JPS6064579A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To obtain an accurate ghost eliminating function by preventing a tap coefficient at a position other than the ghost position of a transversal filter from being biased positively or negatively because of noise. CONSTITUTION:When a positive and a negative difference signal are inputted alternately to a comparator 11 by a polarity switching circuit 15, an output of the comparator 11 (let L1 be the ghost detection level) is as shown in (b) to a positive difference signal (a) and becomes as shown in (d) to a negative difference signal (c). As to the comparator output (d), it is nearly equal to the inversion of the output obtained by using a level L2 being symmetrical to a level L1 based on a reference level L0 from a differential signal of opposite polarity to that of the signal (c) as the detection level. Thus, when the polarity switching circuit 16 inverts the output (d) when it is inputted thereto, it is equivalent by comparing alternately the positive differential signal like the signal (a) at the levels L1 and L2 and no malfunction due to noise is caused.

Description

[Detailed description of the invention] (a) Industrial application field The present invention is provided in a television receiver in order to eliminate the ghost phenomenon caused by interference between direct waves and indirect waves of television radio waves. The present invention relates to a ghost removal device.

(→ Prior Art Figure 1 shows a ghost removal device using a transversal filter. (1) shows a composite video signal (hereinafter simply referred to as video signal) from a video detection stage of a television receiver. The input terminal (2) is a transversal filter (hereinafter referred to as TF) to which the video signal is input, (3
) is the first gate circuit that extracts a minute section of about 20μ80e (see Figure 2 (→)) that includes the front part of the vertical synchronization signal in the video signal, and [4] is the difference between the gate outputs (or (5) is an A/D circuit that samples the differential output (see Figure 2 (b)) at a frequency of about 10.7 MHz and converts it into digital data.
The D conversion circuit 16 is a first memory that sequentially stores each data.

On the other hand, (7) is a subtraction circuit that subtracts the video signal that has passed through the TF (2) from the original video signal, (8) is an output terminal from which the video signal from this subtraction circuit is derived, and (9) 0 is a second gate circuit and a second difference circuit similar to those in (3) and [4] above, aυ is a comparator that compares the difference output with the ghost detection level to detect the presence or absence of a ghost component, and 0
converts the output of the comparator into the A/D conversion circuit (5).
The second memory αJ sequentially stores data corresponding to each sampling point in the second memory t17J and the first memory (6), and performs a correlation calculation. The arithmetic circuit consisting of a microprocessor, etc., which performs the correlation calculation, is a tap setting memory that increases or decreases the tap coefficient of each stage of TF[2J] according to the positive or negative sign of the result of each correlation calculation.

The operation of such a ghost removal device has already been described in detail in various documents, so it will be briefly explained below.

Now, each data of each sampling point stored in the first memory (6) is expressed as Xk(k'' Ot 1 t 2 e
..., n), and each data stored in the second memory circle is Yk (however, when the output of the second differential circuit is positive, Yk
-1, Yk=-1 when zero or negative, then the arithmetic circuit (l, Xk-Yk+j (however, j-o
, 1, 2, -, rnte, m is the number of tap stages of TF(2)] is a unit that sequentially performs correlation calculations and increases or decreases the tap coefficient of TF(2) depending on whether the calculation result is positive or negative. The values are sequentially set in the tap setting memory α4.

In other words, when the operation starts immediately after the power is turned on, X<-Y
1 +
α > 0), if negative, tap 1 α in setting memory I
Store at the th address. Next, Xl・Y2+X2・Y
5+...+Xn@Yn+, the value α or -α is stored in the second address of the tap setting memory a♦ depending on whether the calculation result is positive or negative. Sequentially in the same manner as above/-E-riu4 (D the final m-th address is
-Ym+ 1+-+Xn-α depending on the positive or negative of Ym+n
Or a value of -α is set. Then, each set value is applied as each tap coefficient of the first to mth stages of TF(2).

In this way, when the first tap coefficient setting of TF(2) is completed for the data for the minute section of the first field, the first tap coefficient is changed to the first second memory again. The data for the next field is stored in 61u21, and this time a correlation calculation is performed on this data in the same manner as described above, and each second tap coefficient is stored in each address of the tap setting memory I. At that time, 2α and -2α are set respectively for the stages (addresses) where the operation result becomes positive or negative again after the first time, and conversely, for the stage where the operation result is positive or negative again. is set to zero. This series of operations is repeated for each subsequent field, and each time,
The tap coefficients of each stage of TF (2H) increase or decrease, and as a result, the corresponding ghost correction signal output from TF121 is subtracted from the original video signal by the subtraction circuit (7), so the output terminal (8) The ghost component appearing in the video signal gradually decreases and is eventually removed.

Here, in such a ghost removal device, the composite video signal obtained by reception and detection generally contains noise, as shown in FIG. 2 (IL) above. In addition to the pulse 00 indicating the leading edge of the vertical synchronizing signal and the position of its ghost, noise appears in the differential output (FIG. 2(b)).

This applies not only to the output of the first differential circuit (4) but also to the output of the second differential circuit. Therefore, the influence of such noise becomes a problem. Therefore, this point will be explained below.

Now, the comparator 1υ in FIG.
In order to increase the accuracy of ghost detection with respect to the output of α, the detection level is set sufficiently low.

Therefore, if the detection level of this comparator 1υ is now set to the reference level (LO) K of the output of the second differential circuit flG (Fig. 6 (a)), this level (LO) will cause noise (to This means that the positive half-wave and negative half-wave of can be detected approximately symmetrically. However, the above detection level is L in the diagram.
When the output of the comparator αυ is set to
] The period in which it is detected as negative [-1] is greater than the period in which it is detected as negative [-1].Then, the correlation between the comparator output (+1) (-1) and the output signal of the A/D conversion circuit (1) The calculations are performed as described above.

However, if the previous comparator output is often [-1] during periods other than pulse 00 in Figure 6(a), the tap coefficients of each stage of TF(2) become ghosts. As shown in Figure 4, the position will be biased towards the negative side. Conversely, if the comparator output is often [1] [when the detection level is set to L2 in FIG. 6 (SL)], the tap coefficient will be biased toward the positive side.

When the tap coefficients of the TF are biased toward one side in this way, the ghost correction signal output from TF [2] is cumulatively added, so that, for example, the original video signal (see Fig. 5) is added. (a)) becomes as shown in (b) of the same figure,
As a result, the image signal after ghost removal obtained at the output terminal (8) becomes like that shown in FIG. 3(C), resulting in an unsightly image with smear, and the synchronization is disturbed.

Therefore, as mentioned above, it is sufficient to accurately set the ghost detection level of the comparator αυ to LO in FIG. This is extremely difficult when considering fluctuations due to temperature, etc.

(9. Purpose of the Invention The present invention has been made in view of the above points, and uses a relatively simple configuration. The goal is to achieve accurate ghost removal without bias.

B) Structure of the Invention The ghost removal device of the present invention removes ghost components by combining a ghost correction signal created by a transversal filter with a television video signal, and also removes a ghost component from a predetermined minute section of the video signal after the combination. After extracting and subtracting (or differentiating) the signal, it is binarized by a comparator for ghost detection, and a correlation calculation is performed between this binary signal and the video signal in the minute section, and based on the calculation result, the tap of the filter is In the ghost removal device that sets the coefficients, each time the tap coefficient setting operation completes, the polarity of the difference signal input to the comparator is switched, and the binary signal from the comparator is inverted to perform the correlation calculation. It is characterized by the fact that it performs the following.

(E) Embodiment FIG. 6 shows a schematic configuration of a ghost removal device according to the present invention. The same parts as in FIG. 1 are given the same numbers, and the basic operation of ghost removal itself is the same as in FIG. 1. The feature in this figure 6 is that the second
The polarity of the output signal of the differential circuit is switched and the comparator I
and a second polarity switching circuit σe that inverts the output of the comparator αυ and inputs it to the second memory a4 in synchronization with this switching.
The second switching circuit a9 Kasumi is 1 to m of TF (2) on the arithmetic circuit side.
The switching is made each time the correlation calculation operation for the stage is completed (one round).

Here, the first polarity switching circuit (19 is, for example, as shown in FIG. 7, the second difference circuit (1G output signal polarity inversion circuit (15a) It consists of an analog switch (15b) that is alternately switched by the inverted control signal (Fig. 8(a)), and a direct derivation path (15c) for the above-mentioned differential output.The second polarity switching circuit ae is also similar. However, since the output of comparator I is binary (+1] (-1), ζ can be constructed with a digital circuit. Note that ψ in FIG. 8 is the output from the first polarity switching circuit L51. Showing a signal.

Now, in the ghost removal device shown in FIG. 6, when positive and negative polarity difference signals are alternately input to the comparator αυ by the first polarity switching circuit Kasumi, this comparator is activated (the ghost detection level is set to L1). For the positive polarity difference signal (Fig. 9(a)), the output is as shown in Fig. 9(b).
On the other hand, for a negative polarity differential signal (FIG. 9(C)), the result is as shown in FIG. 9(D). Here, regarding the comparator output (d), this is the output obtained by inverting the difference signal of the opposite polarity to that of (e) in the same figure, with L2, which is symmetrical to Ll, as the detection level with respect to the reference level (La). Almost equal to something. Therefore, if the second polarity switching circuit is inverted when the above output (d) is input, the result is as shown in FIG. 9(a).
This is equivalent to alternately comparing positive polarity differential signals such as levels (Ll) (L2). In this case, as explained with reference to FIG. 3, the periods during which the positive half-wave and the negative half-wave of the noise are detected are approximately equal. Therefore, if during the first tap setting operation of TF (2), the tap coefficients of each stage due to noise are biased toward the negative side, during the second setting operation, they are switched to the positive side, and the first
Cancel the second tap coefficient. At this time, the tap coefficients due to the ghost are calculated with the same polarity and at the same position both in the first and second times. Therefore, a ghost correction signal that correctly represents the ghost waveform and is not affected by noise is derived from TF(2).

Note that the noise waveform is not exactly a symmetrical waveform as shown in Figures 6 and 9, but it appears randomly, so as the tap setting operation is repeated many times, the bias of the tap coefficient due to the noise will increase. Effects of the Invention According to the ghost removal device of the present invention, the settings of the tap coefficients of the transversal filter can be set without being influenced by noise. Therefore, ghosts can be accurately removed, malfunctions due to noise can be prevented, and deterioration in the image quality of television images can be avoided.

[Brief explanation of the drawing]

1 to 5 show conventional examples, FIG. 1 is a diagram showing a schematic configuration of a ghost removal device, FIG. 2 is a diagram explaining its operation, and FIG. 3 is a signal waveform diagram for explaining the operation of a comparator. FIG. 84 is a diagram showing the tag coefficients of each stage of the transversal filter, and FIG. 5 is a signal waveform diagram for explaining malfunctions due to noise. 6 to 9 illustrate the present invention, FIG. The figure is a signal waveform diagram for explaining the operation. . 15...First polarity switching circuit, (161-...Second polarity switching circuit. 111Figure 2-ay-+v5 Figure 8Figure 4Figure 6Figure 6 □Time

Claims (1)

[Claims] (1) A device for creating a shiboust correction signal by passing a television video signal through a transversal filter, and combining this correction signal with the video signal to remove ghost components. A predetermined minute section of the synthesized video signal is extracted, the difference (or differentiation) is performed, and then it is binarized by a comparator for ghost detection, and a correlation calculation is performed between this binary signal and the video signal of the minute section. In the device that sets the tap coefficient of the filter based on the calculation result, the polarity of the difference signal input to the comparator is switched every time the tap coefficient setting operation completes one cycle, and the polarity of the difference signal input to the comparator is changed. A ghost removal device characterized in that the correlation calculation is performed by inverting the signal.