JPH0159789B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television ghost canceling device suitable for eliminating ghosts in teletext signals.

An automatic equalization type ghost canceling device that uses a transversal filter to cancel television ghosts is attracting attention. Figure 1 shows an example of this. A video signal input to input terminal 1 is applied to a transversal filter 5 consisting of a tap delay 2, a multiplier 3, and an adder 4 to eliminate ghost components. , is output to the output terminal 6.
The input signal and output signal of the transversal filter 5 are each divided into two parts and sent to a tap gain calculation circuit 7, where the tap gain is determined and sent to the tap gain memory 8. In the tap gain arithmetic circuit 7, a portion of the input signal having a certain length from the leading edge of the vertical synchronizing signal is first differentiated by a differentiator 9, and is stored in the input waveform memory 10 as an impulse waveform. On the other hand, a portion of the output signal having a certain length from the leading edge of the vertical synchronization signal is differentiated by the differentiator 11 and becomes an impulse waveform. This waveform is
The subtracter 13 subtracts the ideal impulse waveform stored in the reference waveform memory 12 to obtain an error waveform, which is stored in the error waveform memory 14. Waveform in input waveform memory 10 and error waveform memory 14
The waveforms within are input to the correlator 15, a cross-correlation calculation is performed, and the tap gain is determined.

In a device that eliminates the ghost of a video signal by such an operation, the shift clock of the delay device 2 has a video signal band of about 4 MHz, so
It is set to around 10.7MHz. That is, since real-time processing is required to eliminate ghosts in a video signal, such a high-speed clock is required. In this case, unless the multiplier 3 performs one multiplication within a time of 1/10.7M≈93 nsec, a transversal filter that processes the video signal in real time cannot be constructed. When processing video signals in real time in this manner, each circuit constituting the transversal filter 1 is required to operate at high speed.

On the other hand, in television, text broadcasting that utilizes the vertical retrace period of television signals is expected to become popular in the future. As shown in Figure 2, this teletext signal is inserted into a certain line during the vertical retrace period of the television signal, and usually consists of a fixed pattern header section and an information data section representing character information. It is formed by a binary digital signal. The clock frequency of this digital signal is 5.737MHz, that is, the minimum pulse width is 0.17μsec.

When such teletext signals suffer waveform deterioration due to transmission path distortion such as ghosting, they are not decoded correctly, resulting in problems such as incorrect text information being displayed on the screen or malfunctions. . In order to reduce reception interference of teletext broadcasts due to such ghosts, it has been considered to use the conventional video signal ghost canceling device described above, but this device does not convert video signals in real time as described above. Since the circuit size is large and the cost is high, it is economically disadvantageous to use it to eliminate ghosts from teletext signals, which have a narrower band than video signals.

SUMMARY OF THE INVENTION An object of the present invention is to provide a television ghost erasing device for teletext signals that has a simple hardware configuration and is inexpensive.

As mentioned above, the teletext signal is a transmission method that uses one line during the vertical retrace period, and since it is a signal that appears once every 1/30 sec or 1/60 sec, real-time processing is required to eliminate the ghost component. It is not necessarily necessary to do this, and there is enough time to process waveforms and the like to eliminate ghosts over time during the video signal period.

This invention was made by focusing on the above points, and it temporarily stores the waveform of the teletext signal area of the television signal, reads it out at a slower speed than when writing, inputs it to an automatic equalizer, and converts it into characters. The ghost component existing in the broadcast signal area is erased during the video signal period of the television signal and then output.

Hereinafter, the present invention will be explained in detail by way of examples.

FIG. 3 shows the configuration of a television ghost erasing device according to an embodiment of the present invention. A demodulated television signal with a teletext signal inserted into the vertical retrace period is input to the input terminal 20;
One line of the television signal, including the teletext signal, is controlled by the timing control circuit 21 using a high-speed sample clock of 5.73 MHz and can be read out using a low-speed clock of about 500 KHz, such as a CCD charge coupling circuit. The data is stored in an analog memory 22 composed of elements and the like. The teletext signal written in this memory 22 is read out at low speed and sent to an automatic equalizer 10 for ghost elimination.
It is input to 0. The signal input to the automatic equalizer 100 is converted into a digital signal by the A/D converter 23 using a low-speed sample clock, and then
The data is input to the digital memory 24 of. This first
The signal stored in the digital memory 24 is the flat part from the start point to the end point of the teletext signal and the horizontal periodic signal before and after that, and its contents are x _n
(m=0, 1, 2, ..., M-1). The output of this first digital memory 24 is applied to one input terminal of an arithmetic circuit 26.

On the other hand, 25 is a set of coefficients C _o (n=0,
1, 2, ...N-1), and its output _Co is the second digital memory that stores
6 to the other input terminal. Arithmetic circuit 26
is a circuit that performs a digital filter operation, such as a convolution operation, using the contents x _n of the first digital memory 24 as an input signal sequence and the contents C _o of the second digital memory 25 as a filter coefficient, and the output sequence is y _n (m=0, 1, 2,...
M-1). In this case, y _n is expressed as y _n = _o-1 〓 ⁱ⁼⁰ x _n −iC _i , and the nearby ghost is eliminated.

Arithmetic circuit 26 that computes convolution
can be realized, for example, by an N-stage (N is approximately 5 to 10) transversal filters. FIG. 4 shows an example of the configuration of the arithmetic circuit 26 using a transversal filter when N=6. Input signal series applied in series from input terminal 41
x _n is sent to a group of multipliers 43 via the tap delay device 42, and after being multiplied by the filter coefficient (tap gain series) C _o in the second digital memory 25 by these multipliers 43, The adder 44 takes the sum and sends it to the output terminal 45.

Another example of the configuration of the arithmetic circuit 26 for calculating convolution is shown in FIG. In this case, the input signal sequence x _n from the first digital memory 24 and the filter sequence C _o from the second digital memory 25 are read out at timings shifted by m samples,
They are multiplied by the multiplier 51 to obtain the value x _n −iC _i . This value is cumulatively added by an adder 52.
This cumulative addition is performed N times until the contents of the memory 53 become _N-1 〓 ⁱ⁼⁰ x _n -iC _i , and are sent to the output terminal 54. Such an operation is equivalent to the operation performed during one sample clock by the transversal filter described above. This operation is m=0, 1,
...It is repeated M times up to M-1, and all y _n are obtained.

Now, assuming that the teletext signal during the vertical retrace period of the television signal input to the input terminal 31 in Fig. 3 originally has a waveform as shown in Fig. 6, this will have a ghost delay of 0.17 μsec. , if an in-phase ghost having an amplitude ratio of 0.4 to the main signal is included, the ghost signal component will have a shape as shown in FIG. 6b. In this case, a waveform as shown in FIG. 6c, which is a combination of the waveforms in FIGS. 6a and 6b, is actually input as the input signal sequence x _n . After the ghost component is removed from the waveform of FIG. 6c, the waveform becomes like that of FIG. 6a again. At the stage where ghost elimination is insufficient, a waveform as shown in FIG. 6c is output to the output terminal 30, but this waveform is
The signal is input to a level determiner 27 that determines the value level, and is sampled at sample timings S ₁ , S ₂ , and S ₃ to generate an original waveform r _n as shown in FIG. 6a. Then, this waveform r _n is subtracted from the output signal sequence y _n by the subtracter 28, resulting in the error signal sequence e _n =y _n −r _n . This error signal sequence e _n is input to the correlator 29 together with the input signal sequence x _n , and
A cross-correlation calculation Δc _o = _o-1 〓 ⁱ⁼⁰ xiei+ _o is performed. Then, the contents of the second digital memory 25 are successively corrected using this correlation output Δc _o so that e _o is minimized.

Note that the output signal may be taken out from the output terminal 30, but since a more regular waveform can be obtained from the output of the level determiner 27, this may also be taken out as an output signal to the output terminal 31.

Due to the above operation, the output signal series becomes the 6th
Since the waveform is equalized to a waveform with ghost components eliminated, as shown in Figure 6, even if the S/N is slightly degraded, the waveform shown in Figure 6, c.
This greatly reduces errors in decoding digital signals as in the case of . In other words, although the level determiner 27 can still determine the level as shown in FIG. 6a,
If the S/N deteriorates even to some extent, an erroneous determination will occur. However, when waveform equalization is performed to the level shown in FIG. 6a, the eye opening of the digital signal constituting the teletext signal becomes sufficiently large, so that there is no possibility of code errors due to ghosts. In this case, even if the level of the proximity ghost is very high and the eye aperture ratio is practically close to 0, the waveform of the teletext signal is such that the header part is the information data part as shown in Figure 2. Since this is a fixed pattern that is unrelated to the contents of , this pattern may be stored in advance and used as a reference signal to obtain an error signal.

As explained above, according to the present invention, the waveform of the teletext signal region of the input television signal is stored in an analog memory, and is sequentially outputted at low speed and processed by an automatic equalizer during the video signal period. In order to eliminate ghost components in the teletext signal area, the automatic equalizer has the advantage of operating at a low speed (for example, about 500 KHz) and having a relatively simple configuration. Furthermore, in the above embodiment, since the teletext signal itself, which is a digital signal, is used as the reference signal for ghost elimination, the waveform equalization that is most suitable for the teletext signal is performed to maximize the eye opening of the digital signal. be able to.

Further, since the automatic equalizer digitizes the signal read from the analog memory using an A/D converter and then performs digital processing to eliminate ghosts, its operation is reliable and highly reliable.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment allows a teletext signal to be correctly received even when there are distant ghosts in addition to nearby ghosts.
Here, a remote ghost means, for example, a delay time
Refers to 0.5 μsec or more. In other words, as a ghost included in the input signal, the delay time is 0.17μsec,
In-phase ghost (proximity ghost) with amplitude ratio 0.4,
Consider a case where there is a delay time of 10 μsec, an opposite phase with an amplitude ratio of 0.3, and a ghost (remote ghost). At this time,
The waveform near the leading edge of the vertical synchronizing signal of the television signal input to the input terminal 20 has a shape as shown in FIG. 8a. G ₁ is a melee ghost and G ₂ is a remote ghost. The waveform obtained by inverting and differentiating this waveform becomes an impulse waveform as shown in FIG. 8b. Also, when considering a teletext signal with a shape as shown in Figure 8c, its nearby ghost will be as shown in Figure 8d, and if there is a horizontal synchronization signal 10 μsec before the teletext signal, then the nearby ghost will be as shown in Figure 8d. The remote ghost will look like Figure 8e. The waveform obtained by adding these ghosts d and e to the teletext signal c becomes as shown in FIG. 8f, which is actually input to the input terminal 20.

In FIG. 7, the television signal that enters the input terminal 20 passes through the analog memory 22 and is applied to the A/D converter 23, as in the case of FIG.
The output of the A/D converter 23 is input to the first digital memory 24A. The output signal series x _n of the first digital memory 24A is applied to the arithmetic circuit 26A together with the output signal series c _oA of the second digital memory 25A, where x _n is converted into the input signal series,
By performing a convolution operation using c _oA as a filter coefficient, the remote ghost is eliminated as shown in FIG. 8g. The output signal series u _n of this arithmetic circuit 26A is applied to another arithmetic circuit 26B together with the output signal series c _oB of another second digital memory 25B via another first digital memory 24B. , by performing a similar convolution operation here, the proximity ghost is further eliminated and the output terminal 3 is
Sent to 0. The output signal series y _n of the arithmetic circuit 26B has a waveform as shown in FIG. 8c with ghosts eliminated.

The operation of this embodiment will be explained in more detail. A predetermined length from the leading edge of the vertical synchronization signal during the vertical retrace period is used to eliminate remote ghosts.
At this time, the waveform near the leading edge of this vertical synchronization signal is selectively input to the analog memory 22, and this is transferred to the digital memory 24 via the A/D converter 23.
A and is calculated by the calculation circuit 26A.

As the arithmetic circuit 26A, a convolution arithmetic circuit as shown in FIG. 4 or FIG. 9 is used.

Here, the convolution calculation circuit having the configuration shown in FIG. 9 is in a so-called ghost erasing mode, in which it cannot erase close ghosts, but it can erase distant ghosts, and it uses the main tap (tap corresponding to the main signal). The tap gain of the taps in the vicinity of the main tap excluding the main taps is fixed to zero. In FIG. 9, a signal input to an input terminal 91 is cleared of ghost by a transversal filter 95 composed of a delay device 92 with a tap, a multiplier 93, and an adder 94, and then an output terminal 96
is output to. This configuration eliminates the need for a memory or the like to store the ideal reference waveform, and can be simplified. In addition, when the arithmetic circuit 26A has the configuration shown in FIG. 4, the appearance is the same as in the previous embodiment, but the gain of the multiplier connected to the taps near the main tap other than the main tap is set to 0. Similarly, by setting the tap gain to 0, it is possible to erase only remote ghosts.

The output signal sequence u _n of this arithmetic circuit 26A is also applied to the correlator 29A, where the input signal sequence x _n
The filter coefficient c _oA is determined by performing a cross-correlation calculation, etc., and is stored in the digital memory 25A.
is input. By using the waveform near the leading edge of the vertical synchronization signal as the reference signal waveform in this way, remote ghosts are eliminated.

When the filter coefficient _coA , which is the content of the digital memory 25A, converges, the ghost erasing operation is temporarily stopped, and the tap gain _coA is maintained as it is.

Next, the teletext signal portion of the television signal input to input terminal 20 is selected and input to analog memory 22, and similarly input to digital memory 24A via A/D converter 23. The contents of this digital memory 24A are stored in the arithmetic circuit 26A.
, a filter coefficient for erasing remote ghosts stored in the digital memory 25A.
A convolution operation is performed with c _oA , and the output signal series u _n of this arithmetic circuit 26A is input to the digital memory 24B. This signal sequence u _n is an example of a signal system in which distant ghosts are removed from the teletext signal area, leaving only nearby ghosts. This signal series u _n is subjected to a convolution operation with the filter coefficient _coB , which is the content of the digital memory 25B, in the arithmetic circuit 26B, and is sent to the output terminal 30 as an output signal series y _n . This output signal series
The level of y _n is determined by the level determiner 27 to generate a reference signal waveform sequence, which is the original transmission waveform, and this is subtracted from the output signal sequence y _n by the subtractor 28 to produce an error signal sequence e. _n is created. The correlator 29B performs a cross-correlation operation with the input signal sequence y _n to generate a correction amount Δc _oB of the filter coefficient, and sequentially corrects the filter coefficient c _oB .
It is sent to the digital memory 25B. By such an operation, the proximity ghost in the teletext signal area in the television signal is eliminated, so that the digital memory signal can be correctly decoded.
In this embodiment as well, the output signal may be taken out from the output terminal 31 as in the previous embodiment.

Note that although there are parts in this embodiment where there are two circuits that operate in the same way, it is also possible to combine these circuits into one and use them differently according to the signals. For example, the calculation circuits 26A and 26B are circuits that perform the same digital filter calculation, for example, convolution calculation, and since they do not need to perform the same operation at the same time, they are combined into one circuit and can be switched to perform two types of operation in a time-sharing manner. You can use it. Further, the correlators 29A, 29B or the first digital memories 24A, 24B can also be combined into one. Furthermore, a second digital memory 2
5A and 25B can also be combined into one if ghost erasure is to be performed only once.

Furthermore, in the above embodiment, a vertical synchronization signal was used as a reference signal to eliminate remote ghosts;
Control is performed by using a part of the VITS signal inserted during the vertical retrace period, an impulse waveform, or a reference signal specially created for the purpose of ghost cancellation as a reference signal for ghost cancellation. You may also do this.

Furthermore, in the above embodiment, as a reference signal for ghost erasure, a vertical synchronization signal was used for erasing distant ghosts, and a teletext signal was used for erasing nearby ghosts. Control can also be performed using only the same reference signal, for example a vertical synchronization signal.

Further, in the configuration shown in FIG. 3, the input signal may be one in which remote ghost components are removed by a general video signal ghost canceling device. Furthermore, in the above embodiment, the boundary between close and remote ghosts is set to 0.5 μsec, but this can be changed by changing the method of the two convolution calculations.

Furthermore, although the above explanation has described ghost erasure of teletext signals, the content of the signal is not limited to text information, but as long as it is inserted as a digital signal within the vertical retrace period,
Of course, ghosts can be similarly erased using any graphic information, control information, etc. Furthermore, the present invention can be similarly applied even when the form of the digital signal changes from binary to multi-value. Further, in each of the embodiments described above, the arithmetic circuits 26, 26A, and 26B have been described as having a non-cyclic filter configuration, but they may also have a cyclic filter configuration. In the convolution operation for eliminating distant ghosts, the configuration of the filter can be made circular, and in the case of close ghosts, apart from eliminating so-called advanced ghosts that arrive before the main signal, It can be configured in a circular manner. Of course, it is also possible to use both acyclic and cyclic configurations.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an example of a conventional ghost canceling device for video signals, FIG. 2 is a diagram showing an example of the transmission format of a teletext signal, and FIG. 3 is a diagram showing a television according to an embodiment of the present invention. FIG. 4 and FIG. 5 are diagrams showing an example of the configuration of a convolution calculation circuit, and FIG.
The figure is a waveform diagram for explaining the operation of the same embodiment, FIG. 7 is a diagram showing the configuration of another embodiment of the present invention, and FIG. 8 is a waveform diagram for explaining the operation of the same embodiment.
FIG. 9 is a diagram showing a configuration of a convolution calculation circuit suitable for the same embodiment. 22...Analog memory, 23...A/D converter, 24, 24A, 24B...First digital memory, 25, 25A, 25B...Second digital memory, 26, 26A, 26B... Arithmetic circuit , 27...Level determiner, 28...Subtractor, 2
9, 29A, 29B... correlator.

Claims (1)

[Scope of Claims] 1. In an apparatus for erasing a ghost component existing in a teletext signal area of a television signal in which a teletext signal is inserted within a vertical retrace period, the ghost component in the teletext signal area of the television signal is storage means for temporarily storing waveforms; means for reading out the contents of the storage means at a slower speed than when they were written; What is claimed is: 1. A television ghost canceling device comprising: an automatic equalizer that cancels and outputs a ghost component during a video signal period of a television signal. 2. The television ghost erasing device according to claim 1, wherein the storage means is constituted by an analog memory and an A/D converter that converts the output of the memory into a digital signal. 3. The automatic equalizer includes a first digital memory that stores the signal read from the storage means, a second digital memory that stores a plurality of sets of coefficients,
An arithmetic circuit that performs a digital filter operation using the contents of a first digital memory as an input signal sequence and the contents of a second digital memory as filter coefficients; 2. The television ghost erasing device according to claim 1, further comprising means for sequentially modifying the contents of the digital memory. 4. The television ghost erasing device according to claim 3, wherein the arithmetic circuit is a convolution arithmetic circuit. 5. The television ghost erasing device according to claim 1, wherein the storage means selectively stores the waveform of the teletext signal region and the waveform near the leading edge of the vertical synchronization signal in a time-division manner.