JPH0516227B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a ghost removal device in a television receiver. [Prior art] Radio waves arriving directly from the transmitting antenna (desired waves)
When radio waves reflected from a building or the like are simultaneously received by a receiving antenna, a so-called ghost occurs, where the image of the desired wave and the image of the reflected wave appear out of sync. Ghosts that appear on television receivers are a major cause of deterioration in image quality, and various methods have been used in the past to try to eliminate or prevent ghosts. One of them is a ghost removal method using a transversal filter in the video band. This method removes ghosts by connecting a large number of delay elements in series, each with a minute delay time determined by the highest frequency component included in the video signal, and adding the outputs of each delay element using a coefficient circuit. This is to obtain a ghost compensation signal. An example of a ghost removal device using such a transversal filter is shown in a block diagram in FIG. In the figure, 1 is a video signal input terminal, 2 is a video signal output terminal, 3 is a transversal filter, 4 is a subtracter, 5 is a reference signal generation circuit, 6 is a differentiation circuit, 7 is a comparator, 8 is a shift register, 9 is a subtracter, 10 is a tap gain memory, 11
is a D/A (digital/analog) converter, 12
13 is a synchronization signal separation circuit, and 13 is a timing generation circuit. FIG. 2 is a block diagram showing details of the transversal filter 3 in FIG. 1. In the figure, 14 is an adder, 15 is a delay element with a delay time τ, and 16 is a tap amplifier. Note that the tap amplifier 16 is connected to the D/A from the tap gain memory 10.
This is an amplifier whose amplification gain can be varied by a control voltage input via a converter 11. First, an overview of the operation of the circuit configuration shown in FIG. 1 will be explained. The video signal input from input terminal 1 is sent to the next stage circuit from output terminal 2 via transversal filter 3, but if this sent video signal contains a ghost component,
We want to remove this component before sending it out. Therefore, it is necessary to detect ghost components contained in the video signal output from the filter 3. A technically easy method is to select the vertical synchronization signal from the video signal according to convenience and detect the ghost component superimposed on it (ghost component superimposed on the picture). When trying to detect ghost components, it is difficult to detect ghost components because the picture is a signal that constantly fluctuates). The video signal at the input terminal 1 is separated into a vertical synchronization signal by a synchronization signal separation circuit 12 .
The separated synchronization signal is sent to the timing generation circuit 13.
and is used as a reference for timing signal generation. The reference signal generation circuit 5, according to the timing instructed by the timing generation circuit 13,
The vertical synchronization signal is generated as a reference signal. Therefore, by subtracting the vertical synchronization signal contained in the video signal output from the filter 3 and the vertical synchronization signal as a reference signal output from the circuit 5 using the subtracter 4, the vertical synchronization signal in the video signal can be obtained. The ghost component superimposed on the signal is found. This ghost component is differentiated by a differentiating circuit 6, and the differential output is further digitalized (binarized) by a comparator 7, and this digital output is written into a shift register 8. The write timing is controlled by a timing generation circuit 13. According to the data read out from the shift register 8, the gain data stored in the tap gain memory 10 is modified. That is, data is read from the memory, modified in the subtracter 9 according to the data read from the shift register 8, and then written to the memory 10 again. In the above description of the conventional example, a case has been described in which a reference signal is set in advance and subtracted from the transversal filter 3, but the above-mentioned reference signal is not necessarily necessary. That is, in other conventional techniques, the output signal of the transversal filter 3 is directly supplied to the differentiating circuit 6. In this case, the first few taps malfunction due to the differential output caused by the vertical synchronization signal, so the tap gain values for these taps are fixed. When this process is finished, the tap gain data is then read from the memory 10 and the D/A converter 1
1, this analog voltage is applied as a control voltage to the tap amplifier 16 in the transversal filter 3 to control its amplification gain. As a result, the filter 3 outputs a video signal with reduced ghost components. By repeating the above process, the filter 3 will eventually output a video signal on which no ghost components are superimposed. The above is an overview of the operation of the ghost removal device shown in FIG. 1, but the explanation will be slightly supplemented with reference to FIG. 3 which shows the signal waveforms of the main parts in FIG. 1. In FIG. 3, (a) shows a vertical synchronizing signal as a reference signal output from the reference signal generating circuit 5, and F indicates its leading edge. (b) shows the vertical synchronizing signal contained in the video signal output from the transversal filter 3, and the shaded part shows the superimposed ghost component. (c)
A ghost component obtained as a result of subtraction in the subtracter 4 is shown, and (d) shows its differential output pulse P. A control signal (gate pulse) is generated from the timing generation circuit 13 at the timing of the leading edge F of the vertical synchronization signal.
If the signal is sent to the shift register 8 and the operation of the shift register 8 is started from that point, the binary output of the pulse P will be taken into the shift register 8 at a timing T time after the timing of the leading edge F. In this way, the shift register 8
Ghost information consisting of a series of bit numbers is stored and the information is sequentially output to the subtracter 9. Next, as mentioned above, the correction operation of the stored data in the tap gain memory 10 is started, but the address of the tap gain memory 10 and the number of the tap amplifier 15 in FIG. 2 (C ₁ , C ₂ . . . ) In this case, the tap gain data at the corresponding addresses are corrected in the order of the smallest delay time of the input signal, C ₁ , C ₂ , C ₃ , etc. It will be done. When the modification of the data in the tap gain memory 10 is completed, the new tap gain data is transmitted to each tap amplifier 16 of the transversal filter 3.
The data read from the tap gain memory 10 is converted into an analog voltage by the D/A converter 11 and applied to each tap amplifier 16. The applied voltage is held in a small capacitor (not shown), but once it has been applied to each tap amplifier, voltage application starts again from tap amplifier _C1 , and by repeating this, the capacitor is discharged. is prevented. The processes of ghost detection, data correction in the tap gain memory 10, and control voltage application to each tap amplifier as described above are performed once per field because the vertical synchronization signal is used as a reference signal. , is repeated until no ghosts are detected. In this way, ghosts can be gradually removed. Now, in such a ghost removal apparatus, the data in the tap gain memory 10 is constantly modified during ghost removal. Therefore, even in the absence of ghosts, the noise contained in the video signal causes the least significant bit of the data to oscillate to 0 or 1 every vertical period. For this reason, if the ghost removal operation is performed, there is a risk that the S/N ratio will deteriorate, or that ghosts will be added due to disturbances caused by radio waves reflected from airplanes, resulting in unstable operation. For this reason, in many cases, completion of ghost removal is detected and data modification in the tap gain memory 10 is thereby prohibited. An example of the above ghost removal completion detection device will be shown below along with drawings. This example is disclosed in Japanese Unexamined Patent Publication No. 56-149184, and the main points are as follows. In FIG. 4, 17 and 18 are comparators, 19 and 20 are reference voltage V _R and -V _R generation circuits, and 2
1 is an OR gate, 22 is a counter, and 23 is a 0 detection circuit. In the figure, +,
- A ghost signal, which is the output of the subtracter 4, is input to the input. At the comparator 17, the reference voltage
A positive ghost larger than V _R and a negative ghost smaller than the reference voltage -V _R are detected by the comparator 18 and output to the OR gate 21 .
This situation is shown in Figures 5a and 5b. a is the relationship between the ghost signal and the threshold of each comparator, b is the OR
The output of gate 21 is shown. The counter 22 counts the number of output pulses of the OR gate 21, and the 0 detection circuit 3
2 detects that the count value of the counter 22 is 0. If the count value of the counter 22 is 0, the ghost is sufficiently small, that is, the ghost is suppressed, and the 0 detection circuit 23 outputs a pulse.
This prohibits rewriting of the tap gain memory 10. The above prevents S/N deterioration and malfunction due to noise and the like. However, in this example, the threshold values V _R and −V _R of the comparators 17 and 18 are as follows.
There is a problem in that the setting method is difficult.
That is, the amount of remaining ghosts generally differs depending on the size of the input ghost, and the larger the ghost, the larger the amount of remaining ghosts. Therefore,
If a large value is selected for V _R , the ghost removal operation will end before sufficient suppression effect is obtained, and if a small value is selected for V _R , especially if a large ghost is input, it will disappear. Since the remaining amount was large, there was a problem that a signal indicating completion of ghost erasure was not output. Also, when considering LSI implementation, comparator 1
7 and 18 handle video signals, so high speed is required, and when converted to LSI, power consumption and size increase, making it inevitable to increase costs. [Object of the Invention] An object of the present invention is to eliminate the drawbacks of the above-mentioned prior art, to provide a ghost removal device that can stably detect the completion of ghost erasure regardless of the size of the input ghost, and that is easy to implement in LSI. be. [Summary of the Invention] In order to achieve the above-mentioned object, the present invention does not observe the remaining amount of ghost disappearance, but rather observes the shift of each tap gain from its initial value, and when the sum of the shift amounts saturates, ghost erasure is completed. The present invention is characterized in that erasing completion is detected without being affected by the size of the input ghost. [Embodiments of the Invention] Specific embodiments of the present invention will be described below with reference to the drawings. FIG. 6 is a block diagram showing one embodiment of the present invention, in which 24 is a detection circuit;
25 is a -1 detection circuit, 26 is a positive detection circuit, 27 is a 0 detection circuit, 28 is a negative detection circuit, 29 is a decoder, 30 is an up-down counter, 31 is an absolute value conversion circuit, 32 is an N or less detection circuit, and 33 is a This is a ghost erasure completion detection circuit. The operation of this circuit will be described below. It has already been mentioned that when the tap gain memory 10 is corrected, the data in the shift register 8 is shifted one bit at a time and output, and the tap gain correction circuit 9 corrects the synchronously read data in the tap gain memory 10. At this time, the output of the shift register 8 is detected to be +1 or -1 by the ±1 detection circuits 24 and 25, respectively. Furthermore, the data in the tap gain memory 10 read out for correction is positive, negative,
In the 0 detection circuits 26, 27, 28, positive and
Negative or zero is detected. 24-2
Each detection circuit up to 8 is led out to a decoder 29,
The decoder 29 controls the up count (up) and down count (down) of the up/down counter 30 according to the table below. When ghost removal starts, all tap gain memory 10 data is reset to 0.

〔Effect of the invention〕

As described above, the ghost erasure completion detection device according to the present invention considers only the change in the tap gain data and does not observe the remaining amount of ghost erasure.
Completion of ghost erasure can be correctly detected regardless of the size of the input ghost. Furthermore, as is already clear, this method can be realized using a low-speed digital circuit, and can be easily integrated into LSI, making it highly economical.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example of a ghost removal device, Fig. 2 is a block diagram showing details of the transversal filter in Fig. 1, and Fig. 3 is a waveform showing the signal waveform of the main part in Fig. 1. 4 is a block diagram showing a conventional ghost erasure completion detection device, FIG. 5 is a signal waveform diagram of the main part in FIG. 4, FIG. 6 is a block diagram showing an embodiment of the present invention, and FIG. The figure is a signal waveform diagram of the main part in Figure 6,
FIG. 8 is a graph showing the relationship between the count value of the counter 30 and the change in area of the shaded area in FIG. 7d, and FIG. 9 is a block diagram showing another embodiment of the present invention. Symbol explanation, 1...Input terminal, 2...Output terminal,
3...Transversal filter, 4...Subtractor, 5...Reference signal generation circuit, 6...Differentiating circuit,
7... Comparator, 8... Shift register, 9
...Subtractor, 10...Tap gain memory, 11...
...D/A converter, 12...Synchronization signal separation circuit, 1
3... Timing generation circuit, 14... Adder, 1
5...Delay element, 16...Tap amplifier, 17,
18... Comparator, 19, 20... Reference voltage generation circuit, 21... OR gate, 22... Counter, 23... 0 detection circuit, 24... 1 detection circuit,
25...-1 detection circuit, 26... Positive detection circuit, 2
7...0 detection circuit, 28...negative detection circuit, 29...
...Decoder, 30...Up-down counter, 3
1...Absolute value conversion circuit, 32...N or less detection circuit,
33... Ghost erasure completion detection circuit, 34... Frequency divider, 35... Inverter, 36... AND gate.

Claims (1)

[Scope of Claims] 1. A transverse filter, a tap gain memory that stores the tap gain of each tap amplifier included in the filter, and a predetermined reference signal included in the video signal that has passed through the filter, and a separate tap gain memory that stores the tap gain of each tap amplifier included in the filter. means for detecting a ghost component associated with the reference signal by comparing it with a generated reference signal; means for determining correction data to be applied to the tap gain of the tap gain memory in accordance with the detected ghost component; means for modifying tap gain data stored in said tap gain memory by data; and controlling the gain of each tap amplifier in said filter in accordance with the modified data to eliminate ghosts from the video signal passed through said filter. A ghost removal device comprising: means for removing a component; and correcting each tap gain in each correction operation using the correction data and tap gain data as data to be corrected read from a tap gain memory. A measuring means for calculating the sum of the amounts and a detecting means for detecting that the output of the measuring means is saturated are provided, and the correction operation of the tap gain memory is prohibited by the detection output from the detecting means. Ghost removal device. 2. The ghost removal device according to claim 1, wherein the detection means includes means for detecting that the sum of correction amounts of each tap gain in one correction is less than or equal to a certain number. A distinctive ghost removal device. 3. In the ghost removal device according to claim 1, the measuring means and the detecting means include first means for detecting the sign of the corrected data and a tap gain read out from the tap gain memory. a second means for determining the sign of the data; a means for inputting the outputs of the first and second means and outputting a counting control signal; and determining whether to count up or down depending on the sign of the counting control signal. A counter that is controlled and counts by inputting an address clock for the tap gain memory, means for determining the absolute value of the counted value of the counter, and means for detecting that the absolute value is smaller than a specific number. A ghost removal device characterized by: 4 Any one of claims 1 to 3
In the ghost removal device according to the above, if the control signal for inhibiting the correction operation of the tap gain memory is not output within a predetermined time, the input signal of the ghost removal device is directly outputted. Device.