JPH0217985B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ghost removal device built into a television receiver.

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 heights of buildings in urban areas. Countermeasures have been taken such as developing wall materials that prevent radio waves from being reflected by these buildings, increasing the directivity of receiving antennas, and implementing diversity reception using horizontal stacks and antennas, but none of these measures are effective. Due to the above-mentioned complexity and rising cost, it has not become widespread.

Therefore, the present invention provides a fully automatic ghost removal system built into a television receiver at low cost.

First, the configuration of a television receiver and an outline of a ghost removal device in which the present invention is implemented will be explained.

FIG. 1 shows a part of the structure of a television receiver. In the figure, 1 is an intermediate amplified video detection circuit which amplifies and detects an intermediate frequency modulated signal from a tuner to obtain a baseband video signal. A shown in the figure is 0 to 4.2M in the NTSC system.
It becomes a Hz composite video signal. In a typical television receiver, signal A is directly supplied to both the video signal processing amplifier circuit 3 and the chroma signal processing amplifier circuit 4. Ghost reduction device 2 receives composite video signal A
After removing the ghost signal, the output signal has a function of supplying the ghost-free signal B to the circuits 3 and 4. C shown in the figure is supplied to a video display device (CRT, etc.) as a ghost-free signal.

FIG. 2 is a more detailed block diagram of the ghost removal device 2 shown in FIG. The feature of this device is that it uses a transversal filter 5.

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

The other parts in FIG. 2 are ghost detection, which automatically controls each tap so that the transversal filter 5 has an inverse transfer function G ^-1 (S) corresponding to the ghost at that time. It performs operations such as calculation, tap weighting coefficient generation, and storage.

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. Ghost detection is usually performed by observing the flatness of the signal before and after the beginning of the vertical synchronization signal. The signal in this part can be regarded as a unit step function, and if there is a ghost, the unit step function will be distorted accordingly, and the position and size of the ghost can be detected at each sampling point. 8 is a timing pulse generation circuit, which generates horizontal and vertical synchronization signals D in order to extract the signals of this part.
The sampling pulse is generated based on the 7
In this method, the video signal processed by the transversal filter 5 is clamped to eliminate DC fluctuations, and the sampled portion is converted into A-D by an A-D converter circuit.
Convert and digitize ghost information to memory 1
This is a clamp and A-D conversion circuit that accumulates 0.

The arithmetic circuit 9 processes the ghost information stored in the memory 10 and generates signals for controlling 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 coefficients for each tap of the transversal filter 5 based on the calculation results of the calculation circuit 9, and its output is usually 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, 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 not memorized. It is necessary to do so. In addition, since the A-D conversion circuit 7 handles video signals, the sampling frequency of the A-D conversion circuit 7 is 3 of the band frequency.
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. Similarly, the memory 10 is often a high-speed one, and the arithmetic circuit 9 is usually a microcomputer, so it is not very fast. Only the memory 10 is disconnected from the microcomputer, so-called DMA (direct memory access) operation is performed.

In this way, this device can be configured mainly with digital circuits including a microcomputer, and the transversal filter 5 can also be integrated using a solid-state delay line such as a CCD, so it can be used in televisions at a relatively low cost. It can be built into the receiver.

The present invention provides a ghost removal device for a television receiver using a transversal filter, in which an automatic gain control (AGC) voltage from a video intermediate frequency amplification circuit is applied to an A-D conversion circuit used to obtain ghost information. By switching connection and changing the ghost information processing method using information obtained by A-D converting the AGC voltage, stable ghost removal operation can be performed even when there is a lot of noise in the detected signal, and it can be performed in a short time when there is little noise. The object of the present invention is to provide a device that allows the user to perform a removal operation.

In the circuit shown in Figure 2, the leading edge of the vertical synchronizing signal is regarded as a unit stage function, and for ghost detection, approximately one horizontal period before and after it is A-D converted and transferred to memory within the sample time. This information is used as waveform information, and based on that information, the position and size of the ghost are calculated, and the tap weighting coefficient of the transversal filter is modified to create a filter with a transfer function opposite to that of the ghost generation system. In this case, when the received electric field strength becomes weak, ghost information cannot be obtained correctly due to noise contained in the video detection signal. Therefore, a stable ghost removal operation cannot be performed.

In order to reduce the influence of such noise, it is possible to average the waveform information obtained by A-D conversion many times, but since the vertical synchronization signal is detected as a reference signal for ghosts, the waveform information is It can only be obtained every vertical synchronization time, and as the average number of times is increased, the time required for ghost removal becomes longer.

Therefore, in the present invention, the amount of noise included in the video detection signal is equivalently judged by the IF-AGC voltage, and the number of times the waveform information is averaged is changed depending on the IF-AGC voltage, which is different from the conventional circuit. This is intended to reduce the instability of the ghost removal operation in a weak electric field, or to reduce the time required for the ghost removal operation in a field other than a weak electric field.

FIG. 3 shows the configuration of a ghost removal device according to an embodiment of the present invention. 5 is a transversal filter, and 6 is its tap weighting coefficient correction circuit.
7 is an A-D conversion circuit, 14 is a clamp circuit, and 8 is a timing pulse generation circuit, which generates a 3f _SC sampling clock in synchronization with the color subcarrier f _SC , and also generates the leading edge of the vertical synchronization signal. A pulse of approximately 1 horizontal period is generated at the center, and a pulse of approximately 7 horizontal periods is generated.
The A-D converted digital value is stored in memory 10.
The address for direct transfer is generated by the address counter. Reference numeral 9 denotes an arithmetic circuit that calculates the position and size of a ghost from the waveform information in the memory 10 to obtain tap correction information.

E is an input video detection signal containing ghosts, and F is an output video detection signal from which ghosts have been removed. 11 is the IF-AGC voltage G to the A-D converter 7
This is a level shift circuit that converts the level so that it can be input by switching to the conversion input terminal of.
12 is a switching circuit that switches between the video signal from the transversal filter 5 and the IF-AGC voltage, and 13 is a switching circuit that switches and outputs the A-D converted digital data onto the data bus.

FIG. 4 is a more detailed diagram of the switching part of the input signal to the A-D conversion circuit 7. Ghost information is obtained by observing flatness for about one horizontal period before and after the leading edge of the vertical synchronization signal. In the timing pulse generation circuit 15, a pulse I for extracting about one horizontal period near the leading edge of the vertical synchronization signal is generated by the vertical synchronization signal and the horizontal synchronization signal.
The microcomputer 20 is held at this pulse I. When this hold is applied, a hold response signal J is output from the microcomputer 20, and this signal J controls the switching circuit 12 to connect the input composite video signal E to the A-D conversion circuit 7 through the clamp circuit 14. . The frequency 3f _SC which is three times that of the color subcarrier in the A-D conversion circuit 7
The signal is sampled using the clock K and A-D converted. The digital data output is directly transferred to the memory 10 within the sampling time.
The bus buffers 16 and 1 perform this switching control.
It is 7,18. The address of the memory 10 to be transferred is generated by the address counter 19 using the clock pulse K and the pulse I, and the memory address is updated. The IF-AGC voltage is connected to the A-D conversion circuit 7 through the level shift circuit 11 and the switching circuit 12 except for about one horizontal period before and after the leading edge of the vertical synchronization signal. During this period, the microcomputer 20 controls the data in the memory 10 and the bus buffer 16, reads the data on the IF-AGC voltage G, and performs a tap correction operation on the transversal filter 5.

FIG. 5 illustrates the state in which the input composite video signal E and the AGC voltage G are connected to the A-D converter 7. With this configuration, one A-D converter 7
The calculation circuit 9 calculates the state of the AGC voltage G by multiplexing the
The waveform information processing method can be changed depending on the state of the AGC voltage G. In other words, when it can be determined that there is a lot of noise in the detected signal based on the AGC voltage, the waveform information obtained by A-D conversion is averaged many times to reduce the influence of noise, and when it can be determined that there is little noise, the waveform information obtained by A-D conversion is averaged. By reducing the number of times, processing time can be shortened.

By using multiple A-D converters in this manner, it is possible to construct a ghost removal device for a television receiver that performs stable ghost removal operation in a weak electric field and fast ghost removal operation in a strong electric field at low cost.

[Brief explanation of drawings]

1 and 2 are block diagrams showing the basic configuration of a ghost removal device, FIGS. 3 and 4 are block diagrams of a ghost removal device in an embodiment of the present invention, and FIG. 5 explains its operation. FIG. 5... Transversal filter, 6... Weighting coefficient correction circuit, 7... A-D conversion circuit, 8... Timing pulse generation circuit, 9... Arithmetic circuit, 10
...Memory, 11...Level shift circuit, 12
...A-D input switching circuit, 13...A-D output switching circuit, 14...clamp circuit, 15...timing pulse generation circuit, 16, 17, 18...bus buffer, 19...address counter.

Claims (1)

[Claims] 1 Equipped with a transversal filter that removes ghost signals contained in an input video signal and its tap weighting coefficient correction circuit, and by obtaining tap correction information from the output of the transversal filter and correcting its tap weighting coefficient. The analog-to-digital conversion circuit converts the synchronization signal portion of the video detection signal that has passed through the transversal filter during approximately one horizontal period before and after the leading edge portion of the vertical synchronization signal to remove ghosts contained in the television video signal. is connected to digitize the ghost information to obtain it, and during other periods, the IF-AGC voltage output is switched and connected to the analog-to-digital conversion circuit to equivalently detect the amount of noise included in the detection circuit. 1. A ghost removal device characterized in that the ghost information processing method is changed based on the AGC voltage information obtained by A/D conversion.