JP2882798B2 - Ghost removal device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ghost removal device installed in a television receiver.

(Prior Art) In addition to signal components directly received by an antenna, a video signal received by a television receiver is slightly reflected through various reflection paths by moving objects such as trees, buildings, and vehicles in the vicinity. Signal components received with a delay are also included. Therefore, in general, multiple images appear in the reception screen even though the degree differs. A signal component that causes a multiplex image to appear in the reception screen is called a ghost, and a phenomenon in which the multiplex image becomes so large as to be unsightly and deteriorates the image quality is called a ghost disorder.

A ghost removing device for removing such a ghost includes a transversal filter for generating a pseudo ghost, a tap gain control circuit for controlling a tap gain of the transversal filter, and a signal combining circuit. . This transversal filter generates a pseudo ghost by simulating the mechanism of ghost generation based on multiple reflections of signal delay, attenuation and mutual addition by cascaded delay circuits, coefficient circuits, and an addition circuit. . This pseudo ghost is usually generated with the opposite polarity, added to the original received television signal in the signal synthesis circuit, and canceled with the ghost component contained therein.

In general, ghosts change the wavelength of the received radio wave due to switching of the reception channel, vehicles passing through
It changes every moment due to various factors such as a change in the traffic situation of a moving object such as a ship or an aircraft. Therefore, the tap gain of the transversal filter is adaptively controlled from time to time so as to always have the optimum value. For this adaptive control, a reference waveform for detecting a ghost occurrence state on the transmission side is inserted into the television signal. Further, the tap gain control circuit on the receiving side generates an optimal tap gain at the current time based on the analysis result of the distortion of the reference waveform extracted from the received television signal and the ghost removal result fed back from the subsequent detection unit, Supply to transversal filter.

(Problems to be Solved by the Invention) The above-mentioned conventional ghost removing apparatus is susceptible to various kinds of noise, and has a problem that the ghost removing function is reduced due to the noise.

(Means for Solving the Problems) The ghost elimination device of the present invention provides a tap gain generation circuit with noise reduction means for reducing noise appearing in a generated tap gain based on noise included in a received television signal. In addition, the apparatus is configured to effectively prevent the ghost removal function from being deteriorated due to the influence of noise.

As one of the noise reduction means, there is provided extraction reference waveform smoothing means for adding and averaging the extraction reference waveform over a predetermined number of appearances, and further, detecting the magnitude of noise included in the received television signal. An adaptive control means for dynamically changing the predetermined number of additions is provided.

As another one of the noise reduction means, there is provided a means for performing a Fourier transform on the generated tap gain, performing a low-pass filtering, and performing an inverse Fourier transform, and further detects the magnitude of the ghost component from the generated tap gain to obtain the low Adaptive control means for dynamically changing the bandpass band is provided.

As still another noise reduction means, there is provided a means for performing a beat removal process of a specific frequency component from the tap gain subjected to the Fourier transform.

 Hereinafter, the operation of the present invention will be described in detail with examples.

(Embodiment) FIG. 1 is a block diagram showing a configuration of a ghost removing apparatus according to an embodiment of the present invention, wherein 1 is a transversal filter for generating a pseudo ghost, 2 is a tap gain generating circuit, and 3 is a tap gain generating circuit. It is an addition circuit.

In the tap gain generation circuit 2, reference numeral 11 denotes an A / D converter;
Is an extracted reference waveform memory, 13 is a reference waveform detection circuit, 14 is a gate circuit, 15 is an averaging circuit, 16 is a level comparison circuit, 17 is a noise detection circuit, 18 is a reference waveform memory, and 19 is a difference calculation circuit. Further, reference numeral 20 denotes a Fourier transform circuit, 21 denotes a low-pass filtering circuit (LPF), 22 denotes a beat removing circuit, 23 denotes an inverse Fourier transform circuit, 24 denotes a ghost intensity detecting circuit, and 25 denotes a tap gain holding register.

As shown in FIG. 2, the transversal filter 1 of FIG. 1 includes a plurality of delay units 32a, 32b, 32c connected in cascade.
.. 32n, multipliers 33a, 33b, 33c... 33n for multiplying the respective outputs of these delay devices by tap gains, and a transformer including an adder 34 for adding the respective outputs of these multipliers A pseudo ghost based on a tap gain supplied from the tap gain control circuit 2 is generated from a versal filter portion, and an A / D converter 31 and a D / A converter 35 arranged before and after the versatile filter portion.

On the transmitting side of the television signal, a reference waveform for ghost detection is inserted at a predetermined position such as a vertical blanking period of the television signal. As the reference waveform, a signal subjected to band limitation by passing an isolated pulse waveform through a low-pass filtering circuit that simulates a transmission band of a television signal is selected. The predetermined reference waveform to be inserted on the transmitting side is held in advance in a reference waveform memory 18 in the tap gain generation circuit 2.

The reference waveform actually included in the received television signal is distorted by ghost and other transmission characteristics. Accordingly, a tap gain for generating a pseudo ghost can be generated by extracting a distorted reference waveform and calculating a difference between the distorted reference waveform and the reference waveform stored in the reference waveform memory 18 without distortion.

A reference waveform included in a predetermined portion of the received television signal is extracted from the television signal under the timing control of the reference waveform detection circuit 13 through the input terminal IN and the A / D converter 11 in FIG. Is written to the extraction reference waveform memory 12. This extracted reference waveform is read from the memory 12 and supplied to the averaging circuit 15 via the gate circuit 14. Averaging circuit
15 removes noise components included in the reference waveform by adding and averaging the extracted reference waveform supplied through the gate circuit 14 over a predetermined number of continuous waveforms. The noise detection circuit 17 detects a noise component included in the extracted reference waveform read from the extraction reference waveform memory 12, and instructs the averaging circuit 15 of the number of continuous additions according to the detected value.

The level detection circuit 16 compares the output of the extracted reference waveform memory 12 with the output of the averaging circuit 15, and if there is a difference of a predetermined value or more between the two due to the mixing of noise, the gate circuit
By blocking 14, the extraction reference waveform including a large noise component is prevented from being supplied to the averaging circuit 15.

The difference calculation circuit 19 calculates a difference between the extracted reference waveform supplied from the averaging circuit 15 and the reference waveform held in the reference waveform memory 18 to generate a time-series tap gain to be supplied to the transversal filter 1. I do. The generated tap gain is converted into a frequency component by a Fourier transform circuit 20, passed through a low-pass filtering circuit 21 and a beat removing circuit 22, and then restored to a time-series tap gain by an inverse Fourier transform circuit 23. It is supplied to the holding register 25.

The ghost intensity detection circuit 24 detects the intensity of the ghost being generated from the tap gain output from the difference calculation circuit 19. The pass band of the low-pass filtering circuit 21 can be changed as shown by a solid line and a dotted line in FIG.
It is dynamically changed according to the output of 17 and the output of the ghost intensity detection circuit 24. As the pass band of the low-pass filtering circuit 21 becomes narrower, the high-frequency component of noise included in the frequency component of the tap gain is removed, but the removal of the high-frequency component of the ghost becomes insufficient. Therefore, the pass band of the low-pass filtering circuit 24 is determined by considering the noise level and the ghost intensity, and is controlled to be narrower as the noise level is higher and the ghost intensity is lower.

The received television signal has beats caused by city noise such as radio waves of a specific frequency radiated from various electrical equipment, or a clock signal of a specific frequency output from a family computer connected to the television receiver. Easy to appear. The beat included in the tap gain output from the difference calculation circuit 19 is
As shown in FIG. 4, an abnormally large level appears in the specific frequency component ωj as compared with the preceding and following frequency components ωi and ωk. Such a beat is removed by the beat removing circuit 22 having the configuration shown in FIG.

The frequency component ω of the tap gain appearing at the input terminal in is
The signal is transmitted to the output terminal out while being delayed by one sampling time in the delay circuits 22a and 22b. The comparison circuit 22c compares the input to the delay circuit 22a with the output from the delay circuit 22b, and outputs "1" if the difference between them is equal to or greater than a predetermined value, and outputs "0" otherwise. I do. The comparison circuit 22d includes a delay circuit 22b
Is compared with the output to be output. If the difference between them is equal to or greater than a predetermined value, "1" is output. Otherwise, "0" is output.
Is output. The judgment circuit 22e outputs “0” from the comparison circuit 22c.
If the output of the comparison circuit 22d is "1", the delay circuit 22a
It is assumed that a frequency component due to the beat is appearing in the middle of steps 22b and 22b, and the holding operation to the delay circuit 22b is prohibited.

The frequency component of the tap gain that has passed through the low-pass filtering circuit 21 and the beat removing circuit 22 is restored to the tap gain by the inverse Fourier transform circuit 23, and is held in the tap gain holding register 25.
It is supplied to the transversal filter 1. The pseudo ghost generated by the transversal filter 1 is generated in a phase opposite to that of the ghost included in the received television signal, and is added to the ghost in the television signal by the addition circuit 3 in a destructive manner. The television signal from which the ghost has been removed is supplied from an output terminal OUT to a subsequent signal processing unit.

Processing such as difference calculation, Fourier transform, low-pass filtering, beat removal, and inverse Fourier transform may be realized by dedicated hardware, or may be realized by software processing by a processor.

Also, the case where a band-limited isolated pulse is used as the reference waveform has been described. However, another appropriate waveform such as a band-limited waveform of a staircase waveform can be used.

(Effect of the Invention) As described in detail above, the ghost elimination device of the present invention includes the noise reduction unit for reducing the noise appearing in the generated tap gain based on the noise included in the received television signal. With this configuration, it is possible to effectively avoid a reduction in the ghost removal function due to noise.

In particular, since Fourier transform is performed to perform noise removal processing on the frequency axis, there is an advantage that noise reduction such as removal of high-frequency noise components and removal of beat components can be easily performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a ghost removing device according to an embodiment of the present invention, and FIG. 2 is a transversal device shown in FIG.
FIG. 3 is a block diagram illustrating the configuration of the filter 1, and FIG.
Conceptual diagram illustrating the filtering characteristics of the low-pass filtering circuit 21 of the figure,
FIG. 4 is a conceptual diagram for explaining a frequency characteristic of a tap gain including a beat to be removed by the beat removing circuit 22 of FIG. 1, and FIG. 5 is an example of a configuration of the beat removing circuit 22 of FIG. FIG. 1 transversal filter, 2 tap gain control circuit, 3 addition circuit, 11 A / D converter, 12
Reference waveform memory, 15: Averaging circuit, 17: Noise detection circuit, 18: Reference waveform memory, 19: Difference calculation circuit, 20:
... Fourier transform circuit, 21 ... Low-pass filtering circuit, 22 ...
Beat removal circuit, 23: inverse Fourier transform circuit, 24: ghost intensity detection circuit, 25: tap gain holding register.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Bunzen Sasaki 2-2-1 Jinnan, Shibuya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Center (72) Inventor Miyazaki Tetsuro 2-2-1 Jinnan, Shibuya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Center (72) Inventor Reiichi Kobayashi 3-5-24 Miyahara, Yodogawa-ku, Osaka-shi, Osaka Within NEC Home Electronics Co., Ltd. (72) Inventor Tatsuya 3-chome, Miyahara, Yodogawa-ku, Osaka-shi, Osaka No. 5-24 Inside NEC Home Electronics Co., Ltd. (72) Inventor Michio Kobayashi 3-5-24 Miyahara, Yodogawa-ku, Osaka City, Osaka Prefecture Inside NEC Home Electronics Co., Ltd. (56) References JP-A Sho 62- 181579 (JP, A) JP-A-61-198978 (JP, A)

Claims (7)

(57) [Claims] 1. A transversal filter for generating a pseudo ghost from a received television signal, a combining circuit for combining a pseudo ghost generated by the transversal filter and a received television signal, A ghost removal apparatus comprising: a tap gain generation circuit that extracts a reference waveform included and calculates a difference between the extracted reference waveform and a held reference waveform to generate a tap gain and supplies the tap gain to the transversal filter. The gain generation circuit includes noise reduction means for reducing noise appearing in the generation tap gain based on noise included in the television signal, and the noise reduction means changes the extracted reference waveform over a predetermined number of times. An extraction reference waveform smoothing means for adding and averaging, wherein the extraction reference waveform smoothing means A ghost removing device comprising adaptive control means for detecting the magnitude of noise included in the television signal and dynamically changing the number of times of the addition. 2. A transversal filter for generating a pseudo ghost from a received television signal, a synthesizing circuit for synthesizing the pseudo ghost generated by the transversal filter and a received television signal, and A ghost removal apparatus comprising: a tap gain generation circuit that extracts a reference waveform included and calculates a difference between the extracted reference waveform and a held reference waveform to generate a tap gain and supplies the tap gain to the transversal filter. The gain generation circuit includes noise reduction means for reducing noise appearing in the generation tap gain based on noise included in the television signal, and the noise reduction means changes the extracted reference waveform over a predetermined number of times. An extraction reference waveform smoothing means for adding and averaging, wherein the extraction reference waveform smoothing means Means for comparing the level of each extracted reference waveform with the level of the reference waveform being smoothed, and excluding the extracted reference waveform from the target of averaging if there is a difference between the two by a predetermined value or more. A ghost removing device. 3. A transversal filter for generating a pseudo ghost from a received television signal, a combining circuit for combining the pseudo ghost generated by the transversal filter and a received television signal, A ghost removal apparatus comprising: a tap gain generation circuit that extracts a reference waveform included and calculates a difference between the extracted reference waveform and a held reference waveform to generate a tap gain and supplies the tap gain to the transversal filter. The gain generation circuit includes noise reduction means for reducing noise appearing in the generation tap gain based on noise included in the television signal, and the noise reduction means changes the extracted reference waveform over a predetermined number of times. An extraction reference waveform smoothing means for adding and averaging, wherein the extraction reference waveform smoothing means And adaptive control means for dynamically changing the number of times of addition by detecting the level of noise included in the television signal, and comparing the level of each extracted reference waveform with the level of the reference waveform being smoothed. A ghost eliminator characterized in that if there is a difference equal to or more than a predetermined value between the two, the extracted reference waveform is excluded from averaging targets. 4. The apparatus according to claim 1, wherein said noise reduction means includes low-pass filtering means for performing Fourier transform, low-pass filtering, and inverse Fourier transform on the generated tap gain. 4. The ghost removing device according to claim 2, 2 or 3. 5. The apparatus according to claim 1, wherein said low-pass filtering means includes adaptive control means for detecting a magnitude of a ghost component from said generated tap gain and dynamically changing a pass band. The ghost removing device according to claim 4. 6. A transversal filter for generating a pseudo ghost from a received television signal, a synthesizing circuit for synthesizing the pseudo ghost generated by the transversal filter and a received television signal, and A ghost removal apparatus comprising: a tap gain generation circuit that extracts a reference waveform included and calculates a difference between the extracted reference waveform and a held reference waveform to generate a tap gain and supplies the tap gain to the transversal filter. The gain generation circuit includes noise reduction means for reducing noise appearing in the generation tap gain based on noise included in the television signal, and the noise reduction means performs a Fourier transform on the generation tap gain, and Low-pass filtering means for performing low-pass filtering and inverse Fourier transform, and the Fourier-transformed A ghost eliminator comprising means for performing a beat elimination process of a specific frequency component from a step-up gain. 7. A transversal filter for generating a pseudo ghost from a received television signal, a synthesizing circuit for synthesizing the pseudo ghost generated by the transversal filter and a received television signal, and A ghost removal apparatus comprising: a tap gain generation circuit that extracts a reference waveform included and calculates a difference between the extracted reference waveform and a held reference waveform to generate a tap gain and supplies the tap gain to the transversal filter. The gain generation circuit includes noise reduction means for reducing noise appearing in the generation tap gain based on noise included in the television signal, and the noise reduction means performs a Fourier transform on the generation tap gain, and Low-pass filtering means for performing low-pass filtering and inverse Fourier transform, and the Fourier-transformed Means for performing beat removal processing of a specific frequency component from the tap gain, wherein the low-pass filtering means detects the magnitude of the ghost component from the generated tap gain and dynamically changes the pass band. A ghost removal device comprising: