JPH0670197A - Waveform equalizer - Google Patents

Abstract

PURPOSE:To improve the equalization accuracy by correcting a clipped part of a VIT signal so as to equalize a waveform. CONSTITUTION:An input signal of MUSE is corrected by a TF(transversal filter) 5 and the result is inputted to an adder circuit 4, in which the signal is added to a delayed input signal, from which a MUSE signal subjected to waveform equalization is outputted and a waveform memory 8 extracts a VIT signal from the output and stores the signal. Then the signal is read and inputted to a control circuit 11 via a correction filter 9. The control circuit 11 compares the inputted and clipped VIT signal with a prescribed reference signal and calculates them and a tap gain of the correction filter 9 is changed based on the result of arithmetic operation, the clipped part of the VIT signal is corrected and outputted, the control circuit 11 compares the output with a prescribed reference signal and calculates them, a tap gain of the TF 5 is changed based on the result of arithmetic operation to correct the input signal of MUSE.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform equalizer for removing transmission distortion generated when transmitting a MUSE signal. Since the MUSE system adopts the sample value transmission system, if the transmission characteristic deviates from the Nyquist characteristic and the transmission signal is distorted, intersymbol interference occurs and ringing occurs on the reproduction screen. Therefore, by incorporating a waveform equalizer in the signal reproduction decoder, the occurrence of ringing is prevented.

[0002]

2. Description of the Related Art In a conventional waveform equalizer, as shown in FIG. 3, an A / D converter 2 for sampling an MUSE input signal, converting it into a digital signal, and outputting the digital signal is converted into a digital signal. A transversal filter 5 for correcting the MUSE input signal, an output from the transversal filter 5, and a signal obtained by delaying the MUSE input signal converted into the digital signal are added,
An adder circuit 4 for outputting a waveform equalized MUSE signal;
A circuit for branching the output from the adder circuit 4 and inputting it to the control circuit 7, and detecting the VIT signal in the MUSE signal from the input, writing it to the memory 12 (RAM) and reading it out, and storing it in advance in the memory 13 (ROM). Comparing with a predetermined reference signal stored in the calculation unit to obtain a correction coefficient and transfer it to the transversal filter 5 to transfer it to the transversal filter 5.
With the control circuit 15 that changes the tap gain of (1), the waveform distortion component included in the input signal is removed, waveform equalization is performed, and the addition circuit 4 outputs the result.

In the case of the MUSE signal transmitted from the satellite, since the FM system is used, the distortion in the transmission line is small and the input signal level is kept within the input range of the A / D converter. As a result, the input signal can be prevented from being clipped. However, when transmitting a MUSE signal by CATV or the like, the AM transmission method is used in order to effectively use the transmission frequency band. In this case, the maximum value of the amplitude level of the input signal is that of the A / D converter. Although it is set within the input range, when the distortion in the transmission path becomes large, the amplitude level of the input signal exceeds the conversion window of the A / D converter and the input signal is clipped.

[0004]

In such a case, the VIT signal superimposed on the MUSE signal is clipped, and the clipped portion of the VIT signal is not equalized in the waveform equalizer. There was a problem that the accuracy of conversion was poor. SUMMARY OF THE INVENTION It is an object of the present invention to improve the equalization accuracy as compared with the prior art by providing a waveform correction means to correct the clip portion of the VIT signal, and to enable the waveform equalization while maintaining the equalization speed to the level of the prior art. And

[0005]

FIG. 1 is a block diagram of an electric circuit of a waveform equalizer showing an embodiment of the present invention. As shown in FIG. The D converter 2, the transversal filter 5 that corrects the output of the A / D converter 2, the output from the transversal filter 5, and the signal obtained by delaying the output of the A / D converter 2 are added. Then, an adder circuit 4 for outputting a waveform-equalized MUSE signal, a circuit for branching the output from the adder circuit 4 and inputting it to the control circuit 11,
A control circuit 1 which detects a VIT signal in the USE signal, compares it with a predetermined reference signal for calculation, and changes the tap gain of the transversal filter 5 based on the calculation result.
In the waveform equalization circuit in which the waveform distortion component included in the input signal is removed by 1 and 1, the waveform correction means 7 is provided,
The output from the adder circuit 4 is input to the control circuit 11 via the waveform correction means 7, the clipped VIT signal transmitted by the waveform correction means 7 is corrected and input to the control circuit 11 to perform waveform equalization. The waveform correction means 7 is composed of a waveform memory 8 and a correction filter 9. The VIT signal is taken out from the output of the adder circuit 4, stored in the waveform memory 8 and read out to obtain the calculation result of the control circuit 11. Based on this, the tap gain of the correction filter 9 is changed so that the clipped portion of the VIT signal is corrected and output.

[0006]

According to the present invention, waveform equalization is performed by the above-described configuration, and when a clipped VIT signal is input, the control circuit 11 detects the VIT signal in the MUSE signal to determine a predetermined reference signal. Is calculated by changing the tap gain of the correction filter 9 based on the calculation result.
The control circuit 11 corrects the clipped portion of the IT signal.
Since it is possible to input to the input terminal, waveform equalization can be performed with higher equalization accuracy than before and maintaining the same equalization speed as before.

[0007]

1 is a block diagram of an electric circuit of a waveform equalizer showing an embodiment of the present invention, in which the same components as those shown in FIG. 3 are designated by the same symbols. . 1 is MU
This is an input terminal for inputting the baseband signal of the SE signal, and the MUSE signal input via the input terminal 1 is input to A /
The D converter 2 samples the signal, converts it into a digital signal and outputs it. The output is branched and one is input to the delay circuit 3 and the other is input to the transversal filter 5 (hereinafter referred to as TF).
Abbreviated as 5). FIG. 4 is a flowchart showing the signal processing procedure of the control circuit 11, and an embodiment will be described with reference to FIG. The delay circuit 3 delays and outputs the input signal by a time equal to the time for which signal processing is performed by the TF 5, and inputs the delayed signal to one end of the adder circuit 4. The TF 5 uses the correction coefficient signal input from the control circuit 11 to tap gain To correct and output the input MUSE signal, which is input to the other end of the adder circuit 4. The adder circuit 4 adds the two inputs and outputs a waveform-equalized MUSE signal, which is output terminal The signal is inputted to the MUSE signal decoding processing circuit via 6 for signal processing. The TF 5 receives the control signal input from the control circuit 11 and outputs M from the input signal.
The VIT signal superimposed on the USE signal is detected and input to the control circuit 11.

As the control circuit 11, for example, a microcomputer is used. The control circuit 11 is provided with a memory 12 (RAM) and a memory 13 (ROM), and a predetermined reference signal (ideal The VIT signal) is stored, and the control circuit 11 fetches the VIT signal from TF5 as shown in S1 (step 1) of FIG.
It is written and stored in the memory 12. FIGS. 2A and 2B are explanatory diagrams of waveforms of the VIT signal. In the case where AM transmission is used and distortion in the transmission path is large, the conversion window of the A / D converter 2 or the like is used for the VIT signal. Amplitude level exceeds, (A)
As shown in the figure, it is assumed that the upper or lower part of the VIT signal is clipped and the clipped VIT signal is input. Reference numeral 7 is a waveform correction means, for example, a waveform memory 8
The output from the adder circuit 4 is branched and input, and the VIT signal clipped from the input is stored in the waveform memory 8 and read and input to the correction filter 9. I am trying.

In the control circuit 11, as shown in S2, T
The clipped VIT signal fetched from F5 and a predetermined reference signal stored in the memory 13 are calculated to obtain VI
Correction filter 9 for correcting the clipped portion of the T signal
Of the tap coefficient of the
To the coefficient storage unit 10 provided in the correction filter 9.
To memorize. Alternatively, the clipped VIT signal stored in the waveform memory 8 is passed through the correction filter 9 and input to the control circuit 11, and the control circuit 11 calculates a predetermined reference signal stored in the memory 13, VIT
You may make it obtain the tap coefficient of the correction filter 9 which corrects the clipped part of a signal, input this tap coefficient into the correction filter 9, and make it memorize | store in the coefficient storage part 10 provided in the correction filter 9.

The correction filter 9 changes the tap gain of the clipped VIT signal input from the waveform memory 8 with the tap coefficient stored in the coefficient storage unit 10, as shown in FIG.
As shown in (1), the clipped portion of the VIT signal is corrected and output, and is input to the control circuit 11. Control circuit 1
1, the VIT signal in which the clipped portion is corrected is fetched from the correction filter 9 as shown in S3, the data written in the memory 12 is updated and written and stored, and the same data is written in S4. Is read out and compared with a predetermined reference signal read out from the memory 13 to detect an error. As shown in S5, it is determined whether the error is less than or equal to a desired value, and if it exceeds the desired value, as shown in S6,
A correction coefficient is calculated according to the error and transferred to TF5,
The tap gain of the TF5 is changed, and the MUS is performed with the TF5.
The input signal of E is corrected and output, and input to the other end of the adder circuit 4. In the adder circuit 4, the input from the delay circuit 3 and T
The inputs from F5 are added, and the MUSE input signal is further waveform-equalized and output.

The output from the adder circuit 4 is branched and input to the waveform memory 8, and the VIT waveform-equalized by the waveform memory 8 is input.
The signal is stored, read out and input to the correction filter 9,
In the correction filter 9, the tap coefficient of the correction filter 9 is switched by the tap coefficient stored in the coefficient storage unit 10, and the VIT signal in which the clipped portion is corrected is input to the control circuit 11, and the control circuit 11 outputs the VIT signal. An error is detected by writing and reading in the memory 12 and comparing with a predetermined reference signal read out from the memory 13. If the error exceeds a desired numerical value, a correction coefficient is calculated according to the error and TF is calculated.
5, the waveform equalization is further performed, and if the error is equal to or smaller than a desired numerical value, the waveform equalization is ended.

[0012]

As described above, according to the present invention,
A waveform equalizer capable of correcting a clipped portion even when a clipped VIT signal is input due to distortion of a transmission line, improving waveform equalization accuracy, and maintaining speed. Can be provided, which contributes greatly to improving the performance of the waveform equalizer.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit of a waveform equalizer showing an embodiment of the present invention.

2A and 2B are waveform explanatory diagrams of a VIT signal.

FIG. 3 is a block diagram of an electric circuit of a waveform equalizer showing a conventional example.

4 is a flowchart showing a signal processing procedure of the control circuit 11. FIG.

[Explanation of symbols]

 1 Input Terminal 2 A / D Converter 3 Delay Circuit 4 Adder Circuit 5 Transversal Filter 6 Output Terminal 7 Waveform Correction Means 8 Waveform Memory 9 Correction Filter 10 Coefficient Storage Unit 11 Control Circuit 12 Memory 13 Memory 15 Control Circuit

Claims (2)

[Claims] 1. An A / D converter for sampling an MUSE input signal, a transversal filter for correcting the output of the A / D converter, an output from the transversal filter, and the A / D converter. Adder and a signal obtained by delaying the output of the adder to output a waveform-equalized MUSE signal, a circuit for branching the output from the adder circuit and inputting it to the control circuit, and a MUSE signal from the input V inside
IT signal is detected and calculated by comparing with a predetermined reference signal,
In a waveform equalization circuit that removes a waveform distortion component included in an input signal with a control circuit that changes the tap gain of the transversal filter based on the calculation result, a waveform correction unit is provided to perform the addition. The output from the circuit is input to the control circuit via the same waveform correction means, the clipped VIT signal transmitted by the same waveform correction means is corrected and input to the control circuit to perform waveform equalization. A waveform equalizer characterized in that 2. The waveform correction means includes a waveform memory and a correction filter, extracts the VIT signal from the output of the adder circuit, stores the VIT signal in the waveform memory, reads the VIT signal, and outputs the VIT signal based on the calculation result of the control circuit. The waveform equalizer according to claim 1, wherein the tap gain of the correction filter is changed to correct and output the clipped portion of the VIT signal.