JPS58124377A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To eliminate variance of ghost erasing at each channel, by providing a high peak circuit between a clamp circuit and an A-D conversion circuit. CONSTITUTION:A video signal is inputted from a terminal D to a filter 11 for noise prevention, the clamp circuit 12, and the A-D conversion circuit 14. The high peak circuit 13 is inserted between the clamp circuit 12 and the conversion circuit 14. Thus, in a waveform as shown in T, the signal in A-D conversion is made steep at the leading edge as shwon in U through a high peak circuit. Even if the leading edge is varied between channels, the variance is absorbed in the high peak circuit, allowing to reduce the variance and to obtain the position (t) of ghost accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, the reception of television broadcasts has become increasingly problematic due to the increased deterioration of received images due to various types of radio wave interference. %, the received images are duplicated, mainly due to the rise of buildings in urban areas.

The so-called triple ghost phenomenon has begun to occur frequently. Countermeasures for this include the development of wall structures that prevent the reflection of radio waves from these buildings, higher directivity of receiving antennas, and diversity reception using bows and horizontal stack antennas. However, due to the complexity of operation and the increase in loss l-1, it is difficult for them to become widespread.

Therefore, there is a growing need to provide a fully automatic ghost removal system that can be built into television receivers at low cost.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a television receiver and a ghost removal device in which the present invention can be implemented will now 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 is a signal of .about.4.2 MHz in the NTSC system. In a normal television receiver, this composite video signal A is directly supplied to both the video signal processing and amplification circuit 3 and the ROM signal processing and amplification 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 ghost removal device 20 portion in FIG. 1. A feature of this device is that it uses a transversal filter 6.

As is generally well known, in a television transmission/reception system, the transfer function in the radio wave propagation system is )t(S),
If the transfer function of the propagation system due to ghosts is G (S), then the transfer function of the l·-tal signal propagation system including ghosts is H(S)·G (S). On the other hand, since the transversal filter 6 can have any transfer function, ghosts can be removed by controlling it to have an inverse transfer function G −' (S) of the propagation system due to ghosts.

The other parts in FIG. 2 are this transversal filter 5.
is the inverse transfer function G-1(S) depending on the ghost at each time
It automatically controls the weighting coefficient of each turn knob to have ghost detection and debugging.

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

Detection of ghosts in received television signals is performed at the 6th point before and after the beginning part (front part) of the vertical synchronization signal.
This is done by observing the flatness of the signal during period a in Figure S. Ideally, this portion of the signal can be regarded as a unit step function, and if there is a ghost, distortion of the step function is detected accordingly. For example, the location and size of a ghost is detected at each zumbling point. Reference numeral 8 denotes a timing pulse generation circuit for the control, which generates sampling pulses based on the horizontal and vertical synchronizing signals in order to extract the signals of this portion.

The video signal B processed by the transversal filter 6 is passed through a clamp A-D converter circuit, and after being clamped to eliminate DC fluctuations, the sampled portion is A-D converted by the A-D converter circuit. Ghost information is obtained, digitized, and stored in a memory 10.

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 6. This part is usually a microcomputer
Configure using.

The weighting coefficient correction circuit 6 is used to actually generate and hold weighting coefficients for each tap based on the calculation results of the calculation circuit 9, and since the output of the calculation circuit 9 is normally a digital signal, If the weighting coefficient is an analog signal, a D-A conversion circuit is required, in which case it is also included.In addition, this detection → calculation → weighting is performed repeatedly using the so-called adaptive equalization method. Therefore, the weighting coefficients are modified one after another many times, and it is necessary to store the previous coefficients in the memo IJ 10. Also, T
The sampling frequency of the internal A-D converter circuit is required to be three times the band frequency since it handles video signals, and in the NTSC system, it is 10.7MH which is three times the chroma sub carrier frequency.
z is often used. Therefore, this eight-way conversion circuit is required to be high-speed. Memo IJ 10 is also often used as a high-speed device, and a microcomputer is also used as the arithmetic circuit 9, so it is not that high-speed (the memory is only used when the A-D conversion circuit handles the vertical synchronization signal part). So-called DMA (Direct Memory Access) that disconnects 10 from the microcomputer.
It is possible to perform operations according to the following.

In this way, this circuit device can be constructed mainly of digital circuits including a microcomputer, and since the transversal filter 5 also has variable integration using a solid-state delay line such as COD, it can be used for TVs at relatively low cost. It is possible to incorporate it into a John receiver.

The above is an explanation of ghost removal as a whole, and the present invention is particularly designed to accurately detect the location of ghosts.

As explained above, ghosts in the received television signal are detected by observing the flatness in the beginning part a of the vertical synchronization signal, as shown in S in Figure 5. . T in FIG. 5 is an enlarged view of the beginning part a of the vertical synchronizing signal, showing a signal containing a normal ghost. Now, as mentioned earlier, this signal is A-D converted using a 10.7MHz clock, the data is input to the microcomputer, and the rise of the vertical synchronization signal is detected from the change in the data. At the same time, the position t of the ghost is determined.

It detects the ghost level @, 1 much more accurately than Niri, leaving the ghost and ghost undisappeared, or worse, causing system oscillation.

While accuracy is required in this way, the rise of signals currently being broadcast varies considerably depending on the broadcasting station, and ghost cancellation varies from channel to channel.

Therefore, the present invention was devised to reduce this erase variation.

FIG. 3 shows an example of this. The block shown in FIG. 3 is a detailed block diagram of the clamp circuit/A-D conversion circuit shown in FIGS. 2 and 7.

A video newsletter is input from the terminal. Reference numeral 11 is a filter for eliminating feedback noise, and reference numeral 12 is a clamp circuit, in which a clamped Shingetsu signal is usually input to the 1iA, -D converter. In such a configuration, the same thing as described above will occur. Therefore, the high peak voltage circuit 1 is connected between the clamp circuit 12 and the A, -D conversion circuit 14.
3 was inserted.

In this way, until now the waveform shown at T in Figure 5 is A.
-D Compatibility, as shown in U in Figure 5, the rise has become high peaked and steep, and even if the rise varies between channels, it is absorbed by the high peak, and the variation is small and accurate. This makes it possible to determine the location t of the ghost.

FIG. 4 shows a high-beam circuit, in which a video signal is input from terminal B, and the high peak is generated by a resonant circuit of a coil 16 and a capacitor 17 connected to the commit terminal of a transistor 15. The transistor 18 and the resistor 19 constitute a buffer amplifier, and a high-peaked signal is obtained from the terminal I.

As described above, according to the present invention, by providing the no-epeak circuit between the clamp circuit and the 8-D conversion circuit, it is possible to eliminate variations in ghost cancellation from channel to channel.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of a television receiver having a ghost removal device, FIG. 2 is a basic block diagram of a ghost removal device in an embodiment of the present invention, and FIG. 3 is a block diagram of the same device. FIG. 4 is a specific block diagram of a portion of the device shown in FIG. 3, and FIG. 5 is a waveform diagram for explaining the device. 61101 Transversal filter, 6...00 Weighting coefficient correction circuit, 7... Clamp circuit/A-D
Conversion circuit, 10...Memory, 9...
Arithmetic circuit, 0 8... Timing pulse generation circuit -, 11...
...Filter, 1211・Fist・ν・Clamp circuit,
13o...High peak circuit, 14...A-
D conversion circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 5 Figure 3 Figure 4

Claims (1)

[Claims] The received television coefficient is processed by a transversal filter, and a weighting coefficient correction circuit is applied so that this transversal filter has an inverse transfer function corresponding to the ghosts of the television signal.・A ghost detection circuit is provided in order to add a transversal filter KILI N signal and create a signal to be added to the weighting coefficient correction circuit from the video signal that is the output of the transversal filter, and becomes the input of this ghost detection circuit. A ghost removal device characterized by passing a video signal through a high peak circuit.