JPS6386965A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To reduce the number of necessary taps and a coefficient multiplier by providing a variable delaying circuit provided with an equalizing circuit for proximity on the pre-stage, and providing a transversal filter behind said circuit. CONSTITUTION:An equalizing circuit for proximity 102 which cannot negate a front ghost g0 by an equalizing unit block, when said ghost adjacent to a main signal exists constituted of a equalizing unit YA, a subtracter 300, and a variable delaying circuit 301. The variable delaying circuit 301 is prepared so that the delay quantity is set by a leading time T3 of the proximity ghost g0, and the equalizing unit YA can cover the ghost g0. In this way, a ghost in the vicinity of a main signal is eliminated by providing the proximity equalizing circuit on the feedback line, so that the equalizing unit block is not affected by the proximity ghost, by which the number of taps of the inside of the equalizing unit can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a ghost removal device that removes ghosts from television signals.

(Prior Art) There is a device that uses an equalization circuit to automatically and digitally remove television ghosts. Figure 2 is an example. The details of the operation of this device can be found in the literature (Haka Murakami “Digitalized Ghost Automatic Eraser” Technical Research Report E of Institute of Electronics and Communication Engineers)
MCJ 78-37. November 1978).

This device is entirely digitalized, and a digital video signal including ghosts is input to an equalization circuit 2 via an input terminal 1. This equalization circuit 2, as shown in FIG.
N 10M unit time delay elements 201 (delay time Tse
c), N1M+1 tap coefficient units 202 (digital multipliers), an adder 203 for adding together the outputs of the respective tap coefficient units, and a tap gain memory 204.

The tap coefficients C(-M) to C(N) of this tap coefficient multiplier are set to appropriate values by the control circuit 3, and a digital video signal from which ghosts have been removed is outputted to the output terminal 5.

The reference signal for removing ghosts is the differential waveform of the trailing edge a of the vertical synchronization signal shown in FIG. The peak corresponding to the falling portion of the trailing edge is set as a time reference O, and each peak d1 after this time reference is detected.

di −d(IT) = [−Y (t)kod t
t-iT (1--M-N,)...(1) The sign of this differential value di corresponds to the positive or negative of the residual ghost having the delay time IT. Therefore, the tap gain correction circuit 31 uses this differential value d1 to sequentially correct each tap gain according to the following equation.

Ci, new = CI, old −△・s
gn di(1--M-N, i≠0)... (2
) Here, CI, old is the tap gain before modification, C1゜new is the tap gain after modification, and Δ is a small positive modification coefficient. Equation (2) is widely known as the Zero Forcing method. . Note that the center tap coefficient CO is C
It is fixed at 0-1...(3). Every time a vertical synchronization signal arrives (176
0 seconds), the ghost is removed by performing this sequential correction.

The sequence controller 4 includes the control circuit 3 described above.
It can be configured using, for example, a ROM. There is also known a device that removes ghosts using a combination of fixed delay circuits and a transversal filter (Japanese Patent Laid-Open No. 158579/1983).

(Problems to be Solved by the Invention) However, in the conventional digital ghost removal device as described above, in order to perform sufficient ghost removal, a very large number of coefficient units (multipliers) are required. Since the general-purpose digital multiplier used in the coefficient multiplier is expensive and its scale is large (one multiplier is one IC), a practical ghost removal device has not been obtained. on the other hand,
Although an analog equalization circuit using a CCD has been put to practical use as a ghost removal device, it has problems in terms of residual image and S/N ratio.

The equalization circuit used in the ghost removal device that has already been put into practical use is described in the literature (Murakami et al. "Ghost Clean System" Toshiba Review Vol. 38 No. 4g, No. 7, 1982)
COD (ChargOCou)
pled Device) This device uses a transversal filter. However, since this is an analog signal processing device, the linearity of the coefficient unit (multiplier) and the overall S/N were insufficient. This drawback, when viewed as a ghost removal device, has led to an increase in ghosts remaining on the screen and a decrease in S/N.

Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 511i-158579 has a problem in that even if the ghost is removed at the primary ghost removal stage, grandchild ghosts remain.

Furthermore, in order to reduce the number of taps of the transversal filter, a method has been proposed in which the video signal input to the transversal filter is delayed in advance by a variable delay circuit, and a ghost is assigned to the transversal filter ( For example, Japanese Patent Application No. 59-273262).

That is, as shown in FIG. 5, the video signal at the input terminal 0 is delayed by a variable delay circuit 211 and then supplied to a digital transversal filter 212. The ghost removal signal obtained by the transversal filter 212 (a signal that cancels the ghost, and has a polarity opposite to that of the ghost) is supplied to the adder 213, where it is combined with the video signal from the input terminal I2. . If the video signal from the input terminal I2 contains a ghost, this ghost will be canceled by the ghost removal signal. The variable delay circuit 211 is provided to compensate for the time difference between the original television signal and the ghost signal, and the transversal filter 212 removes the ghost by locally covering the time position where the ghost exists. All you have to do is create a signal. The equalization unit memory 214 is a memory for storing data for controlling the amount of delay of the variable delay circuit 211 and a tap gain given to the multiplier of the transversal filter 212. Furthermore, the latch circuit 215 is for synchronizing the output of the adder 213 with the system clock.

With the above configuration, the interval t1 is compensated for by the delay amount of the variable delay circuit 211 as shown in FIG. Just take charge. Therefore,
The transversal filter does not need to cover all sections where ghosts may exist, and the number of taps can be reduced.

The above example is explained as a device for removing one ghost, but in order to create a system for removing multiple ghosts, as shown in FIG. 6, equalization unit Y1 of FIG.
Equalization units y2 and Y3 similar to the above are prepared, each equalization unit generates ghost removal signals corresponding to ghosts at different positions (phases), and these combined signals are supplied to the adder 220, and the input video is It may be added to the signal as a subtraction element. The control circuit 221 is for performing ghost detection and tap gain calculation processing, and supplying the results to each equalization unit.

However, it is advantageous in terms of cost and size to further reduce the number of taps of the transversal filter.

Furthermore, in the above device, if there is a ghost very close to the main signal, there is a problem that sufficient shield-strike removal cannot be obtained with the minimum number of taps required to cancel the ghost. The effect of reducing the number is not sufficiently achieved. The solution to this problem will be explained later with reference to FIG.

Therefore, this invention was made to solve the above-mentioned problems, and it is possible to further reduce the number of required taps and reduce the number of coefficient multipliers without deteriorating the performance of the equalization unit. Therefore, it is an object of the present invention to provide a ghost removal device that is sufficient for practical use in terms of price and hardware.

[Structure of the Invention] (Means for Solving the Problems) First of all, the present invention requires only a small number of taps whose gain etc. need to be changed in order to actually remove ghosts, and other taps are It focuses on the fact that it is necessary for time alignment between the signal and the ghost signal (CT Application No. 59-273284).
No., Patent Application No. 59-273262, Patent Application No. 59-273
No. 269). Therefore, if an equalization unit is configured in which a variable delay circuit is provided at the front stage and a transversal filter is provided after this, the transversal filter can be used locally to handle the portion where ghosts exist to create a ghost cancellation signal. Fewer taps are required. Second, if a proximity equalization circuit is further provided before the equalization unit to remove waveform distortion in the vicinity of the main signal, the equalization unit can create a signal with only ghost components removed. If possible, the number of taps can be further reduced. The transfer characteristic of the proximity equalization circuit is (transmission distortion), and the transfer characteristic of the other equalization unit with a reduced number of taps is G (ω) - GA (ω), tG (ω); total transmission distortion). It is controlled so that the

(Operation) According to the present invention, by the above means, it is possible to exclusively target ghosts other than the original vicinity of the main signal in the subsequent equalization unit block without being affected by ghosts in the vicinity of the main signal. This eliminates the need for taps in the equalization unit block, which until now had to take care of ghosts outside the vicinity of the main signal, resulting in a significant reduction in the number of taps.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows one embodiment of the present invention, in which a digital video signal is input to a subtracter 100 via an input terminal 1. In this subtracter 100, an equalization unit 1 is input from an input video signal.
A process of subtracting the output of 01 (ghost removed signal) is performed. The output of the equalization unit block 101 is supplied to a proximity equalization circuit 102. This proximity equalization circuit 102 is set to have a characteristic that reduces unnecessary ghost burden on the equalization unit block 101, and is a characteristic part of this system and will be explained in more detail later.

The output of the proximity equalization circuit 102 is guided to the output terminal 5 and is also supplied to the equalization unit block 101.

The control circuit 103 detects ghost positions, calculates tap gains, etc., and also controls the equalization unit block 10.
1. Control the proximity equalization circuit 102.

The circuit shown in FIG. 7 is a more specific representation of the above circuit.

The equalization unit block 101 has the same circuit configuration as that shown in FIG. 6 described above, and therefore is given the same reference numeral.

Further, each equalization unit Y-Y3 has the same circuit configuration as that shown in FIG.

The operation of the equalization unit block 101 will now be briefly explained.

Now, as shown in FIG. 8, three ghosts g1, g2.
g3 shall be removed. The equalization unit Y1 uses the output of the subtracter 300 to create a ghost-removed signal g11 (FIG. 8(b)), and supplies this to the equalization unit Y2. This equalization unit Y2 uses the output of the subtracter 300 to create a ghost removed signal g12 corresponding to the ghost g2, and also creates a ghost removed signal gt at a different time position.
t (Fig. 8(C)). This signal is fed to equalization unit Y3. This equalization unit Y3 uses the output of the subtracter 300 to create a ghost removal signal g13 corresponding to the ghost g3, and synthesizes it with ghost removal signals gll and g12 at different time positions (FIG. 8(d)).
). As a result, a ghost removal signal having a polarity completely opposite to that of the plurality of ghosts shown in FIG. 8(a) is obtained, and the ghosts are canceled by the subtracter 100.

To detect ghosts, the signal y at the leading edge of the vertical synchronization signal
k (FIG. 8(d)) is detected by being differentiated by the control circuit 103, and is taken into the output waveform memory of the control circuit as a differential value dk. This operation is performed every time a vertical synchronization signal arrives. The control circuit 103 detects the maximum peak value of the differential value dk, and sets the data position as the time base iTΦ. At this time, the quantity reference corresponds to the main signal phase. Next, the second
The peak value, the third peak value, and the fourth peak value are detected, and these data positions are regarded as the first to third ghost positions, and each equalization unit Y1 to Y3 is assigned to each ghost. , the delay amount of the variable delay circuit of each unit is controlled through a control line.

Next, each tap gain Ci of each equalization unit is modified according to the following equation.

Ci, new −Ci, old−△・sgn di(i
--M-N, i≠0)...(2) Here, Ci, ol
d is the tap gain before correction, C1゜new is the tap gain after correction 1), Δ is a small positive correction coefficient, and sgn d
i is the sign of the sample value of the differential value d of the output signal y corresponding to the sample timing TΦ. By modifying in this way, the time position and amplitude of each ghost (
It is possible to obtain an equal ghost cancellation signal (of opposite polarity).

Next, the characteristic parts of the present invention will be further explained using FIG. 9 and FIG. 8 together.

Here, it is assumed that the number of taps in each of the equalization units Y1 to Y3 is enough to cancel one ghost, and this is assumed to be a KT tap as shown in FIG. 9. Here, if there is a front ghost go close to the main signal, the front ghost go cannot be canceled with this number of taps,
The number of taps αKT is required, which is the number of taps multiplied by a constant α (α>1) determined by the size and advance time of the front ghost gO. .

This will be explained in more detail with reference to FIG.

First, if ghosts g1 and g2 are canceled by the equalization unit, the ninth
As shown in Figure (b), new ghosts gla and g2a are generated by ghost go. Next, when these ghosts gla and g2a are canceled, ghosts g1b and g2b are further generated as shown in FIG. 9(C). In this way, to cancel the ghost to the extent that it does not affect the signal,
The ghost coverage range of one equalization unit must be wide, and a KT tap is insufficient, so a predetermined multiplied tap type αKT is required.

Therefore, in the present invention, as shown in FIG. 7, a proximity equalization circuit 102 is used to eliminate the proximity ghost. In this way, the number of taps of the equalization unit is the minimum number to cancel the ghost. The number of taps KT will suffice.

In FIG. 7, the proximity equalization circuit 102 includes an equalization unit YA, a subtracter 300, and a variable delay circuit 301. The equalization unit YA and the variable delay circuit 301 are
It is controlled by a control circuit 103. That is, the variable delay circuit 301 has a delay amount set by the advance time T3 (see FIG. 9) of the nearby ghost gO, and is adjusted so that the equalization unit YA can cover the ghost go.

Further, the tap gain of the transversal filter in the equalization unit YA is controlled so as to obtain a ghost removal signal for canceling the ghost go. Therefore, the subtracter 300 is also supplied with a signal for canceling the nearby ghost go from the equalization unit YA.

Let us now consider the transfer characteristics of the system. The transmission characteristic of the entire ghost distortion is assumed to be GA (ω). When control is performed to remove the proximity ghost on the return path, the proximity equalization circuit 10
If the transfer characteristics of Y1, Y2, and Y3 are controlled to become G(ω) - GA(ω), the ghost can be canceled, and the number of taps required for this is GA(ω).
Since it is subtracted, it is no longer affected by GA(ω), and the number of taps of KT suffices.

In other words, the point of view of the present invention is to remove the ghost near the main signal by providing an equinorth exit path for proximity in the return path, and to make the equalization unit block unaffected by the proximity ghost. The number of taps inside the conversion unit can be reduced. The equalization units inside the equalization unit block may be connected in parallel or in series, and the equalization units are not limited in any way.

[Effects of the Invention] As explained above, the present invention can further reduce the number of required taps and reduce the number of coefficients without deteriorating the performance of the equalization unit, thereby reducing the cost and hardware. From this point of view, it is possible to provide a ghost removal device that is sufficient for practical use.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a system explanatory diagram of a ghost removal device, Fig. 3 is a circuit diagram of a conventional transversal filter, and Fig. 4 explains a ghost detection method. FIG. 5 is a configuration diagram of an equalization unit, FIG. 6 is an explanatory diagram showing a block using a plurality of equalization units, FIG. 7 is a diagram showing the configuration of FIG. 1 in more detail, and FIG. The figure is a signal waveform diagram for explaining the ghost removal process of a ghost removal device having an equalization unit block.
FIG. 9 is a signal waveform diagram for explaining the main points of the ghost removal process of the apparatus of this invention. 100... Subtractor, 101... Equalization unit block, 102... Equalization circuit for proximity, 103... Control circuit. Applicant's Representative Patent Attorney Takehiko Suzubayashi Figure 3 Figure 4 Control Line Figure 5 Figure 6 Main Signal Figure 8

Claims (1)

[Claims] An equalization unit block composed of a variable delay circuit and a transversal filter capable of varying tap gain, a proximity equalization circuit, and an output signal of the equalization unit block from an input signal from an input terminal. and a subtracter that supplies the output to the proximity equalization circuit, and obtains an error waveform between the output waveform of the proximity equalization circuit and the reference waveform, and applies the subtracter to the transformer so that the error waveform becomes flat. It consists of a control circuit that controls the gain of each tap of the versatile filter. When distortion other than near the signal is G(ω)-GA(ω), the transmission characteristic of the proximity equalization circuit is 1/1+GA(ω), and the transmission characteristic of the equalization unit is G(ω)-GA. A ghost removal device characterized by controlling the ghost so as to approach (ω).