JPH0430790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television signal control device used in a television receiver.

Conventional configurations and their problems In television receivers, there are cases where multiple types of signals are switched and displayed on one screen.

In the following description, a case where two types of signals are displayed will be described to make the description easier to understand.
FIG. 1 is a block diagram showing a conventional example. The output of the video chroma circuit of the television receiver is R.
Assume that the three primary colors are (red), G (green), and B (blue).
In FIG. 1, 1 _R is the first R signal input terminal;
2 _R is a second R signal input terminal, 3 _R is an R signal switching circuit, 4 is a switching signal input terminal, and 5 _R is an R output terminal. Further, 1 _G is a first G signal input terminal, 2 _G is a second G signal input terminal, 3 _G is a G signal switching circuit,
5 _G is the G output terminal, 1 _B is the first B signal input terminal,
2 _B is a second B signal input terminal, 3 _B is a B signal switching circuit, and 5 _B is a B output terminal. R signal switching circuit 3
Since the functions of _{the R} , G signal switching circuit 3 _G and the B signal switching circuit 3 _B are exactly the same, the R signal, G signal, and B signal are used without distinction. Furthermore, when the output of the video chroma circuit of a television receiver is a color difference signal and a luminance signal, only one more switching circuit is added, and the output is the same as in the case of RGB three primary color signals.

In FIG. 1, a first signal input terminal 1 receives RGB three primary color signals or a color difference signal and a luminance signal from a video chroma circuit, and a second signal input terminal 2 receives an RGB three primary color signal or a color difference signal. Luminance signals are input, these signals are switched by the switching circuit 3 in accordance with the switching signal input from the switching signal input terminal 4, and outputted to the output terminal 5.

However, in the conventional configuration shown in FIG.
If the luminance level and chroma level of the first input signal and the second input signal become approximately the same, it becomes extremely difficult to see on the screen.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a television signal control device that eliminates the above-mentioned drawbacks and displays a plurality of types of signals on the same screen in an easy-to-see manner.

Structure of the Invention The television signal control device of the present invention includes a first clamp circuit having a first signal input terminal and a clamp pulse input terminal, and a first clamp circuit connected to the first clamp circuit and having a brightness control terminal. a brightness control circuit; a gain control circuit connected to the first brightness control circuit and having a control signal input terminal; a second clamp circuit having a second signal input terminal and a clamp pulse input terminal;
a second brightness control circuit connected to the clamp circuit and having a brightness control terminal; and a switching circuit connected to the gain control circuit and the second brightness control circuit and having a switching signal input terminal. This allows multiple types of signals to be displayed on the same screen in an easy-to-see manner.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of one embodiment of the present invention. In FIG. 2, 1 to 5 are the same as those described in FIG. Also, video
As in the case of FIG. 1, four systems are used when the output of the chroma circuit is a color difference signal and a luminance signal, and three systems are used when the output is an RGB three primary color signal.

In Fig. 2, suffix R indicates the R signal system, 6 _R indicates the first clamp circuit, and 7 _R indicates the second clamp circuit.
clamp circuit, 8 is the clamp pulse input terminal,
9 _R is the first brightness control circuit, 10 _R is the second brightness control circuit.
11 is a brightness control terminal, 12 _R is a gain control circuit, and 13 is a control signal input terminal. Other systems such as 6 _G and 6 _B are shown in the same way as in Figure 1.

The television signal input from the first input terminal 1 is transmitted to the first clamp circuit 6 by the clamp pulse input from the clamp pulse input terminal 8.
and the first brightness control circuit 9
After the brightness level is controlled in accordance with the input applied to the brightness control terminal 11, the signal is input to the gain control circuit 12. In the gain control circuit 12, the gain is changed in accordance with the control signal inputted from the control signal input terminal 13, and a television signal whose level is lowered is obtained as the output of the gain control circuit 12.

On the other hand, the other television signal input from the second signal input terminal 2 is clamped in the second clamp circuit 7 by the clamp pulse input to the clamp pulse input terminal 8, and the second brightness control signal is clamped by the clamp pulse input to the clamp pulse input terminal 8. The brightness level is controlled by the circuit 10 according to the input given to the brightness control terminal 11. The output of the gain control circuit 12 and the output of the second brightness control circuit 10 are switched in the switching circuit 3 by a switching signal inputted from the switching signal input terminal 4, and an output is obtained at the output terminal 5.

As described above, according to the embodiment of the present invention shown in FIG. 2, when displaying by switching two signals, the level of the television signal around the second signal is lowered, so that the second signal output This has the effect of making it easier to see. Further, the first signal and the second signal are transmitted to the first clamp circuit 6 and the second clamp circuit, respectively.
Since the brightness level is controlled by the first brightness control circuit 9 and the second brightness control circuit 10, the brightness level of both signals is stable, and the two signals are switched. This has the effect of making the signal output easier to see when displaying images.

Next, the characteristics of the gain control circuit 12 shown in FIG. 2 will be described. The gain control circuit 12 in FIG.
When a control signal is input from the control signal input terminal 13, the level of the television signal applied to the first input terminal 1 is lowered.

FIG. 3 shows an example of the input/output characteristics of the gain control circuit 12 used in the present invention. As shown in Figure 3,
When the input is below _V1 , the output is equal to the input, and when the input is above _V1 , the input level is suppressed as shown by the solid line.

The input/output characteristics of the polygonal line shown in FIG. 3 have the following advantages over the characteristics of a conventionally used clip circuit. That is, in a conventional clip circuit, for example, when the input is less than or equal to V ₁ , the output is equal to the input, and when the input is greater than or equal to V ₁ , the output is equal to the _input .
It has an input/output characteristic that provides a constant output. However, if a television signal is input to such a clip circuit, the output will be saturated at V ₁ , so if this output is projected onto a cathode ray tube (CRT), it will be unnatural and difficult to see, and in some cases It becomes impossible to distinguish the contents of the video.

On the other hand, when a television signal is input to a circuit with the input/output characteristics shown in Figure 3, the output is suppressed for inputs of V ₁ or more, but the input gradation is not impaired. Even when this output is displayed on a CRT, there is no unnatural appearance, and the image content is accurately transmitted.

Based on the above reasons, when the output of the video chroma circuit of a television receiver is an RGB three primary color signal, a gain control circuit having the characteristics shown in FIG. 3 is used. In this case, if V _{1 is} set to a voltage equal to or higher than the pedestal level, the television signal obtained at the output of the gain control circuit 12 can be controlled by the CRT without any fluctuation in the pedestal level. Only the signal that causes the light to emit light has its level suppressed. Furthermore, the second
If V ₁ and a/b are selected so that the level of the television signal obtained as the output of the gain control circuit 12 is lower than the signal level of the second signal obtained as the output of the brightness control circuit 10,
When displaying two signals, the second signal output is easy to see,
Furthermore, since the gradation of the first signal output is not impaired, it is possible to obtain the effect of eliminating unnaturalness.

FIG. 4 shows a block diagram of an embodiment of the present invention in which the output of the video chroma circuit of a television receiver is a luminance signal and a color difference signal.

In FIG. 4, the first luminance signal input terminal is
_Y , second luminance signal input terminal 2 _Y , first R-Y
The input terminal is 1 _GY , the second G-Y input terminal is 2 _G-
Y , the first G-Y input terminal is 1 _RY , the second R-Y
The input terminal is 2 _RY , the first B-Y input terminal is 1 _B-
Y , the second B-Y input terminal is 2 _BY , and the circuit system connected to each input terminal is Y, R-Y.
It shall be expressed by adding, etc.

When the luminance signal is of negative polarity (the synchronization signal is upward), a gain control circuit _12Y having the characteristics shown in FIG. 5 is used for the luminance signal. In this case, V ₂ is set equal to the pedestal level or V ₂ is set to a voltage lower than the pedestal level.

Compared to the level of the luminance signal input to the second signal input terminal _2Y and obtained as the output of the brightness control circuit _10Y , the luminance signal level of the first television signal obtained as the output of the gain control circuit _12Y is Choose a/b so that it is higher.

Furthermore, gain control circuits 12 _RY , 12 _GY , and 12 _BY having the characteristics shown in FIG. 3 are also used for color difference signals. As in the case of the RGB three primary color signals, V ₁ is set to a voltage equal to or higher than the pedestal level, and is input to the second _signal input terminals 2 _RY , 2 _GY , 2 _BY to control brightness. V 1 , so that the level of the color difference signal obtained as the output of the gain control circuits 12 _RY , 12 GY , 12 _BY is lower than the level of _the color difference signal obtained as the output of the circuits 10 _RY , 10 _GY , _{10 BY} . a/
If b is selected, the effect of suppressing the high level part, that is, the signal part that causes the CRT to emit light, can be obtained, and the first
Since the signal output has gradation, there is no unnaturalness, and it is possible to obtain the effect that the second signal output is easier to see.

Next, FIG. 6 shows a specific circuit example of the gain control circuit 12 having the input/output characteristics shown in FIG. 3. In FIG. 6, 13 is the same as in FIG. 2, and 15
is an input terminal of the gain control circuit 12, 16 and 17 are resistors, 18 is a PNP transistor, and 19 is an output terminal of the gain control circuit 12. Let R ₁ be the sum of the resistance value of the resistor 16 and the output impedance of the brightness control circuit 9, and let R ₂ be the resistance value of the resistor 17. Also,
The control signal level applied to the control signal input terminal 13 is set to V _cc when there is no control, and V ₃ when there is control. In the absence of control, the transistor 18 is in a cutoff state, and the television signal input to the input terminal 15 is transmitted to the output terminal 19 as is. In the case of control, if the level of the television signal input to the input terminal ₁₅ is below _V3 , the transistor 18 is cut off, but if the level of the television signal input to the input terminal 15 is ignored, the level of the television signal is
When the voltage exceeds V ₃ , a current flows between the emitter and collector of the transistor 18, and a signal whose level is suppressed is obtained at the output terminal 19. That is,
The input/output characteristics of the circuit example in FIG. 6 are as shown in FIG. 3, and have the relationship a/b=R ₂ /R ₁ +R ₂ and V ₁ =V ₃ .

Further, a specific circuit example of the gain control circuit 12 having the input/output characteristics shown in FIG. 5 is shown in FIG. In FIG. 7, 13 is the same as in FIG. 2, 20 is an input terminal of the gain control circuit 12, 21 and 22 are resistors,
23 is an NPN transistor, and 24 is an output terminal of the gain control circuit 12. The sum of the resistance value of the resistor 21 and the output impedance of the brightness control circuit 9 is
R ₁ is the resistance value of the resistor ₂₂ , and the control signal level applied to the control signal input terminal 13 is 0 when no control is provided, and V ₄ when there is control. Also, V _BE
Ignoring this, when there is no control and when the level of the television signal input to the input terminal 20 is _V4 or higher with control, the transistor 23 is cut off and the television signal is directly passed to the output terminal 24. However, in the case of control, when the level of the television signal input to the input terminal 20 falls below _V4 , a current flows between the collector and emitter of the transistor 23, and the DC potential at the output terminal 24 rises. It becomes a mess. Therefore, the input/output characteristics of the circuit example in FIG. 7 are as shown in FIG. 5, with the relationships a/b=R ₂ /R ₁ +R ₂ and V ₂ =V ₄ .

In the example shown in FIG. 6, the control signal level in the case of no control is explained as _Vcc , but this level may be just enough to turn off the transistor 18, and the level of the television signal input to the input terminal 15 is sufficient. You can set the level to be higher than the level. Similarly, in the example of FIG. 7, the level of the control signal in the case of no control is sufficient as long as it is enough to turn off the transistor 23.

In addition, in the above explanation, we have described the case where two signals are switched and displayed, but in addition to this, there are also cases where two different channels are switched and displayed on one screen. It goes without saying that the present invention can also be applied to cases in which signals are switched and displayed.

Effects of the Invention As is clear from the above description, the present invention provides a first television signal which is clamped by a first clamp circuit and whose brightness level is controlled by a first brightness control circuit. A gain control circuit changes the level, while a second television signal is clamped by a second clamp circuit,
After controlling the brightness level with the second brightness control circuit, the switching circuit switches and outputs the first signal and the second signal, so the second signal output becomes easier to see, and the first signal output becomes easier to see. Since the signal output also has gradations, it has the advantage of eliminating unnaturalness, so it can be very effective when used in television receivers.

In addition, in the present invention, since the first television signal and the second television signal are clamped and brightness control is performed, in the case of displaying two signals, each television signal is very It has the advantage of being stable.

Furthermore, the present invention has gain control input/output characteristics as illustrated in FIG. 3 or FIG. 5,
If V ₁ is set to a voltage higher than the pedestal level, or if V ₂ is set to a voltage lower than the pedestal level, the low level part of the input signal will not be suppressed, but the high level part will be suppressed. be done. In other words, the effect is that the portions of the CRT where the brightness is high are suppressed, but the portions where the brightness is low are not suppressed. Also, by brightness control, the first
Even if the pedestal level of the television signal changes, the gain control start voltage V ₁ in FIG. 3 or the gain control start voltage V ₂ in FIG.
By setting it outside the range of changes in the pedestal level described above, it is possible to obtain the effect of not being affected by changes in the pedestal level.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a main part of a conventional example, FIG. 2 is a block diagram of a main part of an embodiment of the present invention, FIG. 3 is an example of input/output characteristics in the present invention, and FIG. FIG. 5 is a block diagram of the embodiment, FIG. 5 is a diagram showing another example of input/output characteristics according to the present invention, and FIGS. 6 and 7 are circuit configuration diagrams each showing an example of a gain control circuit that can be used in the present invention. 3 _R , 3 _G , 3 _B , 3 _Y , 3 _RY , 3 _GY , 3 _BY ...
Switching circuit, 12 _R , 12 _G , 12 _B , 12 _Y , 12 _R-
Y , 12 _GY , 12 _BY ...gain control circuit, 6 _R , 6
_G , 6 _B , 6 _Y , 6 _RY , 6 _GY , 6 _BY , 7 _R , 7 _G , 7
_B , 7 _Y , 7 _RY , 7 _GY , 7 _BY , ... Clamp circuit, 9 _R , 9 _G , 9 _B , 9 _Y , 9 _RY , 9 _GY , 9 _BY ,
10 _R , 10 _G , 10 _B , 10 _Y , 10 _RY , 10 _GY ,
10 _BY ...Brightness control circuit, 16, 17,
21, 22...Resistor, 18...PNP transistor, 23...NPN transistor.

Claims (1)

[Claims] 1: a first clamp circuit having a first signal input terminal and a clamp pulse input terminal; a first brightness control circuit connected to the first clamp circuit and having a brightness control terminal; and the first brightness control circuit. a gain control circuit connected to said second clamp circuit and having a control signal input terminal; a second clamp circuit having a second signal input terminal and a clamp pulse input terminal; and a second clamp circuit connected to said second clamp circuit and having a brightness control terminal. 1. A television signal control device comprising: a brightness control circuit; and a switching circuit connected to the gain control circuit and the second brightness control circuit and having a switching signal input terminal.