JPS5887979A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To attain recommencing of control even if any video signal of dull rising is inputted, by the constitution that the relative relation between the weight coefficient and the weighting device of a transversal filter can be varied. CONSTITUTION:A video signal processed at a transversal filter 5 is applied to an A/D converting circuit 7 to obtain a digital video signal including ghost information and is stored in a digital memory 10. An operation circuit 9 processes a digital video signal including ghost information stored in the memory 10 and generates a signal to control the weight coefficient in picking up an output signal from each tap of the transversal filter 5. A coefficient correction circut 6 generates the weight coefficient of each tap based on the result of operation of the operation circuit 9 and stores it.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ghost removal device built into a television receiver using a transversal filter, and particularly relates to the coast signal detection and control portion of the transversal filter. It is something.

In recent years, when receiving television broadcasts, the deterioration of received images due to various radio wave interferences has become a problem. In particular, the main reason for the rise in buildings in urban areas is double received images.

The so-called triple ghost phenomenon has begun to occur frequently. Countermeasures against this problem include the development of wall construction materials that prevent the reflection of radio waves from these buildings, higher directivity of receiving antennas, and diaperity reception using horizontally stacked antennas, but none of these methods are effective. - It has not become widespread due to reasons such as complexity and rising costs.

Therefore, there has been an increasing need to provide a fully automatic ghost removal system that can be built into television receivers at low cost.

Without further ado, the configuration of a television receiver and a ghost removal device in which the present invention can be implemented will be described. 1st
The figure shows a part of the configuration of the television receiver. In the figure, reference numeral 1 denotes an intermediate amplified video detection circuit which amplifies and detects an intermediate frequency modulated signal from a tuner to obtain a baseband composite video signal A. This composite video signal A becomes a signal of ○ to 4.2 hh in the NTSC system.

In a normal television receiver, this composite video signal A is directly supplied to both the video signal processing amplifier circuit 3 and the chroma signal processing amplifier circuit 4. The ghost removal device 2 has a function of inputting the composite video signal A, removing the ghost component signal, and then supplying a ghost-free video signal B to the circuits 3 and 4. C shown in the figure is supplied to a video display device (such as a CRT) as a display signal without ghosts.

FIG. 2 is a more detailed block diagram of the portion of the ghost removal device 2 in FIG. 1. The % characteristic of this device is that it uses a transversal file.

As is generally well known, in a television transmitting and receiving system, if the transfer function in the radio wave propagation system is H(S) and the transfer function in the ghost propagation system is G(S), then
The transfer function of the total signal propagation system including ghosts is H(
S)・(, (S).On the other hand, since the transversal filter 6 can have any transfer function, if it is controlled to have the inverse transfer function G-'(S) of the propagation system due to ghosts, the ghost can be removed.

The other parts in FIG. 2 show that this trans-gusal filter 5 has an inverse transfer function G-'
Ghost detection, operation to automatically control the weighting factor of each tap to have S).

It performs operations such as generating and storing weighting coefficients. In the figure, A is an input composite video signal, B is a cost-removed output composite video signal, and D is a synchronization signal.

A ghost in a received television signal is detected by observing the flatness of the signal in approximately one horizontal period before and after the beginning (leading edge) of the vertical synchronization signal. Ideally, this portion of the signal can be regarded as a unit step function, and if there is a ghost, whether or not it is a unit step function is detected accordingly. For example, the location and size of a ghost is detected at each sampling point. Reference numeral 8 denotes a timing pulse generation circuit for controlling the timing pulse generating circuit, which generates a sampling pulse based on horizontal and vertical synchronizing signals in order to extract the signal of this portion.

The image signal B processed by the transversal filter 6 is added to the clamp A-D converter circuit 7, and after being clamped to eliminate DC fluctuations, the sampled portion is A-D converted by the human converter circuit. A digital video signal including ghost information is obtained and stored in the digital memory 1o.

The arithmetic circuit 9 processes the digital video signal containing the ghost information stored in the memory 1o and generates a signal for controlling the weighting coefficient when extracting the output signal from each tap of the transversal filter 6. This part is usually configured using a microcomputer. The weighting coefficient correction circuit 6 is for actually generating and holding a weighting coefficient for each tap based on the calculation result of the calculation circuit 9, and since the output of this calculation circuit 9 is normally a digital signal, If the weighting coefficient is an analog signal, a DA conversion circuit is required, and in that case it is also included.

This kind of detection, calculation, and weighting is performed repeatedly using a so-called adaptive equalization method, so the weighting coefficients are modified many times one after another, and the previous coefficients are It is necessary to memorize it in memo IJ10. Also, 7
The sampling frequency of the internal A-D conversion circuit must be at least twice the band frequency since it handles video signals.
In the NTSC system, the frequency is three times the Chromasub carrier frequency (
7) It is recommended to use 107■. Therefore, this A-D
Conversion circuits are required to be high-speed. Similarly, a high-speed memory 10 is used. On the other hand, when a microcomputer is used as the arithmetic circuit 9, the speed is not so high, so the memory 1o is disconnected from the microcomputer only when the A-D conversion circuit is handling the vertical synchronization signal part. memory access)
It is recommended to perform the following actions.

In this way, this circuit device can be constructed mainly of digital circuits including a microcomputer, and since the L.Lancebarzal filter 5 also has variable integration using a solid-state delay line such as COD, it has a relatively low cost. It can be built into a television receiver at low cost.

Next, the means for detecting ghost information by the A-D conversion circuit 7 will be explained based on the signal waveforms shown in FIG. In Fig. 3, O is the output of the transversal filter 6 in Fig. 2, which is a composite video signal in the al base band.
The leading edge portion of the vertical synchronization signal is illustrated. Determination as to whether or not there is a ghost signal is performed by detecting the presence or absence of distortion occurring before and after the leading edge portion of the vertical synchronization signal, which is indicated by a circle, as a reference.

The sampling pulse b indicates a pulse generated by the sampling pulse generation circuit 8 to extract the video signal during the detection period, and only this portion of the video signal digitized by the A-Di conversion circuit 7 is stored in the memory 10 by DMA operation. . If there is no ghost signal, the period of this sampling pulse b is flat except for the rising edge of the leading edge of the vertical synchronization signal.

If there is a ghost signal between the leading edge and ±IA horizontal deflection period, waveform distortion will be detected somewhere within the sampling pulse b period, and it will be the ghost signal of the rising edge of the vertical synchronizing signal. Conceivable.

C is an enlarged view of the rising portion of the leading edge of this vertical synchronization signal. In the case of an NTSC television signal, the bandwidth of the video signal is at most 4.21 ht, so when viewed under magnification, the same portion rises slowly as shown in the figure.

On the other hand, as mentioned above, when digitizing such a signal, the sampling clock must be at least twice the bandwidth, but here, for convenience, we use a clock with a frequency three times that of the chroma subcarrier (approximately 107 ■). Use signals. Figure d shows a sample extracted from this clock at regular intervals, and in this figure, approximately 3
A clock will be included. These sampling clocks are numbered A- from the left as shown in the figure. A-D
The leading edge portion of the vertical synchronizing signal of the video signals a and c at each sampling point A to K is sampled by the FI conversion circuit 7 and converted into a digital signal. Now, to simplify the explanation, each sampling value ′! The digital signal diagram resulting from the conversion to f-4 bits is shown in e.

The A-D converted signal e is the original video signal a,
It corresponds to c and includes all information that can be included in the video signal.

In reality, there are a number of clock pulses in addition to the one shown A- between them, with which a digitized signal is obtained that is sampled over the entire duration of sampling pulse b. All of them are stored in the memory 1o by DMA operation. In this way, the sampling clock has a frequency of 10. 1h, which is faster than the operating speed of the microcomputer for the arithmetic processing circuit 9, so it is directly stored in the memory 10 by DMA operation as described above.

The arithmetic circuit 90 microcomputer then reads the digital video signal from this memory 1o and processes it in the following order.

(1) Averaging information from several sampling pulse periods.

(2) Take the difference between them.

(3)) Weight each tap of the Lanceversal filter 6.

By repeating these operations (1) to (3), ghost signals are gradually erased. This corresponds to finding the transfer function G (S) of the ghost propagation system using the adaptive equalization method, as described above.

FIG. 3f is a differential signal obtained by subtracting the previous signal at each sampling point B-K of the digitized signal θ of e. Originally, this is done after the signal e is averaged as described in (1) above, but for the sake of convenience, it is shown here without being averaged. In the differential signal shown in f, negative values are shown in 2' complement representation. Looking at this, points F and G show large positive values, which can be recognized as rising portions of the leading edge. In addition, 52' at point B, '''-2' at point 0, '1' at point E, '-2' at point ■, 5+2' at point J, and '-3p at point J are all waveform distortions, that is, ghost signals. Therefore, the weighting coefficient of each tap of the transversal filter 6 corresponding to each of these points may be controlled in a direction that eliminates the distortion.

FIG. 4 shows an example of the transversal filter 6 with a feedback configuration and its correspondence. The filter 6 includes an adder 51, a unit delay element 62, and weighters 63. For example, if 5+3' is used as a weighting coefficient in the direction of eliminating distortion corresponding to '''-3' of the differential signal at point K, the weighter 63 at point K operates and outputs a signal that cancels out the distortion. is added to the adder 61, added to the input signal, removes the ghost signal, and outputs it. By repeating this operation, the transfer function G (S) of the propagation system due to the ghost signal is The transversal filter 6 can be provided in the filter 5.The weighter 63 is usually composed of a multiplier, and calculates and outputs the product of the video signal passed through the unit delay element 62 and the weighting coefficient signal. In this case, if point F is recognized as a rising edge, the weighted signal of weighter 53 of F is set to the maximum gain.Furthermore, in the tap where the difference signal is 'o#', the weighted signal is also 0', The output of weighter 63 is 0#.

In such a weighting coefficient calculation circuit 9 and correction circuit 6, as well as in the transversal filter 5, it is important to clearly know the time reference of the signal. That is, in the above example, the differential signal f has a value of 6' at point F.
, 14' at point G, and a larger value at point F, which was determined to be a rising point. However, the rising edge of the vertical synchronization signal is not always constant.

This can be greatly influenced by the reception conditions of each channel and the characteristics of the video detection circuit. Furthermore, its rise is also affected by ghost signals that are very close to each other. In a device like this that inputs a video signal and removes its ghost, it is practical to ensure that the ghost is removed stably no matter what kind of video signal with 9 is input. There is a need.

Therefore, in this device, for example, the above-mentioned point F is determined as the rising edge of the leading edge of the vertical synchronization signal, a weighting coefficient correction operation is performed on each tap, and the next weighting coefficient correction operation is performed based on the result. It is okay if the waveform caused by the ghost signal decreases each time the process is repeated, but if the distortion does not decrease below a certain limit no matter how many times it is performed, then Now, the weighting coefficient of each tap of the transversal filter and its output state can be changed, such as determining the G point instead of the F point as a rising edge and redoing the weighting coefficient correction operation. It is characterized by doing so.

These series of steps are performed in a device such as the present device, which uses a microcomputer as the arithmetic circuit 9 and the weighting coefficient correction circuit 6 to read the digitized video signal from the memory 10, process it, and correct the weighting coefficient. This can be easily implemented in the ghost removal device. That is, when outputting a weighting coefficient signal based on the differential signal f as shown in FIG. , instead of inputting the weighting coefficient at one point to the mechanical weighter 53, switch 1
It is sufficient to control the microcomputer by switching 1 to input the shift by 1 to the weighter 63 of J, and this can be done by software without changing the wiring on the hardware.

Of course, by shifting at one point, the correspondence between all weighting coefficients and weighters will be shifted. Of course, the switching of the coefficient signal to the weighter 53 can also be performed by software.

Still another means is to set the weighter 53 of the machine to the maximum gain of 16 instead of setting the weighter 63 of F to the maximum gain when the F point is determined to be a rising edge as described above. It is. That is, the output of the weighter 53 with the maximum gain becomes the main video signal, and the relative relationship between it and the output of the weighter 53 at each distortion point (which becomes a ghost correction signal) is changed.

As described above, by configuring the relative relationship between the weighting coefficient and the weighting device of the traversal filter to be variable as in the present invention, it is possible to perform redo control no matter how slow the rise of the video signal is input. By doing so, a ghost removal device with great practical effects can be obtained. Furthermore, the present invention can be implemented by changing the control program of the microcomputer, does not involve any change in hardware, and can be implemented at a cost comparable to that of the prior art.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television receiver in which a ghost removal device according to an embodiment of the present invention can be used;
FIG. 2 is a block diagram of the ghost removal device, and FIG. 3 is a waveform diagram and signal diagram for explaining its operation.
FIG. 4 is a circuit diagram of an example traversal filter used in the same device. 6... Traversal filter, 6... Weighting coefficient correction circuit, 7... Clamp/A-D conversion circuit, 8... Timing pulse generation circuit, 9...
...Arithmetic circuit, 10...Memo IJ-111・Mountain・
·switch. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3

Claims (1)

[Claims] A transversal filter receives a baseband video signal extracted from a received television signal and a weighting coefficient signal of each tap and outputs a video signal from which ghosts have been removed, the video signal from which ghosts have been removed and at least the baseband signal are input. An analog device that outputs a digital video signal by inputting a clock that is twice the bandwidth of the video signal of the band and pulses for extracting the portions before and after the leading edge position of the vertical synchronization signal in the video signal as the center. a digital converter, a memory that temporarily stores the digital video signal, and an arithmetic circuit that receives the digital video signal and calculates and outputs a weighting coefficient signal for each tap of the transversal filter; A ghost removal device characterized in that a ghost removal state can be selected by changing the relative relationship between the weighting coefficient signal of each tap, which is an output of an arithmetic circuit, and the output state from each tap of a transversal filter. .