll-off filter that satisfies the Nyquist criterion is L (f), the equation (1) is satisfied.

[0016]

[Equation 1]

Since the intersymbol interference is suppressed in the output of the equalization circuit 5, it is possible to determine whether the original digital signal is "1" or "0" with a certain probability by comparing it with a predetermined reference value. It can be estimated correctly. Therefore, the output of the equalization circuit 5 is input to the comparator 6. The comparator 6 compares the output of the equalization circuit 5 with a predetermined reference value (not shown) to estimate the original digital signal. Thus, the difference between the output of the equalization circuit 5 and the original digital signal estimated by the comparator 6 is calculated by the subtractor 7, so that the noise signal included in the output signal of the equalization circuit 5 can be detected.

Next, the output of the noise detection circuit 8 is the control circuit 9
Entered in. The control circuit 9 converts the coefficient control signal 31 into a variable partial response equalization circuit 10 and a Viterbi decoder 11.
Output to. The operation of the control circuit 9 will be described later.

The signal amplified by the head amplifier 2 is also input to the variable partial response equalization circuit 10 so that the tap coefficient of the impulse response has intersymbol interference set by the coefficient control signal 31. Are equalized.

FIG. 2 is a block diagram of the variable partial response equalization circuit 10 having three tap coefficients. The variable partial response equalization circuit of FIG.
And delay circuits 25, 26, variable tap coefficient unit 27,
28 and 29 and an adder 30. The equalization circuit 24 performs equalization so as to suppress intersymbol interference.
The same characteristics as the equalization circuit 5 of FIG. In the variable tap coefficient units 27, 28, and 29, the tap coefficient is controlled by the coefficient control signal 31 of the control circuit 9 in FIG.

Further, the output of the variable partial response equalization circuit 10 shown in FIG. 1 is input to the Viterbi decoder 11, and the original digital signal determined by the tap coefficient of the variable partial response equalization circuit 10 controlled by the control circuit 9. Maximum likelihood estimation of signal state transitions.

For details of the Viterbi decoder, refer to Ryo Jun Eto et al., "Digital Video Recording Technology" (1990.8.3).
1), Nikkan Kogyo Shimbun, p. 75-77 and the like. Therefore, although a detailed description is omitted, the number of tap coefficients of the preset variable partial response equalization circuit 10 is set to L, and the possible values of the original digital signal are two such as “1” or “0”. In that case, there are 2 (L-1) different intersymbol interferences with respect to the input signal having no noise signal. Since such a state is determined by the tap coefficient of the variable partial response equalization circuit 10, the operation of the Viterbi decoder 11 is controlled by the coefficient control signal 31 of the control circuit 9. That is, a metric for determining which state an input signal including a noise signal is most likely is calculated, and the state transition over time is estimated to determine the original digital signal.

By the way, it is known that the theoretically best detecting method is to whiten noise and perform maximum likelihood decoding. Therefore, when the signal is decoded by the Viterbi decoder 11 which is the maximum likelihood decoding, the Viterbi decoder 11
The code error rate can be lowered by equalizing the noise signal included in the input of the so that it becomes white noise. Therefore,
If the noise signal is detected by the noise detection circuit 8 and the tap coefficient of the variable partial response equalization circuit 10 is controlled by the control circuit 9 so that the noise signal at the input of the Viterbi decoder 11 approaches whitening, the code error rate is reduced. Can be made smaller.

Therefore, the control circuit 9 uses the Viterbi decoder 11
The tap coefficient of the variable partial response equalization circuit 10 is obtained so that the noise signal at the input of ## EQU1 ## approaches whitening. As shown in FIG. 2, if the tap coefficients of the variable partial response equalization circuit are a0, a1, a2 and the bit frequency of the original signal is fb, the output of the equalization circuit 24 of FIG. Frequency characteristic P of the system leading to the output of
(F) satisfies (Equation 2).

[0025]

[Equation 2]

At this time, the control circuit 9 controls the Viterbi decoder 11
In order to bring the noise signal at the input of the above into whitening, the tap coefficient of the variable partial response equalization circuit 10 is determined so as to minimize (Equation 3).

[0027]

[Equation 3]

However, N (f) is the spectrum of the noise signal at the output of the equalization circuit 5. Since the number of tap coefficients of the variable partial response equalization circuit 10 is a preset finite number (3 in this case), the tap coefficient obtained by (Equation 3) is a noise signal at the input of the Viterbi decoder 11. Is an approximate one for whitening. By using the tap coefficient obtained by the control circuit 9 in the variable partial response equalization circuit 10 in this way, the noise signal at the input of the Viterbi decoder 11 can be approximated to whitening.

As described above, in the digital magnetic reproducing apparatus of the present embodiment, the variable partial response equalization is performed by detecting the noise information without limiting the intersymbol interference amount and limiting the intersymbol interference amount. The tap coefficient of the circuit 10 and the operation of the Viterbi decoder 11 are optimally controlled. Therefore, the control is performed so as to perform the optimal partial response equalization and Viterbi decoding from the noise spectrum, so that the error is much lower than that in the case where the inter-code interference is fixed in the conventional (1, 0, -1). The original digital information can be detected at a rate. Furthermore, even if the characteristics of the tape, head, etc. change, information can always be detected in an optimum state, and there is an excellent effect that deterioration of the code error rate can be suppressed.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing a second embodiment in which the digital information detecting device of the present invention is applied to a digital magnetic reproducing device.

In FIG. 3, blocks having the same functions as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The present embodiment differs from the first embodiment described above in that the signal used for noise detection is the output of the variable partial response equalization circuit 10 which is the first variable partial response equalization means and the Viterbi decoder 11. That is the output.

The noise detection circuit 15 includes a delay circuit 12 and a second circuit.
The variable partial response equalization circuit 14 and the subtracter 13 are variable partial response equalization means. However, the variable partial response equalization circuit 14 has a configuration in which the equalization circuit 24 for suppressing intersymbol interference is omitted from the configuration of the variable partial response equalization circuit 10 of FIG. 2 used in the first embodiment. .

The delay time in the delay circuit 12 is the time at which the output of the variable partial response equalization circuit 10 is delayed between the Viterbi decoder 11 and the variable partial response equalization circuit 14 to the subtractor 13. be equivalent to.
The output of the Viterbi decoder 11 is input to the variable partial response equalization circuit 14 and equalized using the same tap coefficient as the variable partial response equalization circuit 10 so as to have intersymbol interference. Therefore, the noise signal at the input of the Viterbi decoder 11 is detected by calculating the difference between the output of the delay circuit 12 and the output of the variable partial response equalization circuit 14.

In this embodiment, since the output of the Viterbi decoder 11 is used for the estimated value of the original digital information, the code error rate becomes lower, and the noise detection is performed more accurately than in the first embodiment. As a result, the present embodiment is characterized in that the original digital information can be detected with a lower code error rate than the first embodiment.

(Embodiment 3) Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a block diagram showing a third embodiment in which the digital information detecting device of the present invention is applied to a digital magnetic reproducing device.

In FIG. 4, blocks having the same functions as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The present embodiment is different from the first embodiment described above in that the automatic equalization circuit 16 is used as an equalization method for suppressing intersymbol interference, and that the variable partial response equalization circuit 17 is shown in FIG. The variable partial response equalization circuit 14 has the same configuration. Further, a comparator 6 that compares the output of the automatic equalization circuit 16 with a predetermined reference value to estimate the original digital signal, and a subtractor 7 that subtracts the difference between the output of the automatic equalization circuit 16 and the output of the comparator 6. The noise detection circuit 22 is composed of

For details of the automatic equalizer, see, for example, Ryozumi Eto et al., "Digital Video Recording Technology", (199).
0.8.31), Nikkan Kogyo Shimbun, p. 65-68 and the like. Therefore, although a detailed description is omitted, the automatic equalization circuit 16 does not fix the equalization characteristic in advance according to the frequency characteristic of the magnetic recording system, but automatically changes between the codes according to the characteristic change of the tape, the head, or the like. The equalization characteristics can be changed to suppress the interference. As a result, the equalization error due to the characteristic change can be suppressed low.

As a result, the inter-symbol interference amount can be suppressed to a lower level in the automatic equalization circuit 16, and the variable partial response equalization can be performed more accurately. Further, also in the Viterbi decoder 11, the deterioration of the code error rate can be suppressed to be lower than that of the first embodiment.

Although the first, second and third embodiments apply the present invention to a digital magnetic reproducing apparatus, the present invention is not limited to this, and the present invention is not limited to this. It can also be applied to detection of digital information and detection of digital information in an optical recording / reproducing apparatus.

Although the number of tap coefficients for variable partial response equalization is set to 3 in the first, second and third embodiments, the present invention is not limited to this. further,
The noise detection method is not limited to the first, second and third embodiments, and other methods may be used.

[0041]

As described above, the digital information detecting apparatus of the present invention always optimally controls the intersymbol interference amount of the variable partial response equalization according to the noise contained in the signal reproduced from the transmission or recording medium. Therefore, a low code error rate can always be realized even if the characteristics of the transmission or recording medium change.

Further, since the intersymbol interference amount is set based on the noise characteristic of the input signal so that the code error rate is low, a code error rate lower than that of the conventional method is obtained even when the characteristics of the tape, head, etc. do not change. Can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a digital magnetic reproducing apparatus in a first embodiment of a digital information detecting apparatus of the present invention.

FIG. 2 is a block diagram of a variable partial response equalization circuit according to the first embodiment.

FIG. 3 is a block diagram of a digital magnetic reproducing apparatus in a second embodiment of the digital information detecting apparatus of the present invention.

FIG. 4 is a block diagram of a digital magnetic reproducing apparatus in a third embodiment of the digital information detecting apparatus of the present invention.

FIG. 5 is a block diagram showing a conventional digital information detecting device.

[Explanation of symbols]

 5 Equalization circuit (means) 6 Comparator (means) 8 Noise detection circuit (means) 9 Control circuit (means) 10 Variable partial response equalization circuit (means) 11 Viterbi decoder (means) 15 Noise detection circuit (means) ) 16 automatic equalization circuit (means) 31 tap coefficient control signal

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[Procedure amendment]

[Submission date] April 19, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

[0027]

[Equation 3]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number for FI Technical location H03M 13/12 8730-5J H04L 25/08 B 9199-5K // G11B 5/09 321 A 8322- 5D

Claims (6)

[Claims] 1. A variable partial response equalizing means for optimally controlling an intersymbol interference amount of a signal reproduced from a transmission or recording medium according to noise information, and the variable partial response equalizing means. Viterbi decoding means for estimating the maximum likelihood of the state transition of the original digital signal from the output of the converting means, and noise detection means for detecting noise contained in the signal reproduced from the transmission or recording medium,
A digital information detecting device comprising: a control means for controlling the inter-code interference amount of the variable partial response equalization means and the Viterbi decoding means based on the noise information obtained by the noise detection means. 2. The noise detecting means compares an equalizing means for equalizing a signal reproduced from a transmission or recording medium so as to suppress intersymbol interference with an output of the equalizing means and a predetermined reference value. 2. The digital information detecting device according to claim 1, further comprising: a comparing means for estimating a digital signal; and a calculating means for calculating a difference between the output of the equalizing means and the output of the comparing means. 3. A first variable partial response equalization means for optimally controlling an intersymbol interference amount of a signal reproduced from a transmission or recording medium according to noise information, and the first variable partial response equalizing means. Viterbi decoding means for maximum likelihood estimation of the state transition of the original digital signal from the output of the variable partial response equalization means, noise detection means for detecting noise contained in the signal reproduced from the transmission or recording medium, The noise detection means includes a control means for controlling the inter-code interference amount of the first variable partial response equalization means and the Viterbi decoding means based on the noise information obtained by the noise detection means. Delay means for delaying the output of the first variable partial response equalization means, and equalization of the output of the Viterbi decoding means so as to have intersymbol interference A second variable partial response equalization means, digital information detecting apparatus comprising a comparison means for comparing the outputs of said second variable partial response equalization means of said delay means. 4. An equalization means for equalizing a signal reproduced from a transmission or recording medium so as to suppress intersymbol interference, and a variable partial signal for giving intersymbol interference to the output of the equalization means.
Response equalization means, Viterbi decoding means for maximum likelihood estimation of the state transition of the original digital signal from the output of the variable partial response equalization means, and noise detection means for detecting noise included in the output of the equalization means A digital information detecting device comprising: a control means for controlling the inter-code interference amount of the variable partial response equalization means and the Viterbi decoding means based on the noise information obtained by the noise detection means. 5. The noise detecting means calculates a difference between an output of the equalizing means and a predetermined reference value to estimate an original digital signal, and a difference between the output of the equalizing means and the output of the comparing means. The digital information detecting device according to claim 4, further comprising a computing means. 6. The digital information detecting apparatus according to claim 4, wherein the equalizing means is an automatic equalizing means for automatically setting a characteristic in accordance with a change in an input signal.