JPS59212084A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To perform ghost elimination speedily even when a ghost component is large by varying the increase/decrease amount of tap coefficients of a transversal filter according to how large the ghost component is. CONSTITUTION:An input video signal arriving at an input terminal 1 is inputted to the transversal filter 2 and a subtracter 3, and also inputted to a timing circuit 6 and a ghost detecting circuit 4b. The ghost detecting circuit 4b generates the difference signal of the leading edge part of a vertical synchronizing signal by the video signal applied to an A/D converter 7 to input the difference signal to a correlator 10, and the difference component due to the falling of the synchronizing signal and a difference component due to a ghost are generated by the output video signal of the subtracter 3 and applied to the 1st and the 2nd comparators 12a and 12b respectively. When a signal indicating the presence of the ghost is outputted only from the 1st comparing circuit 12a, it is judged that the ghost component is small, and when signals indicating the presence of the ghost are outputted from both comparing circuits, it is judged that the ghost component is large.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ghost removal device using a transversal filter, and an object thereof is to shorten ghost removal time.

Conventionally, the ghost phenomenon, which is a reception disturbance of television receivers, occurs because the direct wave of the television broadcast signal and the reflected wave from buildings etc. are overlapped and received.
To remove the ghost that has occurred, you must find out the delay time, strength, and phase of the ghost appearing on the screen in some way, and find out the same amplitude as the ghost component contained in the television composite video signal obtained by detecting the received radio wave. The ghost correction signal may be generated at the time position of the ghost component, and the ghost correction signal may be subtracted from the video signal.

Various ghost removal devices based on the above-mentioned principle have been proposed in the past, but devices using transversal filters have recently been in the spotlight.

By the way, a conventional transversal filter basically consists of a tapped delay element in which a plurality of CODs are connected in series, and a plurality of multipliers that multiply the output of each tap by the tap coefficient of each tap. and an adder that calculates the sum of the outputs of each multiplier to obtain a ghost correction signal.

Note that the transversal filter includes each of the above-mentioned CCDs.
Instead, a system has been devised in which a plurality of sample and hold circuits are provided, and each multiplier is formed by a capacitor charging/discharging circuit.

In other words, the transversal filter performs tap gain weighting and delay addition on the input signal, and when used in a ghost removal device, it has the advantage of being able to simultaneously control two parameters, the amplitude and delay time, of the ghost correction signal. ing.

A conventional ghost removal device using a transversal filter is, in principle, configured as shown in Fig. 1, from the video detection circuit of the television receiver to the input terminal (
The television composite video signal derived in step 1), that is, the input video signal, is input to a transversal filter (2) and a subtracter (3), and the subtracter (3) combines the input video signal and the transversal filter (2). A television composite video signal, ie, an output video signal, is formed and output by subtracting and synthesizing the ghost correction signal output from the.

Furthermore, the input video signal and the output video signal are input to a ghost detection circuit (4a).
) calculates the correlation function between the digital conversion signal of the leading edge of the vertical synchronizing signal of the input video signal and the ghost information signal obtained by binarizing the leading edge of the vertical synchronizing signal of the output video signal depending on the presence or absence of ghosts, A coefficient switching signal is repeatedly output to the coefficient switching circuit (5a).

Based on the coefficient switching signal, the coefficient switching circuit (5a) repeatedly increases or decreases the coefficient of each tap of the transversal filter (2) by a predetermined amount until the ghost is removed from the output video signal. is corrected according to the ghost component.

In other words, the input video signal when calculating the correlation function is
, when the output video signal is Ek, the correction value CJ of the υ-th tap coefficient of the first tap of the transversal filter (2) is controlled by the method shown by the following equation (1).

It shows one increase/decrease of the tap coefficient.

The control method using the method of equation (1) is based on the MAE of the adaptive automatic equalization algorithm in digital signal processing.
What is known as the (mean absolute error) method means taking the sign of the result of a correlation operation between the input video signal Xk and the binary signal of the output video signal Elc, that is, a signal indicating positive or negative. If the correlation calculation result is positive, the transversal filter (
The tap coefficient of filter (2) is increased, and conversely, if the result of the correlation calculation is negative, the tap coefficient of filter (2) is decreased, and the ghost correction signal is corrected according to the ghost component.

In order to form a ghost→presence signal, the ghost detection circuit (4a) includes a differential circuit that outputs a differential signal of the leading edge of the vertical synchronization signal of the output video signal, and a differential circuit that determines the presence or absence of the differential signal and ghost. A ghost presence information signal indicating the presence of a ghost is output from the comparison circuit while the level of the difference signal is higher than the level of the reference signal made of the threshold signal of the comparison circuit.

Note that since the polarity of the ghost component changes between positive and negative, the comparator circuit is provided with a comparator for positive polarity and a comparator for negative polarity.

However, the reference signal of the comparison circuit is set to a signal at a detection threshold level for detecting the presence or absence of a ghost component in order to determine whether or not there is a ghost component. The one-time increase/decrease of the original tap coefficient is set to a predetermined amount A that does not cause the ghost correction signal to increase rapidly, and when the ghost component is large, it is necessary to repeatedly correct the tap coefficient.
The disadvantage is that it takes a long time to remove ghosts.

This invention was made with the above points in mind,
A television composite video signal is input to a transversal filter, a tap coefficient of the filter is increased or decreased to form a ghost correction signal, and the correction signal and the composite video signal are combined to eliminate the ghost component of the composite video signal. A ghost removal device for removing a ghost signal includes a difference circuit that obtains a difference signal of a leading edge of a vertical synchronization signal of a composite signal of the correction signal and the composite video signal, and a plurality of reference signals each having a different level from the difference signal. a plurality of comparison circuits that compare and output a ghost signal when the level of the difference signal is large; and a plurality of comparison circuits that determine the magnitude of the ghost component from the number of human inputs of the ghost signal, and output terminals corresponding to the number of comparison circuits. a determination circuit that selectively outputs a determination signal from the above, and a coefficient switching circuit for the number of comparison circuits to which the determination signal is alternatively input and increases or decreases the tap coefficient by a set amount, and The present invention provides a ghost removal device characterized in that the setting amount of each of the coefficient switching circuits is different, and the increase/decrease of the tap coefficient can be changed by switching depending on the magnitude of the ghost component.

Therefore, according to the ghost removal device of the present invention, the number of comparison circuits that output ghost signals is increased or decreased according to the magnitude of the ghost component, and the coefficient switching circuit is alternatively selected. When the component is large, the coefficient switching circuit 9 with a large setting amount is selected, so that even when the ghost component is large, ghost removal can be performed quickly, and the ghost removal time can be significantly shortened.

Next, this invention will be explained in detail with reference to the drawings from FIG. 2 onwards showing an embodiment of the invention.

As shown in FIG.
), and is also input to the analog/digital conversion circuit (hereinafter referred to as A/D conversion circuit) (7) of the timing circuit (6) and the ghost detection circuit (4b).

The timing circuit (6) generates the waveform a shown in FIG.

As shown in b, the vertical synchronization signal is separated from the input video signal, and one flat horizontal section of the leading edge of the vertical synchronization signal for ghost detection is extracted, or it is separately inserted into the input video signal. A reference waveform signal for ghost removal is extracted.

Note that the waveform in FIG. 3 is a waveform obtained by enlarging and inverting waveform a in section H.

2LTC, the timing circuit (6) is 10.7MH2 or l4,3 synchronized to the subcarrier of the color signal.
Extraction and formation of the MHz clock signal is also performed simultaneously with the above-mentioned extraction.

By the way, the waveform of the input video signal and the output video signal on which the ghost is superimposed has a waveform in section H with nine steps due to the ghost g, as shown in FIG. Contains information such as magnitude, delay time, and phase.

Still, the A/D conversion circuit (7) converts only the section (2) of the input video signal into an N-bit digital signal based on the clock signal of the timing circuit (6).

That is, of the input video signal on which ghosts are superimposed, only the flat section H at the leading edge of the vertical synchronization signal is converted into a digital signal every field period or every frame period by the A/D conversion circuit.

Further, the digital signal of the A/D variable conversion circuit is input to a cyclic integration circuit (8), and the noise of the digital signal is reduced by cyclic integration of the integration circuit (8).

Next, the digital signal whose noise has been reduced by the cyclic integration circuit (8) is input to a one-clock difference circuit (9), and the difference circuit (9) inputs the digital signal of the cyclic integration circuit (8) at time (t+l). The signal is added to the two's complement calculation value signal of the digital signal of the cyclic integration circuit (8) at time t, and the N-bit digital signal Xlc consisting of the one-clock difference signal of the horizontal section H described above is obtained. The signal Xk is input to the correlator f'll.

On the other hand, the output video signal of the subtracter (3) is
If the horizontal section H of the transversal filter is disturbed by the ghost g as shown in FIG. , the difference component p due to the falling edge of the synchronization signal
A difference signal having a difference component P' caused by the ghost g is formed and outputted under the control of the clock signal of the timing circuit (6).

And the difference signal is the first one. Second comparison circuit (128).

(+2b), and at this time, the first comparison circuit (12
The level of the first reference signal consisting of the threshold signal of a) is:
The level indicated by the broken line in FIG. 4 (1)), that is, the detection threshold level L for the presence or absence of a ghost component, similar to the conventional comparison circuit.
a, and the level of the second reference signal consisting of the threshold signal of the second comparator circuit (12b) is the level Lb, which is higher than the level indicated by the dashed line in FIG.
is set to .

Therefore, when the level of the difference signal is lower than level La, no signal is output from both comparison circuits (12B) and (12b), and when the level of the difference signal is lower than level L1], the first comparison circuit (12a) When the level of the difference signal is greater than the level Lb, the ghost presence →→ signal is output from both comparison circuits (12a) and (12b).

Furthermore, the output signal of the first comparison circuit (12a) is input to the determination circuit (1] and memory 04), and the second comparison circuit (
The output signal of 12b) is inputted only to the determination circuit 03.

The ghost presence information signal of the first comparison circuit (12a) is written to the memory 04) at the timing of the clock signal of the timing circuit (6), and is also written to the memory 04) at the timing of the clock signal of the timing circuit (6).
) is read out to the correlator at), and the signal of sgn Ek in equation (1) is output from the memory 04) to the correlator a1.

Therefore, the correlator section uses the Xk signal output from the 1-clock difference circuit (9) and the sg signal output from the memory 04).
Correlation calculation with the signal of n Elc is performed based on the following equation (2), and the coefficient switching signal is converted to the first .n Elc signal. By the way, the judgment circuit 0 east of the second section is a comparison circuit (12a), (12b
), and when a ghost signal is output only from the first comparison circuit (128), it is determined that the ghost component is small and the output terminal (a) is output terminal (a).
outputs a determination signal to the first coefficient switching circuit (5h), and when a ghost signal is output from both comparison circuits (128) and (+2b), it is determined that the ghost component is large and the output terminal ( b) to the second coefficient switching circuit (5
A determination signal is output to C).

Both coefficient switching circuits (5b) and (5G) operate when the judgment signal is input, and the first coefficient circuit (5b) converts the first coefficient signal of the set amount A based on the method of equation (1). , a plurality of or games provided for each tap of the transversal filter (2)) (15a), (15b),...
. , (15n) to each tap, and each tap coefficient of the filter (2) is increased or decreased by a predetermined amount A.

In addition, the second coefficient circuit (5C) calculates the set amount α by multiplying the set amount A by α (a>1) based on the method of formula 31.
The second coefficient signal of A is input to each OR gate (15a), (+
5b) , , , .

(15n) to each tap, and each tap coefficient of the filter (2) is increased or decreased by a predetermined amount αλ.

That is, when the ghost component of the output video signal is large, the first. A ghost repair signal is output from the second comparison circuit (12B), (12h), and at this time, a judgment signal is output from the output terminal (1) of the judgment circuit 0, and the second coefficient switching circuit (5C) When activated, the tap coefficient of the transversal filter (21) is increased or decreased by a set amount αA, and is modified more quickly than when it is increased or decreased by a set amount A.

And when the ghost component of the output video signal becomes smaller,
A ghost FI signal is output only from the first comparator circuit (128), and at this time the determination circuit (1, 1 output terminal (a)
A judgment signal is output from the first coefficient switching circuit (51
)) is activated, and the tap coefficient of the transversal filter (2) increases or decreases by the set amount A, as in the case of FIG.

On the other hand, when the ghost component of the output video signal is small from the beginning, the second comparator circuit (12b) indicates that there is a ghost! ! No signal is output, and the tap coefficient is increased or decreased by the set amount A from the beginning only by the ghost signal from the first comparison circuit (12a).

Therefore, when the ghost component of the output video signal is large, the tap coefficient of the transversal filter (2) rapidly increases or decreases by the set amount αλ while the second comparison circuit (+2h) outputs the ghosted n signal. The ghost removal effect appears in a short time, and the ghost removal time can be significantly shortened.

In addition, in the case of the above embodiment, No. 1. Second comparison circuit (1
2a), (+2b) and the first. Second coefficient switching circuits (511) and (50) are provided to selectively increase or decrease the tap coefficient of the transversal filter (2) using the setting amount A and the setting amount αA. It goes without saying that the ghost removal time can be further shortened by providing three or more of each comparison circuit, by making the level of the reference signal of each comparison circuit different, and by making the setting amount of each coefficient switching circuit different.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a ghost removal device, FIG. 2 and the following drawings show an embodiment of the ghost removal device of the present invention,
FIG. 2 is a block diagram, FIG. 3 is a waveform diagram for explaining the leading edge of the vertical synchronization signal, and FIG. 4(a). (1)) is a waveform diagram of a television composite video signal and a difference signal on which a ghost component is superimposed. (1)...Input terminal, (2)...Transversal filter, (3)...Subtractor, (4h)...Ghost detection circuit, (5b), (5C)...First ．． Second coefficient switching circuit, (6)...timing circuit, (7)
...Analog/digital conversion circuit, (8)...Cyclic integration circuit, (9)...1 clock difference circuit, aO...
・Correlator, (11)--differential circuit, (12&), (1
2h) ... 1st. Second comparison circuit, (1:1...
Judgment circuit, Q4)...Memory, (15a), (15
h). ..., (15n)...or gate. Agent: Patent Attorney Ryutabe Fujita

Claims (1)

[Claims] ■ Inputting a television composite video signal to a transversal filter, increasing or decreasing tap coefficients of the filter to form a ghost correction signal, and combining the correction signal and the composite video signal; In the ghost removal device for removing a ghost component of the composite video signal, the difference circuit obtains a difference signal of a leading edge of a vertical synchronization signal of a composite signal of the correction signal and the composite video signal, and a difference signal having a different level from the difference signal. A plurality of comparison circuits compare each of a plurality of base signals and output a ghost presence signal when the level of the difference signal is large, and the magnitude of the ghost component is determined from the number of inputs of the ghost presence signal. a determination circuit that selectively outputs a determination signal from output terminals corresponding to the number of comparison circuits; and a coefficient corresponding to the number of comparison circuits to which the determination signal is alternatively input and increases or decreases the tap coefficient by a set amount. What is claimed is: 1. A ghost removal device comprising: a switching circuit, wherein the setting amount of each of the coefficient switching circuits is different, and the increase/decrease amount of the tap coefficient can be switched and varied depending on the magnitude of the ghost component.