JPH08147610A - Circuit and method for adaptive equalization - Google Patents

Abstract

PURPOSE: To prevent the instability or divergence of a weighting factor given to a transversal filter included in an adaptive equalization circuit becomes unstable or is dispersed when the distortion of a signal which is read out from a digitally recorded magnetic tape is large or when an S/N ratio is bad. CONSTITUTION: A distortion amount expressed by the maximum peak value and the minimum peak value of a signal which is read out from a digitally recorded magnetic tape is detected by a distortion detection circuit 15. A detection signal which expresses the distortion amount is given to a reference-value output circuit 30. When the distortion amount is large, the reference-value output circuit 30 is adjusted in such a way that a reference value becomes small. When the distortion amount is small, the circuit is adjusted in such a way that the reference value becomes large. The output of the reference-value output circuit 30 is subtracted from the output of a transversal filter 21, and an error signal is obtained. A tap factor value is decided on the basis of the error signal and a reproduced signal so as to be given to the transversal filter 21, and a waveform equalization processing operation is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an adaptive equalization circuit and method applied to a reproducing apparatus for outputting a digital magnetic recording / reproducing signal.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a recording signal for digitally recording on a magnetic tape and a reading signal when the recording signal is read by a magnetic head. In the case of ternary identification, when the recording signal recorded on the magnetic tape is read and the reading signal is obtained, the reading signal is compared with the positive threshold value and the negative threshold value. By this comparison, the read signal is judged to be above the positive threshold value or below the negative threshold value, whereby the data is detected.

However, as the recording density of data increases, read signals of adjacent data interfere with each other. Therefore, as shown in FIG. It may not fall below a negative threshold. Therefore, the data may not be detected even though the data is recorded. Therefore, the signal read from the magnetic tape is subjected to adaptive equalization processing, and the signal waveform is shaped as shown in FIG. As a result, the presence or absence of data corresponds to the read signal, and the presence or absence of data can be detected from the read signal. When the partial response class 4 is used, the presence or absence of data is detected from the signal obtained by adding the signal delayed by 1 bit and the reproduction signal as shown in FIG.

In the adaptive equalization processing, for example, a reproduction signal from a magnetic tape is input to a delay line group in which a plurality of delay lines are connected in series, the output of each delay line is multiplied by a weighting coefficient, and this output is synthesized. A transversal filter is used.

The weighting coefficient given to the transversal filter used in the adaptive equalization circuit is such that the signal read from the magnetic tape has a large distortion (difference between the maximum peak value and the minimum peak value) or the S / N ratio. If it is bad, it may become unstable or diverge.

[0006]

DISCLOSURE OF THE INVENTION According to the present invention, the weighting coefficient value given to the transversal filter included in the adaptive equalization circuit is unsatisfactory when the distortion of the signal read from the magnetic tape is large or the S / N is bad. It is intended to be stable and prevent divergence.

A first aspect of the present invention represents a filter serving as an equalizer for compensating the characteristics of a reproduction signal output from a magnetic reproducing apparatus for reproducing magnetic data recorded on a magnetic recording medium, an output signal of the filter and a reference value. An error signal generating means for generating an error signal from the signal and a weighting coefficient given to the filter based on the error signal generated by the error signal generating means, and a weighting coefficient giving the generated weighting coefficient to the filter In the adaptive equalization circuit provided with the generating means, the reference value becomes smaller as the distortion amount detecting means for detecting the distortion amount of the magnetic reproduction signal, and the larger the distortion amount detected by the distortion amount detecting means, A reference value adjusting means for adjusting the reference value is provided so that the reference value increases as the amount of distortion decreases. That.

The first invention is a filter which serves as an equalizer for compensating for characteristics of a reproduction signal outputted from a magnetic reproducing apparatus for reproducing magnetic data recorded on a magnetic recording medium,
Based on the error signal generating means for generating an error signal from the output signal of the filter and the signal representing the reference value, and the error signal generated by the error signal generating means,
An adaptive equalization circuit having a weighting coefficient generating means for generating a weighting coefficient to be given to the filter and giving the generated weighting coefficient to the filter is to detect the distortion amount of the magnetic reproduction signal, and the detected distortion amount is large. The reference value is adjusted so that the reference value becomes smaller as the distortion amount becomes smaller and the reference value becomes larger as the distortion amount becomes smaller.

The weighting coefficient given to the filter is obtained by subtracting a signal representing a reference value from the output signal of the filter to obtain an error signal and generating from the error signal. Usually, the reference value is set to 1/2 of the maximum peak value of the reproduction signal (peak value of the isolated reproduction waveform). When the amount of distortion of the reproduction signal is large and the difference between the maximum peak value and the minimum peak value is large, the size from the reference value to the maximum peak value and the size from the reference value to the minimum peak value are generally extremely different. In some cases, the weighting coefficient may not converge because the amount of error signal does not converge to a constant value.

According to the first invention, the amount of distortion of the reproduced signal is detected. The larger the distortion amount and the larger the difference between the maximum peak value and the minimum peak value of the read signal, the smaller the reference value becomes, and the smaller the distortion amount, the smaller the difference between the maximum peak value and the minimum peak value of the read signal becomes. Is increased.

Therefore, the magnitude from the reference value to the maximum peak value and the magnitude from the reference value to the minimum peak value are almost equal, the amount of the error signal also converges to a constant value, and the weighting coefficient also converges. The weighting coefficient given to the filter is stable and divergence is prevented.

According to a second aspect of the present invention, a filter serving as an equalizer for compensating for characteristics of a reproduction signal output from a magnetic reproducing apparatus for reproducing magnetic data recorded on a magnetic recording medium, an output signal of the filter and a reference value are provided. An error signal generating means for generating an error signal from the expressed signal, and a weighting coefficient to be given to the filter based on the error signal generated by the error signal generating means, and a weighting to give the generated weighting coefficient to the filter. In the adaptive equalization circuit including the coefficient generating means, the error signal increases as the amplitude level detecting means for detecting the amplitude level of the magnetic reproduction signal and the amplitude level detected by the amplitude level detecting means increase. , Adjust the error signal so that the smaller the amplitude level, the smaller the error signal. Characterized in that it comprises a differential signal adjusting means.

A second invention is a filter which serves as an equalizer for compensating for characteristics of a reproduction signal outputted from a magnetic reproducing apparatus for reproducing magnetic data recorded on a magnetic recording medium,
Based on the error signal generating means for generating an error signal from the output signal of the filter and the signal representing the reference value, and the error signal generated by the error signal generating means,
An adaptive equalization circuit having a weighting coefficient generation means for generating a weighting coefficient to be given to the filter and giving the generated weighting coefficient to the filter is to detect the amplitude level of the magnetic reproduction signal, and the detected amplitude level is large. The error signal is adjusted so that the error signal becomes larger as the amplitude level becomes smaller and the error signal becomes smaller as the amplitude level becomes smaller.

The weighting coefficient is obtained by accumulating the error signal for a certain period. If the reproduced signal contains a noise component, the error signal also shows the influence of the noise component, and the weighting coefficient also shows the influence of the noise component.
It may not be possible to accurately determine the weighting coefficient. On the other hand, if the accumulation period of the error signal is lengthened, the noise component will converge to zero, so that an accurate weighting coefficient can be determined.

According to the second invention, the amplitude level of the reproduction signal is detected. The error signal is adjusted such that the error signal increases as the amplitude level increases and the error signal decreases as the amplitude level decreases. Even if the accumulation period of the error signal is the same as the conventional one, the error signal becomes smaller than the reproduction signal, and as a result, it becomes the same as when the accumulation period is lengthened, and the influence of noise can be reduced.

In the above, the reference value is adjusted so that the reference value becomes smaller as the distortion amount becomes larger, and becomes larger as the distortion amount becomes smaller, and the reference value becomes larger as the amplitude level becomes larger. The error signal may be adjusted so that the error signal becomes larger and the error signal becomes smaller as the amplitude level becomes smaller.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention and shows the electrical construction of a device for reproducing a signal recorded on a magnetic tape in a digital VTR.

The signal recorded on the magnetic tape 10 is read by the magnetic head 11 and given to the reproducing / amplifying circuit 12. The reproduction signal is amplified in the reproduction amplifier circuit 12 and given to the low pass filter 13 to remove high frequency noise components. The signal output from the low pass filter 13 is AG
The signal amplitude is given to a C (Auto Gain Controll) circuit 14 to make the signal amplitude constant. The signal output from the AGC circuit 14 is given to the adaptive equalization circuit 20 and the distortion detection circuit 15.

The distortion detection circuit, as shown in FIG.
This circuit detects the amount of distortion represented by the maximum peak value and the minimum peak value of the read signal output from the circuit 14. A signal representing the amount of distortion is given to the adaptive equalization circuit 20 as a distortion detection signal.

The signal read from the video tape (or magnetic tape) 10 as shown in FIG.
It changes to positive or negative depending on the rising and falling of the signal recorded in 10. In the reproducing apparatus, positive and negative thresholds are set, data is detected by detecting whether the signal read from the video tape 10 is above the positive threshold or below the negative threshold. Further, in the magnetic recording / reproducing method using the partial response, after equalizing the waveform of the reproducing signal of FIG. 7 and passing through the demodulation circuit called decoding, in the case of class 4, the signal as shown in FIG. 9 is obtained. Similarly, a threshold value is set and data is detected.

The adaptive equalization circuit 20 has a high recording density like the recording signal of the video tape 10 shown in FIG. 7, and is shown in FIG. 8 when a read signal having an effective level cannot be obtained at the time of data switching. It is a circuit that performs waveform shaping. By performing adaptive equalization processing using the adaptive equalization circuit 20 on the reproduction signal, it is possible to accurately detect the presence or absence of data.

In the adaptive equalization circuit 20 applied to the reproducing apparatus of the digitally recorded magnetic tape shown in FIG. 1, the distortion amount of the reproduction signal is detected, the detected distortion amount is large, and the maximum peak value of the read signal is detected. The larger the difference between the peak value and the minimum peak value, the smaller the reference value. As a result, the weighting coefficient value does not diverge or become unstable, and the amplitude of the reproduction signal becomes substantially constant, and optimal equalization is performed. The adaptive equalization processing will be described in detail later.

The signal output from the adaptive equalization circuit 20 is given to the demodulation circuit 16 and the PLL circuit 17. Demodulation circuit 16
Is 1 in the partial response class 4 method.
This is a decoder circuit that adds the bit-delayed signal and the original signal. The video signal demodulated in the demodulation circuit 16 is supplied to the data detection circuit 18. The PLL circuit 17 is a circuit that generates and outputs a timing signal representing the data detection timing in the data detection circuit 18. PL
The data detection timing signal output from the L circuit 17 is given to the data detection circuit 18.

In the data detection circuit 18, the PLL circuit 17
The data is detected from the signal given from the demodulation circuit 16 at the timing determined by the data detection timing signal given from. The detected data is sent as reproduction data to a synchronization detection circuit (not shown) and then displayed. .

FIG. 2 is a block diagram showing an electrical configuration of the adaptive equalization circuit 20 included in the reproducing apparatus shown in FIG.

The video signal output from the AGC circuit 14 is applied to the transversal filter 21 and the error signal quantization circuit 28. The transversal filter 21 inputs the reproduced signal, multiplies the tap coefficient value given to the inputted reproduced signal, delays the inputted reproduced signal, multiplies the delayed signal with the given tap coefficient value, and taps the tap coefficient value. It is a circuit for synthesizing a signal multiplied by and a video signal delayed and multiplied by a tap coefficient value and outputting the synthesized signal. Transversal filter
By 21, the equalization process is performed to shape the distorted waveform into a waveform suitable for identifying the presence or absence of data. The error signal quantization circuit 28 is used to determine the tap coefficient value. The reproduction signal output from the AGC circuit 14 is delayed corresponding to the amount delayed by the transversal filter 21, multiplied by the error signal provided, and output from the error signal quantization circuit 28.

The signal representing the tap coefficient value output from the error signal quantizing circuit 28 is applied to the adding circuit 24. In the adding circuit 24, the signals output from the error signal quantizing circuit 28 are added for a fixed period. The output signal of the adder circuit 24 is transversal as a signal representing the tap coefficient value.
It is given to the filter 21. As a result, the transversal filter 21 performs equalization processing of the video signal.

The reproduced signal output from the transversal filter 21 is supplied to the subtraction circuit 31 and also output from the adaptive equalization circuit 20.

The adaptive equalization circuit 20 includes a reference value output circuit 30. The reference value output circuit 30 is supplied with the output signal of the transversal filter 21 and the distortion detection signal output from the distortion detection circuit 15. Normally, the reference value is set to ± 1/2 of the maximum amplitude. From the reference value output circuit 30, the positive reference value is output when the output signal of the transversal filter 21 is positive, and the negative reference value is output when the output signal is negative. Is output to the subtraction circuit 31. This reference value has an absolute value of 1 as the distortion amount represented by the distortion detection signal increases.
Positive and negative reference values are adjusted to be less than / 2.

Therefore, the magnitude from the reference value to the maximum peak value and the magnitude from the reference value to the minimum peak value are almost equal, the amount of the error signal also converges to a constant value, and the tap coefficient also converges. The tap coefficient applied to the digital filter is stable and divergence is prevented.

The signal representing the reference value output from reference value output circuit 30 is applied to subtraction circuit 31. In the subtraction circuit 31, the signal representing the reference value output from the reference value output circuit 30 is subtracted from the reproduction signal output from the transversal filter 21, and an error signal is obtained. This error signal is given to the error signal quantization circuit 28.

The transversal filter 21 includes a plurality of delay circuits 22b, 22c, 22d and 22e, a multiplication circuit 23a,
23b, 23c, 23d and 23e and an adder circuit 29 are included. The video signal output from the AGC circuit 14 is given to the multiplication circuit 23a and is multiplied by the tap coefficient value given from the addition circuit 24. The delay circuits 22b, 22c, 22d and 22e are connected in cascade, and the delay circuits 22b, 22c, 22
The video signals delayed in d and 22e are given to the multiplication circuits 23b, 23c, 23d and 23e, and the addition circuit 24
Is multiplied by the tap coefficient value given by Multiplier circuit 23
The video signals output from a, 23b, 23c, 23d and 23e are applied to the adder circuit 29 and added, and become the output of the transversal filter 21.

The error signal quantization circuit 28 includes a delay circuit 26b,
26c, 26d and 26e, multiplication circuits 25a, 25b, 25c, 25
d and 25e and a quantizer circuit 27 are included. The delay circuits 26b, 26c, 26d and 26e are connected in cascade. The video signal output from the AGC circuit 14 and the error signal output from the subtraction circuit 31 are applied to the multiplication circuit 25 a, and the video signal is multiplied by the error signal and output, which is applied to the quantization circuit 27. The video signals output from the delay circuits 26b, 26c, 26d and 26e are the multiplication circuits 25b,
It is applied to 25c, 25d and 25e and multiplied by the error signal. The signals output from the multiplication circuits 25b, 25c, 25d and 25e are also given to the quantization circuit 27. In the quantizing circuit 27, the signals output from the multiplying circuits 25a, 25b, 25c, 25d and 25e are quantized.

The signals quantized by the quantizing circuit 27 are given to the adding circuit 24 for each signal and added for a certain period of time for each signal. This added value is output as the tap coefficient value, and the transversal filter 21
To the respective multiplication circuits 23a, 23b, 23c, 23d and 23e.

3 to 5 show another embodiment.

FIG. 3 is a block diagram showing the electrical construction of an apparatus for reproducing a signal recorded on a magnetic tape in a digital VTR. In FIG. 3, the same parts as those shown in FIG. FIG. 4 is a block diagram showing an electrical configuration of the adaptive equalization circuit 20A included in the reproducing apparatus shown in FIG. 3, FIG. 5 (A) is a signal waveform diagram showing a read signal when there is no noise component, and FIG. 10] is a signal waveform diagram showing a read signal when there is a noise component.

In the reproducing apparatus shown in FIG. 3, the distortion detecting circuit 15 is removed and the amplitude level detecting circuit 19 is added in comparison with the reproducing apparatus shown in FIG. The video signal from which the high frequency noise component has been removed by the low pass filter 13 is supplied to the AGC circuit 14 and also to the amplitude level detection circuit 19. The amplitude level detection circuit 19 is a circuit for detecting the amplitude level (average level) of the input video signal, and the detection signal representing the amplitude level is given to the adaptive equalization circuit 20A.

As will be described later, the adaptive equalization circuit 20A increases the feedback amount as the amplitude level detected by the amplitude level detection circuit 19 increases, and decreases the feedback amount as the amplitude level decreases.
This is a circuit for performing adaptive equalization processing by adjusting the feedback amount in the adaptive equalization circuit 20A.

In FIG. 4, the same parts as those of the adaptive equalization circuit shown in FIG.

In the adaptive equalization circuit shown in FIG. 4, the circuit shown in FIG.
A feedback amount control circuit 32 is included unlike the adaptive equalization circuit shown in FIG. The reference value output circuit 30A is a circuit for outputting a signal representing a reference value generated in advance,
The signal output from the reference value output circuit 30A is given to the subtraction circuit 31.

An amplitude level detection signal output from the amplitude level detection circuit 19 is applied to the feedback amount control circuit 32. The output signal of the error signal quantization circuit 28 is also given to the feedback amount control circuit 30. When the amplitude level represented by the amplitude level detection signal is large, the signal output from the feedback amount control circuit 30 becomes large, and when the amplitude level is small, the signal output from the feedback amount control circuit 30 becomes small. The feedback amount control circuit 32 is adjusted.

Since the larger the amplitude level is, the larger the feedback amount is, and the smaller the amplitude level is, the smaller the feedback amount is. Therefore, the ratio of the noise component to the read signal becomes small. Even if the accumulation period of 24 adder circuits is the same as the conventional one, the result is the same as when the accumulation period is lengthened, and as shown in FIG. Figure 5
Adaptive equalization can be performed in the same way as a signal with few noise components as in (A).

In the circuit shown in FIG. 4, the amplitude level detection signal may be input to the error signal quantization circuit 28 to control the reference level at the time of quantization.

In addition, the AG before the error signal quantization circuit 28
The feedback amount may be controlled by connecting a C circuit, controlling the error signal by this AGC circuit, and controlling the magnitude of the error signal.

[Brief description of drawings]

FIG. 1 shows an electrical configuration of a playback device.

FIG. 2 shows an electrical configuration of an adaptive equalization circuit.

FIG. 3 shows an electrical configuration of a reproducing device.

FIG. 4 shows an electrical configuration of an adaptive equalization circuit.

5A illustrates a signal waveform of a read signal that does not include a noise component, and FIG. 5B illustrates a signal waveform of a read signal that includes a noise component.

FIG. 6 is a signal waveform diagram of a recording signal and a reading signal.

FIG. 7 is a signal waveform diagram of a recording signal and a reading signal.

FIG. 8 is a signal waveform diagram of a read signal.

FIG. 9 is a read signal waveform diagram after decoding in the partial response class 4 system.

[Description of code] 15 Distortion detection circuit 19 Amplitude level detection circuit 20, 20A Adaptive equalization circuit 21 Transversal filter 28 Error signal quantization circuit 30, 30A Reference value output circuit

Claims (4)

[Claims] 1. A filter serving as an equalizer for compensating the characteristics of a reproduction signal output from a magnetic reproduction apparatus for reproducing magnetic data recorded on a magnetic recording medium, and an error between an output signal of the filter and a signal representing a reference value. Error signal generating means for generating a signal, and weighting coefficient generating means for generating a weighting coefficient to be given to the filter based on the error signal generated by the error signal generating means, and giving the generated weighting coefficient to the filter. In the adaptive equalization circuit provided, the distortion amount detecting means for detecting the distortion amount of the magnetic reproduction signal, and the distortion amount so that the reference value becomes smaller as the distortion amount detected by the distortion amount detecting means increases. An adaptive equalization circuit provided with a reference value adjusting means for adjusting the reference value such that the reference value increases as the value becomes smaller. 2. A filter serving as an equalizer for compensating the characteristics of a reproduction signal output from a magnetic reproduction device for reproducing magnetic data recorded on a magnetic recording medium, and an output signal of the filter and a signal representing a reference value. Error signal generating means for generating an error signal, and weighting coefficient generating means for generating a weighting coefficient given to the filter based on the error signal generated by the error signal generating means, and giving the generated weighting coefficient to the filter, In the adaptive equalization circuit including: the amplitude level detecting means for detecting the amplitude level of the magnetic reproduction signal; and the amplitude signal so that the error signal increases as the amplitude level detected by the amplitude level detecting means increases. Error signal adjustment that adjusts the error signal so that the smaller the level, the smaller the error signal Means for adaptive equalization circuit. 3. A filter serving as an equalizer for compensating the characteristics of a reproduction signal output from a magnetic reproduction device for reproducing magnetic data recorded on a magnetic recording medium, and an output signal of the filter and a signal representing a reference value. Error signal generating means for generating an error signal, and weighting coefficient generating means for generating a weighting coefficient given to the filter based on the error signal generated by the error signal generating means, and giving the generated weighting coefficient to the filter, In the adaptive equalization circuit including, the amount of distortion of the magnetic reproduction signal is detected, the larger the detected amount of distortion, the smaller the reference value, and the smaller the amount of distortion, the larger the reference value. An adaptive equalization method that adjusts the above reference values. 4. A filter serving as an equalizer for compensating the characteristics of a reproduction signal output from a magnetic reproducing device for reproducing magnetic data recorded on a magnetic recording medium, and an output signal of the filter and a signal representing a reference value. Error signal generating means for generating an error signal, and weighting coefficient generating means for generating a weighting coefficient given to the filter based on the error signal generated by the error signal generating means, and giving the generated weighting coefficient to the filter, In the adaptive equalization circuit including, the amplitude level of the magnetic reproduction signal is detected, the error signal increases as the detected amplitude level increases, and the error signal decreases as the amplitude level decreases. An adaptive equalization method for adjusting the error signal.