JPS58222673A - Signal switching controller of television receiver - Google Patents

Abstract

PURPOSE:To decrease number of pins in circuit integration, by superimposing two signals; a gain control signal and a switching signal. CONSTITUTION:A signal inputted from a control signal input terminal 10 is separated at a control signal separating circuit 9, an output of the control signal separating circuit 9 is inputted to a gain control circuit 6 and another output is inputted to a switching circuit 3. As a result, an output obtained at an output terminal 5 is an output where the level of the television signal around characters and graphs in case of superimposing display is suppressed, allowing to make the characters and graphs easy to see on a picture played on a CRT.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal switching control device for a television receiver.

In some television receivers, multiple types of signals are switched and displayed on one screen. - Let's take the case of a teletext receiver as an example. The signal obtained by receiving conventional television broadcasting will be called a television signal, and the digital signal obtained by receiving text broadcasting will be called a text signal.

As a display mode for teletext receivers, there is a super display mode in which a text signal and a television signal are switched and displayed. - In this case, in order to make the character signal easier to see, the level of the television signal surrounding the character signal may be lowered and displayed. In other words, the television signal is displayed using a gain control circuit that lowers the level of the television signal only when the gain control signal is input.Furthermore, in the same teletext receiver, the character signal is displayed depending on the input level of the switching signal. A switching circuit is used to switch between the television signal and the television signal.

In this way, when super display is performed using two signals, the gain control signal and the switching signal, the character signal projected on the screen becomes easier to see, but in the circuit inside the teletext receiver, the gain control signal and the switching signal are Since two signals are used, input terminals are required for each of the gain control signal and the switching signal, and when integrated into an IC, the number of pins increases and the cost increases.

In view of the above points, it is an object of the present invention to provide a means that is particularly advantageous when integrated into an IC by superimposing two signals, the gain control signal and the switching signal.

FIG. 1 is a block diagram showing a conventional example. In FIG. 1, 1 is a television signal input terminal, 2 is a character signal input terminal, 3 is a switching circuit, 4 is a switching signal input terminal, and 5 is an output terminal. The television signal inputted from the television signal input terminal 1 and the character signal inputted from the character signal input terminal 2 are switched by the switching circuit 3 by the switching signal inputted from the switching signal input terminal 4, and the output terminal 6 is output to. In the configuration shown in Figure 1, when in super display,
It has the disadvantage that text and graphic signals are difficult to see on a CRT.

FIG. 2 is a block diagram of the circuit shown in FIG. 1 provided with a gain control function. In FIG. 2, numbers 1 to 5 are the same as those described in FIG. 1, so their explanations will be omitted here. In FIG. 2, 6 is a gain control circuit, 7 is a gain control signal input terminal, and 8 is an output terminal of the gain control circuit 6. In this figure 2, television signal input terminal 1
The level of the television signal inputted from the switch circuit 3 is lowered in accordance with the gain control signal inputted from the gain control signal input terminal 7, and then inputted to the switching circuit 3. As a result, the output obtained at output terminal 5 is super display.
In this case, the level of the television signal surrounding the text/figure signal is lowered, so the text/figure becomes easier to see in the image projected on the CRT.

However, in the configuration shown in FIG. 2, two different terminals, the switching signal input terminal 4 and the gain control signal terminal 7, are required, so when converting to an IC, for example, two pins are required, which increases the cost. The present invention, which has the disadvantage of high energy consumption, is aimed at eliminating the above-mentioned disadvantage.

FIG. 3 shows a block diagram of an embodiment of the present invention.

In the figure, numerals 1 to 7 are the same as in FIGS. 1 and 2. 9 is a control signal separation circuit, and 10 is a control signal input terminal. The control signal input from the control signal input terminal 1o is separated by the control signal separation circuit 9, and one output of the control signal separation circuit 9 is input to the gain control circuit 6, and the other is input to the switching circuit 3. is input. As a result, output terminal 6
In the case of super display, the output obtained is an output in which the level of the television signal surrounding the character/figure signal is suppressed, and in the image projected on the CRT,
It has the advantage of making characters and figures easier to see.
This is the same as the case in FIG.

Next, FIG. 4 shows a specific example of the control signal input to the control signal input terminal 1o of FIG. 3. In Figure 4,
When the control signal level is between 0 and vl, the television signal is transmitted as is and outputted to the output terminal 5, and when the control signal level is between v1 and v2, the level of the television signal is lowered and outputted to the output terminal 6. , the control signal level is 72
The above case indicates that the character signal is output to the output terminal 5. If the control signal level is 72 or higher, as long as a character signal is output to the output terminal 5, the gain control of the television signal may be controlled in any manner.

An example of a specific circuit for generating an example of the control signal in FIG. 4 is shown in FIG. In Figure 5, 11ν 12
is an input terminal, 13 is an open collector output NAND circuit, 14 is an open collector output inverter circuit, 1
6 is a resistor, 16 is a capacitor, 1°7 is a resistor, and 18 is an output terminal.

A gain control signal is applied to the input terminal 11.

When the input gain control signal is at H level, the television signal is transmitted as is, and when it is at L level, it means that the level of the television signal is lowered. Further, a switching signal is applied to the input terminal 12. When the input switching signal is at H level, it means switching to output a television signal, and when it is at L level, it means switching to output a character signal. Capacitor 16 is connected to output terminal 18
This is used to improve the pulse waveform obtained.

Using the circuit example shown in FIG. 6, the control signal shown in FIG. 4 is obtained.

Next, a specific circuit example of the control signal separation circuit 9 in FIG. 3 is shown in FIG. 6. In FIG. 6, 21 is a control signal input terminal, 22 is a current source, 23 is a PNP transistor, 24 is a current source, 26 is an i'NP) transistor, 2
6 is a current source, 27.28 is a PNP transistor, 29
．． 30 is a resistor, 31 is a current source, 32 is a PNP transistor, 33 is a DC voltage source, 34.35 is an output terminal, 36
is a current source, 37.38 is a PNP) transistor, 39.4
0 is a resistor, 41 is a current source, 42 is a PNP) transistor,
43 is a DC voltage source, 44.45 is an output terminal, and 46 is a DC power source.

One of the control signals inputted from the control signal input terminal 21 is subjected to voltage comparison through the emitter follower of the transistor 23 and the differential amplifier of the transistors 27 and 28.
Output is available at output terminals 34.36. The other voltage comparison is performed by the differential amplifier of transistors 37 and 38 through the emitter follower of transistor 26.
Output is available at output terminals 44F 45. Now, the voltage values of the DC voltage sources 33 and 43 are set to 'V1. V2, a gain control signal is obtained at the output terminals 34,35, and a switching signal is obtained at the output terminal 44145.

By using the circuit example shown in Figure 6, the gain control signal and switching signal can be superimposed and input to one input terminal, which is particularly effective when integrated into an IC, and the number of pins can be reduced. This has the advantage of reducing costs.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional example, Fig. 2 is a block diagram when a gain control function is added to the circuit of Fig. 1, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is a block diagram showing a conventional example. FIG. 5 is a waveform diagram showing an example of a control signal, FIG. 5 is a circuit diagram showing an example of a specific circuit for generating a control signal in the present invention, and FIG. 6 is a circuit diagram showing a specific example of a control signal separation circuit in the present invention. . 3...Switching circuit, 6...Gain control circuit, 9...Control signal separation circuit, 15.17.29
730139゜4o...Resistance, 16...
・Capacitor, 23, 25p27s 28+ 32
p 37t 38t 42...transistor, 33y 43y 46...DC voltage source,
22゜24y 26y 31 g 36) 41・
...Current source, 13...NARD circuit, 1
4...Inverter. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3 Figure 3 Figure 4

Claims (1)

[Claims] a control signal separation circuit having a control signal input terminal; a gain control circuit connected to the control signal separation circuit and having a first signal input terminal; a second gain control circuit connected to the control signal separation circuit and the gain control circuit; A signal switching control device for a television receiver, comprising a switching circuit having a signal input terminal.