JPH05145905A - Character signal/r, g, b signals switching device - Google Patents

Abstract

PURPOSE:To always make a black level coincident with a character signal by using the horizontal blanking level of R, G and B signals completely equal to the horizontal blanking level of the character signal. CONSTITUTION:The values of resistors R-R are decided so that the horizontal blanking level of the R, G and B signals can be equal to that of the character signal. Then, signals from a video camera or the like is inputted to an R, G and B signals input line 1 and the character signal received from a teletext is inputted from character signal input line 2 to an electronic changeover switch 3 as well. The output from the switch 3 is changed over by a switch control signal 8 impressed to an OR gate 4, connected to the side of the input line 2 only for a horizontal blanking period and connected to the side of the input line 1 for the other period. Since a horizontal flyback section has a level equal to the horizontal blanking period obtained in the character signal, signals outputted from an output line 7 are obtained as the R, G and B signals and supplied to an RGB signals processor 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching device for character signals and R, G, B signals for making the horizontal blanking levels of character signals and R, G, B signals coincide with each other in a television receiver.

[0002]

2. Description of the Related Art In recent years, while the frequency of character multiplex broadcasting in television broadcasting has increased, the widespread use of video equipment such as video cameras has been remarkable.

Conventionally, in a television receiver, when a character signal obtained by receiving a character multiplex broadcast and R, G, B signals which are video signals output from a video camera or the like are simultaneously received, A device for switching a character signal from a character multiplex broadcast and an R, G, B signal from a video camera device or the like is used before the G, B signal processing device.

A conventional character signal and R, G, B signal switching device will be described below with reference to FIG. As shown in the figure, an R, G, B signal input line 1 and a character signal input line 2 are added to the electronic changeover switch 3, and the electronic changeover switch 3 selects either the R, G, B signal or the character signal. A changeover switch for selecting a signal is changed over by a control signal 8 and outputted from an output line 7 and added to an R, G, B signal processing device 7. On the other hand, the transistor Q ₁ is turned on by the voltage generated by the resistors R ₂ , R ₃ and R ₄ and outputs a DC bias voltage to the DC bias input line 9 for the R, G and B signals.

The character signal and R, which are configured as described above,
The operation of the G and B signal switching device will be described below. First, the character signal received from the character multiplex broadcast is applied with a predetermined DC bias voltage, the horizontal blanking level is always constant, and this signal is applied to the character signal input line 2 in FIG. .. On the other hand, the R, G, B signals input from the R, G, B signal input lines 1 generally do not have a DC bias, and the transistor Q ₁ , resistors R ₂ , R ₃ ,
The circuit constituted by R ₄ inputs the voltage to the changeover switch 3 through the DC bias input line 9 so that the voltage is biased to a voltage equal to the horizontal blanking level of the character signal. Next, the changeover switch control signal 8
Generally, either one of the signals is selected by and is input from the output stage 7 to the RGB signal processing device 10 at the next stage.

[0006]

However, in the above conventional configuration, the horizontal blanking level of the character signal is changed, the amplification degree of the transistor Q ₁ is changed by temperature, and the resistance values of the resistors R ₂ , R ₃ and R ₄ are changed. Due to changes and variations in constants, the horizontal blanking level of the R, G, B signals does not completely match the horizontal blanking level of the character signal.
Therefore, the conventional configuration has a problem that the horizontal blanking interval of the R, G, B signals does not become the black level when the horizontal blanking level of the R, G, B signals becomes higher than the horizontal blanking level of the character signal. Was there.

The present invention solves the above-mentioned problems of the prior art, and is such that the horizontal blanking level of the R, G, B signals can be completely matched with the horizontal blanking level of the character signal and the character signal R, An object is to provide a G, B signal switching device.

[0008]

To achieve this object, in the character signal and R, G, B signal switching device of the present invention,
In any of the R, G, B signal modes and the character signal mode, the input line of the character signal is selected in the horizontal blanking interval, and the horizontal blanking level of the R, G, B signals is set to the horizontal blanking level of the character signal. It is configured to use exactly the same as the ranking level.

[0009]

With this configuration, even in the R, G and B signal modes, the horizontal blanking interval has the same voltage level as that of the character signal mode, so that the horizontal blanking level, that is, the black level always coincides with the character signal. ..

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an R, G, B signal input line 1 meaning a video signal from a video camera or the like, and a character signal input line 2 obtained by receiving a character multiplex broadcast are electronic. In addition to the changeover switch 3, the electronic changeover switch 3 outputs the R, G, B signals from the OR gate 4 to which the changeover control signal 5 for changing over the character signal and the horizontal synchronizing signal 6 is added. The signals are electronically switched by a switch control signal 8 for switching between the G and B signals and the character signal, output from the output line 7, and added to the RGB signal processing device 10.

Next, the horizontal synchronizing signal 6 passes through the resistor R ₁ and then is applied to the output line 7 of the electronic changeover switch 3 through the diodes D ₂ and D ₃ and also passes through the resistor R ₃ and the transistor Q. _{Entered in} the base of ₁ . The output DC voltage appearing across the emitter resistance R ₂ of the transistor Q ₁ is output to the DC bias input line 9 for supplying the DC bias to the R, G, B signal input line 1 through the diode D ₁ .

The character signal and R, which are constructed as described above,
The operation of the G and B signal switching device will be described below.

The normal operation is as described in the conventional example and is omitted here, and the operation during the horizontal blanking period of the present invention will be described. First, the resistance values of R ₁ , R ₂ and R ₃ are determined so that the horizontal blanking levels of the R, G and B signals and the character signal are equal. Next, R,
A signal from a video camera or the like is input to the G and B signal input lines 1, and a character signal received from a character broadcast is also input to the electronic changeover switch 3 from the character signal input line 2. Here, the output from the electronic changeover switch 3 is O
It is switched by the changeover switch control signal 8 applied to the R gate 4, but the electronic changeover switch 3 is connected to the character signal input line 2 side only during the horizontal blanking period of the character signal, and R, G, B
The signal output from the output line 7 by connecting to the signal input line 1 side is obtained by outputting R, G, B signals having a level equal to the horizontal blanking period of the character signal in the horizontal blanking interval. It is supplied to the RGB signal processing device 10 in the next stage. Further, during the horizontal blanking period, the horizontal synchronizing signal 6 becomes high, the transistor Q ₁ becomes conductive, and the horizontal blanking level of the character signal output from the output line 7 through the diodes D ₁ , D ₂ , D ₃ and the transistor Q ₁ is held. Are transmitted to the R, G, B signal input line 1. That is, since the feedback is fed back to the DC bias of the R, G, B signals so as to be equal to the horizontal blanking level of the character signal, it is not affected by the fluctuation of the horizontal blanking level of the character signal, and Transistor Q
Even when the temperature of H _fe of ₁ is changed, the diodes D ₁ , D ₂ , D
Offset by ₃ .

[0015]

As described above, according to the present invention, by adding a simple circuit, the R, G, B signals obtained from a video camera or the like and the character signal obtained by receiving the character multiplex broadcast can be obtained. An excellent character signal and R, G, B signal switching device capable of completely matching the horizontal blanking levels can be realized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a character signal and R, G, and
Block diagram of B signal switching device

FIG. 2 is a block diagram of a conventional character signal and R, G, B signal switching device.

[Explanation of symbols]

 1 R, G, B signal input line 2 Character signal input line 3 Electronic changeover switch 4 OR gate 5 Changeover control signal 6 Horizontal synchronization signal 8 Changeover switch control signal

Claims (1)

[Claims] 1. A changeover switch for switching between a character signal input and an R, G, B signal input to output either one of the signals, and a horizontal blanking signal included in the character signal during a horizontal blanking period. A character signal and R, G, B signal switching device configured to generate a changeover switch control signal for selective output.