JPH0793721B2 - Video amplifier - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video amplification device of a television receiver in a system such as a cable television which superimposes various data on a video signal for transmission.

2. Description of the Related Art In recent years, cable television systems have simultaneously transmitted various data in addition to conventional video signals and audio signals in order to improve the quality and increase the number of functions.

Hereinafter, a conventional video amplifier will be described with reference to the drawings. FIG. 3 is a block diagram of a conventional video amplifier and its surroundings, and FIG. 4 schematically shows waveforms in the vicinity of the horizontal blanking period of each part of the conventional video amplifier shown in FIG. It is a thing. In FIG. 3, 21 is an input terminal, 22 is a video amplification circuit, 23 is a color demodulation circuit, 24 is a synchronization circuit, 25 is a color subcarrier trap, 26 is a delay circuit, 27 is a video amplification circuit, and 28 is a DC reproduction circuit. , 29 is an output circuit, 30 is a cathode ray tube, and the part indicated by the dotted line 31 is an image amplification device. In FIG. 4, a is a video signal waveform input to the input terminal 21 of the video amplifier circuit in FIG. 3, b is an output waveform of the video amplifier circuit 27 in FIG. 3, and c is a clamp pulse. , DC regeneration circuit 28 in FIG.
Represents the clamp period.

The operation of the conventional video amplifying apparatus configured as described above will be described below. Video amplifier circuit from input terminal 21
The video signal as shown in FIG. 4a input to 22 is amplified,
One is branched to the color demodulation circuit 23, the other is branched to the synchronization circuit 24, and the other is removed by the color subcarrier trap 25 to remove the color subcarrier component, and a signal as shown in FIG. The signal passes through the circuit 26 and is further amplified by the video amplifier circuit 27.
Here, the level corresponding to the clamp period of the signal shown in FIG. 4b is generated by the clamp pulse of the period shown in FIG. 4c made from the horizontal synchronizing signal separated by the synchronizing circuit 24 by the direct current reproducing circuit 28. Is clamped to a certain DC level, is combined with the signal from the color demodulation circuit 23 by the output circuit 29, and drives the cathode ray tube 30.

With the above operation, the level of the signal shown in FIG. 4B (a video signal from which the color subcarrier is removed, hereinafter referred to as a luminance signal) corresponding to the clamp period shown in FIG. The luminance of the image is determined by clamping the level and using the level as a reference level. In the video signal waveform as shown in FIG. 4A, the relative relationship between the level of the clamp period and the white level and the black level of the image is constant, so if the level of the clamp period is clamped to a certain reference level. The absolute values of the white level and the black level are also determined at the same time, and a normal image is reproduced. (For example, the Institute of Electronics and Communication Engineers, Electronic Communication Handbook P1566, NHK Color Television Textbook Chapters 4 and 5) Problems to be Solved by the Invention However, in the above configuration, the luminance signal is clamped by the DC regeneration circuit. Since the level of the period is clamped to the reference level of luminance, in order to reproduce a normal image, the relative relationship between the level of the luminance signal and the white level and the black level at least is constant at the value determined by the standard. Must be Therefore, when a data signal that cannot be removed by the color subcarrier trap is superimposed in the clamp period, the relative relationship between the level of the luminance signal in the clamp period and the white level and the black level fluctuates or even if it is constant. Since the value is not the value defined by the standard, the luminance of the reproduced image becomes abnormal. As a specific phenomenon, if the level of the luminance signal clamp period is shifted toward the white level by a certain ratio, the entire image is darker than the normal image and is shifted toward the farther from the white level by a certain ratio. The whole image becomes brighter than the normal image. When the level of the luminance signal clamp period fluctuates, the time constant of the DC reproducing circuit, that is, when the luminance signal during the clamp period deviates from the reference level to be clamped, the level of the deviated luminance signal Although the degree varies depending on the time constant for pulling in to the reference level, the luminance of the image fluctuates as the level of the luminance signal clamp period changes. As described above, in the conventional video amplifier, it is impossible to superimpose a data signal that cannot be removed by the chrominance subcarrier trap during the clamp period for direct current reproduction of the luminance signal without fluctuation or deterioration of the video. Had a point. Moreover, in the image amplification device of an actual television receiver, the set clamp period is not necessarily constant depending on the manufacturer and model, and the luminance signal is chrominance subcarrier trap in a form that avoids the clamp period for a specific model. Even if a data signal that cannot be removed by superimposing is superposed, it is completely meaningless in a model having a different clamp period, so it is difficult to support all television receivers.

The present invention solves the above problems and superimposes and transmits a data signal that cannot be removed by the chrominance subcarrier trap even during a period including a clamp period for direct current reproduction of a luminance signal, thereby increasing the amount of data that can be transmitted and reducing the amount of video. The present invention provides a video amplification device that does not fluctuate or deteriorate.

Means for Solving the Problems In order to solve the above problems, the video amplification device of the present invention is
After detecting the data transmitted superimposed on the video signal, erase the data signal in the period including at least the clamp period of the DC reproduction circuit, or at least only the low frequency component that the DC reproduction circuit follows. A filter for erasing, and a switching circuit for switching the filter,
It has a switching timing setting circuit for setting the timing for switching.

Operation According to the present invention, the data signal in the period including at least the clamp period of the DC reproducing circuit is removed by the above-described configuration, and the mutual relationship between the level of the luminance signal and the white level and the black level in the period is made constant. Alternatively, if a low frequency component that follows the direct current reproduction circuit is removed, even if the level of the luminance signal fluctuates, the average level of the portion where the data signal is superimposed is made to match the level of the luminance signal before the data signal is superimposed. If so, the DC reproducing circuit clamps the average level of the data signal during the clamp period to the reference level, so that the luminance signal level before superimposing the data signal matches the reference level, and the mutual relationship between the white level and the black level is maintained. Be drunk As described above, even if a data signal that cannot be removed by the color subcarrier trap is superimposed during the clamp period, the luminance signal is clamped to the correct reference level and a normal image can be obtained.

Embodiment An image amplifying apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image amplifying apparatus and its periphery in an embodiment of the present invention, and FIG. 2 is a horizontal blanking of each part of the image amplifying apparatus of the embodiment of the present invention shown in FIG. It is a diagram schematically showing the waveform near the return line. In FIG. 1, 1 is an input terminal, 2 is a data detection circuit, 3 is a switching timing setting circuit, 4 is a switching circuit, 5 is a filter, 6
Is an image amplification circuit, 7 is a color demodulation circuit, 8 is a synchronization circuit, 9 is a color subcarrier trap, 10 is a delay circuit, 11 is an image amplification circuit, 12 is a direct current reproduction circuit, 13 is an output circuit, and 14 is a cathode ray tube. , 6 to 14 of the conventional image amplifying apparatus shown in FIG.
It is the same as 22 to 30, and has the same function.
In FIG. 1, a portion indicated by a dotted line 15 is the image amplifying device in this embodiment.

In FIG. 2, a is a signal input to the input terminal 1 of the video amplifying device in FIG. 1, b is a clamp period of the DC reproducing circuit 12 in FIG. 1, and c is a switching timing setting in FIG. 3 is a switching timing signal waveform generated by the circuit 3, d is an input signal to the video amplifier circuit 6 in FIG. 1, and e is an output waveform from the video amplifier circuit 11 in FIG.

In the waveform shown in FIG. 2, 16 is a color burst signal for color synchronization, and 17 is a data signal, which is superposed on the back porch of the video signal in this embodiment. Further, 18 and 19 are residual data signals, and 20 is a color burst signal which is the same as 16.

Regarding the video amplifier circuit configured as described above,
This will be described with reference to FIGS. 1 and 2. The signal of FIG. 2a input from the input terminal 1 is guided to the data detection circuit 2 on the one hand, and the superimposed data signal 17 is detected. Therefore, since the data signal 17 is not necessary thereafter, no matter how the data signal 17 is dealt with, it does not matter. On the other hand, the switching timing signal setting circuit 3 produces the switching timing signal of FIG. 2c including the clamp period of the DC reproducing circuit shown in FIG. 2b from the signal of FIG. 2a input from the input terminal 1. The switching circuit 4 is operated by this switching timing signal, and in the waveform of FIG. 2c, the signal input from the input terminal 1 is guided to the video amplifier circuit 6 through the filter 5 only when the waveform is "H". , "L", the signal input from the input terminal 1 is guided to the video amplifier circuit 6 as it is. The characteristics of the filter 5 here are the color burst signal 16
Is a band-pass filter that passes the signal, and has a phase rotation of 0 ° or an integral multiple of 360 ° at the frequency of the color burst signal, and has sufficient attenuation in the frequency band of the data signal 17. The signal thus input to the video amplifier circuit 6 is as shown in FIG. 2d. The operation after the image amplification circuit 6 is exactly the same as that of the image amplification device described in the conventional device. Therefore, the output waveform of the video amplifier circuit 11 shown in FIG.
The brightness of the image is determined by clamping at the timing indicated by. As is clear from the relationship between FIGS. 2b and 2e, the data signal including the clamp period of FIG. 2e is erased and the level of the video signal before the data signal is superimposed is clamped to the reference level. The image is reproduced with high brightness.

In addition, the clamp period is usually taken before the color burst signal of the back porch in an actual television receiver, but it may be taken after the color burst signal of the back porch depending on the manufacturer and model. In such a case, it suffices to widen the switching timing signal shown in FIG. 2c and erase the data signal for all the expected clamp periods.

Further, as shown in FIG. 2e, the residual data signal 19 remains as a luminance signal, but in an actual television receiver, it is usually irrespective of the level of the luminance signal during the blanking period. , It doesn't matter since it is configured to erase the return line.

Also, the signal supplied to the color demodulation circuit 7 is the residual data signal 18 on top of the color burst signal 20 as shown in FIG.
However, in an actual television receiver, the input part of the normal color demodulation circuit 7 has a filter for extracting a color subcarrier, and the color demodulation circuit is a synchronous detection circuit using a PLL. Therefore, it is strong against interference, and even if there is a residual data signal, it does not affect the color of the image at all.

As described above, according to the present embodiment, the video signal is affected by the superimposed data signal by erasing the data signal in the clamp period of the DC reproducing circuit by using the filter, the switching circuit and the switching timing setting circuit. Without being clamped to a normal level, you can get a video with normal brightness.

In this embodiment, the characteristic of the filter is a bandpass filter that allows the color burst signal to pass, the phase rotation at the frequency of the color burst signal is 0 ° or an integral multiple of 360 °, and the frequency of the data signal is It is assumed that there is sufficient attenuation in the band, and all the data signals during the period of passing through this filter are erased. This is because the average level of the part where the data signal is superimposed is the luminance signal before the data signal is superimposed. A filter that removes only low frequency components, which the DC recovery circuit follows, may be used if it matches the level. Since the time constant of the DC regeneration circuit is usually sufficiently larger than the cycle of the color burst signal, it is easy to use a filter that allows the color burst signal to pass without rotating the phase and removes low frequency components that the DC regeneration circuit follows. can get. If such a filter is used, the high-frequency component contained in the data signal remains in the luminance signal during the clamp period, but the direct current reproduction circuit does not follow the remaining data signal component, and the luminance signal Is clamped to the normal level.

As described above, according to the present invention, a filter, a switching circuit, and a switching timing setting circuit are provided to erase a part or all of a data signal in a period including at least a clamp period of DC regeneration. It is possible to obtain an image amplifying device capable of reproducing a normal image without being disturbed by the data superimposed in the horizontal blanking period of the image signal.

[Brief description of drawings]

FIG. 1 is a block diagram of an image amplifying device and its periphery in one embodiment of the present invention, and FIG. 2 is a horizontal blanking period of each part of the image amplifying device of one embodiment of the present invention shown in FIG. 3 schematically shows the waveform of FIG. 3, FIG. 3 is a block diagram of a conventional video amplifier and its surroundings, and FIG. 4 is a horizontal blanking period of each part of the conventional video amplifier shown in FIG. It is the figure which showed the waveform of. 1 ... input terminal, 2 ... data detection circuit, 3 ... switching timing setting circuit, 4 ... switching circuit, 5 ... filter,
6 ... Video amplification circuit, 7 ... Color demodulation circuit, 8 ... Synchronization circuit, 9 ... Color subcarrier trap, 10 ... Delay circuit, 11 ...
… Video amplification circuit, 12 …… DC reproduction circuit, 13 …… Output circuit, 14 …… CRT, 15 …… Video amplification device.

Claims (1)

[Claims] 1. When transmitting a data signal superimposed on a color video signal, a filter for passing at least a direct current component and a color burst signal and attenuating a frequency band in which a direct current reproducing circuit responds, a switching circuit, and a switching timing. A setting circuit is provided, and a period including at least a clamp period for direct current reproduction of a video signal in which the data signal is superimposed over part or all of the horizontal blanking period is set by the switching timing setting circuit and set. A video amplifying device configured to erase a part or all of data superimposed on the video signal by inserting the filter into the video signal passing circuit in the switching circuit only for a period.