JP2570291Y2 - Black noise removal circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black noise elimination circuit for a video signal, and more particularly to a black noise elimination circuit suitable for extracting a sync separation signal of a video signal.

[0002]

2. Description of the Related Art Conventionally, many black noise elimination circuits included in a video signal have been provided in a block diagram shown in FIG. In the figure, reference numeral 1 denotes an input terminal of a video signal. The video signal supplied to the input terminal 1 is subjected to signal processing such as synchronization separation in a video processing circuit 30, and at the same time, is supplied to a black noise detection circuit 31. You. Reference numeral 32 denotes a switching circuit, and the switching circuit 32 is switched by the black noise detection signal detected by the black noise detection circuit 31.

Reference numeral 33 denotes a DC power supply. A DC voltage from the DC power supply 33 is supplied to the switching circuit 32 via a level adjuster VR, and the DC voltage controlled by the switching circuit 32 is supplied to the video processing circuit. Supplied to 30.

The video signal noise elimination circuit configured as described above eliminates black noise in which the amplitude level of the pulse noise is lower than the synchronization signal level. The operation of this noise elimination circuit will be described with reference to the waveform diagram shown in FIG.

In FIG. 4, FIG. 4H shows an input video signal waveform, and FIG. 4J shows an output video signal waveform. Reference numeral 20 denotes a video signal synchronization signal, and reference numeral 21 denotes pulsed black noise superimposed on the video signal. Also, 40 indicates the black level of the video signal, 41 indicates the noise detection level set by the black noise detection circuit 31, and 42 indicates the DC voltage of the DC power supply 33 set by the level adjuster VR. is there.

A noise detection level 41 is set so that the threshold level of the black noise detection circuit 31 for detecting the pulsed black noise 21 of the input video signal H is lower than the synchronization signal 20 as shown in FIG. The black noise detection circuit 31 generates a timing pulse of the detected black noise 21 based on the noise detection level 41, and controls the switching circuit 32 according to the timing pulse to switch the DC voltage from the DC power supply 33 to the video processing circuit 30. The supplied DC voltage is supplied to a level adjuster VR, for example, the DC voltage level shown in FIG.
Set as 42.

That is, the DC voltage level 42 is added to the black noise 21 of the input video signal H to reduce the noise amplitude, and the output video signal J from which the black noise 21 having a large pulse level is removed is obtained. It can be output from the output terminal 13.

[0008]

However, in the above-described conventional black noise elimination circuit, the noise detection level 41 for detecting the black noise 21 is always set to be lower than the amplitude level of the synchronizing signal 20, so that the pulse noise amplitude is large. There is a disadvantage that only the black noise 21 can be detected.

That is, it is not possible to remove black noise at or above the amplitude level of the synchronizing signal 20, and it is not possible to accurately separate video signals due to the unremovable black noise (not shown). there were. Further, since the amplitude level of the black noise 21 to be removed by the DC voltage level adjustment of the DC power supply 33 is set, the output voltage of the DC power supply 33 needs to be stabilized, and the cost of the stabilized power supply increases. There was a disadvantage.

The present invention has been made in view of the above points, and aims at solving the drawbacks of the prior art and detecting a black noise 21 having an amplitude level of 40 or less in a video signal. To provide a black noise elimination circuit capable of eliminating noise.

[0011]

A black noise elimination circuit according to the present invention is a noise elimination circuit for removing black noise, which is superposed on a video signal and has a pulse level having an amplitude level up to the black level of the video signal. Low-pass filter (hereinafter referred to as LPF) that removes high frequency components of the signal
A first synchronization separation circuit for extracting a synchronization signal from the output video signal of the LPF, a first inversion buffer circuit for inverting the synchronization output signal of the first synchronization separation circuit, and a delay for delaying the video signal Circuit, a synchronous clamp circuit for synchronously clamping the delayed output signal with the output signal of the first inversion buffer circuit, a second synchronous separation circuit for extracting a synchronous signal from the synchronously clamped video signal, and a second synchronous separation circuit. An exclusive (hereinafter, referred to as EX-OR) circuit for arithmetically processing the sync separation signal and the first sync separation signal, a second inversion buffer circuit for inverting the sync clamp output video signal, and the inverted video signal A switching circuit controlled by the output signal of the EX-OR circuit to perform a switching operation, a switching circuit for adjusting the level of the output of the switching circuit, and an output of the switching circuit for which the level is adjusted. An addition circuit for adding the output signal of the synchronous clamp circuit and the input signal is provided to remove black noise from the video signal.

[0012]

According to the present invention, the video signal is supplied to the LPF to remove the black noise, which is a pulse noise having an amplitude level below the black level of the video signal, which is superimposed on the video signal. , And the synchronization signal can be accurately separated and extracted from the video signal in which the black noise has been reduced by the first synchronization separation circuit.

On the other hand, the video signal is supplied to a delay circuit (hereinafter, referred to as a DLY circuit), the video signal is delayed by the same delay time as the delay time of the LPF, and the output of the DLY circuit is supplied to a synchronous clamp circuit. This synchronous clamp circuit is the first
The synchronization output signal of the first synchronization separation circuit is supplied through the inversion buffer circuit of the first embodiment, and the output video signal of the DLY circuit supplied to the synchronization clamp circuit is synchronously clamped to perform the second synchronization separation circuit. And supplied to the buffer circuit.

The second sync separation circuit separates a sync signal below the pedestal level from a black noise signal component, and outputs a sync separation output signal of the second sync separation circuit and the first sync separation circuit. To the EX-OR circuit.
The EX-OR circuit can perform an OR operation and output a timing pulse synchronized with the black noise signal.

On the other hand, the output video signal of the synchronous clamp circuit supplied to the buffer circuit is inverted by a second inversion buffer circuit and supplied to the switching circuit. This switching circuit
The ON / OFF control is performed according to the presence or absence of the black noise signal extracted by the EX-OR circuit.
By performing the ON operation, only the black noise signal of the inverted output video signal of the second inverting buffer circuit can be extracted, and the level of the black noise output signal is adjusted by the level adjuster VR and supplied to the adding circuit.

On the other hand, the adder circuit is supplied with the output video signal of the buffer circuit, adds the inverted video level signal to the inverted black level signal, and removes a black noise signal of the video signal.

As described above, black noise having an amplitude level equal to or lower than the black level of the video signal can be detected and black noise can be removed. Therefore, for example, the synchronization separation operation of the subsequent video signal processing circuit or the like is stably operated. Synchronous separation can be performed accurately. In addition, the black noise elimination circuit can eliminate noise without changing the synchronization signal waveform or level of the input video signal.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a black noise elimination circuit according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram showing operation waveforms of respective parts. The same parts as those in the conventional example are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, reference numeral 2 denotes a delay circuit. The delay circuit 2 (hereinafter referred to as a DLY circuit 2) delays an input video signal by a predetermined time and supplies the delayed video signal to a synchronous clamp circuit 3. . Reference numeral 4 denotes a low-pass filter for removing a high-frequency component of the video signal. The output signal of the low-pass filter 4 (hereinafter referred to as LPF 4) is supplied to a first sync separation circuit 5, where the output signal is sync-separated. The synchronous clamp circuit 3 and the EX-
It is supplied to the OR circuit 8.

Reference numeral 7 denotes a second sync separation circuit for performing sync separation of the sync-clamped video signal. The output of the second sync separation circuit 7 is supplied to an EX-OR circuit 8, and the first sync separation circuit 8 outputs the first sync separation signal.
EX-OR operation with the output of the sync separation circuit 5 of FIG. Reference numeral 9 denotes a buffer circuit, and reference numeral 10 denotes a second inversion buffer circuit for inverting the output of the buffer circuit 9. The output of the second inversion buffer circuit 10 is supplied to a switching circuit 11. This switching circuit
The switching operation 11 is controlled by the output signal of the EX-OR circuit 8.

An adder circuit 12 is supplied with the output signal of the buffer circuit 9 and the output signal of the output of the switching circuit 11 whose level has been adjusted by a level adjuster VR. Output from terminal 13.

In FIG. 2, reference numeral 22 denotes a second synchronization separation circuit 7.
Is a threshold level at which synchronization is separated, 23 is a 0 V level of the video signal, and 24 is a threshold level at which synchronization is separated by the first synchronization separation circuit 5.

The black noise elimination circuit having the above-described configuration is used for the video signal A on which the pulsed black noise 21 of the high frequency component is superimposed.
When (the signal waveform in FIG. 2A) is applied to the input terminal 1,
This video signal A is supplied to the LPF 4. The LPF4 characteristic is set to a cutoff frequency that does not degrade the video signal, especially the synchronization signal 20 or the like, for example, f _C ≧ 3 MHz, and the black noise 21 of the video signal A is attenuated by this LPF4. A low-frequency video signal B having a signal waveform as shown in FIG.
Only the first synchronization separation circuit 5 is supplied.

The first sync separation circuit 5 can set the threshold level 24 of the sync separation operation and can sync-separate the low-frequency video signal B which is not affected by the black noise 21 which has been reliably attenuated. As shown in (), the synchronizing signal 20 and the black noise 21 having an amplitude level equal to or lower than the black level of the input video signal A can be extracted. This synchronously separated output signal D
Is supplied to the synchronous clamp circuit 3 via the first inversion buffer circuit 6 and at the same time to the EX-OR circuit 8.

On the other hand, the input video signal A is supplied to the DLY circuit 2 and is delayed by a delay time (not shown) equivalent to the delay time of the low-frequency video signal B signal-processed by the LPF 4. Is supplied to the synchronous clamp circuit 3. This delayed output signal is synchronized with the sync tip clamp (clamp level = DC.0V) operation at the timing of the inverted output synchronization signal obtained by inverting the output signal D of the first synchronization separation circuit 5 by the first inversion buffer circuit 6. The signal is clamped and supplied to the second synchronization separation circuit 7.

The second sync separation circuit 7 sets the threshold level 24 shown in FIG. 4B and performs the sync separation operation.
As shown in (C), the synchronizing signal 20 of the output signal of the synchronizing clamp circuit 3 and the black noise 21 below the pedestal level can be separated and extracted. The output signal C of the second synchronization separation circuit 7 and the output signal D of the first synchronization separation circuit 5 are supplied to the EX-OR circuit 8, and the synchronization signals 20 do not cancel each other out and are output. A timing pulse synchronized with the timing of the black noise 21 of the separated output signal D can be output as shown in FIG. That is, only the black noise 21 can be detected.

On the other hand, the synchronous clamp output signal of the synchronous clamp circuit 3 is supplied to a second inverting buffer circuit 10 via a buffer circuit 9, and the video signal inverted by the second inverting buffer circuit 10 is supplied to a switching circuit. Supplied to 11. The DC level of the inverted video signal is set so that, for example, the 100% white level of the input video signal A is close to the DC.0 V level.

The switching circuit 11 is controlled to be switched by the output signal E of the EX-OR circuit 8, and the black noise of the output signal E
The switching circuit 11 is turned on by the timing pulse 21 and the black noise of the inverted video signal supplied to the switching circuit 11 is turned on.
Only 21 components can be extracted with an amplitude from DC.0V as shown in FIG. 4 (F).

The output timing pulse F synchronized with the black noise 21 of the switching circuit 11 is adjusted in level by the level adjuster VR and supplied to the adding circuit 12. On the other hand, this addition circuit 12
Is added to the output video signal of the buffer circuit 9 supplied to the output video signal. The black noise 21 of the output video signal is canceled by the addition circuit 12 and the output from which the black noise 21 is removed as shown in FIG. The video signal G can be output from the output terminal 13.

As described above, the pulsed black noise 21 having an amplitude level equal to or lower than the black level superimposed on the input video signal A can be removed by the inversion timing pulse synchronized with the black noise 21, so that the subsequent video signal It is possible to prevent the adverse effects of the black noise 21 and the like on the synchronization separation operation of the processing circuit and the like.
The output video signal G from which noise has been removed can be output without changing the 20 waveforms or the amplitude level.

[0031]

As described above, the black noise elimination circuit according to the present invention can remove all of the pulsed black noise 21 having an amplitude level equal to or lower than the black level of the input video signal A. Since the noise removal processing can be performed without deforming the waveform of the synchronization signal 20 of the video signal A or the like, the synchronization separation operation in the subsequent video signal processing circuit or the like can be stably and reliably separated.

Further, the black noise elimination circuit of the present invention is EX-
The complete black noise 21 can be detected by the OR circuit 8, and the black noise 21 can be almost completely canceled by the addition circuit 12 by the detected black noise 21. There is also an effect that there is no unstable element such as setting of a black noise 21 removal level, and unnecessary pulse noise can be removed stably.

In addition, it has excellent features such as simple structure and easy implementation because it can be constructed at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a black noise elimination circuit according to the present invention.

FIG. 2 is a waveform chart showing output signals of each circuit block of the embodiment.

FIG. 3 is a block diagram of a conventional black noise elimination circuit.

FIG. 4 is a waveform diagram showing input / output video signals of a conventional example.

[Explanation of symbols]

 2 Delay circuit (DLY circuit) 3 Sync clamp circuit 4 Low pass filter (LPF) 5 First sync separation circuit 6 First inversion buffer circuit 7 Second sync separation circuit 8 Exclusive (EX-OR) circuit 9 Buffer circuit 10 Second inverting buffer circuit 11 Switching circuit 12 Addition circuit 13 Output terminal A Input video signal B Low-pass filter output signal C Output signal of second sync separation circuit D Output signal of first sync separation circuit E EX-OR circuit Output signal F Output signal of switching circuit G Output video signal

Claims (1)

(57) [Scope of request for utility model registration] 1. A noise removing circuit for removing black noise which is superimposed on a video signal and has an amplitude level up to the black level of the video signal, wherein the low-pass filter removes a high frequency component of the video signal. A first synchronization separation circuit for extracting a synchronization signal from the output video signal of the low-pass filter, a first inversion buffer circuit for inverting the synchronization output signal of the first synchronization separation circuit, and a delay for delaying the video signal Circuit, a synchronous clamp circuit for synchronously clamping the delayed output signal with the output signal of the first inversion buffer circuit, a second synchronous separation circuit for extracting a synchronous signal from the synchronously clamped video signal, and a second synchronous separation circuit. An exclusive OR circuit for performing an arithmetic operation on the synchronization separation signal and the first synchronization separation signal; and a second circuit for inverting the synchronization clamp output signal. An inverting buffer circuit, a switching circuit that switches and controls the inverted video signal with the output signal of the exclusive OR circuit, and a level adjuster that adjusts the level of the output of the switching circuit; A black noise elimination circuit comprising an addition circuit for adding an output signal of the circuit and an output signal of the synchronous clamp circuit.