JPH0231913B2 - - Google Patents

Description

[Detailed Description of the Invention] In recent years, when receiving television broadcasts,
Deterioration of received images due to various types of radio wave interference is becoming more and more problematic. In particular, the so-called ghost phenomenon, in which received images become double or triple, has become more common, mainly due to the rise in the height of buildings in urban areas. 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 diversity reception using horizontal stack antennas, but none of these measures are effective. It has not become widespread due to the above 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.

First, a configuration of a television receiver and a ghost removal device in which the present invention can be implemented will be described. FIG. 1 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 A is a video detection output whose amplitude is kept constant through automatic gain control by an intermediate frequency amplification circuit. This composite video signal A is
In the NTSC system, the signal ranges from 0 to 4.2MHz. In a typical 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 circuit 2 has a function of inputting the composite video signal A, removing the ghost signal, and then supplying the 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 ghost removal circuit 2 in FIG. 1. A feature of this device is that it uses a transversal filter 5.

As is generally well known, in a television transmitting and receiving system, if the transfer functions in the radio wave propagation system are H and S, and the transfer functions of the propagation system due to ghosts are G and S, then the total signal propagation system including ghosts is transferred. The functions are H, S・G, and S. On the other hand, since the transversal filter 5 can have any transfer function, ghosts can be removed by controlling it to have the inverse transfer functions G ^-1 and S of the propagation system due to ghosts.

The other parts in FIG. 2 are ghost filters for automatically controlling the weighting coefficients of each tap so that the transversal filter 5 has inverse transfer functions G ^-1 and S depending on the ghost at the time. It performs operations such as detection, calculation, weighting coefficient generation and storage. In the figure, A is the input composite video signal, B
is the ghost-removed output composite video signal,
D is a synchronization signal.

Detection of a ghost in a received television signal is performed by observing the flatness of the signal at the beginning (leading edge portion) 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, distortion of the 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 generating circuit for controlling the timing pulse generating circuit, which generates sampling pulses based on the horizontal and vertical synchronizing signals D in order to extract the signals of this portion.

The video signal B after being processed by the transversal filter 5 is added to the clamp A-D conversion circuit 7,
After clamping to eliminate DC fluctuations, the sampled portion is A-D converted by an A-D converter circuit to obtain ghost information, which is digitized and stored in the memory 10.
Accumulate in.

The arithmetic circuit 9 processes the ghost information stored in the memory 10 and generates a signal for controlling the weighting coefficient when extracting the output signal from each tap of the transversal filter 5. This part is usually configured using a microcomputer.
The weighting coefficient correction circuit 6 is used to actually generate and hold a weighting coefficient for each tap based on the calculation result of the calculation circuit 9, and normally the output of this calculation circuit 9 is a digital signal. , if the weighting coefficient is an analog signal, a D-A conversion circuit is required, and in that case it is also included.

In addition, since this detection → calculation → weighting is repeated many times using the so-called adaptive equalization method, the weighting coefficients are modified one after another many times, and the previous coefficients are stored in memory. 10 must be memorized. Furthermore, since the sampling frequency of the A/D converter circuit in 7 is handled as a video signal, it is necessary to be three times the band frequency, and in the NTSC system, 10.7MHz, which is three times the chroma subcarrier frequency, is often used. Therefore, this A-D conversion circuit is required to be high-speed. The memory 10 is also often high-speed, and a microcomputer is also used as the arithmetic circuit 9, so it is not very high-speed and is used only when the A-D conversion circuit is handling the vertical synchronization signal part. It can perform operations using so-called DMA (direct memory access), which is disconnected from the microcomputer.

In this way, this circuit device can be composed mainly of digital circuits including a microcomputer,
Since the transversal filter 5 also uses a solid-state delay line such as a CCD and has variable integration, it can be built into a television receiver at relatively low cost.

Here, ghost removal is performed by an adaptive equalization method that repeats detection → calculation → weighting, but as mentioned earlier, this method also uses the vertical synchronization signal in the video signal section. Since ghosts are detected based on the data at the beginning of the process, at least 1/60 sec is required for one processing.
In addition, in order to detect ghost signals with good S/N,
A method of averaging the signals of each vertical period is also used, but if averaging is performed six times, for example, 1/10 sec is required. If the ghost could be eliminated using this data by performing adaptive equalization 10 times, it would take 1/10 x 10 = 1 second. Furthermore, when weighting the output of an arithmetic circuit using a microcomputer or the like, it often interferes with the screen and makes it look ugly. In this way, during the equalization period, various disturbances occur to the screen, making it very sluggish.It would be fine if the period lasted for a short period of time, but it takes at least 1 second, and if nothing is done, the screen becomes quite unsightly. .

In order to eliminate this drawback, an apparatus shown in FIG. 3 was devised. As shown in FIG. 3, the ghost-containing video signal A, which is the output of the intermediate amplified video detection circuit 12, and the ghost-removed signal E are output from the ghost removal circuit 11 and indicate whether or not equalization is being performed. The resulting video signal B is switched by a switch circuit 13 and applied to a video signal processing amplification circuit 14 and a chroma signal processing amplification circuit 15. That is, during the ghost equalization period, the A signal is outputted, and once the equalization is completed, the B signal is output. Ghost removal circuit 1
1 is shown in FIG. 2, and a signal E indicating whether equalization is being performed or not is taken out from the arithmetic circuit 9. That is, the signal containing the ghost is A-D converted by the circuit 7, and then processed via the memory 10 by the arithmetic circuit 9, which is often a microcomputer or the like.
A weighting coefficient is added to the tap of the transversal filter 5, and this process is repeated, but ghost information always enters the arithmetic circuit during each equalization, and the equalization depends on the presence or absence of that ghost information. It is common practice to issue a signal to stop the microcomputer and stop the microcomputer, but you can use that signal by outputting it as E. This signal E is used to switch between A and B.

By the way, since the chroma signal is automatically gain controlled in the chroma processing circuit, the change before and after ghost removal is not the same as the change in the luminance signal. Therefore, unlike when there is no ghost, since the luminance signal and chroma signal are matrixed even after the ghost is eliminated, the ghost is removed, but the saturation, luminance, and contrast are changed. FIG. 4 shows this state. I is before ghost removal,
J indicates a luminance signal after ghost removal, k indicates a change in a chroma signal before ghost removal, and L indicates a change in a chroma signal after ghost removal. If the brightness, contrast, and saturation of the screen after ghost removal change, the screen becomes extremely unsightly. For example, the polarity of the ghost changes depending on the receiving channel.
I can think of many things. In this case, if the brightness, contrast, or saturation of the screen changes after ghost removal, the correction volume must be readjusted each time, which is extremely troublesome. The present invention aims to provide a ghost removal device that can automatically perform this adjustment, and one embodiment of the present invention will be described below with reference to the drawings.

In FIG. 5, 11, 13, 14, and 15 are the same as those in FIG. 3, so the same numbers are given and explanations are omitted. The intermediate amplified video detection circuit 16 includes a video intermediate frequency amplifier 16a and a detection circuit 16b.
An AGC detection circuit 16c is provided. There are two switch circuits, 13 and 17, which are switched in conjunction with signal E. During the ghost removal period, the switch circuit 13 is a-c, and the switch circuit 17 is f.
-d is connected, and at the end of ghost processing, b-c in the switch circuit 13 and fe in the switch circuit 17 are connected. The signal C after ghost removal is a composite video signal whose amplitude has been changed, as shown at J in FIG. If this signal is subjected to AGC detection by the AGC circuit 16c and the gain of the amplifier is controlled using the detection signal, the output signal of C can be a composite video signal having the same amplitude as before ghost removal.

As described above, according to the present invention, video demodulation adds marketable ghost removal without displaying an unsightly image during equalization on the screen, without changing brightness, contrast, or saturation. You can get the equipment.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional video demodulation device, FIG. 2 is a specific block diagram of the ghost removal circuit shown in FIG. 1, and FIG. 3 is a block diagram of a video demodulation device conceived prior to the present invention. Figure 4 is a waveform diagram for explaining the video demodulation device of the present invention, Figure 5 is a diagram.
The figure is a block diagram of a video demodulator according to an embodiment of the present invention. 16... Intermediate amplified video detection circuit, 11... Ghost removal circuit, 13, 17... Switch circuit, 1
4...Video signal processing circuit, 15...Chroma processing signal amplification circuit, 16c...AGC detection circuit, 16a
...Amplification circuit, 16b...Detection circuit.

Claims (1)

[Claims] 1 The output signal of a video intermediate frequency amplifier whose gain can be changed is detected by a detection circuit and applied to a transversal filter, and the ghost signal present at the beginning of the vertical synchronization signal is extracted from the output signal of this transversal filter. , the extracted signal is digitized and stored in a memory, the output of this memory is applied to an arithmetic circuit to generate a weighting coefficient control signal, and this weighting coefficient control signal is applied to a weighting coefficient correction circuit to control the transversal filter. The transversal filter is controlled to have an inverse transfer function of the propagation system due to the ghost signal by changing the weighting coefficient, and the output of the transversal filter and the signal before passing through the transversal filter are added to the switch circuit and selected. A signal indicating whether or not the ghost signal is being equalized is taken out from the arithmetic circuit to control the switch circuit, and while the ghost signal is being equalized, the signal before passing through the transversal filter is and when equalization of the ghost signal is completed, the output of the transversal filter is taken out, a switch circuit other than the above switch circuit is provided, and this other switch circuit is interlocked with the above switch circuit. During ghost signal equalization, the signal before passing through the transversal filter is added to the AGC detection circuit, and when equalization is completed, the output of the transversal filter is used as the input signal. A video demodulation device characterized in that outputs of a video signal processing amplifier circuit and a chroma processing signal amplifier circuit are added to the AGC detection circuit, and the gain of the video intermediate frequency amplifier is controlled by the output of the AGC detection circuit.