JPH0430231B2 - - 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 coming 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 explanation, the reference waveform is set in advance and subtracted from the transversal filter 3. However, the above reference waveform is not necessarily necessary, and even if the output of the transversal filter 3 is directly input to the differentiating circuit 6. good. In this case, the first few taps malfunction due to the differential output caused by the vertical synchronization signal, so it is necessary to fix the tap gain for these taps.

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 apparatus shown in FIG. 1, but the explanation will be slightly supplemented with reference to FIG. 3, which shows signal waveforms of important parts in FIG. 1.

In FIG. 3, A indicates a vertical synchronizing signal as a reference signal outputted 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. Ha is
The ghost component obtained as a result of subtraction in the subtracter 4 is shown, and D shows its differential output pulse P. When a control signal (gate pulse) is sent from the timing generation circuit 13 to the shift register 8 at the timing of the leading edge F of the vertical synchronization signal and the operation of the shift register 8 is started from that point, the binary output of the pulse P is as follows. The signal is taken into the shift register 8 at a timing T time after the timing of the leading edge F. In this way, shift register 8
stores ghost information consisting of a series of bit numbers and sequentially outputs the information to the subtractor 9.

As mentioned above, the correction operation of the stored data in the tap gain memory 10 is then started.
The addresses of the tap gain memory 10 and the numbers (C ₁ , C _{2 .} . .) of the tap amplifiers 16 in FIG. _C1 , _C2 , _C3 ...
In this order, the tap gain data at the corresponding addresses are modified.

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.

As previously explained, in such a ghost removal device, a gate pulse is supplied from the timing generation circuit 13 to the shift register 8 as a timing signal for starting the operation of the register. , it will be explained in detail below that it is extremely important not to make a mistake in the timing of gate pulse generation in order to achieve the effect of ghost component removal.

Figure 4A shows in particular detail only the circuit part that creates the gate pulses supplied to the shift register 8 from the video signal input to the terminal 1 in the circuit part M in Figure 1 as M'. It is a block diagram.

In the figure, 20 is a clamp circuit, 21, 2
2 is a sample hold circuit, 23 is an average value circuit, 24 is a comparator, 25 is an AND circuit,
26 is a gate pulse generation terminal, 27 is a synchronization signal separation circuit, and 28 is a timing pulse generation circuit.

FIG. 4B is a waveform diagram of each part signal in FIG. 4A. In the figure, the video signal is
Only the vertical synchronization signal is shown. F indicates the leading edge of the vertical synchronization signal, and E ₁ and E ₂ both indicate equalization pulses.

Refer to Figure 4 A and B. First, a video signal as shown in FIG. 4B is input to the video signal input terminal 1. Here, only the leading edge F of the vertical synchronization signal of the video signal is shown. This video signal is sent to sample and hold circuits 21 and 22 and a synchronization signal separation circuit 27 after the levels of the leading ends of the synchronization signals are equalized in a clamp circuit 20 . The output of the synchronization signal separation circuit 27 is input to a timing pulse generation circuit 28, and various timing signals indicated by A, B, and C are generated.

In the sample and hold circuit 21, the timing pulse A samples the pedestal voltage between the equalization pulse _E1 and the leading edge F of the vertical synchronization signal.
In the sample and hold circuit 22, the synchronization tip voltage between the vertical synchronization signal leading edge F and the equalization pulse _E2 is sampled by the sample pulse B. These voltages are averaged by the averaging circuit 23, that is,
1/2 of the amplitude of the vertical synchronization signal is determined and input to the comparator 24. On the other hand, comparator 24
The output of the clamp circuit 20 is input to the other input. Therefore, when the signal amplitude of the vertical synchronizing signal in the input video signal reaches a predetermined level 1/2, the output of the comparator 24 changes from low to high. Since there is a synchronizing signal for each horizontal period, by selecting only the vertical synchronizing signal part using the selection pulse C and the AND circuit 25, a desired gate pulse can be obtained.

The reason why we chose the point at which the output of the comparator 24 changes from low to high when the amplitude of the vertical synchronization signal reaches 1/2 of the predetermined amplitude is because the leading edge F of the vertical synchronization signal is not necessarily vertical. This is because, even in that case, the point in time when the rising edge of the leading edge F reaches 1/2 of the predetermined level is regarded as the point in time when the leading edge F starts. The selection pulse C is a mask pulse that selects the vicinity of the leading edge F of the vertical synchronization signal.

Regarding the generation method of the various timing pulses A, B, and C, as is clear from the matters described in the specification of Japanese Patent Application No. 57-72582, the input video signal is processed by the synchronization signal separation circuit 12 (No. 1), the synchronization signal is separated and only the synchronization signal is extracted, and from this, the vertical synchronization signal and a group of equalization pulses at 1/2H intervals (where H indicates the horizontal scanning period) existing in the vicinity of the vertical synchronization signal are extracted. By counting a predetermined number of equalized pulses, the equalized pulse _E1 shown in FIG.
It is only necessary to make it occur continuously.

FIG. 5 is a waveform diagram showing the timing of the gate pulse generated in the circuit of FIG. 4A in comparison with the vertical synchronizing signal.

After explaining the operation with reference to FIG. 4, a gate pulse G as shown in FIG. 5b is generated for the leading edge F of the vertical synchronization signal of the video signal containing the ghost in FIG. 5a. , are supplied to the shift register 8. Then, the shift register 8 starts operating,
Clock C ₁ , C ₂ , C ₃ , and C ₄ all take in low inputs up to 4 bits.

At clock _C5 , a ghost component (shaded area in Figure 5a) superimposed on the vertical synchronizing signal is detected, and the pulse output P shown in Figure 5c is input to high through the differentiator 6 and comparator 7. be taken in as. As a result, shift register 8
A series of ghost information captured in [10000]
becomes. This allows transversal filter 3
The gain of tap amplifier _C5 at is reduced and the ghost is gradually eliminated.

However, if a very large ghost is input or if impulse noise is mixed in by the ignition of the car, this gate pulse may occur at a position completely different from the leading edge F of the vertical synchronization signal.

That is, Fig. 6a shows the video signal near the vertical synchronizing signal part, and b shows the video signal in the vicinity of the vertical synchronizing signal part, and b shows the video signal after synchronizing and separating it into 1/2H.
The waveform of only the interval equalized pulses is shown.
It was previously mentioned that it is sufficient to count the equalization pulses using a counter (not shown), and after counting a predetermined number such as 6 if there are 6 equalization pulses, generate each timing pulse A, B, and C continuously. stated. However, a
As shown in the figure, there is impulse noise N in the TV signal.
is mixed in and exceeds the tip level of the synchronization signal Sy, this noise N is also considered to be a synchronization signal, and c
The result is an equalized pulse ′ as shown in . Noise N
However, the synchronous signals happen to be separated by 1H period from each other.
Assuming that it occurs between Sy and the equalization pulse,
The interval between the noise N and the synchronizing signal Sy becomes 1/2H, and as a result, even the synchronizing signal Sy, which would not otherwise have been extracted, is extracted as an equalization pulse', so that two more equivalent pulses are generated in c than in b. As a result, timing pulses A, B, and C are not located at the vertical synchronization signal, but at the equalization pulses that precede it.
It will occur at E ₀ . In this case, the timing diagram shown in FIG. 5 becomes as shown in FIG. 7.

In FIG. 7, a is an equalization pulse E ₀ in the video signal, and b is a gate pulse that was generated by mistake at an incorrect timing. A synchronizing signal as a reference signal generated separately from the equalization pulse E ₀ in the video signal is subtracted by a subtracter 4 (see FIG. 1) and differentiated by a differentiating circuit 6. Since the equalization pulse E ₀ has a narrower pulse width than the vertical synchronization signal serving as the reference signal, the output of the differentiating circuit 6 is as shown in c. That is, even if there is no ghost, if the gate generation timing is incorrect due to impulse noise, a differential output P' for correcting tap _C3 is generated in this case. As a result, the ghost removal device ends up adding ghosts instead of suppressing them.

The above explanation deals with the case where only one impulse noise is mixed in, but in general, many impulse noises are mixed in completely randomly, so gate pulses occur everywhere in the video signal, and even in picture signals, gate pulses are generated everywhere. Situations may also arise where the tap needs to be modified.

Furthermore, if a strong ghost exists, a picture signal will be mixed into the synchronization signal section, causing a malfunction of synchronization separation and causing the timing of gate generation to be incorrect.

Due to these circumstances, conventional ghost removal devices have the problem of causing unstable operation depending on the environmental conditions, resulting in a significant deterioration of image quality.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-described drawbacks of the prior art and to provide a ghost removal device that operates stably even in the presence of impulse noise and strong ghosts.

[Summary of the invention]

To achieve the above object, the present invention includes a transversal filter, a memory for storing tap gain of the filter as data, and a predetermined reference signal included in a video signal to be input to the filter. means for setting a time standard for detecting the location of the ghost component;
correction means for correcting the tap gain data stored in the memory according to the location of the detected ghost component according to the set time reference;
a control means for controlling the gain of each tap of the filter according to the corrected data; a shape determining means for determining whether the reference signal has a predetermined shape in light of timing positions before and after the reference signal; The ghost removal apparatus is constituted by means for prohibiting modification of the tap gain data stored in the memory when the shape determining means makes a negative determination.

If impulsive noise or a strong ghost exists, the shape determining means determines that the reference signal does not have a predetermined shape. This enables stable operation of the device.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 8 shows the main part of one embodiment of the present invention (i.e.
FIG. 2 is a block diagram showing a circuit portion added to a conventional ghost removal device according to the present invention. In the figure, 30 and 31 are D-type flip-flops, 32 is an inverter, 33 is an AND circuit, and 34 is a D-type flip-flop.
35 is the input terminal of the synchronous signal obtained by synchronous separation (the output of the synchronous signal separation circuit 27 in FIG. 4A), and 35 is the input terminal of the sample pulse A (timing pulse generation circuit
8 is a timing pulse A) input terminal, 36 is a sample pulse B (timing pulse B from the same circuit 28) input terminal, and 37 is a memory write control signal output terminal (write control to the tap gain memory 10 in FIG. 1). (a terminal that outputs a signal).

FIG. 9 is a waveform diagram showing signal waveforms at various parts in the circuit of FIG. 8.

The operation will be explained with reference to FIGS. 8 and 9. First, if the gate pulse is generated at the correct timing, that is, the synchronous separated output (34) shown in FIG.
It is input to each D input terminal of 0 and 31. Sample pulses A (35) and B (36) shown in FIG. 9A are input to the CK terminals of the D flip-flops 30 and 31 through terminals 35 and 36, respectively. Therefore, the outputs of the inverter 32 and the D flip-flop 31 go to high level in synchronization with each sample pulse A and B, respectively, as shown in c and e of FIG. 9A, and the output f of the AND circuit 33 also goes to high level. , the tap gain memory 10 can be rewritten.

Next, as in the case of Figure 9B, when the gate pulse is generated not at the normal timing position F but at a shifted timing position _E0 , the process exactly the same as that explained in Figure 9A is performed. After that, inverter 3
2 output c is high level, D flip-flop 3
The output e of 1 becomes low level, and the AND circuit 33
The output f becomes low level, and rewriting of the tap gain memory 10 is prohibited.

Furthermore, if the gate pulse is generated not at the normal timing position F but at a shifted timing position _E2 , as in the case shown in FIG. , the output of the D flip-flop 31 becomes high level, and rewriting of the tap gain memory 10 is also prohibited.

In this way, paying attention to the fact that there is a flat portion of sufficient length before and after the rising edge F of the vertical synchronizing signal that should be generated in synchronization with the gate pulse,
With a very simple circuit as shown in Figure 8,
It is possible to determine whether the gate pulse is generated at the correct timing.

Note that when the present invention is implemented, if impulse noise or a strong ghost exists, correction of the tap gain memory 10 is temporarily prohibited, which slows down the speed of ghost removal; however, the ghost is added instead. It is possible to avoid abnormal operations that have been seen in the past.

In the explanation so far, an example has been described in which a vertical synchronization signal is used as a reference signal, but the same applies to separately input reference signals such as 2T pulse and 2T bar. This is because these signals are normally detected based on the vertical synchronization signal.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a ghost removal device that solves the problems of conventional ghost removal devices, such as deterioration of the removal function and unstable operation when impulse noise and strong ghosts are present. This makes it possible to perform stable ghost removal operations even under adverse environmental conditions.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventionally known ghost removal device, Fig. 2 is a block diagram showing details of the transversal filter in Fig. 1, and Fig. 3 is a waveform diagram showing signal waveforms of the main parts in Fig. 1. , Figure 4A is a block diagram showing the gate pulse generation section in Figure 1, Figure 4B is a waveform diagram showing the signal waveforms of each part in Figure 4A, and Figure 5 shows the gate pulse and differential in normal operation. Figure 6 is a timing diagram showing the timing relationship between pulses, Figure 6 is a waveform diagram showing the video signal and its synchronization separation output, Figure 7 is a timing diagram showing the timing relationship between gate pulses and differential pulses in the case of malfunction, and Figure 8 is a timing diagram showing the timing relationship between gate pulses and differential pulses. FIG. 9 is a circuit diagram showing essential parts of an embodiment of the present invention, and FIG. 9 is a signal waveform diagram of each part in the circuit of FIG. Explanation of symbols 1...Video signal input terminal, 2...
...Video signal 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...
Synchronous signal separation circuit, 13... Timing generation circuit, 30, 31... D-type flip-flop, 32
...Inverter, 33...AND circuit.

Claims (1)

[Scope of Claims] 1. A transversal filter having a plurality of taps, the gain of each of which can be varied, a tap gain memory that stores the gains of the taps of the filter as data, and a tap gain memory that stores the gains of the taps as data; means for setting a time reference for detecting the location of a ghost component from a predetermined reference signal included in a video signal to be detected; Therefore, there is provided a modification means for modifying the tap gain data stored in the tap gain memory, a control means for controlling the gain of each tap of the filter according to the modified data, and a control means for modifying the tap gain data stored in the tap gain memory; shape determining means for determining whether or not the tap has a predetermined shape in light of the timing position; and means for prohibiting modification of the tap gain data stored in the tap gain memory when the shape determining means determines that the tap has a predetermined shape; A ghost removal device comprising: 2. In the ghost removal device according to claim 1, the reference signal is a vertical synchronization signal included in a video signal, and the shape determination means for the reference signal is configured to determine the shape of the vertical synchronization signal and the equalization immediately before it. a first circuit that generates a first sampling pulse between the pulses; and a second circuit that generates a second sampling pulse between the vertical synchronization signal and the immediately following equalization pulse.
a third circuit that samples the television signal or its synchronously separated output using the first and second sampling pulses; and a third circuit that logically judges these sampling results to determine whether or not the reference signal has a predetermined shape. A ghost removal device comprising a fourth circuit for determining.