JPH0758984A - Removal circuit of impulse noise of video signal - Google Patents

Abstract

PURPOSE: To provide an impulse noise elimination circuit for a video signal which has a simple circuit structure and eliminates impulse noise that is included in a video signal. CONSTITUTION: This device contains a white noise detector 11 to which a video signal is inputted, white noise more than a white peak level and which outputs a 1st pulse signal, a black noise detector 12 to which a video signal is inputted and which detects black noise that is below the level of a sink signal, a pulse width expanding device 13 to which the outputs of the white noise detector and the black noise detector are inputted and which expands prescribed time pulse width and a track and hold circuit 14 to which the video signal is inputted and which holds the level that is tracked by the output of the pulse width expanding device as long as the pulse width and outputs it, tracking and holding the video signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a television receiver and a V receiver.
The present invention relates to a noise removal circuit for removing noise contained in a video signal from a video system such as a CR, and more particularly to an impulse noise removal circuit for removing impulse noise that misses a white peak level or a sync level of the video signal.

[0002]

BACKGROUND OF THE INVENTION Television receivers are generally susceptible to the impulsive noise of electromagnetic radiation generated by other household appliances such as hair dryers and vacuum cleaners. Such impulsive noise is placed on a video signal to randomly form bright spots or dark spots on the screen, which causes deterioration of image quality. White noise refers to the impulse noise that is generated on the white level side associated with the video signal, and black noise refers to the noise that occurs on the black level side. Occasionally, it may not be possible.

An example of a circuit for removing such impulse noise is shown in US Pat. No. 4,353,093 (198).
October 5, 2000) and U.S. Pat. No. 4,524,389 (June 18, 1985). Here, in the former case, impulse noise is detected in response to an audio signal, and in the latter case, a black noise detector, a pulse width extender, and an adder are provided at the output end of a synchronous video detector using a PLL (Phase Locked Loop). And connect a subtractor to remove impulse noise. The black noise detector outputs a positive polarity pulse when detecting the black noise, and the adder adds the output pulse of the black noise detector with the video signal containing the black noise to remove the black noise. The pulse width extender inputs the output of the black noise detector, extends the pulse width for a predetermined time and outputs it to the subtractor, and the subtractor subtracts the output pulse of the pulse width extender from the output of the adder. To remove white noise.

FIG. 1 is a block diagram showing an impulse noise removing circuit for a video signal according to the prior art, which includes an input terminal 1, a delay unit 2, a track & hold circuit 3, a noise detector 4, a pulse width extender 5 and an output. A terminal 6 is provided. In FIG. 1, the delay device 2 delays the video signal Sv containing the impulse noise input from the input terminal 1 by a predetermined time (t1 in FIGS. 2A and 2B).
Further, the noise detector 4 uses the video signal S from the input terminal 1.
White noise higher than the reference level E1 of the white peak level is detected in v and a pulse signal is output. The pulse width extender 5 receives the output pulse signal of the noise detector 4 and extends the pulse width for a predetermined time t2,
The track & hold circuit 3 inputs the output of the delay device 2 and removes a noise component according to the output of the pulse width expander 5. That is, if the output of the pulse width extender 5 is "low",
When the input video signal is output as it is and becomes "high", the video signal level at this time is held according to the output of the pulse width extender 5 and the video signal Sv 'from which impulse noise is removed is output. Output to terminal 6.

2A to 2E are operation waveform diagrams schematically shown to explain the operation of the circuit of FIG.
FIG. 2A schematically shows a video signal Sv containing noise, which is input to the input terminal 1. Here, "N" indicates impulsive noise, "E1" indicates a white noise reference level slightly higher than the white peak, and "E2" indicates a black noise reference level slightly lower than the sync level.

FIG. 2B shows a video signal obtained by delaying the video signal Sv of FIG. 2A by the delay device 2 for a predetermined time t1. The reason why the input video signal is delayed will be described below. Normally, both white noise and black noise occur in impulse noise, but the noise detector 4 detects only white noise.
Therefore, when black noise occurs first and white noise occurs later, the black noise that occurs earlier cannot be removed. On the contrary, in the case of the noise detector proposed for detecting only black noise, if white noise occurs first and black noise occurs later, white noise that occurred before black noise can be removed. Disappear. Therefore, regardless of whether the noise detector 4 detects white or black noise,
The input video signal is delayed to remove noise before detection.

FIG. 2C shows the output of the noise detector 4 shown in FIG. Here, the noise detector 4 regards an input having a white noise detection level E1 or more in the input video signal Sv as noise and outputs a pulse signal. FIG. 2D shows the output of the pulse width extender 5 shown in FIG. Here, in order to input the output of the noise detector 4 and remove the remaining noise, the pulse width is expanded for a predetermined time t2. Figure 2
(E) is a waveform diagram showing the output Sv 'of the video signal from which noise has been removed.

As described above, in the conventional impulse removing circuit, the white noise and the black noise both occur in the normal impulse noise as described above. Therefore, the delay device 2 becomes indispensable and the number of parts necessary for completing the circuit increases. At the same time, there is a problem that the video signal is removed together with the noise. Further, the noise removing circuit (US Pat. No. 4,524,389) as described above does not use a delay device, but in the video signal after the noise is removed, the signal level in the noise period is a white level or a black level. There was a problem of fixing to.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to track a video signal without using a delay circuit, hold the video signal level during a noise period when impulse noise is detected, and drop the video signal. It is an object of the present invention to provide an impulse noise removing circuit for a video signal improved so as to reduce the noise.

[0010]

In order to achieve the above object, the impulse noise removing circuit of the present invention is a video signal impulse noise removing circuit for removing impulse noise included in a video signal. And a white noise detector that detects white noise above the white peak level and outputs a first pulse signal, and a second pulse that detects the black noise below the level of the sync signal when the video signal is input. A black noise detector for outputting a signal, the first pulse signal and the second pulse signal
A pulse width extender for inputting a pulse signal to extend the pulse width for a predetermined time, and a video signal input for tracking and outputting the video signal, according to the output of the pulse width extender. And a track & hold circuit for holding and outputting the tracked level by the expanded pulse width.

Further, in the impulse noise removing circuit for removing the impulse noise contained in the video signal, the white noise detector for receiving the video signal and detecting the white noise above the white peak level, and the white noise detector. A first pulse width extender for inputting the output of the device and extending the pulse width for a predetermined time,
A black noise detector that receives the video signal and detects black noise below the level of the sync signal, and a second pulse width extender that receives the output of the black noise detector and extends the pulse width for a predetermined time. While the video signal is input, the video signal is tracked and output, and the tracked level is held according to the outputs of the first pulse width expander and the second pulse width expander. And a track & hold circuit for outputting.

[0012]

With such a configuration, the impulse noise removing circuit for the video signal does not include a delay device, and the circuit configuration is simplified to reduce the cost and remove the noise.

[0013]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 3 is a configuration diagram of the impulse noise removal circuit of the present embodiment. The circuit includes a white noise detector 11 for detecting a white noise by inputting a video signal Sv containing impulse noise from an input terminal 1.
The black noise detector 12 that is connected in parallel to the white noise detector 11 and detects the black noise included in the video signal Sv, and the output of the white detector 11 and the output of the black noise detector 12 are input, A pulse width expander 13 that expands the pulse width for a predetermined time t2 and the video signal Sv are input, and the video signal is held according to the output of the pulse width expander 13 while tracking to remove impulse noise. And a track-and-hold circuit 14 for outputting the video signal Sv ′ from which the impulse noise has been removed through the output terminal 6.

The white noise detector 11 is constructed by using a comparator, and the input video signal Sv has a white noise reference level E slightly higher than the white peak level.
If it is larger than the reference level E1 as compared with 1, the first pulse signal is output. The black noise detector 12 is configured by using a comparator, and inputs the input video signal Sv to a black noise reference level E slightly lower than the level of the sync signal.
If it is smaller than the reference level E2 as compared with 2, the second pulse signal is output.

The pulse signals of such black or white noise detectors 11 and 12 have a very short pulse width. However, in general, impulsive noise does not have black noise and does not occur only in white noise or in the opposite state.
A'N ') exists for a predetermined time. Therefore, the pulse width expander 13 determines the pulse widths of the first and second pulse signals input from the noise detectors 11 and 12 for the predetermined time t2.
So that the influence of residual noise can be removed.

The track & hold circuit 14 tracks the video signal Sv input from the input terminal 1 and outputs the input video signal as it is to the output terminal 6 if there is no impulse noise. At this time, the signal input from the pulse width extender 13 is "low". However, when the impulse noise is detected, the signal input from the pulse width expander 13 becomes "high", and the track &
When the output of the pulse width expander 13 becomes "high", the hold circuit 14 holds the level tracked immediately before and removes the impulse noise included in the video signal. The output of the pulse width expander 13 may be designed to be "high" when normal and "low" when impulsive noise is detected.

FIGS. 4A to 4D are operation waveform charts schematically shown for explaining the operation of the apparatus of FIG.
FIG. 4A schematically shows the video signal Sv including impulse noise input to the input terminal 1, where “N” indicates impulse noise and “E1” indicates white peak. The white noise reference level is slightly higher than the level, and "E2" indicates the black noise reference level slightly lower than the level of the sync signal.

FIG. 4B shows a signal at the node 30, and the white noise detector 11 receives the input video signal S.
Of the v, the input having the white noise reference level E1 or higher is regarded as noise, and the first pulse is output. Consideringly outputting a second pulse, these appear at node 30. still,
The second pulse is so short that it is not clearly visible. As described above, in the present embodiment, both black noise and white noise are detected, so that the delay device (2 in FIG. 1) for delaying the video signal is unnecessary.

FIG. 4C shows the output of the pulse width expander 13, and the pulse width is expanded for a predetermined time t2 in order to remove the remaining noise by inputting the pulse signal of FIG. 4B. Indicates that FIG. 4D is a waveform diagram showing the video signal output Sv ′ from which impulse noise has been removed. FIGS. 5A and 5B are examples of video signals from which impulse noise has been removed by performing track-and-hold on a video signal containing impulses according to this embodiment. Here, FIG. 5A shows the track and hold circuit 1
4 is output, and the video signal level a at the time when the output waveform of the pulse width expander 13 as shown in FIG. 5B becomes "high" is held during the "high" pulse period to eliminate impulse noise. Indicates that it will be done.

FIG. 6 is a block diagram showing an impulse noise removing circuit according to another embodiment of the present invention. In FIG. 6, the impulse noise removing circuit inputs the video signal Sv containing impulse noise from the input terminal 1,
A white noise detector 21 for detecting white noise,
And the output of the white noise detector 21 to expand the pulse width for a predetermined time.
And a black noise detector 22 for detecting black noise included in the video signal Sv input from the input terminal 1.
And a second pulse width expander 24 for expanding the pulse width by inputting the output of the black noise detector 22 and the input terminal 1.
The video signal Sv containing impulse noise is input from the first pulse width extender 23 or the second pulse width extender 24.
Track-and-hold circuit 25 that removes impulse noise and outputs the noise-removed video signal Sv ′ to the output terminal 6.

According to this embodiment, the pulse width extender 2
Since 3 and 24 are provided at the output sections of the white noise detector 21 and the black noise detector 22, respectively, even if one of the detectors or the pulse width expander fails, noise can be removed, and the impulse noise The reliability and flexibility of the removal circuit is increased.

[0022]

As described above, the impulse noise removing circuit of the present invention does not include a delay device in the impulse noise removing circuit of the video signal and simplifies the circuit structure to reduce the cost and reduce the noise generation area. It has the effect of accurately detecting and removing only noise. Further, when impulse noise is detected while tracking the video signal, the video signal level at this time can be maintained to reduce the loss of the video signal and improve the solidity.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional impulse noise removal circuit for video signals.

FIG. 2 is a schematic operation waveform chart for explaining the operation of the apparatus of FIG.

FIG. 3 is a block diagram showing an impulse noise removing circuit according to an embodiment of the present invention.

FIG. 4 is a schematic operation waveform chart for explaining the operation of the circuit of FIG.

FIG. 5 is a diagram showing an example of a video signal in which impulse noise is removed from a video signal containing an impulse by the circuit of the present embodiment.

FIG. 6 is a block diagram showing an impulse noise removing circuit according to another embodiment of the present invention.

Claims (2)

[Claims] Claim: What is claimed is: 1. A video signal impulse noise removal circuit for removing impulse noise contained in a video signal, wherein the video signal is input, and white noise of a white peak level or higher is detected to output a first pulse signal. A detector, a black noise detector that receives the video signal, detects black noise below a level of a sync signal, and outputs a second pulse signal, and inputs the first pulse signal and the second pulse signal ,
A pulse width expander for expanding the pulse width for a predetermined time, and the video signal is input, and while tracking and outputting the video signal, the level tracked according to the output of the pulse width expander is expanded. An impulse noise removing circuit for a video signal, comprising: a track-and-hold circuit which holds and outputs the held pulse width. 2. An impulse noise removing circuit for removing impulse noise contained in an image signal, wherein the image signal is input, and a white noise detector for detecting white noise at a white peak level or higher; A pulse width extender for inputting the output of the device to extend the pulse width for a predetermined time, a black noise detector for detecting the black noise below the level of the sync signal, and the black signal for inputting the video signal, A second pulse width expander that receives the output of the noise detector and expands the pulse width for a predetermined time; and the first pulse width while tracking and outputting the video signal when the video signal is input. Hold the level tracked according to the output of the extender and the second pulse width extender Impulse noise reduction circuit of a video signal, characterized by comprising a track-and-hold circuit for force.