JPH07264443A - Ghost eliminating device - Google Patents

Abstract

PURPOSE:To provide a television receiver eliminating ghost without residual ghost even when the television receiver receives a signal with inverted phase ghost. CONSTITUTION:The device is made up of a tuner 102, a VIF circuit 103, an AGC circuit 104, a pedestal clamp circuit 106, an A/D converter circuit 109, a ghost elimination circuit 110, an amplitude control circuit 115, a synchronizing signal shaping circuit 118, a D/A converter circuit 125, a video processing circuit 126 and a picture tube 127. The ghost elimination circuit 110 eliminates ghost from a video signal whose level is increased because of addition of inverted phase ghost. The level of the synchronizing signal portion of the video signal from which ghost is eliminated is reduced, but since the synchronizing signal shaping circuit 118 shapes the signal to a synchronizing signal waveform with a normal level, a ghost elimination signal without distortion in the synchronizing signal is provided as an output finally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost eliminating device and a television receiver having a ghost eliminating function.

[0002]

2. Description of the Related Art In a television receiver, when a radio wave directly coming from a transmitting antenna (desired wave) and a radio wave reflected from a building (reflected wave) are simultaneously received by a receiving antenna, a desired wave is received. The image due to the reflected wave is superimposed on the image due to, and a ghost occurs. Ghosts associated with television receivers are a major factor in deteriorating image quality. Conventionally, various methods have been tried to remove or prevent ghosts, and recently digital ghost elimination devices using digital technology have become common. ing. However, when this digital ghost elimination device is used, the synchronizing signal is distorted by the ghost, so that the amplitude level of the synchronizing signal is extended and falls below the lowest potential of the input dynamic range of the AD converter (hereinafter referred to as the lowest input reference potential). Therefore, the information in the sync signal portion cannot be converted into digital data. Therefore, when the ghost removing circuit removes the ghost by using the video signal in which the information of the sync signal portion is missing, the sync signal is distorted, which causes a problem that the sync separation circuit such as the video processing circuit in the subsequent stage malfunctions. .

A conventional technique for solving such a problem is disclosed in, for example, Japanese Patent Laid-Open No. 4-196991. In this technique, a clamp circuit for controlling the clamp level is provided in the preceding stage of the AD converter. This clamp circuit sets the clamp level of the clamp circuit high when the ghost level is higher than a predetermined value, and sets the predetermined clamp level to a predetermined value when the ghost level does not exceed the predetermined value, thereby synchronizing the AD conversion. It is stated that information loss in the signal part is prevented.

[0004]

In the above-mentioned conventional clamp circuit, when the ghost level is higher than a predetermined value, the clamp level is set high to prevent loss of information in the ghost signal portion added to the synchronization signal. To do. However, when a reverse-phase ghost with a delay time that is added to the sync signal portion is added, the amplitude level of the video signal becomes extremely large, so by increasing the clamp level, the ghost information added to the video signal portion , The maximum potential of the input dynamic range of the AD converter (hereinafter referred to as the maximum input reference potential) is exceeded, so that it is missing. Therefore, since the ghost removing circuit removes the ghost by using the video signal in which the ghost information in the video signal portion is missing, there is a problem that the ghost cannot be removed correctly and the ghost remains.

An object of the present invention is to solve the above-mentioned problems of the prior art and prevent the disappearance of the ghost information added to the video signal portion even if the amplitude level of the video signal increases due to the anti-phase ghost and disappear. It is an object of the present invention to provide a ghost removing device that removes all ghosts and a television receiver including the ghost removing device.

[0006]

To achieve the above object, in the present invention, a clamp means for fixing the DC level of the video signal to a constant potential and an output of the waveform equalization means are provided in the preceding stage of the AD conversion circuit. This is achieved by providing amplitude control means for controlling the video signal after the ghost removal to an amplitude level before the ghost removal and synchronization signal reproduction means for reproducing the synchronization signal.

[0007]

The clamp means can be set so that the signal of the video portion of the video signal does not exceed the maximum input potential of the AD converter. The amplitude control means can adjust the amplitude level of the video signal after ghost removal to the amplitude level before ghost removal. The sync signal reproducing means can reproduce a sync signal portion having a small amplitude level and being distorted, and can reproduce even a normal level. Therefore, even with respect to a video signal whose amplitude level is greatly distorted by the anti-phase ghost, the ghost can be removed without disappearing. Also, by reproducing the synchronization signal, it is possible to prevent malfunction in synchronization separation in the processing circuit in the subsequent stage.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

Reference numeral 101 is a receiving antenna, 102 is a tuner, 103 is a VIF circuit, 104 is an AGC circuit, and 105.
Is a sync tip clamp circuit, 106 is a pedestal clamp circuit, 107 is a sync separation circuit, 108 is a timing generation circuit, 109 is an AD conversion circuit, 110 is a ghost removal circuit, 111 is a ghost removal filter, 112 is a reference signal acquisition circuit, 113 Is an error detection circuit, 114 is a tap coefficient control circuit, 115 is an amplitude control circuit, 116 is an amplitude control coefficient arithmetic circuit, 117 and 119 are multiplication circuits, 11
8 is a synchronizing signal reproducing circuit, 120 and 121 are clamp circuits, 122 is a switching circuit, 123 is a limiter circuit, 12
4 is a delay circuit, 125 is a DA conversion circuit, 126 is a video processing circuit, and 127 is a picture tube. Further, FIG. 2 is a waveform diagram for supplementary explanation of FIG. 1, and 201 shows a video signal of a 100% white bar waveform.

A television high frequency signal (hereinafter referred to as an RF signal) input from the receiving antenna 101 is input to the tuner 102. The tuner 102 selects a channel and RF
The signal is converted into a video intermediate frequency signal (hereinafter, IF signal) and output. The IF signal output from the tuner 102 is the VIF circuit 1
03, the VIF circuit 103 detects and outputs a baseband video signal. And this video signal is A
It is input to the GC circuit 104. This AGC circuit 104
Controls the gain of the amplifier circuit in the VIF circuit 103 to the tuner 102 and outputs a video signal whose amplitude level is held at 140 IRE as shown by the waveform 201 from the output of the VIF circuit 103. Amplitude level 1 of this video signal
The breakdown of 40 IRE is that the amplitude level of the video part of the 100% white bar waveform is 100 IRE and the sync signal part is 40 IR.
It is E.

Next, an in-phase ghost (DU ratio is -6 dB,
The RF signal with a delay time of 2 μs is added to the receiving antenna 1
The case of input from 01 will be described. Reference numeral 202 shown in FIG. 2 denotes a 100% white bar waveform video signal added with an in-phase ghost.

The RF signal added with the in-phase ghost is input to the tuner 102, and the tuner 102 selects a channel, converts the RF signal into a video intermediate frequency signal (hereinafter, IF signal), and outputs it. The IF signal output from the tuner 102 is VI
The VIF circuit 103, which is input to the F circuit 103, detects and outputs a video signal to which a baseband in-phase ghost is added. Then, this video signal is input to the AGC circuit 104. Since this AGC circuit 104 performs gain control on the signal including the in-phase ghost, the VIF circuit 1
The 03 output outputs a video signal in which the amplitude level of the signal including the in-phase ghost is held at 140 IRE as shown by the waveform 201.

Further, an anti-phase ghost (DU ratio is -6d
B, a case where an RF signal with a delay time of 2 μs) is input from the receiving antenna 101 will be described. Reference numeral 203 shown in FIG. 2 represents a video signal of a 100% white bar waveform added with an antiphase ghost. The RF signal added with the anti-phase ghost is input to the tuner 102, and the tuner 10
2 selects a channel, converts the RF signal into a video intermediate frequency signal (hereinafter, IF signal), and outputs it. Tuner 102
The output IF signal is input to the VIF circuit 103 and
The circuit 103 detects and outputs the video signal to which the baseband anti-phase ghost is added. Then, this video signal is input to the AGC circuit 104. This AGC circuit 104
Performs gain control on a signal including an in-phase ghost, the VIF circuit 103, as shown by the waveform 203,
The amplitude level of the signal including the anti-phase ghost is 140 IRE.
The video signal held at is output. Therefore, the video part of the part which is not cut by the negative phase ghost is 200 IRE, and the sync signal side of the part which is not cut by the negative phase ghost is 80I.
Become RE. That is, the amplitude level of the waveform 203 is 28
It is 0IRE, which is twice as large as the waveforms 201 and 202.

Since the optimum VIF circuit 103 output for explaining the effect of the present invention is the waveform 203 with the anti-phase ghost added, the description will be made using this detected signal waveform 203.

The video signal waveform 203 detected and output from the VIF circuit 103 is input to the sync tip clamp circuit 105. The sync tip clamp circuit 105 outputs a video signal (hereinafter, sync tip clamped video signal) in which the level of the sync signal tip portion is regulated to a constant potential. One of the sync tip clamped video signals is input to the sync separation circuit 107 and the other is input to the pedestal clamp circuit 106.

The sync separation circuit 107 sets, for example, an intermediate level between the pedestal level of the video signal and the level of the sync signal tip (this is called a slice level).
If the level is lower than this slice level, 1 is generated,
If it is higher, 0 is generated to generate the gate pulse of the horizontal synchronizing signal and the vertical synchronizing signal. These gate pulses are input to the timing generation circuit 108. The timing generation circuit 108 generates various timing signals necessary for the digital circuit, such as a gate pulse (hereinafter, a clamp pulse) generated within the back porch period of the video signal.

On the other hand, the pedestal clamp circuit 106 is
By applying a constant potential to the back porch portion of the video signal by the clamp pulse output from the timing generation circuit 108, a video signal in which the pedestal level of the video signal is regulated to a constant potential (hereinafter, pedestal clamped video signal) is output. .

Here, the amplitude level of the video signal to be input to the AD conversion circuit 109 and the set value of the clamp level of the pedestal clamp circuit 106 will be described with reference to FIG. The design specifications include a ghost removing circuit 11 to be described later.
0 means that a ghost with a DU ratio of -6 dB can be removed. To do so, waveform 3 with anti-phase ghost added
As shown in 01, the amplitude level and the pedestal clamp level are set so that the input maximum potential of the dynamic range is not exceeded and about 40 IRE, which is about half of the sync signal portion, is below the input minimum potential. Set.

The video signal waveform 301 clamped and output from the pedestal clamp circuit 106 is the AD conversion circuit 10.
9 is input and converted into digital data. Less than,
In order to facilitate the description, description will be made using analog waveforms even after AD conversion.

Output waveform 302 of this AD conversion circuit 109
Is input to the ghost removing circuit 110 in the subsequent stage.

The principle of the ghost removing operation of the ghost removing circuit 110 will be briefly described.

The output waveform 302 of the AD conversion circuit 109 is
It is input to the ghost removal filter 111 and the ghost is suppressed. The ghost removal filter 111 performs the following operation in order to suppress the ghost. The video signal output from the ghost removing filter 111 is input to the reference signal capturing circuit 112 to capture the GCR signal. An error detection circuit 113 obtains an error signal from this GCR signal, and the ghost delay time and level information is detected from this error signal. The tap coefficient control circuit 114 gives the tap coefficient to the ghost removing filter 111 so that the level of the error signal becomes small. By repeating this operation, the error signal becomes smaller and the tap coefficient converges.
Finally, the ghost removal filter 111 outputs the waveform 303 from which the ghost has been removed. However, this waveform 30
In No. 3, the ghost of the video signal part is removed, but the sync signal part is distorted.

Output waveform 303 of ghost elimination circuit 110
Is input to the amplitude control circuit 115 at the subsequent stage. The ghost removing operation of the amplitude control circuit 115 will be briefly described.

The operating principle of the amplitude control circuit 115 is described in detail in Japanese Patent Laid-Open No. 4-196991, so that it will be briefly described.

The tap coefficient input to the ghost removal filter 111 by the above-mentioned tap coefficient control circuit 114 is
It is also input to the amplitude control coefficient calculation circuit 116. The amplitude control coefficient calculation circuit 116 uses this tap coefficient to output the reciprocal value of the gain of the ghost removal filter 111 (hereinafter referred to as the amplitude control coefficient). Here, the value of this amplitude control coefficient is DU ratio -6 of the antiphase of the ghost removal filter 111.
Since the ghost of dB is removed, it is 0.5 which is the reciprocal value of the gain 2 of the ghost removal filter 111. Amplitude control coefficient 0.
5 is input to the multiplication circuit 117. Multiplication circuit 117
Is calculated by multiplying the amplitude control coefficient of 0.5 by the output waveform 303 of the ghost removing circuit 110 and setting the amplitude level to 140 IRE.
And outputs the video signal waveform 304 controlled to. However, the level of the synchronization signal in the waveform 304 is -40 at the top value.
Although it is IRE, the part with the width of the original synchronization signal is-
The waveform is distorted with only 20 IRE. The output waveform 304 of the amplitude control circuit 115 is input to the synchronization signal reproducing circuit 118 in the subsequent stage.

The sync signal reproducing circuit 118 of the present invention will be described below with reference to FIG.

The clamp pulse output from the timing generating circuit 108 is also input to the delay circuit 124. The delay circuit 124 delays and outputs the clamp pulse so that it appears in the back porch period of the video signal, and the delayed clamp pulse outputs the clamp circuit 120 and the clamp circuit 1.
21 is input.

The output waveform 304 of the amplitude control circuit 115 is
One is input to the multiplication circuit 119, and the multiplication circuit 119
Is a waveform 4 obtained by amplifying the amplitude level by a predetermined factor, for example, 3 times.
01 is output. The waveform 401 shows only the sync signal portion necessary for the explanation, but the video signal portion is also tripled. This waveform 401 is input to the clamp circuit 121. The clamp circuit 121 clamps the back porch period of the waveform 401 to a constant potential (Va) to regulate and output the pedestal level to Va. On the other hand, the output waveform 304 of the amplitude control circuit 115 is the clamp circuit 120.
Also, the clamp circuit 120 clamps the back porch period of the waveform 304 to a constant potential (Va) to regulate and output the pedestal level to Va.

The output waveform 401 and the clamp circuit 121 of the clamp circuit 120 whose pedestal level is regulated to Va.
The output waveforms 304 are input to the switching circuit 122. The switching circuit 122 outputs the waveform 401 during the synchronizing signal period by the gate pulse output from the timing generating circuit 108, and only the synchronizing signal outputting the waveform 301 is amplified during the video signal period. And outputs the video signal waveform 402. The waveform 402 is input to the limiter circuit 123, and the limiter circuit 123 outputs a video signal waveform 403 in which a synchronizing portion that does not output a signal of -40IRE or less is shaped. The waveform 403 is input to the DA conversion circuit 125, and the DA conversion circuit 125 converts the waveform 403 into an analog signal. The output signal of the DA conversion circuit 125 is input to the video processing circuit 126, and the video processing circuit 126 stably performs the sync separation, and projects the ghost-removed video with stable synchronization on the picture tube 127.

According to the present embodiment, the pedestal clamp circuit 106 outputs the signal of the video portion added with the inverse ghost,
Since the setting is made so as not to exceed the maximum input potential of the AD converter 109, it is possible to input to the AD converter 109 a video signal having no loss of information in the video portion. Since the amplitude control circuit 115 adjusts the amplitude level of the video signal after ghost removal to the amplitude level before ghost removal, the contrast before and after ghost removal can be controlled to be constant. The sync signal reproducing circuit 118 can reproduce a reduced and distorted sync portion of the video signal output from the amplitude control circuit 115 into a sync signal of a normal level. Therefore, even if a video signal whose amplitude level is greatly distorted due to the addition of the anti-phase ghost, the ghost is removed without disappearing. In addition, since the sync signal is reproduced, there is an effect that no malfunction occurs in the sync separation in the video processing circuit in the subsequent stage.

FIG. 5 is a block diagram showing another embodiment of the ghost removing device according to the present invention. Reference numeral 501 is a clamp circuit, 502 is a multiplication circuit, 503 is a limiter, and 504 is a switching circuit. The same reference numerals as those in FIG. 1 indicate the same functions.

The difference from the embodiment of FIG. 1 is that the configuration example of the synchronization signal reproducing circuit 118 is different, and this will be described. In explaining, FIG. 6 is a waveform diagram for explaining FIG. 5.

The output waveform 302 of the amplitude control circuit 115 is
It is input to the clamp circuit 501. The clamp pulse that appears in the back porch period delayed by the delay circuit 124 controls the clamp circuit 501, and the clamp circuit 501.
As shown in the waveform 601, the pedestal level of the video signal is clamped to the value of the digital data 0 in the 2's complement display and output. Output waveform 60 of clamp circuit 501
One of the 1s is input to the switching circuit 504 and the other is input to the multiplication circuit 502. The multiplication circuit 502 outputs a waveform 602 obtained by amplifying the amplitude level of the output waveform 601 by a predetermined multiple, for example, triple. The waveform 602 shows only the sync signal portion necessary for the explanation, but the video signal portion is also amplified three times. This waveform 603 is input to the limiter circuit 503, and the limiter circuit 503 outputs a signal of -40 IRE or less.
3 is output. This waveform 603 is input to the switching circuit 504. The switching circuit 122 outputs the waveform 601 and the waveform 603, the waveform 603 in which the synchronization signal is shaped during the synchronization signal period by the gate pulse output from the timing generation circuit 108, and the waveform 601 during the video signal period. Is output, the waveform shown in the waveform 604 is output.

This waveform 403 is input to the DA conversion circuit 125, as in the embodiment of FIG.
5, and the DA conversion circuit 125 converts the waveform 403 into an analog signal. The output signal of the DA conversion circuit 125 is input to the video processing circuit 126, and the video processing circuit 12 receives the output signal.
6 stably performs synchronization separation, and projects a synchronically stable ghost-removed image on the picture tube 127.

According to this embodiment, the sync signal reproducing circuit 11
Similar to the embodiment of FIG. 1, 8 can reproduce a reduced and distorted sync portion in the video signal output from the amplitude control circuit 115 into a sync signal of a normal level. Therefore, even if a video signal whose amplitude level is greatly distorted due to the addition of the anti-phase ghost, the ghost is removed without disappearing. In addition, since the sync signal is reproduced, there is an effect that no malfunction occurs in the sync separation in the video processing circuit in the subsequent stage.

FIG. 7 is a block diagram showing another embodiment of the ghost removing device according to the present invention. 701 is a clamp circuit, 702 is a synchronizing signal generating circuit, 703 is a switching circuit, and 704 is a delay circuit. The same reference numerals as those in FIG. 1 indicate the same functions.

The difference from the embodiment of FIG. 1 is that the structure of the synchronizing signal reproducing circuit 118 is different, which will be described. FIG. 8 is a waveform diagram for explaining FIG. 7.

The output waveform 302 of the amplitude control circuit 115 is
It is input to the clamp circuit 701. The clamp pulse appearing in the back porch period delayed by the delay circuit 124 controls the clamp circuit 701 and the clamp circuit 701.
As shown in the waveform 801, the pedestal level of the video signal is clamped to the value of the digital data 0 in the 2's complement display and output. This waveform 801 corresponds to the switching circuit 70.
Input to 3. On the other hand, as shown in the waveform 802, the synchronization signal generation circuit 702 has a pedestal level of digital data 0 in the complement display of 2 and an amplitude level of 40.
Generates and outputs the IRE sync signal. The output waveform 802 of the synchronizing signal generation circuit 702 is also input to the switching circuit 703. By the gate pulse output from the timing generation circuit 108, the switching circuit 703 outputs the waveform 802 in which the synchronizing signal is shaped during the synchronizing signal period, and outputs the waveform 801 during the video signal period. It is output from the switching circuit 703.

According to this embodiment, the synchronization signal reproducing circuit 11
Similar to the embodiment of FIG. 1, 8 can reproduce a reduced and distorted sync portion in the video signal output from the amplitude control circuit 115 into a sync signal of a normal level. Therefore, even if a video signal whose amplitude level is greatly distorted due to the addition of the anti-phase ghost, the ghost is removed without disappearing. In addition, since the sync signal is reproduced, there is an effect that no malfunction occurs in the sync separation in the video processing circuit in the subsequent stage.

[0040]

As described above, according to the present invention, even a video signal having a large amplitude level when receiving an RF signal in which a reverse-phase ghost is added to a synchronizing signal portion, which has been a problem in the past, disappears. Ghosts can be removed without leaving any residue.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating FIG.

FIG. 3 is a waveform diagram illustrating FIG.

FIG. 4 is a waveform diagram illustrating FIG.

FIG. 5 is a block diagram showing an embodiment of the present invention.

6 is a waveform diagram illustrating FIG. 5. FIG.

FIG. 7 is a block diagram showing an embodiment of the present invention.

8 is a waveform diagram illustrating FIG. 7. FIG.

[Explanation of symbols]

 101 ... Receiving antenna, 102 ... Tuner, 103 ... VIF circuit, 104 ... AGC circuit, 105 ... Sync tip clamp circuit, 106 ... Pedestal clamp circuit, 107 ... Synchronous separation circuit, 108 ... Timing generation circuit, 109 ... AD conversion circuit, 110 ... Ghost removing circuit, 111 ... Ghost removing filter, 112 ... Reference signal capturing circuit, 113 ... Error detecting circuit, 114 ... Tap coefficient control circuit, 115 ... Amplitude control circuit, 116 ... Amplitude control coefficient arithmetic circuit, 117, 119 ... Multiplier circuit, 118 ... Sync signal shaping circuit, 120, 121 ... Clamp circuit, 123 ... Limiter circuit, 122 ... Switching circuit, 124 ... Delay circuit, 125 ... DA conversion circuit, 126 ... Video processing circuit, 127 ... Picture tube.

Claims (3)

[Claims] 1. A clamp means for inputting an analog video signal to regulate a DC level of the video signal to a constant potential, an AD converter for converting the analog video signal output from the clamp means into a digital signal, and a digital conversion. A ghost removal filter that removes and outputs a ghost included in the generated video signal, a reference signal extraction unit that extracts a reference signal included in the video signal from the output of the ghost removal filter, and an output from the reference signal extraction unit. Error signal detection means for inputting a reference signal and a comparison signal to be compared with each other and comparing them to detect an error signal which is a ghost component, and a tap coefficient control for giving a tap coefficient to the ghost removal filter from the error signal detection means. Means for controlling the amplitude level of the video signal before and after the ghost removal of the output of the ghost removal filter to be constant. Means a ghost removal device, wherein the synchronizing signal reproducing means for shaping the distortion of the portion of the synchronization signal amplitude control means outputs, that was provided. 2. The synchronizing signal reproducing means, the clamping means for clamping the video signal output from the amplitude control means to a constant potential, the amplifying means for amplifying the amplitude level of the video signal from the clamping means, and the amplifying means. The ghost removing device is provided with switching means for inputting and outputting the output of the above and the output of the clamping means. 3. In the synchronizing signal reproducing means, a clamping means for clamping the video signal output from the amplitude control means to a constant potential, a synchronizing signal generating means for generating a synchronizing signal of a constant amplitude level, and the synchronizing signal generating means. A ghost removing device comprising switching means for inputting and outputting the output of the means and the output of the clamping means.