JPH0997476A - Automatic equalizer and digital signal reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent malfunction at the time of automatic equalization and to ensure stable operation. SOLUTION: A signal sequence from an analog/digital converter is sent to a transversal filter 12 to make convolutional calculation of tap coefficients and to send the results to a transmission sequence predicting circuit 20. The circuit 20 conducts maximum likelihood decoding based on a specified threshold value by a maximum likelihood decoder 22 of a temporary detection circuit 21 and outputs a prediction signal of the original transmission data from a selector 23. An error calculation circuit 27 subtracts the output of the transversal filter 12 from the output of the circuit 20 to determine the prediction error, and a tap coefficient calculation circuit 30 calculates each tap coefficient of the transversal filter 12 to minimize this prediction error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic equalizer for adaptively waveform-equalizing an input signal obtained by digital transmission and a digital signal reproducing apparatus equipped with such an automatic equalizer. is there.

[0002]

2. Description of the Related Art In recent years, for example, DAT (Digital
In a digital signal recording / reproducing apparatus such as an audio tape recorder, an automatic equalizer has been used on the reproducing side.

FIG. 7 shows an example of a digital signal recording / reproducing apparatus using such an automatic equalizer.

A transmission data sequence {w (n)} corresponding to a signal to be recorded is input to the input terminal 201 of FIG. 7, and a recording including an electromagnetic conversion system such as the above DAT as a transmission path. It is supplied to the reproduction system 202. The impulse response sequence of the recording / reproducing system 202 is {g
(n)}. Recording / playback system 202 to automatic equalizer 203
Let {q (n)} be the input signal sequence sent to the transversal filter 204. This input signal sequence is {q
(n)} corresponds to a signal obtained by sampling the RF signal reproduced from the recording medium in the recording / reproducing system 202 at the channel clock timing by A / D conversion or the like.

The output signal sequence {v (n)} of the transversal filter 204 is converted into a predicted transmission sequence {w (n) '} by the transmission sequence prediction circuit 205 in the automatic equalizer 203,
The prediction error signal sequence {e (n) '} is obtained by sending to the subtractor 206 and subtracting the output signal sequence {v (n)}. Based on this prediction error signal sequence {e (n) ′}, the tap coefficient calculation circuit 207 calculates the tap coefficient of the transversal filter 204, and sends this tap coefficient to the transversal filter 204. The output signal sequence {v (n)} from the transversal filter 204 is sent to the detection circuit 208 as the output of the automatic equalizer 203, data detection is performed, and the detected data is output terminal 20.
It is taken out from 9.

Here, since the input signal sequence {q (n)} is equal to the convolution integral of the transmission data sequence {w (n)}, it is expressed by the following equation (1).

[0007]

[Equation 1]

The output signal v (n) of the transversal filter 204 is the input signal q (n) and the tap coefficient c of the filter.
Since it is equal to the convolution integral with _k (n), it is expressed as the following equation (2).

[0009]

[Equation 2]

In the equation (2), K represents the number of taps of the transversal filter 204.

Substituting this equation (2) into the above equation (1),

[0012]

(Equation 3)

In the equation (3), the sum of the impulse response of the transmission line is infinite and the sum is from -∞ to ∞, but in reality, this length is finite.

Next, the difference between the transmission data w (n) and the output signal v (n) of the transversal filter 204, that is, the error e (n) is calculated by the following equation (4).

E (n) = w (n) −v (n) (4) The theoretical error is expressed by equation (4), but actually the transmission data w (n) is known in advance. Therefore, the predicted transmission data w (n) ′ is actually obtained based on the temporary detection result of the output signal v (n) of the transversal filter 204, and the prediction error e (n) is calculated by the following equation (5). 'Calculate.

E (n) ′ = w (n) ′ − v (n) (5) where the output signal v of the transversal filter 204 is
An example of (n) is shown in (A) of FIG. 8 and this output signal v (n)
An example of the predicted transmission data w (n) ′ obtained by the transmission sequence prediction circuit 205 based on the above is shown in FIG. That is, the white circle (O) in FIG. 8A indicates the output signal v (n) obtained by A / D converting the reproduction RF waveform from the recording / reproduction system, and the white circle in FIG. 8B. (◯) indicates the predicted transmission data w (n) ′. The thick line in (A) of FIG. 8 indicates the prediction error e (n) ′ (= w from the subtractor 206.
(n) '-v (n)) is shown.

The transmission sequence prediction circuit 205 is shown in FIG.
As shown in, a signal sequence having a waveform that would be obtained without noise during transmission, for example, during recording / reproduction, equalization error, etc. is generated, and is used for obtaining the above error. The waveform of FIG. 8 shows an example of transmission by the so-called partial response class I (PRI) system. Since taking the three values in the case of this PRI, the standard amplitude, for example + 1V, 0V, when a -1 V, the detection threshold (+ V _th, -V _th) in the transmission series prediction circuit 205 respectively + 0.5V, -0 It will be 0.5V. The standard amplitude (+1) in FIG. 8 is the envelope of the RF waveform of the reproduced signal that is ideally equalized without noise, the standard amplitude (0) is 0 V,
The standard amplitude (-1) is the envelope x (-1) of the RF waveform of the reproduced signal that is ideally equalized without noise.

The tap coefficient calculation circuit 207 in the automatic equalizer 203 adjusts the tap coefficient so as to minimize the prediction error e (n) '.

[0019]

If the predicted transmission data w (n) 'is almost the same as the true transmission data w (n), the prediction error e (n)' is the true error e. Since the value is close to (n), the automatic equalizer 207 operates correctly, but when the difference between the predicted transmission data w (n) ′ and the true transmission data w (n) is large, The prediction error e (n) 'becomes different from the true error e (n), which may cause the automatic equalizer to malfunction.

The malfunction of the automatic equalizer in this case is the following phenomenon. That is, (1) the operation does not converge even after a lapse of time, diverges, or converges to an incorrect stable point.

(2) The range of transmission path characteristics that can be converged is narrowed. That is, the pull-in range becomes narrow.

(3) The time required for convergence increases.

(4) It converges, but it comes off.

(5) When the transmission path characteristics are shifted, the characteristics cannot be tracked and diverge. That is, the lock range is narrowed.

The above-mentioned predicted transmission data w (n) 'and the true transmission data w (n), which are cited as the causes of such malfunction, are given.
The reason for the large difference with
Generally, the deterioration of the provisional detection accuracy occurs in the following cases.

(1) The accuracy of the temporary detection circuit is poor. The circuit itself is noisy.

(2) There is a lot of noise on the transmission line.

(3) The deviation of the temporary equalization characteristic from the ideal characteristic is large. The temporary equalization error is large.

That is, it can be said that the automatic equalizer has a potential instability factor that accompanies the formation of the predicted transmission sequence therein.

The present invention has been made in view of the above circumstances, and it is possible to improve the provisional detection accuracy in the automatic equalizer and prevent the occurrence of a malfunction of automatic equalization. An automatic equalizer and a digital signal reproducing device are provided.

[0031]

In order to solve the above-mentioned problems, an automatic equalizer according to the present invention comprises a filter means for performing a convolution operation on an input digital signal and a tap coefficient, and a convolution operation means. Prediction means for outputting a prediction signal of the original data using a signal obtained by performing maximum likelihood decoding on the basis of a predetermined threshold for the output of, the output from the prediction means, and the output from the filter means. It is characterized by comprising an error calculation means for calculating a prediction error based on the output and a tap coefficient calculation means for calculating the tap coefficient of the filter means based on the prediction error from the error calculation means.

In this case, the maximum-likelihood decoding may be performed by providing a maximum-likelihood decoder as a temporary detection circuit inside the predicting means, or provided as a detection circuit in the signal reproduction circuit system. The maximum likelihood decoder may be used.

Further, in the digital signal reproducing apparatus according to the present invention, the output from the analog / digital converting means for converting the signal read from the recording medium on which the digital signal is recorded into the digital signal is sent to the automatic equalizer. Supply,
Detect the original data based on the output from the automatic equalizer,
It has at least a configuration for correcting the error of the detected data.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an automatic equalizer as a first embodiment of the present invention. In FIG. 1, an input terminal 11 of the automatic equalizer has a digital input signal q (n) obtained by A / D converting a signal reproduced from a recording medium.
Is supplied. This input signal q (n) is sent to the transversal filter 12. The transversal filter 12 is a filter unit that performs a convolution operation of the input signal sequence and the tap coefficient, and in the example of FIG.
The transversal filter of a tap is shown. That is, in the transversal filter 12 of FIG. 1, the input signal q (n) and the delay circuits 13a, 13b, 13
The signals q (n-1), q (n-2), sequentially delayed by c and 13d,
q (n-3) and q (n-4) are multipliers 14a, 14b and 1 respectively.
4c, 14d, 14e, and are respectively multiplied by tap coefficients c ₀ (p), c ₁ (p), c ₂ (p), c ₃ (p), c ₄ (p), and each multiplication result is The filter output signal v (n) is obtained by sending the sums to the adders 15a to 15d. The output signal v (n) from the transversal filter 12 is sent to the output terminal 16 as the output of the automatic equalizer.

The output signal v (n) is sent to the transmission sequence prediction circuit 20 and the error calculation circuit 27 in the automatic equalizer. The transmission sequence prediction circuit 20 performs maximum-likelihood decoding on the output signal v (n) by the maximum-likelihood decoder 21 in the temporary detection circuit 21 based on a predetermined threshold value, and selects a standard amplitude by the selector circuit 23. Thus, a prediction signal of multi-valued, for example, ternary original transmission data, that is, predicted transmission data w (n) ′ is output.

That is, FIG. 2 shows the transmission sequence prediction circuit 20.
Shows a specific example of the transversal filter 12
The maximum likelihood decoder 22 of the provisional detection circuit 21 to which the output signal v (n) from is supplied performs three-value detection of +1, 0, and −1 based on, for example, predetermined threshold values + V _th and −V _th. ing. By the ternary detection output from the maximum likelihood decoder 22, the selector 2
3 of the switches 24a, 24b, 24c are controlled. Each switch 24a, 24b, 24c of the selector 23
Are supplied with standard amplitudes corresponding to three values (+1, 0, −1) of the data, respectively, and these switches 24 a, 24 b, 2 are supplied in accordance with the detection output from the maximum likelihood decoder 22.
4c is selected and the standard output of the selected value is
It is taken out as the predicted transmission data w (n) '.

FIG. 3 shows an example of a conventional transmission sequence prediction circuit for comparison, and the temporary detection circuit 21 'is
The level of the signal v (n) is discriminated by the threshold value + V _th and + V _th
In the above case, the comparator 25a which outputs a +1 detection signal, in the level discrimination by the threshold value −V _th , the comparator 25c which outputs a −1 detection signal when the threshold value is −V _th or less, and an exclusive OR of these detection signals ( NOR circuit 25b. The selector 23 is similar to that of FIG. 2, and each switch 24a, 24b, 24c is on-controlled by each output from the comparator 25a, the NOR circuit 25b, and the comparator 25c. The operation of the transmission sequence prediction circuit of FIG. 3 is as described with reference to FIG.
1V, 0V, when a -1 V, the detection threshold of the temporary detection circuit _{21 '(+ V th, -V} th) respectively + 0.5V, -
It becomes 0.5V.

According to the conventional temporary detection circuit 21 ', a large number of temporary detection errors occur in a transmission system such as a recording / reproduction system in which noise and equalization error are large, and this causes a transmission sequence prediction error, resulting in a tap coefficient. There was a vicious cycle in which correction errors were caused, which made it easier for temporary detection errors to occur.

On the other hand, the provisional detection circuit 21 using the maximum likelihood decoder 22 of FIG. 2 performs so-called viterbi decoding, sequential decoding, etc. to detect transmission data with high accuracy. is there. In this maximum likelihood decoding, in order to reduce the decoding error when decoding the convolutional code, the signal sequence of the required range is targeted regardless of the constraint length, and the path with the shortest Hamming distance is searched for in the supplied signal sequence. For example, in Viterbi decoding, the search is simplified by discarding paths that have no possibility. Since the detection error can be reduced by the maximum likelihood decoding, it is possible to prevent the conventional vicious cycle from occurring as described above, and a good automatic equalization operation can be expected.

Although the examples shown in FIGS. 2 and 3 are transmitted by the so-called partial response class I (PRI) system, the present invention can be easily applied to signals transmitted by other systems. Of course, it can be applied to.

Next, the error calculation circuit 27 of FIG. 1 uses the transversal filter 12 from the predicted transmission data w (n) 'of the transmission sequence prediction circuit 20 including the maximum likelihood decoding as described above.
By subtracting the output signal v (n) of
The prediction error e (n) 'is calculated.

Prediction error e (n) 'from the error calculation circuit 27
Are sent to the tap coefficient calculation circuit 30. The tap coefficient calculation circuit 30 calculates the tap coefficients c ₀ (p) to c _{4 of the} transversal filter 12 based on the prediction error e (n) ′.
(p) is calculated, and various configurations are conceivable depending on the tap coefficient adjustment algorithm. In the example of FIG. 1, the configuration according to the algorithm of the maximum gradient method, which is one of them, is shown. That is, the tap coefficient calculation circuit 30 in FIG. 1 includes a multiplication circuit 31, an integration circuit 32, and a tap coefficient correction circuit 33. The integration circuit 32 and the tap coefficient correction circuit 33 are controlled by the control circuit 35. It has become.

The multiplication circuit 31 multiplies the prediction error e (n) 'from the error calculation circuit 27 by a constant μ, and the output from the multiplication device 36, which is the input signal q from the input terminal 11. (n) and sequentially delayed signals q (n-1), q (n-2),
Multipliers 37a, 3 for multiplying q (n-3), q (n-4) respectively
7b, 37c, 37d, 37e. As shown in FIG. 1, each of the signals q (n-1) to q (n-4) is a delay circuit 38a, 38b, 38 that sequentially delays the input signal q (n).
c and 38d may be provided, the delay circuits 13a, 13b, 1 of the transversal filter 12 may be provided.
The outputs from 3c and 13d may be used.

The integrating circuit 32 is provided with adders 41a, 41b, 41c, 4 to which the outputs from the multipliers 37a, 37b, 37c, 37d, 37e of the multiplying circuit 31 are respectively supplied.
1d, 41e and their respective adders 41a, 41b, 4
Flip-flops (FF) 42a, 42b, 42c, 4 to which outputs from 1c, 41d, 41e are respectively supplied.
2d and 42e, and each flip-flop 42a, 4e
The outputs from 2b, 42c, 42d, and 42e are supplied to the adders 41a, 41b, 41c, 41d, and 41e, respectively, for cumulative addition. The enable signal EN and the clear pulse CLR from the control circuit 35 are supplied to these flip-flops 42a, 42b, 42c, 42d, and 42e.

The tap coefficient correction circuit 33 includes an integration circuit 32.
Of the adders 41a, 41b, 41c, 41d, and 41e, respectively, of the adders 43a, 43b,
43c, 43d, 43e and their respective adders 43a,
Flip-flops (FF) 44a, 44b, to which outputs from 43b, 43c, 43d, 43e are supplied, respectively.
44c, 44d, 44e, and outputs from the flip-flops 44a, 44b, 44c, 44d, 44e are adders 43a, 43b, 43c, 43d, 43, respectively.
It is supplied to e for cumulative addition. These flip-flops 44a, 44b, 44c, 44
The load pulse LD from the control circuit 35 is supplied to d and 44e.
Is supplied.

The tap coefficient calculation circuit 30 having such a configuration
Will be described, that is, the maximum gradient method algorithm.

Tap coefficient c for each clock timing
_In order to sequentially correct _k (n) by the maximum gradient method, the following equation (6) utilizing partial differentiation of the predetermined evaluation function D by the tap coefficient c _k (n) is used.

[0049]

[Equation 4]

In the equation (6), μ is a constant,
The value of μ is determined by a trade-off between accurate convergence to the optimum point and speed of convergence. That is, when μ is increased, the amount of change per coefficient correction increases, so that the time required for convergence decreases, but the convergence to the optimum point deteriorates.

By the way, in the equation (6),
That is, this means that the tap coefficient c _k (n) is updated for each sample of data, but when the tap coefficient is updated every N times, the tap coefficient updated every N clocks is set. The above equation (6) can be rewritten as the following equation (7) by expressing it as c _k (p).

[0052]

(Equation 5)

Similarly, the above equation (2) is transformed into the following (8)
Can be rewritten as an expression.

[0054]

(Equation 6)

A more specific algorithm is determined by what is selected as the evaluation function D of the above expression (7). Here, an example using the generally-used least squares method (hereinafter referred to as the LMS method) will be described. The evaluation function D of this LMS method is, as shown in the following expression (9),
The mean square error of the prediction error e (n) 'is used.

[0056]

(Equation 7)

In this equation (9), the number of data to be averaged is N. Substituting equation (9) into equation (8) above,

[0058]

(Equation 8)

When the partial differentiation of the evaluation function D of the equation (10) by the i-th tap coefficient c _i (p) is calculated, the following equation (11) is obtained.

[0060]

[Equation 9]

The i in the equation (11) is converted into k and is substituted into the equation (7) to obtain the following equation (12) representing the tap coefficient changing algorithm.

[0062]

(Equation 10)

This equation (12) integrates the result of the input signal q (nk) to the transversal filter 12 and the prediction error e (n) 'N times and corrects it for the tap coefficient c _k (p). It is meant to be a value.

The calculation of the second term on the right side of the equation (12) is performed by the multiplication circuit 31 and the integration circuit 32, and the addition of the second term and the first term is performed by the tap coefficient correction circuit 33. In this way, the tap coefficient calculation circuit 30 calculates the tap coefficient for automatic equalization.

According to the automatic equalizer having the configuration of FIG. 1 described above, the maximum likelihood decoder is used in the temporary detection circuit, so that the temporary detection accuracy is improved, and during the automatic equalization operation, it is higher than in the conventional case. It becomes difficult to diverge, the range of the transmission line characteristics that can be converged is widened, the pull-in range is widened, the time required until convergence is shortened, the followability when the transmission line characteristics change is improved, and the lock range is improved. Widening, good operation can be performed even if there is a lot of noise in the transmission line, and noise resistance increases.
Also, the need to prepare a known random pattern or the like for automatic equalization is reduced.

Next, a specific example of a digital signal reproducing apparatus using the automatic equalizer as shown in FIG. 1 will be described with reference to the drawings.

FIG. 4 shows a digital audio tape recorder (DAT) as an example of a device to which the above-mentioned automatic equalizer is applied.

In FIG. 4, a voice signal to be recorded is converted into a digital signal by the A / D converter 101, error correction parity is added by the error correction parity addition circuit 102, and 8/10 conversion is performed. 8 in circuit 103
The bit data is converted into a 10-channel bit signal for recording, amplified by the recording amplifier 104, and becomes recording data or transmission data w (n).

This transmission data w (n) is used in the recording / reproducing system 11
0 is sent to the recording head 111 and recorded on the recording tape 112, and the recorded contents are reproduced from the recording tape 112 by the reproducing head 113. The signal from the reproducing head 113 is amplified by the reproducing amplifier 114 and is temporarily equalized by the temporary equalizing circuit 115. From the recording head 111 to the provisional equalization circuit 115
Is used as a recording / reproducing system 110, and a recording tape 112
When a magnetic tape is used for each head 111, 11
For example, a rotary magnetic head is used for the recording / reproducing system 11
0 is an electromagnetic conversion system. The impulse response of the transmission path of the recording / reproducing system 110 is g (n).

The signal from the temporary equalizing circuit 115 of the recording / reproducing system 110, a so-called RF signal, is sent to the A / D converter 121, sampled at the channel clock timing and quantized to be converted into a digital signal. Is
It is sent to the input terminal 11 of the automatic equalizer 10 as an input signal q (n). As the automatic equalizer 10, the automatic equalizer configured as shown in FIG. 1 can be used.

From the output terminal 16 of the automatic equalizer 10, as described with reference to FIG. 1, the adaptively waveform-equalized output signal v (n) is taken out and sent to the detection circuit 123. In the detection circuit 123, transmission data detection using a threshold value is performed, the obtained data is sent to the error correction circuit 125, subjected to error correction processing, converted into an analog audio signal by the D / A converter 126, and output. It

As the recording / reproducing system 110, Ach,
A specific example of the operation in the case of using an electromagnetic conversion system having a rotary magnetic head for alternately recording and reproducing two channels of Bch will be described with reference to FIG.

The switching pulse SWP of FIG. 5 is a pulse for switching between Ach and Bch of the rotary magnetic head, and each head reproduces from the magnetic tape only for about 1/4 of one cycle. A signal such as the reproduction signal RF of 5 is obtained. FIG. 5 shows an operation example for Ach, and it is a stable portion of the reproduced signal, such as a period T _{SI from} time t _{2 to} t ₃ excluding the unstable portion before and after in the reproduced signal of Ach. The process for automatic equalization is performed.

The clear pulse CLR and the enable signal EN of FIG. 5 are supplied from the control circuit 35 of FIG. 1 to the flip-flops 42a of the integrating circuit 32 in the tap coefficient calculating circuit 30.
To 42e, the clear pulse CLR is the fall timing t ₁ of the switching pulse SWP.
And the enable signal EN is active, that is, "L", only during the stable period T _SI of the reproduction signal RF. Therefore, the output from the integrating circuit 32 in FIG. 1 becomes as shown in the integrating circuit output SI in FIG.
The integration operation is performed only during the enable period T _SI .

Number of integrations N within this enable period T _SI
S is the period T _SI divided by the channel clock period T _ch (N _S = T _SI / T _ch ). As a specific example, the channel clock frequency f _ch is 9.4 MHz, the channel clock period T _ch is about 106 ns, and the period in which the reproduction signal of Ach is output, that is, about 1/4 of the head rotation period.
Is 7.5 ms, and 1/2 of the central part, that is, 3.75 ms, is the enable period T _SI ,
Since T _SI / T _ch is about 3.75 ms / 106 ns,
The number of integration times N _S is about 35377 times.

The integration result obtained by this integration operation is
It is sent to the tap coefficient correction circuit 33 of FIG. 1, the time t ₃
The load pulse LD is issued at a time t ₄ later than that, and the flip-flops 44 a to 4 a of the tap coefficient correction circuit 33 are output.
Since the integration result is loaded in 4e, the Ach coefficient KA in FIG. 5 corresponding to the tap coefficients c ₀ (p) to c ₄ (p) for Ach is switched at the time t _4. . The load pulse LD has a tap coefficient c _k (p)
Is a pulse for correcting the Ach reproduction signal, and the tap coefficient correction should be performed in a section in which the reproduction RF signal of the Ach is not output. Therefore, in the example of FIG. 5, it is generated immediately after the output of the reproduction signal of the Ach is finished. There is.

By the way, in the above example, the maximum likelihood decoder is used as the temporary detection circuit in the automatic equalizer. However, in the actual equipment, the maximum likelihood decoder is already used as the detection circuit of the reproduction circuit system. In this case, it is conceivable to share the maximum likelihood decoder as a detection circuit as a temporary detection circuit.

That is, FIG. 6 shows an automatic equalizer according to a second embodiment of the present invention, in which the detection circuit 123 of FIG.
Maximum likelihood decoder 51 as a detection circuit in the reproduction circuit system such as
It shows an example in the case of having.

In FIG. 6, the output v (n) from the transversal filter 12 of the automatic equalizer is supplied to the maximum likelihood decoder 51 as a detection circuit. The output from the maximum likelihood decoder 51 is sent to the selector 53 of the transmission sequence prediction circuit 52 in order to be used also as the temporary detection circuit of the prediction circuit. That is, the transmission sequence prediction circuit 52 in the example of FIG. 6 is composed of only the selector 53.

The other configuration of FIG. 6 is basically the same as that of FIG. 1, but the maximum likelihood decoder 51 as a detection circuit has a bus memory for so-called Viterbi decoding processing inside. Therefore, it takes a predetermined delay time (this is the A channel clock cycle) until the detection result is output. Delay circuits 54 and 55 are provided in order to correct the delay time A and adjust the time in the error calculation and the tap coefficient calculation.

That is, the transversal filter 12
The output v (n) from the delay circuit 54 is sent to the delay circuit 54 having the delay time A to be delayed, and the output v (nA) from the delay circuit 54 is delayed.
Is sent to the subtractor 28 of the error calculation circuit 27 to be subtracted from the output from the selector 53 of the transmission sequence prediction circuit 52, and the input signal q (n) from the input terminal 11 is added to the delay time A To the delay circuit 55 for delaying the output q (nA) from the delay circuit 55.
Delay circuit 38a and multiplier 37a in multiplication circuit 31 of 0
I am sending it to. At this time, the outputs from the delay circuits 38b, 38c and 38d in the multiplication circuit 31 are respectively q (nA
-1), q (nA-2), q (nA-3), q (nA-4).

With respect to the other configuration of FIG. 6, parts corresponding to the respective parts of FIG.

According to the embodiment of FIG. 6, the above-mentioned FIG.
In addition to obtaining the same effect as in the above example, since the maximum likelihood decoder 51 already provided as a detection circuit in the playback device is also used as the temporary detection circuit, the configuration can be simplified and the inexpensive supply is possible. Is possible.

The present invention is not limited to the above-described embodiments. For example, a recording / reproducing system as a transmission line is not limited to a digital audio tape recorder, but a digital VTR or a disc recording / reproducing system. Etc. can be used.

[0085]

As is apparent from the above description, according to the present invention, transmission data prediction is performed with high accuracy by using maximum likelihood decoding for transmission sequence prediction, and is calculated from this prediction output and filter output. Since the tap coefficient is modified to minimize the error that occurs, the automatic equalization operation can be reliably and accurately converged in a short time, the pull-in range is wide, the lock range is wide, and the noise immunity is excellent. An equalizer and a digital signal reproducing device can be provided.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a first embodiment of an automatic equalizer according to the present invention.

FIG. 2 is a block circuit diagram showing a specific example of the transmission sequence prediction circuit of FIG.

FIG. 3 is a block circuit diagram showing a specific example of a conventional transmission sequence prediction circuit.

FIG. 4 is a block diagram showing a schematic configuration of a digital audio tape recorder as an example of a digital signal reproducing apparatus to which the present invention is applied.

FIG. 5 is a timing chart for explaining an automatic equalization operation in the digital audio tape recorder.

FIG. 6 is a block circuit diagram showing a second embodiment of an automatic equalizer according to the present invention.

FIG. 7 is a block diagram showing an example of a digital signal reproducing apparatus using a conventional automatic equalizer.

8 is a waveform chart for explaining the operation of the transmission sequence prediction circuit in FIG.

[Explanation of symbols]

 11 Input Terminal 12 Transversal Filter 16 Output Terminal 20 Transmission Sequence Prediction Circuit 21 Temporary Detection Circuit 22 Maximum Likelihood Decoder 27 Error Calculation Circuit 30 Tap Coefficient Calculation Circuit 31 Multiplication Circuit 32 Integration Circuit 33 Tap Coefficient Correction Circuit

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[Procedure amendment]

[Submission date] November 28, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0057

[Correction method] Change

[Correction contents]

In this equation (9), the number of data to be averaged is N. Substituting equation (8) into equation (9),

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0060

[Correction method] Change

[Correction contents]

[0060]

[Equation 9]

Claims (5)

[Claims] 1. A filter means for performing a convolution operation of an input signal sequence and a tap coefficient, and a signal obtained by performing maximum likelihood decoding on the output from the filter means based on a predetermined threshold value. A prediction means for outputting a prediction signal of the data, an error calculation means for calculating a prediction error based on the output from the prediction means, and an output from the filter means, and a prediction error from the error calculation means. And a tap coefficient calculating means for calculating the tap coefficient of the filter means. 2. The automatic equalizer according to claim 1, wherein the predicting means has a temporary detecting means for performing maximum likelihood decoding on the output from the filter means based on a predetermined threshold value. 3. A detection means for performing maximum likelihood decoding on the output from the filter means to detect the original data and outputting the data, wherein the predicting means uses the output from the detection means. 2. A prediction signal of original data is output.
The described automatic equalizer. 4. The automatic equalizer according to claim 1, further comprising delay means for delaying an output from the filter means by a time required for the maximum likelihood decoding. 5. An analog / digital converting means for converting a signal read from a recording medium on which a digital signal is recorded into a digital signal, and a convolution operation of a signal sequence from the analog / digital converting means and a tap coefficient. Filter means, prediction means for outputting a prediction signal of original data using a signal obtained by performing maximum likelihood decoding on the output from the filter means based on a predetermined threshold, and from the prediction means Error calculation means for calculating a prediction error based on the output of the filter means, and a tap coefficient calculation means for calculating the tap coefficient of the filter means based on the prediction error from the error calculation means. A detecting means for detecting the original data based on the output from the filter means, and an error of the data detected by the detecting means. A digital signal reproducing device having an error correcting means for correcting the error.