JP2569960B2 - Waveform equalizer - Google Patents

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 of a video signal.

[0002]

2. Description of the Related Art The MUSE system is a high-definition band compression transmission system known as Japan's high-definition television developed by the Japan Broadcasting Corporation. In this MUSE system, a band-compressed analog signal is transmitted as a sample value. As a result, interference between sample values appears as ringing on the screen, causing deterioration in image quality. The transmission condition that does not cause the inter-sample value interference is to satisfy Nyquist's first criterion. Therefore, in the MUSE system, as a frequency characteristic from a transmission matching filter on the encoder side to an analog-to-digital converter on the decoder side,
It shows a point-symmetric frequency amplitude characteristic with the center of symmetry being 8.1 MHz where the amplitude is -6 dB, and has a characteristic that the phase is linear in the transmission band, that is, -6 dB.
It is necessary to have a roll-off characteristic. by the way,
In the MUSE system, which transmits a band-compressed analog signal as a sample value, transmission line distortion has a large effect on image quality. Therefore, there has been research and development on a waveform equalizer that can automatically remove transmission line distortion. For example, 1989 National Conference of the Institute of Television Engineers of Japan, Proceedings of the Lecture, p. 279, page 12-12, "Waveform Equalizer for Hi-Vision Receiver", Journal of the Institute of Television Engineers of Japan Vol.
0) Pages 71-76 "Development of Waveform Equalizer for MUSE Decoder" and other documents.

FIG. 3 is a block diagram showing a configuration example of a conventional waveform equalizer. In FIG. 3, reference numeral 1 denotes an input terminal of a MUSE signal detected by, for example, a tuner, and a MUSE signal supplied to an input terminal 1. Is converted into a digital signal by an analog-to-digital converter 2, and the digital signal is supplied to a filter (variable coefficient filter) 4 and a delay circuit 3. The variable coefficient filter 4 is a filter for producing a waveform distortion correction signal. The variable coefficient filter 4 convolves the digital signal supplied from the analog-to-digital converter 2 with the coefficient value and performs an addition circuit 5. To supply. The digital signal output from the analog-to-digital converter 2 is supplied to the adder circuit 5 with a signal delayed by the delay circuit 3. The digital signal is given to the digital signal by the delay circuit 3. The time delay is made equal to the time delay of the digital signal by the variable coefficient filter 4 described above. In the adder circuit 5, the MU supplied thereto via the delay circuit 3
The digital signal based on the SE signal is added to the waveform distortion correction signal output from the variable coefficient filter 4, and the MUSE signal with the waveform distortion suppressed is supplied to the MUSE decoder 6.

The coefficient of the variable coefficient filter 4 for producing the waveform distortion correction signal is based on the VIT signal extracted by the VIT signal extraction circuit 7 to which the MUSE signal output from the addition circuit 5 is supplied. And is changed by the generated signal. In other words, in the VIT signal extraction circuit 7 to which the MUSE signal output from the addition circuit 5 is supplied, the VIT signal inserted into the line of the specific line number of the MUSE signal for transmission line equalization (waveform equalization). A VIT signal based on a (negative) polarity impulse is extracted, and the extracted VIT signal is supplied to an error detection circuit 8.

The error detection circuit 8 outputs an error signal between the VIT signal extracted by the VIT signal extraction circuit 7 and the reference waveform supplied from the reference waveform generation circuit 9 as described above.
This is given to a multiplication circuit (magnification coefficient multiplication circuit) 10. The magnification coefficient multiplying circuit 10 generates a magnification coefficient signal obtained by multiplying the error signal by a magnification coefficient α, and supplies it to the addition circuit 11. Since the previous coefficient signal stored in the coefficient memory 12 is given to the adder circuit 11, the adder circuit 11 outputs a coefficient signal in a state where the previous coefficient signal has been corrected. It is supplied to the coefficient memory 12 and the variable coefficient filter 4. The above-described addition circuit 11 and coefficient memory 12 constitute an accumulation circuit 15. The variable coefficient filter 4 filters the signal based on the coefficient value based on the coefficient signal output from the integrating circuit 15 to generate a new waveform distortion correction signal, and supplies it to the adding circuit 5. The digital signal based on the MUSE signal supplied through the delay circuit 3 and the waveform distortion correction signal output from the variable coefficient filter 4 are added to the MUSE signal to suppress the MUSE signal with the waveform distortion suppressed.
It is supplied to the decoder 6 and the VIT signal extraction circuit 7.

In the same manner as described above, the error detecting circuit 8 to which the VIT signal extracted by the above-mentioned VIT signal extracting circuit 7 is applied, generates the VIT signal and the reference waveform supplied from the reference waveform generating circuit 9. The error signal is output and given to a magnification coefficient multiplication circuit (multiplication circuit) 10. The magnification coefficient multiplication circuit 10 generates a coefficient signal obtained by multiplying the error signal supplied thereto by a magnification coefficient α, and generates an integration circuit 15 And outputs a coefficient signal in which the previous coefficient signal has been corrected, and supplies it to the coefficient memory 12 and the variable coefficient filter 4 described above. The signal is filtered by the coefficient value based on the coefficient signal to generate a new waveform distortion correction signal, which is provided to the addition circuit 5, and the addition circuit 5 delays the signal. MU supplied via circuit 3
An operation of adding the digital signal based on the SE signal and the waveform distortion correction signal output from the variable coefficient filter 4 and supplying the MUSE signal with suppressed waveform distortion to the MUSE decoder 6 and the VIT signal extraction circuit 7. The coefficient is repeatedly updated in the direction in which the waveform distortion is suppressed, and the optimum coefficient is obtained, and the MUSE signal in which the waveform distortion is suppressed is generated by the MU.
This is supplied to the SE decoder 6. And
The magnification coefficient α affects the convergence stability and the convergence speed of the repetitive operation, and is set to a value satisfying the condition of 0 <α ≦ 1. That is, when the magnification coefficient α is small, the convergence stability is improved but the convergence speed is slow.On the contrary, when the magnification coefficient α is large, the convergence speed is increased but the convergence stability is deteriorated. The value of the magnification coefficient α is set to a value so that the convergence stability and the convergence speed can be adequately satisfied.

[0007]

The transmission path S
When the state of / N is good, there is no problem even if the magnification coefficient α is fixed as in the conventional example described above. Since it is not possible to determine whether the obtained error signal is due to the frequency characteristic of the transmission path or to a noise component, the convergence stability is deteriorated. That is, the magnification coefficient α set when the S / N of the transmission path is good.
In the case of (1), there is a problem that errors due to noise components are likely to accumulate in a state where the S / N of the transmission path is poor, and good equalization characteristics cannot be expected.

[0008]

According to the present invention, a variable coefficient filter for generating a waveform distortion correction signal and a transmission reference waveform signal which is time-division multiplexed with a video signal to be subjected to waveform equalization are extracted. A transmission reference waveform signal extraction circuit, a standard reference waveform signal generation circuit that outputs a standard reference waveform signal,
An error detection circuit that compares the transmission reference waveform signal output from the transmission reference waveform signal extraction circuit with a standard reference waveform signal and outputs an error signal, and a magnification that multiplies the error signal by a predetermined magnification coefficient A coefficient multiplying circuit, an integrating circuit that integrates an output of the magnification coefficient multiplying circuit and provides a coefficient signal to the variable coefficient filter, and a noise detection that detects a noise level of a video signal to be subjected to waveform equalization Circuit, and according to the detection result of the noise level output from the noise detection circuit, when the noise level in the video signal to be subjected to waveform equalization is high, the small scale factor Is multiplied by the error signal, and when the noise level in the video signal subject to waveform equalization is low, Large magnification factor provides a waveform equalizer comprising a magnification generation circuit that controls the magnification factor of the in such a manner is multiplied by the error signal in the road.

[0009]

According to the present invention, a magnification factor multiplying circuit includes a magnification generating circuit for performing an operation according to a noise level of a video signal to be subjected to waveform equalization detected by a noise detecting circuit.
Control the magnification factor at zero.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific contents of the waveform equalizer of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of one embodiment of a waveform equalizer of the present invention.
In FIG. 1, reference numeral 1 denotes, for example, MUSE detected by a tuner.
Signal input terminal, 2 is an analog-to-digital converter, 3 is a delay circuit, 4 is a filter (variable coefficient filter), 5 and 11 are addition circuits, 6 is a MUSE decoder, 7 is a VIT signal extraction circuit, and 8 is an error detection circuit. , 9 are reference waveform generating circuits, 10
Is a multiplication circuit (magnification coefficient multiplication circuit), 12 is a coefficient memory, 1
Reference numeral 3 denotes a noise detection circuit, 14 denotes a magnification generation circuit, and 15 denotes an integration circuit. For example, a MUSE signal supplied to an input terminal 1 to which a MUSE signal detected by a tuner is supplied is converted into a digital signal by an analog / digital converter 2. After being converted into a signal, the digital signal is supplied to a filter (variable coefficient filter) 4 and a delay circuit 3. The variable coefficient filter 4 is a filter for producing a waveform distortion correction signal. The variable coefficient filter 4 convolves the digital signal supplied from the analog-to-digital converter 2 with a coefficient value and performs an addition circuit 5. To supply. A signal obtained by delaying the digital signal output from the analog-to-digital converter 2 by the delay circuit 3 is supplied to the adder circuit 5. The time delay given to the digital signal by the delay circuit 3 is as follows. The time delay of the digital signal by the variable coefficient filter 4 is set to be equal to that of the digital signal by the MUSE signal supplied to the addition circuit 5 via the delay circuit 3 and the output from the variable coefficient filter 4. The MUSE signal with the waveform distortion suppressed is added to the MUSE signal
The signal is supplied to the USE decoder 6, the VIT signal extraction circuit 7, and the noise detection circuit 13.

By the way, the coefficient of the variable coefficient filter 4 for producing the waveform distortion correction signal is the same as that of the conventional waveform equalizer described above with reference to FIG.
Is changed by a coefficient signal generated by the integrating circuit 15 based on the VIT signal extracted by the VIT signal extracting circuit 7 to which the MUSE signal output from the multiplexing circuit is supplied. In other words, in the VIT signal extraction circuit 7 to which the MUSE signal output from the addition circuit 5 is supplied, the VIT signal inserted into the line of the specific line number of the MUSE signal for transmission line equalization (waveform equalization). A VIT signal based on a (negative) polarity impulse is extracted, and the extracted VIT signal is supplied to an error detection circuit 8.

In the error detection circuit 8, as described above, V
An error signal between the VIT signal extracted by the IT signal extraction circuit 7 and the reference waveform supplied from the reference waveform generation circuit 9 is output and supplied to a multiplication circuit (magnification coefficient multiplication circuit) 10. The magnification coefficient multiplying circuit 10 generates a magnification coefficient signal obtained by multiplying the error signal by a magnification coefficient α, and supplies it to the adding circuit 11, which multiplies the error signal by the magnification coefficient multiplying circuit 10. The magnification coefficient α has a value that changes according to the noise level of the MUSE signal. That is, in the noise detection path 13 to which the MUSE signal output from the addition circuit 5 is supplied, the noise level in the MUSE signal to be subjected to waveform equalization is detected. The output signal is supplied to the magnification generation circuit 14, and the magnification coefficient in the magnification coefficient multiplication circuit 10 is controlled by the magnification generation circuit 14 so that the magnification coefficient α multiplied by the error signal in the magnification coefficient multiplication circuit 10 is: It is assumed that the value changes according to the noise level of the MUSE signal.

FIG. 2 is a flowchart showing an example of the operation of the above-described noise detection circuit 13 and magnification generation circuit 14. In step (1), N samples are extracted.
In step (2), an average value X bar of N samples is obtained. In step (3), an average calculation of the absolute error is performed to obtain an average value eabs bar of the absolute error. In step (4), the absolute error Are set in accordance with the size of the average value eabs bar. FIG. 2 shows an example in which the magnification α has four stages, but it goes without saying that the stage of the magnification α can be set arbitrarily. It is desirable that the setting of the magnification be optimized experimentally. Note that the magnification generation circuit 14 is a multiplication circuit for the magnification coefficient 1 according to the amount of noise in the MUSE signal.
Since the magnification coefficient α multiplied by 0 with the error signal is changed stepwise, when the noise amount in the MUSE signal is small, the magnification coefficient α is set relatively large to increase the convergence speed. When the amount of noise in the MUSE signal is large, the magnification coefficient α is made relatively small to increase the convergence stability. In the waveform equalizer shown in FIG. 1, the input signal to the noise detection circuit 13 is the MUSE signal output from the addition circuit 5, but the noise detection circuit 13 checks the noise level in the MUSE signal. Since the circuit has only this function, the output signal of the analog-to-digital converter 2 may of course be used as the input signal of the noise detection circuit 13.

The magnification coefficient multiplication circuit 10 generates a coefficient signal obtained by multiplying the error signal by the magnification coefficient α generated by the magnification generation circuit 14 described above, and supplies the signal to the addition circuit 11. Since the previous coefficient signal stored in the coefficient memory 12 is given to the adder circuit 11, the adder circuit 11 outputs a coefficient signal in a state where the previous coefficient signal has been corrected. It is supplied to the coefficient memory 12 and the variable coefficient filter 4. The above-described addition circuit 11 and coefficient memory 12 constitute an accumulation circuit 15. The variable coefficient filter 4 filters the signal with a coefficient value based on the coefficient signal output from the integration circuit 15 to generate a new waveform distortion correction signal, and provides the same to the addition circuit 5. The digital signal based on the MUSE signal supplied through the delay circuit 3 and the waveform distortion correction signal output from the variable coefficient filter 4 are added thereto, and the MUSE signal in which the waveform distortion is suppressed is converted to the MUSE decoder 6 and the VIT signal. It is supplied to the extraction circuit 7.

The error detection circuit 8 to which the VIT signal extracted by the above-mentioned VIT signal extraction circuit 7 is applied in the same manner as described above, generates the VIT signal and the reference waveform supplied from the reference waveform generation circuit 9. The error signal is output and provided to a magnification coefficient multiplication circuit (multiplication circuit) 10. The magnification coefficient multiplication circuit 10 multiplies the error signal supplied thereto by the magnification coefficient α generated by the magnification generation circuit 14. A coefficient signal is generated and supplied to the addition circuit 11 in the accumulation circuit 15, and the addition circuit 11 outputs a coefficient signal in which the previous coefficient signal has been corrected, and stores it in the coefficient memory 1 described above.
2 and a variable coefficient filter 4. The variable coefficient filter 4 filters the signal according to the coefficient value based on the coefficient signal to generate a new waveform distortion correction signal, and supplies the corrected signal to the addition circuit 5. Then, the digital signal based on the MUSE signal supplied through the delay circuit 3 and the waveform distortion correction signal output from the variable coefficient filter 4 are added to the MUSE signal, and the MUSE signal with the waveform distortion suppressed is added to the MUSE decoder 6. The operation of supplying the MUSE signal to the VIT signal extraction circuit 7 is repeated, the coefficient is repeatedly updated in the direction of suppressing the waveform distortion, the optimum coefficient is obtained, and the MUSE signal with the suppressed waveform distortion is converted to the MUSE decoder. 6 is provided.

[0016]

As is apparent from the above description, when the amount of noise in the MUSE signal is small, the waveform equalizer of the present invention increases the magnification factor α relatively to increase the convergence speed. If the amount of noise in the MUSE signal is large, the magnification coefficient α is set to a relatively small value to improve the convergence stability. Since the magnification coefficient in the magnification coefficient multiplication circuit is controlled by the magnification generation circuit that operates according to the noise level of the signal, the amount of noise in the signal varies according to the transmission conditions such as the antenna, tuner, and weather according to the present invention. , The waveform equalization performance adapted thereto can be obtained, so that the present invention has advantages such as being suitable for mass production. The present invention can satisfactorily solve the conventional problems.

[Brief description of the drawings]

FIG. 1 is a block diagram of a waveform equalizer of the present invention.

FIG. 2 is a flowchart for explaining the operation of the waveform equalizer of the present invention.

FIG. 3 is a block diagram of a conventional waveform equalizer.

[Explanation of symbols]

 Reference Signs List 1 MUSE signal input terminal 2 Analog-to-digital converter 3 Delay circuit 4 Filter (variable coefficient filter) 5 Addition circuit 6 MUSE decoder 7 VIT signal extraction circuit 8 Error detection circuit 9 Reference waveform generation circuit 10 Multiplication circuit (multiplication coefficient multiplication circuit) 12 Coefficient memory 13 Noise detection circuit 14 Magnification generation circuit 15 Integration circuit

Claims (1)

(57) [Claims] A variable coefficient filter for generating a waveform distortion correction signal; a transmission reference waveform signal extraction circuit for extracting a transmission reference waveform signal time-division multiplexed with a video signal to be subjected to waveform equalization; A standard reference waveform signal generating circuit for outputting a standard reference waveform signal, and comparing the transmission reference waveform signal output from the transmission reference waveform signal extraction circuit with the standard reference waveform signal to output an error signal. An error detection circuit, a magnification coefficient multiplication circuit that multiplies the error signal by a predetermined magnification coefficient, an accumulation circuit that integrates an output of the magnification coefficient multiplication circuit and provides a coefficient signal to the variable coefficient filter, A noise detection circuit for detecting a noise level of a video signal to be equalized, and a waveform equalization target according to a noise level detection result output from the noise detection circuit. When the noise level in the video signal is high, the error signal is multiplied by a small scale factor in the scale factor multiplying circuit.
Further, when the noise level in the video signal to be subjected to waveform equalization is low, a magnification for controlling the magnification coefficient in such a manner that the large magnification coefficient is multiplied by the error signal in the magnification coefficient multiplying circuit. A waveform equalizer comprising a generating circuit.