JPH05906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for controlling television signals.

In some television receivers, two types of signals are switched and displayed on one screen. In this case, if the luminance level and chroma level of each signal are the same, it has the disadvantage that it becomes very difficult to see on the screen.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a means for displaying a plurality of types of signals on the same screen in an easy-to-see manner.

Embodiments of the present invention will be described below with reference to the drawings.

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 is the first R signal input terminal, 2
is the second R signal input terminal, 3 is the R signal switching circuit,
4 is a switching signal input terminal, and 5 is an R output terminal.
Further, 1' is the first G signal input terminal, 2' is the second G signal input terminal, 3' is the G signal switching circuit, and 5' is the G signal input terminal.
Output terminals, 1" is the first B signal input terminal, 2" is the second B signal input terminal, 3" is the B signal switching circuit,
5'' is the B output terminal. R signal switching circuit 3, G
The functions of the signal switching circuit 3' and the B signal switching circuit 3'' are exactly the same, so the R signal, G signal, and B signal are used without distinction.Also, the output of the video chroma circuit of the television receiver is In the case of color difference signals and luminance signals, only one more switching circuit is added, and the process 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. The configuration shown in FIG. 1 has a drawback that it becomes difficult to see on the screen when the luminance level and chroma level of the first input signal and the second input signal become similar.

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 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, 6 is a gain control circuit, 7 is a control signal input terminal, and 8 is an output terminal of the gain control circuit 6.

The television signal input from the first input terminal 1 is transmitted to the gain control circuit 6 only for the specified period of the control signal input from the control signal input terminal 7.
As a result of the change in gain, a television signal with a lowered level is obtained at the output terminal 8. The signal obtained at this output terminal 8 and the other signal input from the second input terminal 2 are switched in the switching circuit 3 by the switching signal input from the switching signal input terminal 4, and the output terminal The output is obtained in 5.

The gain control circuit 6 in FIG. 2 lowers the level of the television signal applied to the first input terminal 1 when a control signal is input from the control signal input terminal 7.

An example of the input/output characteristics of a conventional gain control circuit is shown in Part 3.
As shown in the figure. Figure 3 shows the characteristics of the clip circuit.
With this characteristic, V ₁
Since a constant output of V ₁ is obtained for input levels above, V ₁ must be equal to the pedestal level or
If the level is set higher than this, the pedestal level of the television signal obtained at the output terminal 8 will be stabilized, and high signal levels will be suppressed. When displaying on a television screen, the second signal output is easier to see, but the first signal is saturated and no gradation can be obtained, making it difficult to see.

The present invention eliminates the above drawbacks and provides a circuit in which the second signal output is easy to see when two signals are displayed, and the first signal output is also easy to see.

FIG. 4 shows an example of the input/output characteristics of the gain control circuit 6 used in the present invention. As shown in FIG. 4, when the input is less than _V1 , the output is equal to the input, and when the input is more than _V1 , the input level is suppressed as shown by the solid line.

When the output of the video chroma circuit of a television receiver is an RGB three primary color signal and the signal is oriented as shown in FIG. 4, a gain control circuit 6 having the characteristics shown in FIG. 4 is used. In this case, if V ₁ is made equal to the pedestal level, the television signal obtained at the output terminal 8 will have its level suppressed only by the signal that causes the CRT to emit light without changing the pedestal level. Therefore, when two different signals are displayed on the screen, the first television signal output can be displayed with the gradation preserved without losing the video information, and the second television signal output can be displayed with the surrounding signals. Since the contrast of the television signal No. 1 is lowered, it can be displayed clearly. This effect can be obtained.

In addition, when the output of the video chroma circuit of a television receiver is a luminance signal and a color difference signal, and the luminance signal is of negative polarity (the synchronization signal is upward), the characteristics shown in Figure 5 for the luminance signal are obtained. A gain control circuit 6 is used. In this case, setting _V2 equal to the pedestal level is the same as in the case of the RGB three primary color signals. Furthermore, for color difference signals, a gain control circuit 6 having the characteristics shown in FIG. 4 is used, and V ₁
be equal to the pedestal level. Further, the gain control ratio a/b of each of the luminance signal and color difference signal
If you make them equal, the hue will not change.

This has the effect of suppressing the signals that cause the CRT to emit light, both for luminance signals and color difference signals, and allows two different signals to be displayed on the screen, almost in the same way as the RGB three primary color signals. In this case, the first television signal output can be displayed without losing the gradation and image information, and the second television signal output can be displayed clearly because the contrast of the first television signal around it is lowered. can be displayed.

Next, FIG. 6 shows a specific circuit example of the gain control circuit 6 having the input/output characteristics shown in FIG. 4. 6th
In the figure, 1, 7, and 8 are the same as those in FIG. 2, 9 and 10 are resistors, and 11 is a PNP transistor. The sum of the resistance value of resistor 9 and the output impedance of the video chroma circuit connected to television signal input terminal 1 is R ₁ , and the resistance value of resistor 10 is R 1 .
Let it be R ₂ . Further, the control signal level applied to the control signal input terminal 7 is set to Vcc when there is no control, and _V3 when there is control. In the case of no control, the transistor 11 is off, and the television signal input to the television signal input terminal 1 is transmitted to the output terminal 8 as is. In the case of control, ignoring V _BK of the transistor 11, if the level of the television signal input to the television signal input terminal 1 is below _V3 , the transistor 11 is off, but if the level of the television signal is When the voltage exceeds V ₃ , a current flows between the emitter and collector of the transistor 11, and a signal whose level is suppressed is obtained at the output terminal 8. That is, the input/output characteristics of the circuit example of FIG. 6 are as shown in FIG. 4, 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 6 having the input/output characteristics shown in FIG. 5 is shown in FIG. In Figure 7, 1, 7, and 8 are the same as in Figure 2, and 1
2 and 13 are resistors, and 14 is an NPN transistor. The sum of the resistance value of the resistor 12 and the output impedance of the video chroma circuit connected to the television signal input terminal 1 is R ₁ , the resistance value of the resistor 13 is R ₂ ,
Further, the control signal level applied to the control signal input terminal 7 is set to O when there is no control, and set to _V4 when there is control. Also, if V _BE is ignored, if the level of the television signal input to the television signal input terminal 1 is _V4 or higher in the case of no control or with control, the transistor 14 is off and the television signal is It is transmitted as is to output terminal 8, but
With control, the level of the television signal is
When V ₄ or lower, a current flows between the collector and emitter of the transistor 14, and the DC potential at the output terminal 8 rises. Therefore, the input/output characteristics of the circuit example in FIG. 7 are as shown in FIG. 5, with the relationship a/b=R ₂ /R ₁ +R ₂ and V ₁ =V ₄ . In the example shown in FIG. 6, the control signal level in the case of no control has been explained as Vcc, but this level may be just enough to turn off the transistor 11, and the level of the control signal input to the television signal input terminal 1 is sufficient. You can set the level to be higher than the level. Similarly, in the example of FIG. 7, the control signal level in the case of no control is sufficient as long as the level is sufficient to turn off the transistor 14.

As described above, by configuring the circuit as shown in Fig. 2 using the gain control circuit shown in Figs. Because the image is attenuated, the gradation is preserved and the image information can be displayed without loss.
In addition, the second television signal output can be made clearer because the contrast of the first television signal around it is lowered, and a very large effect can be obtained when used in a television receiver.

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 image. It goes without saying that the present invention can also be applied to the case where signals are switched and displayed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is an input/output characteristic diagram of the conventional example, and FIG. 4 is an input/output characteristic diagram of an example of the present invention. FIG. 5 is an input/output characteristic diagram of another example of the present invention,
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, 3', 3''...Switching circuit, 6, 6', 6''...
Gain control circuit, 9, 10, 12, 13...resistance,
11...PNP transistor, 14...NPN transistor.

Claims (1)

[Claims] 1 A gain control circuit having a first television signal input terminal and a control signal input terminal, the gain control characteristic of which is determined by the output impedance of the signal source of the first television signal and the resistance values of two resistors. and a switching circuit connected to the gain control circuit and having a second television signal input terminal and a switching signal terminal, the control start voltage of the gain control circuit being equal to the pedestal level of the television signal. A television signal control device characterized by: