JPH021431B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform equalizer for modifying and extracting a received signal waveform using a transversal filter in a television receiver or other receiving device.

2. Description of the Related Art Conventionally, in a receiving device, a waveform equalizer has been used to modify a received signal waveform into a waveform in which distortion generated in a transmission path has been removed. Specific examples include a ghost removal device in the video signal circuit stage of a television receiver, and an echo canceller in a telephone receiving station.

For example, a configuration shown in FIG. 1 has been considered as the ghost removal device for a television receiver. This uses a transversal filter, and its general operation is as follows.

That is, the television video signal input to the input terminal 1 is supplied to the transversal filter 2. The transversal filter 2 includes a delay element (for example, a charge transfer element such as a CCD) 2a having a plurality of taps, and an arbitrary weighting coefficient (hereinafter referred to as tap gain) for applying a video signal to each tap of the delay element 2a. The output of the weighting circuit 2b is added to each tap of the delay element 2a so as to be added to the signal passing through the delay element 2a. The signal taken out from the final stage of the delay element 2a is sent to the subtracter 2
c, the difference between the signal and the video signal sent to the input terminal 1 is taken, and the signal is taken out as an output to the output terminal 4. In this case, by appropriately controlling the tap gain, a video signal from which ghost signal components have been removed can be obtained at the output terminal 4.

The tap gain control described above is performed, for example, as follows. That is, the reference waveform in the output signal of the transversal filter 2 is used as the reference waveform for ghost signal component detection, for example, by using the step signal waveform when moving from the third line to the fourth line of the vertical synchronization signal in the video signal. Reference waveforms in the video signal input to input terminal 1 are detected by difference circuits 5 and 6, respectively. The difference circuits 5 and 6 each include delay circuits 5a and 6a and subtracters 5b and 6b, and output a difference signal corresponding to the reference waveform, and also input a ghost signal component corresponding to the reference waveform. If there is a ghost signal component, a difference signal corresponding to this ghost signal component is also output. The respective output signals of these difference circuits 5 and 6 are input to the output signal of the difference circuit 5 via a shift register 7 to a correlator 8, and the correlation is taken. The correlator 8 is a type of multiplier, and includes two sets of delay elements (for example, charge transfer elements) 8a and 8b each having a plurality of taps, and a shift register 7 added to each tap of the delay element 8a.
A weighting circuit 8c which gives a tap gain to the output of the differential circuit 6, a switch 8d and a holding capacitor 8e for sequentially controlling each tap gain with each tap output of a delay element 8b which receives the output of the differential circuit 6 as an input. Ru. A correlation output of a waveform in which the time interval between the difference signal of the reference waveform and the difference signal of the ghost signal is clarified is taken out from the correlator 8.
This correlation output waveform is converted into a "1" or "0" signal according to its polarity by a positive/negative determination circuit 9, and then stored in a digital memory (shift register) 12 via a shift register 10 and an adder 11. . Note that the adder 11 adds the output of the shift register 10 and information already stored in the digital memory 12. After the output of this digital memory 12 is converted into an analog signal by a D/A converter 13, it is sent to the transversal filter 2 via a switch 15 which is controlled to turn on sequentially by a shift register 14. It is applied to the weighting circuit 2b as a tap gain control voltage. Capacitor 3 is used to hold this tap gain control voltage. Further, the timing circuit 16 is connected to the digital memory 1
2. Control the operation of the shift register 14, etc.

However, such a device has the following problems. Now, assume that the number of taps of transversal filter 2 is 256 and the shift clock is 10MHz.
FIG. 2a shows a waveform near the vertical synchronizing signal when moving from the third line to the fourth line used as a reference waveform, and when this is passed through the difference circuit 6, it becomes as shown in FIG. 2b. Here, for convenience, the differential output is shown as a waveform whose sign is inverted. Now delay time
Assuming that there is an in-phase ghost signal component for 20μsec and a relative level of 0.2, the output waveform of the difference circuit 6 will be the second one.
It will look like Figure c. In FIG. 2c, G indicates a ghost signal component. At this time, the transversal filter 2 is controlled so that a tap gain value of -0.2 is given to the 200th tap with a delay time of 20 μsec relative to the first tap. When a signal containing a ghost signal component as described above is input to the transversal filter 2 in such a state,
The ghost signal component is removed, but when looking at the output waveform of the difference circuit 5, as shown in Figure 2 d, the delay time of the original ghost signal component is twice the delay time (40 μsec).
A ghost signal component G′, so-called grandchild ghost, with a relative level of 0.04 newly appears at the delay time position of . Such a grandchild ghost signal component
If G' occurs at the output of the transversal filter 2, it will be detected and an incorrect tap gain value will be given to the transversal filter 2, so that the original ghost signal component will not be removed sufficiently. A similar problem generally occurs when the grandchild ghost signal component appears near the vertical synchronization signal as shown in Figure 2d, that is, the original ghost signal component has a delay time of about 14 to 28 μsec. Occurs in cases.

In order to solve this problem, by holding a certain section before the starting point of the vertical synchronization signal waveform used as a reference waveform at a constant level using a sample and hold circuit, it is possible to prevent malfunctions during the reference waveform after differentiation. There is a known method for preventing the generation of ghost signal components (Japanese Patent Application Laid-Open No. 1983-1999).
Publication No. 134528).

However, with this method, it is difficult to maintain a certain section before the starting point of the vertical synchronizing signal waveform at a correct level due to leakage in the sample-and-hold circuit, and this level change appears as distortion of the differential waveform, which is the reference waveform. Therefore, grandchild ghost components are less likely to occur, but the distortion of the reference waveform increases compared to the case where the vertical synchronization signal waveform is not subjected to the above processing, so the original ghost signal component suppression effect (waveform equalization) This will have a negative effect on

The present invention has been made in view of these points, and its object is to provide a waveform equalizer that is free from malfunctions due to grandchild ghost signal components and which can provide a good waveform equalization effect.

According to the present invention, between a differentiator that differentiates a step signal waveform such as a vertical synchronizing signal waveform, which is used as a reference waveform, and a tap gain control means, a certain interval before an impulse waveform, which is a differentiated waveform of the step signal waveform, is set to zero. The present invention is characterized in that by providing a means for maintaining the level, grandchild ghost signal components and the like are not generated in the reference waveform. Therefore,
According to the present invention, not only can malfunctions caused by grandchild ghost signal components etc. be prevented, but also a certain section of the impulse waveform in the reference waveform can be stably maintained at zero level without using a sample and hold circuit. Since unnecessary distortion is no longer included, it is possible to obtain an extremely good waveform equalization effect.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 3 shows the configuration of a waveform equalizer according to an embodiment of the present invention. This configuration will be explained using an example in which the input signal is a television video signal. The television video signal input to the input terminal 20 is guided to an inverting differentiator 21, where a certain section including the vertical synchronizing signal waveform is inverted and differentiated, and sent to the input waveform memory 23 via the first changeover switch 22. . The first cut-off switch 22 is turned to the contact 22a side in the period after the start point (fourth line start point) of the vertical synchronization signal waveform in the input television signal,
An impulse waveform obtained by differentiating the vertical synchronizing signal waveform with a differentiator 21 is led to an input waveform memory 23. Further, in the period before the start point of the vertical synchronizing signal waveform, that is, in the latter half of the third line, it is pushed to the contact 22b side and gives a zero level to the input waveform memory 23. Figure 4 shows this situation. FIG. 4a is a waveform diagram of the third and fourth lines during the vertical retrace period of the NTSC signal, and the starting point (fourth line starting point) 41 of the differentiated waveform of the vertical synchronizing signal which is passed through the inverting differentiator 21 is shown in FIG. A centrally enlarged waveform is shown in FIG. 4b. In this case, the differential waveform 42 ideally looks like the broken line in FIG. 4b, but when actual broadcast waves are received, ghosts may be added or the band may be limited at a finite frequency and noise may be added. This results in a solid waveform.

Then, the first changeover switch 22 is connected to the contact point 22b.
FIG. 4c shows a waveform in which a section of, for example, 30 μsec before the beginning of the impulse waveform, which is a differentiated waveform of the starting point of the vertical synchronizing signal waveform of the reference waveform, is held at a zero level 43. In this case, if the tap length (time length) of the variable tap gain of the transversal filter is N, then the length of the section held at the zero level before the impulse waveform is required to be N. In this way, the input waveform memory 23
The reference waveform data written in is transferred to the transversal filter 25 via the second changeover switch 24.
and is sent to the output terminal 29 and the output waveform memory 28. On the other hand, the tap gain calculation circuit 27 performs a cross-correlation calculation of the waveforms in the input waveform memory 23 and the output waveform memory 28 to determine the tap gain, and taps the tap gain value in the tap gain memory 26 with the tap gain memory 26. The gain calculation circuit 27 constitutes tap gain control means. When determining this tap gain, the second changeover switch 24 is always turned to the contact 24a side, so that the tap is determined using the waveforms of the third and fourth lines. Also, after the tap gain is determined, the second
The changeover switch 24 is turned to the search point 24b side, and the input television video signal is waveform-equalized by the transversal filter 25 and sent to the output terminal 29.

If the tap gain is determined by such an algorithm, the tap gain calculation circuit 27 will be calculated based on the ghost signal component existing before the impulse waveform used as the reference waveform, the grandchild ghost signal component appearing in the output waveform, noise, etc. can prevent malfunctions. Therefore, a grandchild ghost component as shown in FIG. 2d does not appear. In addition, in this embodiment, the output is output from the output waveform memory 2.
8 and may be taken out from another output terminal 30.

Next, the operation when this embodiment is applied to a teletext ghost canceller will be described. Since the teletext signal is inserted once or several times in one field into the horizontal synchronizing signal portion of the 10th to 21st lines or the 272nd to 283rd lines of the vertical retrace period, the ghost signal component is To remove it, it is sufficient to waveform equalize only this portion of the teletext signal. In this case, as before, a differential waveform obtained by differentiating a certain section including the starting point of the vertical synchronization signal waveform is used as the reference waveform. First, the first selector switch 22 is turned to the contact 22a or 22b side, the tap gain of the transversal filter 25 is determined, and when the tap gain converges, the tap gain is fixed. Next, connect the first changeover switch 22 to the contact point 22.
C side, extracts only the teletext signal part from the input television video signal and writes it into the input waveform memory 23, and the transversal filter 25 removes the ghost signal component using the already determined tap gain. and sends it to the output terminal 29 or output waveform memory 28. At this time, the second changeover switch 24 is always connected to the contact 24b side, so it is virtually unnecessary. In this configuration, since the transversal filter 25 does not need to perform calculation processing in real time because the tap gain is controlled and the ghost removal of the teletext signal is performed via the input waveform memory 23, the built-in tap gain As the weighting multiplier, etc., a low-speed one can also be used.

FIG. 5 shows another embodiment of the present invention, in which the television video signal input to the input terminal 20 is differentiated by a differentiator 21 in the section including the start point of the vertical synchronization signal in the process of tap convergence. , are written into the input waveform memory 23. The contents of the memory 23 are sequentially read out, and the first and second changeover switches 5
Transversal filter 25 via 1, 52
sent to. At this time, in a period before the impulse waveform of the reference waveform in the input waveform memory 23, the first selector switch 51 is tilted toward the contact 51b, so that a zero level is supplied to the tap gain calculation circuit 27. The tap gain calculation circuit 27 determines the tap gain from the input/output waveform, and tap gain memory 2
Write to 6. After the tap gain is determined, the second changeover switch 52 is turned to the contact 52b side, so that the input television video signal is sent as it is to the transversal filter 25, and ghost signal components are removed.

According to this embodiment, since the first changeover switch 51 at the stage subsequent to the input waveform memory 23 sets a certain section of the reference waveform before the step signal waveform to zero level, compared to the embodiment of FIG. Input waveform memory 2 for the period during which the reference waveform is set to zero level.
3 capacity can be saved.

FIG. 6 shows still another embodiment of the present invention, in which the television video signal input to the input terminal 20 has a certain section including the vertical synchronization signal starting point in the process of tap convergence as before. 21 and sent to the transversal filter 25 via the changeover switch 61. At this time, a certain section before the impulse waveform of the output of the differentiator 21 is held at zero level by turning the changeover switch 61 toward the contact 61b, and is input to the transversal filter 25. The output of the transversal filter 25 is sent to an output terminal 29 and also to a tap gain calculation circuit 27. In this case, the reference waveform is the transversal filter 25
is supplied to the tap gain calculation circuit 27 in the tap gain control means. As a result, in the tap gain calculation circuit 27, the transversal filter 2
The tap gain is determined only from the reference waveform of the output of step 5, and the determined tap gain is sent to tap gain memory 26. According to this embodiment, input and output waveform memories are not required, so the configuration is simplified. However, in this case, transversal filter 2
5 needs to operate in real time.

As explained above, according to the present invention, a specific step signal waveform in the input signal (for example, in the case of a television signal, By holding a certain section before the impulse waveform corresponding to the differential waveform of the vertical synchronization signal waveform (vertical synchronization signal waveform) at zero level, malfunctions due to grandchild ghost signal components or ghost signal components with a long delay time can be prevented. In addition, compared to the method in which a certain section before the step signal waveform is held at a constant level by a sample-and-hold circuit at the stage before the differentiator, there is no distortion of the reference waveform due to leakage in the sample-and-hold circuit, and good waveform equalization is achieved. This makes it possible to minimize residual distortion such as ghost signal components.

Note that the circuits shown in FIGS. 3, 5, and 6 may be constructed of either an analog circuit or a digital circuit, in which case a differential circuit will be used as the differentiator 21.

Furthermore, in each of the above embodiments, an impulse waveform obtained by differentiating a certain section including the starting point of the vertical synchronization signal waveform was used as the reference waveform.
Other than this, for example, it is inserted on the 17th line.
The present invention can be similarly applied to cases where an impulse waveform obtained by differentiating VITS or an impulse waveform obtained by differentiating a step waveform specially inserted in a specific portion is used.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a television ghost removal device which is an example of a waveform equalizer, FIG. 2 is a waveform diagram for explaining the problem, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a waveform diagram for explaining its operation, and FIGS. 5 and 6 are configuration diagrams of other embodiments of the present invention. 21...Differentiator, 22, 24, 51, 52, 6
1... Selector switch, 23... Input waveform memory,
25... Transversal filter, 26... Tap gain holding circuit, 27... Tap gain calculation circuit, 28... Output waveform memory.

Claims (1)

[Scope of Claims] 1. A transversal filter with variable tap gain, a differentiator for differentiating a fixed interval including a specific step waveform in an input signal of the transversal filter, and the fixed interval obtained by the differentiator. and a tap gain control means for detecting distortion of the input signal using a differential waveform of the reference waveform as a reference waveform, and controlling the tap gain of the transversal filter based on the detected distortion, the differentiator and the tap gain control means A waveform equalizer characterized in that means is provided between the waveform equalizer and the step signal waveform for holding a certain section before the impulse waveform, which is the differential waveform of the step signal waveform, at zero level. 2. The waveform equalizer according to claim 1, wherein when the input signal is a television video signal, a differential waveform of a certain section of a vertical synchronization signal waveform in the television signal is used as the reference waveform.