JPH05207331A - Chroma circuit - Google Patents

Abstract

PURPOSE:To improve the clamp method of the bottom clamp system chroma integrated circuit of a color television. CONSTITUTION:The video input signal of a bottom clamp system chroma integrated circuit 104 is impressed after a DC interruption is operated, and the synchronizing signal part of the video input signal is omitted, so that the potential of a pedestal potential part can be controlled to be constant. Thus, the effect of a bottom clamp 103 can be reduced, and the effect equivalent to the chroma integrated circuit of a pedestal clamp can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma circuit used in a color television, a color monitor or the like.

[0002]

2. Description of the Related Art In a color television, a color monitor, or the like, a circuit for color signal processing is required in the case of color demodulating a composite video signal. It is called an integrated circuit (hereinafter simply referred to as a chroma IC). The chroma IC inputs the composite video signal and outputs the R signal, the G signal, and the B signal, but the output characteristics obtained differ depending on which part of the input signal is used as the reference in the course of a series of operations. There are two types of chroma ICs currently on the market, one based on the pedestal potential and the other based on the sync signal potential. The pedestal clamp system (abbreviated as P system below) and the bottom clamp system (hereafter B method).

FIG. 7 is a circuit diagram showing a conventional circuit. The composite video signal includes an amplifier (including an attenuator, the same applies hereinafter) 701.
After the amplitude is adjusted by, the voltage is applied to the video signal input terminal of the chroma IC 704 having the clamp circuit 703 via the capacitor 702, and the chroma IC 704 outputs signals R, G, B. The output of the amplifier 701 is VI, the signal applied to the chroma IC 704 is VX, the chroma IC 7
One of the outputs of 04 is designated as VO.

FIG. 8 is a diagram for explaining the difference in the clamp system, and FIG. 8 (a) shows the case of the P system and the signal V
So that the pedestal part of X becomes the clamp potential EC,
The capacitor 702 is charged and discharged by the clamp circuit 703. Therefore, the video signal is demodulated regardless of the magnitude of the synchronization signal.

FIG. 8B shows the case of the B system, in which the capacitance 702 is charged and discharged by the clamp circuit 703 so that the lowest portion (bottom) of the signal VX becomes the clamp potential EC. Commercially available B-type chroma I
In one example of C, normal demodulation can be obtained at a portion above the potential EA higher than the clamp potential EC by a certain voltage, and correct demodulation cannot be performed for an input lower than the potential EA.

In the case of the P system, the output is controlled with reference to the pedestal level, that is, the black level. Therefore, if the output level is adjusted appropriately, the black level does not change no matter how the input signal changes. ..

On the other hand, in the B system, if the sync signal level is constant according to the standard value, the black level does not change, but if the sync signal level becomes lower than the standard, the level of the entire output decreases, and the sync signal level becomes lower than the standard. When it gets larger, the level of the whole output goes up. Therefore, B-type chroma IC
When using, use an AGC circuit, etc.
It is necessary to make the magnitude of the sync signal of the composite video signal input to the device always constant.

In the case of TV radio waves emitted from a broadcasting station,
The ratio of the video signal and the sync signal is controlled very accurately based on the standard, and the size of the sync signal changes depending on the radio wave condition during reception, but at this time, the level of the video signal also changes at the same rate. Therefore, if the composite video signal is amplified and controlled so that the size of the synchronizing signal becomes constant after reception, the size of the video signal also increases / decreases at the same rate. Therefore, there is no problem even if the B-type chroma IC is used. Does not occur.

However, when the composite video signal input to the chroma IC is not a received signal, a problem may occur when the B type chroma IC is used. As an example in this case,
Examples include output from consumer video cameras and playback output from video tape recorders. That is, in a video camera, a sync signal is added to a video signal from a CCD or the like, but at this time, no difference occurs in the ratio between the video signal and the sync signal or the absolute value of the sync signal. Also in video tape recorders, the same applies when adding a synchronizing signal during recording, and in the case of special playback (pause, fast-forward playback, etc.), the relationship between the video signal and the synchronizing signal may deviate greatly from the standard. .. In such a case, B system chroma I
In C, the pedestal level of the output signal obtained fluctuates extremely, and a normal video screen cannot be obtained.

That is, as shown in FIG. 9, the demodulation output VO of the video signal portion varies depending on the size of the synchronizing signal.

In order to avoid the above problems, the P system chroma I
It suffices to use C, but depending on the usage conditions (for example, the range of power supply voltage, power consumption, etc.), the B-type chroma IC may be used.

[0012]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to provide a stable image even when the size of the sync signal changes in the case of using the B type chroma IC. There is a thing.

[0013]

A first solution used by the present invention to solve the above problems is to input a video signal via a capacitor to a video input terminal of a B-system chroma integrated circuit, and Is to provide a potential setting means for applying a specific potential to one end of the capacitor during at least a part of the period when is at the pedestal level.

In addition to the first solving means, the second solving means used by the present invention for solving the above-mentioned problems is that at least a part of the period when the video signal is the synchronizing signal is not applied to the chroma integrated circuit. It is to provide a shutoff means to do so.

In addition to the first solving means, a third solving means used by the present invention for solving the above-mentioned problem is to further insert a resistor between the video input terminal of the chroma integrated circuit and the capacitance. Is.

In addition to the first solving means, a fourth solving means used by the present invention to solve the above-mentioned problems is that the potential setting means supplies more electric charge than the amount of charges supplied by the clamping action of the chroma integrated circuit. That is, at least the amplitude of the synchronizing signal of the video signal is reduced so that the amount of electric charge generated becomes larger.

[0017]

[Function] B-type chroma IC is pedestal clamped,
A stable demodulated output can be obtained regardless of the fluctuation of the synchronizing signal of the video signal.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a first embodiment of the present invention. In FIG. 1, the composite video signal has its amplitude adjusted by an amplifier (including an attenuator; the same applies hereinafter) 101, and is then connected to one end of a switch 106 and the output of a potential setting means 105 via a capacitor 102. The other end of the switch 106 is connected to a video signal input end of a chroma IC 104 having a bottom clamp circuit 103, and the chroma IC 104 outputs signals R, G and B. A signal FS relating to the sync signal portion of the video signal is applied to the control end of the switch 106,
The potential setting means 105 is supplied with the signal FC relating to the period of the pedestal level of the video signal. The output of the amplifier 101 is VI, the signal applied to the chroma IC 104 is VX, and one of the outputs of the chroma IC 104 is VO.

The potential setting means 105 is basically a potential EA obtained by dividing the constant voltage VDD by resistors R1 and R3.
Is applied to one end of the capacitor 102 via the switch S1 while the video signal is at the pedestal level. The transistor T1 and the resistor R2 are a temperature compensating circuit for compensating the temperature characteristic of the chroma IC 104. The capacitor C1 is for stabilizing the potential. The resistor may be replaced with a variable resistor if necessary.

The operation waveforms of FIG. 1 are shown in FIG. In FIG. 2, a signal FS is a signal for controlling the switch 106 to cut off the synchronizing signal of the signal VI.
Is at a low level, the switch 106 is opened and no synchronizing signal portion is applied to the chroma IC 104.
No clamp current flows from the clamp circuit 103 to the capacitor 102. The signal FC is a signal that closes the switch S1 when the signal VI is at a pedestal level, and when the signal FC is at a high level, the switch S1 is closed and the output of the potential setting means 105 becomes a potential EA. Become. When both the signal FC and the signal FS are at a high level, one end of the capacitor 102 is at the pedestal potential of the signal VI and the other end is at the potential EA.
2 is charged and discharged until it becomes equal to the potential difference between the two, and therefore the signal VX is added with the video signal with reference to the potential EA. By doing so, a correct color signal can be obtained as the output signal VO.

FIG. 3 shows a second embodiment of the present invention, in which the switch 106 in the first embodiment shown in FIG. 1 is replaced with a resistor 107. In this embodiment, the action of the resistor 107 is a part of the synchronizing signal of the signal VI, and the clamp circuit 103 of the chroma IC 104 is used.
Is to block the charging current flowing from the capacitor 102 to the capacitor 102.

That is, in FIG. 4, in the sync signal portion of the signal VI, a clamp current is about to flow from the clamp circuit 103 to the capacitor 102, but this current is limited by the resistor 107. Therefore, only a small amount of electric charge is supplied to the capacitor 102, and the original bottom clamp is not performed. After that, when the signal FC becomes high potential, sufficient electric charge is supplied from the potential setting means 105 to the capacitor 102, and the pedestal clamp action is activated.

FIG. 5 shows a third embodiment of the present invention, in which the resistor 107 in the second embodiment shown in FIG. 3 is eliminated to reduce the signal VI. That is, FIG.
As shown in, the amplifier 101 is adjusted so that the amplitude value of the sync signal portion of the signal VI is always smaller than the reference value. With this configuration, the clamp current does not flow from the clamp circuit 103 to the capacitor 102 in the sync signal portion, and the original bottom clamp is not performed. After that, when the signal FC becomes high potential, the potential setting means 105
Sufficient electric charge is supplied to the capacitor 102, and the pedestal clamp action is activated.

Although FIG. 6 shows the case where the amplification factor is uniformly reduced for all parts of the signal VI, it is of course possible to change the amplification factor only for the synchronization signal part.

The object of the present invention is achieved when the bottom clamp type chroma integrated circuit is adopted and the clamp action of the potential setting means works by overcoming the clamp action of the chroma integrated circuit. In the embodiment of FIG. 1, it is not necessary to cut off all the sync signal portions. In the embodiment of FIG. 3, the value of the resistor 107 changes depending on the current supply capacity of the potential setting means 105 which can supply the capacitor 102 during the period when the signal FC is active. May be set to 0 if is sufficiently large. Also in the embodiment of FIG. 5, how much the amplitude of the synchronizing signal is attenuated is determined by the current supply capacity.

[0026]

As described above, according to the present invention, in the case where the bottom clamp type chroma IC is obliged to be adopted, the pedestal clamp type can be substantially adopted, so that the video tape recorder, A color signal can be demodulated with extremely good reproducibility even for a video signal from a signal source such as a video camera in which the amplitude ratio of the synchronization signal deviates from the reference value, which largely contributes to the provision of a high-performance display device. Is.

Incidentally, in the first embodiment shown in FIG. 1, the insertion position of the switch 106 does not have to be the illustrated position, and may be the point J or the point K in FIG. 1, for example.
Further, it may be inserted inside the amplifier 101 or in front of it. Further, it goes without saying that the potential setting means 105 may have a configuration other than that shown.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing operation waveforms of the embodiment shown in FIG.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

4 is a waveform diagram showing operation waveforms of the embodiment shown in FIG.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

6 is a waveform diagram showing operation waveforms of the embodiment shown in FIG.

FIG. 7 is a circuit diagram showing a conventional circuit configuration.

FIG. 8 is an explanatory diagram illustrating a difference in clamp method.

FIG. 9 is an explanatory diagram for explaining problems of the bottom clamp method.

[Explanation of symbols]

 Reference Signs List 101 amplifier (including attenuator) 102 capacitance 103 bottom clamp circuit 104 chroma IC 105 potential setting means 106 106 switch 107 resistance 701 amplifier (including attenuator) 702 capacitance 703 clamp circuit 704 chroma IC

Claims (5)

[Claims] 1. A video signal is input to a video input terminal of a chroma integrated circuit via a capacitor, and a specific potential is applied to one end of the capacitor during at least a part of a period in which the video signal is at a pedestal level. A chroma circuit characterized by being provided with an electric potential setting means for applying. 2. The chroma circuit according to claim 1, further comprising cutoff means for preventing at least a part of a period in which the video signal is a synchronizing signal from being applied to the chroma integrated circuit. 3. The chroma circuit according to claim 1, further comprising a resistor inserted between the video input terminal of the chroma integrated circuit and the capacitance. 4. The amplitude of at least the synchronizing signal of the video signal is reduced so that the amount of charge supplied by the potential setting means is larger than the amount of charge supplied by the clamping action of the chroma integrated circuit. The chroma circuit according to claim 1, characterized in that: 5. The chroma circuit according to claim 1, wherein the potential setting means is provided with a temperature compensating circuit for compensating the temperature characteristic of the chroma integrated circuit.