JPH08275030A - Color video signal processor - Google Patents

Abstract

PURPOSE: To attain clamping stably at a SYNC tip DC potential. CONSTITUTION: A capacitor 22 eliminates a DC component of an input color video, signal CVin, a DC bias Vin is added to the resulting video signal via a resistor 23 and the sum signal is fed to an input of a buffer 24, and an output color video signal CVout is obtained from an output of the buffer 24. An output signal of the buffer 24 is fed to a comparator 28 via a buffer 26 and a filter 27 forming a detection path of a SYNC tip DC potential, in which the output signal is compared with a reference DC potential Vref. The comparator 28 provides an output of a current I as the result of comparison to control charge/ discharge of a capacitor 22 to conduct negative feedback control so that the SYNC tip DC potential of the output color video signal CVout is equal to the reference DC potential Vref. A stable video image is obtained by conducting clamping at the SYNC tip DC potential stably independently of a waveform and an amplitude of a chroma signal in order to allow the filter 27 to attenuate or eliminate the chroma signal component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color video signal processing circuit for keeping a sync tip DC potential at a reference DC potential. More specifically, the present invention relates to a color video signal processing circuit in which a filter for attenuating or removing a chroma signal component is provided in a path for detecting a sync tip DC potential to stably clamp the sync tip DC potential. .

[0002]

2. Description of the Related Art FIG. 5 shows an example of a color video signal processing circuit (sync tip clamp circuit) for maintaining a sync tip DC potential at a reference DC potential in a recording system or a reproducing system of a video tape recorder, for example. . The input terminal 1 to which the input color video signal CVin is supplied is connected to one end of a DC cut capacitor 2, and the other end of the capacitor 2 is connected to one end of a DC bias summing resistor 3 which is connected to the resistor 3. The input DC potential Vin is supplied to the other end of the.

The connection point P1 of the capacitor 2 and the resistor 3 described above is connected to the input side of the buffer amplifier 4, and the output terminal 5 is derived from the output side of the buffer amplifier 4. Further, the output side of the buffer amplifier 4 is connected to the negative input terminal of the comparator 7 via the buffer amplifier 6 forming the sync chip DC potential detection path, and the reference DC potential Vref is supplied to the positive input terminal of the comparator 7. To be done. The output side of the comparator 7 is connected to the connection point P1 described above.

In the above structure, after the DC component of the input color video signal CVin supplied to the input terminal 1 is removed by the capacitor 2, the color video signal from which the DC component is removed is passed through the resistor 3. The input DC potential Vin is added as a DC bias and supplied to the input side of the buffer amplifier 4. The color video signal output from the buffer amplifier 4 is the output color video signal CVout.
Is obtained at the output terminal 5.

The output signal of the buffer amplifier 4 is supplied to the comparator 7 via the buffer amplifier 6 and compared with the reference DC potential Vref. Then, the comparison result is output as the current I from the comparator 7, and the connection point P1
Thus, the DC potential value (DC bias value) of the color video signal supplied to the input side of the buffer amplifier 4 is adjusted. In this case, the change in the DC potential is determined by the time constant determined by the values of the capacitor 2 and the resistor 3 and the magnitude of the current I.

Here, when the sync tip DC potential of the color video signal output from the buffer amplifier 4 rises, the current I flows from the capacitor 2 toward the output side of the comparator 7, and the accumulated charge in the capacitor 2 is discharged. For,
The output color video signal CV output from the buffer amplifier 4 is adjusted so that the DC potential value of the color video signal supplied to the input side of the buffer amplifier 4 is lowered.
The sink tip DC potential of out is lowered.

On the contrary, when the sync chip DC potential of the color video signal output from the buffer amplifier 4 decreases, the current I flows from the output side of the comparator 7 toward the capacitor 2 and the capacitor 2 is charged. Therefore, the DC potential value of the color video signal supplied to the input side of the buffer amplifier 4 is adjusted so as to increase, and thereby the sync tip DC potential of the output color video signal CVout output from the buffer amplifier 4 is increased. That is, negative feedback control is constantly performed so that the sync tip DC potential of the output color video signal CVout becomes equal to the reference DC potential Vref.

FIG. 6 shows another example of the color video signal processing circuit for keeping the sync tip DC potential at the reference DC potential. 6, parts corresponding to those in FIG. 5 are designated by the same reference numerals. In the figure, the input terminal 8 to which the input color video signal CVina added with the DC bias is supplied is connected to the input side of the buffer amplifier 9,
The output side of the buffer amplifier 9 is grounded via a series circuit of a resistor 10 and a capacitor 11. The connection point P2 between the resistor 10 and the capacitor 11 is connected to the input side of the buffer amplifier 4. In addition, the comparator 7
The output side of is connected to the connection point P2. Others are configured similarly to the example of FIG.

Although detailed description is omitted, in the example of FIG. 6 as well, the negative video control of the color video signal supplied from the connection point P2 to the input side of the buffer amplifier 4 is performed by the negative feedback control similar to that of the example of FIG. The DC potential value is adjusted, and the sync tip DC potential of the output color video signal CVout is the reference DC potential Vr.
Negative feedback control is constantly performed so that it becomes equal to ef.

[0010]

By the way, FIG. 7A shows
It shows a color video signal added with an excessive color burst signal CB such that the lower end DC potential VL becomes smaller than the sync tip DC potential Vsc. Further, FIG. 7B shows a color video signal in which the envelope of the color burst signal CB spreads in the time axis direction like the reproduction signal of the video tape recorder, and the end thereof reaches the sync chip. VLa represents the lower end potential of the color burst signal on the sync chip. 7A and 7B
In, HD is a horizontal synchronizing signal.

When a color video signal as shown in FIG. 7A is supplied as the input color video signal CVin in the example of FIG. 5 or as the input color video signal CVina in the example of FIG. 6, the color burst signal CB Lower end DC potential VL
Is controlled so that it becomes equal to the reference DC potential Vref, and therefore the lower end DC potential VL is clamped, and the level of the color burst signal CB fluctuates during special reproduction or the like, the image is disturbed. there were.

Similarly, when a color video signal as shown in FIG. 7B is supplied as the input color video signal CVin in the example of FIG. 5 or as the input color video signal CVina in the example of FIG. There is a possibility that the lower end DC potential VLa of the color burst signal CB on the chip may be controlled to be equal to the reference DC potential Vref.
Therefore, there is a problem that the lower end DC potential VLa is clamped and the image is disturbed.

Therefore, the present invention provides a color video signal processing circuit which is stably clamped at the sync tip DC potential.

[0014]

A color video signal processing circuit according to the present invention comprises a DC potential adjusting means for adjusting a DC potential value of an input color video signal to obtain an output color video signal, and a DC potential adjusting means. A filter for attenuating or removing the chroma signal component included in the output color video signal to be output, and a comparator for comparing the output signal of this filter with a reference DC potential, and the DC potential adjusting means are based on the output signal of the comparator. By adjusting the DC potential value, the sync tip DC potential of the output color video signal is made equal to the reference DC potential.

[0015]

The output color video signal is supplied to the comparator through the filter. The filter attenuates or removes the chroma signal component. Therefore, the comparator compares the sync tip DC potential of the output color video signal with the reference DC potential. Then, in the DC potential adjusting means, the DC potential value is adjusted based on the output signal of the comparator,
The sync tip DC potential of the output color video signal is controlled to be equal to the reference DC potential.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a color video signal processing circuit according to the present invention will be described below with reference to FIG.

In the drawing, an input terminal 21 to which an input color video signal CVin is supplied is a DC cut capacitor 2
2 is connected to one end of the capacitor 22, the other end of the capacitor 22 is connected to one end of a resistor 23 for adding a DC bias, and the input DC potential Vin is supplied to the other end of the resistor 23.

The above-mentioned capacitor 22 and resistor 23
Connection point P1 of the buffer amplifier 24 is connected to the input side of the buffer amplifier 24.
Is derived. Further, the output side of the buffer amplifier 24 is connected to the negative input terminal of the comparator 28 via a series circuit of the buffer amplifier 26 and the filter 27 forming a sync chip DC potential detection path.
The reference DC potential Vref is supplied to the positive input terminal of the reference numeral 8.
The output side of the comparator 28 has the above-mentioned connection point P.
Connected to 1.

The filter 27 is for attenuating or removing the chroma signal component contained in the color video signal. Therefore, the video signal in which the color burst signal CB is attenuated or removed is supplied to the negative input terminal of the comparator 28. The filter 27 is, for example, a low-pass filter having the configuration shown in FIG. By appropriately selecting the cutoff frequency determined by the values of the resistor 27b and the capacitor 27c, the residual chroma signal component can be suppressed to a small value. In FIG. 2, 27a is an input terminal and 27d.
Is an output terminal. The solid line a in FIG. 3 shows the low-pass characteristic of the filter 27. Most of the chroma signal Ca is removed by the filter 27, and only a part Cb of the chroma signal passes.

In the above configuration, after the DC component of the input color video signal CVin supplied to the input terminal 21 is removed by the capacitor 22, the color video signal from which the DC component is removed is passed through the resistor 23. The input DC potential Vin is added as a DC bias, and the buffer amplifier 2
4 is supplied to the input side. Then, the color video signal output from the buffer amplifier 24 is obtained at the output terminal 25 as the output color video signal CVout.

The output signal of the buffer amplifier 24 is supplied to the comparator 28 via the buffer amplifier 26 and the filter 27 and compared with the reference DC potential Vref. Then, the comparison result is output as a current I from the comparator 28, and the buffer amplifier 24 from the connection point P1
The DC potential value (DC bias value) of the color video signal supplied to the input side of is adjusted. In this case, the change in the DC potential is determined by the time constant determined by the values of the capacitor 22 and the resistor 23 and the magnitude of the current I.

Here, if the sync tip DC potential of the color video signal output from the buffer amplifier 24 rises,
The current I flows from the capacitor 22 toward the output side of the comparator 28, and the electric charge accumulated in the capacitor 22 is discharged, so that the DC potential value of the color video signal supplied to the input side of the buffer amplifier 24 is adjusted to decrease. As a result, the sync tip DC potential of the output color video signal CVout output from the buffer amplifier 24 is lowered.

On the contrary, when the sync chip DC potential of the color video signal output from the buffer amplifier 24 decreases, the current I flows from the output side of the comparator 28 toward the capacitor 22 and the capacitor 22 is charged. Therefore, the DC potential value of the color video signal supplied to the input side of the buffer amplifier 24 is adjusted so as to rise, and thereby the sync tip DC potential of the output color video signal CVout output from the buffer amplifier 24 is raised. That is, the negative feedback control is continuously performed so that the sync tip DC potential of the output color video signal CVout becomes equal to the reference DC potential Vref.

Here, in the present example, the color video signal output from the buffer amplifier 24 is compared with the comparator 28.
The filter 27 is arranged in the detection path of the sync tip DC potential to be supplied to the filter to attenuate or remove the chroma signal component. Therefore, even if the input color video signal CVin supplied to the input terminal 21 is the color video signal as shown in FIG. 7A, the comparator 28 outputs the color burst signal CB.
Since the video signal with the attenuated or removed is supplied, the comparator 28 compares the sync tip DC potential with the reference DC potential Vref, and outputs the output color video signal CVo.
The sync tip DC potential of ut is controlled to be equal to the reference DC potential Vref. That is, the clamp is stably applied with the sync tip DC potential. The same applies when the input color video signal CVin supplied to the input terminal 21 is a color video signal as shown in FIG. 7B.

As described above, according to this embodiment, since the filter 27 is arranged in the detection path of the sync tip DC potential and the chroma signal component is attenuated or removed, the comparator 28 always has the sync tip DC potential and the reference DC potential Vref. Are compared with each other, so that the sync tip DC potential of the output color video signal CVout is controlled to be equal to the reference DC potential Vref. As a result, according to this example, since the clamp tip is stably clamped at the sync tip DC potential, a stable image can be obtained regardless of the waveform and amplitude of the chroma signal. Further, according to this example, since the filter 27 has a noise removing effect, even if the input color video signal CVin has a lot of noise, it is relatively stably clamped, and there is an advantage that the video becomes stable.

By implementing the filter 27 with a combination of a resistor 27b and a capacitor 27c as shown in FIG. 2, incorporation in an IC (integrated circuit) can be easily realized. Further, by providing the filter 27, the sync tip waveform of the video signal supplied to the comparator 28 becomes blunt, but it can be sufficiently suppressed within the range where the clamp normally operates, and there is no problem.

Next, a second embodiment of the present invention will be described with reference to FIG. 4, parts corresponding to those in FIG. 1 are designated by the same reference numerals. In the figure, the input color video signal C to which the DC bias is added
The input terminal 29 to which Vina is supplied is a buffer amplifier 30.
Of the buffer amplifier 30, and the output side of the buffer amplifier 30 is grounded via a series circuit of a resistor 31 and a capacitor 32. Then, the resistor 31 and the capacitor 32
The connection point P2 of is connected to the input side of the buffer amplifier 4. The output side of the comparator 28 is connected to the connection point P2. Others are configured similarly to the example of FIG.

Although detailed description is omitted, in the example of FIG. 4 as well, the negative video control of the color video signal supplied from the connection point P2 to the input side of the buffer amplifier 24 is performed by the same negative feedback control as in the example of FIG. The DC potential value is adjusted and controlled so that the sync tip DC potential of the output color video signal CVout becomes equal to the reference DC potential Vref. Then, according to this example, the filter 27 is arranged in the detection path of the sync tip DC potential as in the example of FIG. 1, and the chroma signal component is attenuated or removed, so that the clamp is stably performed at the sync tip DC potential. Therefore, a stable image can be obtained regardless of the waveform and amplitude of the chroma signal.

[0029]

According to the present invention, since the filter for attenuating or removing the chroma signal component is provided in the path for detecting the sync tip DC potential, the sync tip is stably clamped regardless of the chroma signal waveform and amplitude. Therefore, the sync tip DC potential can be controlled to be equal to the reference DC potential, and stable images can be realized regardless of the waveform and amplitude of the chroma signal. Further, since the filter has a noise removing effect, even if the input color video signal has a lot of noise, the image is stabilized because the image is clamped relatively stably.

[Brief description of drawings]

FIG. 1 is a system diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a filter.

FIG. 3 is a diagram for explaining a filter characteristic and an output signal component.

FIG. 4 is a system diagram showing a configuration of a second embodiment of the present invention.

FIG. 5 is a system diagram showing a configuration of a conventional example.

FIG. 6 is a system diagram showing a configuration of a conventional example.

FIG. 7 is a diagram showing an example of a color video signal.

[Explanation of reference numerals] 21,29 Input terminal 22,32 Capacitor 23,31 Resistor 24,26,30 Buffer amplifier 25 Output terminal 27 Filter 28 Comparator

Claims (3)

[Claims] 1. A DC potential adjusting means for adjusting a DC potential value of an input color video signal to obtain an output color video signal, and a chroma signal component contained in the output color video signal output from the DC potential adjusting means. A filter for attenuating or removing, and a comparator for comparing the output signal of the filter with a reference DC potential, the DC potential adjusting means, the DC potential value is adjusted based on the output signal of the comparator, the output A color video signal processing circuit, wherein a sync tip DC potential of a color video signal is made equal to the reference DC potential. 2. The DC potential adjusting means obtains the output color image signal by adding a predetermined DC bias through a resistor after removing the DC component from the input color image signal by a capacitor, and at the same time, the comparator. 2. The color video signal processing circuit according to claim 1, wherein charging / discharging of the capacitor is controlled on the basis of the output signal of to adjust the DC potential value. 3. The DC potential adjusting means grounds an input terminal, to which the input color video signal added with a predetermined DC bias is supplied, via a series circuit of a resistor and a capacitor, and connects the resistor and the capacitor to each other. 2. The DC voltage value is adjusted by obtaining the output color video signal from a connection point and controlling charging / discharging of the capacitor based on the output signal of the comparator.
The color video signal processing circuit according to.