JPS63232770A - Television receiver - Google Patents

Abstract

PURPOSE:To switch a signal switching circuit to a video side only when a video signal exists at a video input terminal by switching a signal switching circuit to a video input terminal side with the detecting output of a video signal detecting device. CONSTITUTION:When a video supplied to a video input terminal 4 is watched, a change-over switch 19 is closed and an and circuit 15 is closed. When a video signal is supplied to a video signal input terminal 4, an output terminal 14 of a video signal detecting circuit 12 comes to be a high level. As this result, since an output terminal 16 of the and circuit 15 comes to be a high level, a tuner video change-over switch 5 is switched to a video side. Consequently, a video signal connected to the video input terminal 4 is reflected through a switching circuit 5 and a color demodulating circuit 10 to a CRT 11. On the other hand, when the video signal does not exist at the video input terminal 4, the output of the detecting device 12 comes to be a low level, the change-over switch 5 is connected to a tuner side as it is and not switched to a video side.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a television receiver (hereinafter abbreviated as television) equipped with a video input terminal.

2. Description of the Related Art A conventional television equipped with a video input terminal has a configuration as shown in FIG.

The following description will be given with reference to the drawings. When receiving a television broadcast, the changeover switch 28 is open and the terminal 27 of the changeover circuit 23 is at a low level. When the terminal 27 is at a low level, the contacts 24 and 26 of the switching circuit 23 are connected, and the TV broadcast radio waves are transmitted to the antenna 20. tuner 2
1. VIF circuit 22. Contact 24 of switching circuit 23. Contact 2
5. It passes through the color demodulation circuit 29 and is connected to a cathode ray tube (hereinafter referred to as CRT).
When it is desired to view the video connected to the video input terminal 31, the terminal 27 of the switching circuit 23 becomes high level when the changeover switch 28 is closed. When the terminal 27 becomes high level, the contacts 26 and 25 of the switching circuit 23 are connected. Switching circuit 23
When the contacts 26 and 25 are connected, the signal connected to the video input terminal 31 is transmitted to the contacts 26 . Contact point 25. The image passes through the color demodulation circuit 29 and is displayed on the CRT 30.

Invention Me; Problem to be Solved However, in the above configuration, when the switching circuit 23 is switched to the video input terminal 31 side with the video changeover switch 28, when no video signal is connected to the video input terminal 31, the C
There is a problem that a noise screen is displayed on RT30.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention provides a television that can switch to the video terminal only when a video signal is present at the video input terminal.

Means for Solving the Problems In order to solve the above problems, the present invention provides a detection means for detecting the presence or absence of a signal at the video input terminal, and detects when a video signal is applied to the input terminal. The circuit is configured so that the signal switching circuit is switched to the video input terminal side based on the detection output signal of the video input terminal.

According to the present invention, with the above-described configuration, the signal switching circuit can be switched to the video input terminal side only when a signal is connected to the video input terminal, so that an image is always displayed on the CR7 screen. It can eliminate unsightliness.

Embodiment Hereinafter, a television with a video signal switching circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

In the figure, 1 is an antenna, 2 is a tuner, 3 is a VIP circuit, 4 is a video input terminal, 5 is a switching circuit, 1o is a color demodulator, 11 is a CRT, and 12 indicates the presence or absence of a video signal applied to the video input terminal 4. 15 is an ANDJTil path, and 19 is a changeover switch for switching between the video signal received from the antenna 1 and an external video signal. The AND circuit 15 inputs the output signal of the video signal detector 12 and the open/close signal of the changeover switch 19, and uses its output to control the switching of the changeover circuit 5.

The operation of the above configuration will be explained next.

When receiving television broadcasting, the selector switch 19 is open and the A
The terminal 18 of the ND circuit 16 is at a low level. AN
When either the terminal 17 or the terminal 18 of the D circuit 16 is at a low level, the output terminal 16 of the AND circuit 15 is at a low level. Therefore, in this case, terminal 1 of the AND circuit 15
8 is at a low level, the output terminal 1 of the AND circuit 16
6 becomes a low level, and the terminal 9 of the switching circuit 5 also becomes a low level. When terminal 9 is at a low level, contacts 6 and 7 of switching circuit 5 are connected. Therefore, the radio waves of TV broadcasting are transmitted by antenna 1. Tuner 2. VIP circuit 3. Switching circuit 5
The CRT
It will be displayed on ll.

When the user wants to view the video connected to the video input terminal 4, the selector switch 19 is closed. Then, terminal 18 of AND circuit 16
becomes high level. When there is a video signal at the video input terminal 4, the output terminal 14 of the video signal detection circuit 12 goes high. When both terminals 17 and 18 of the AND circuit 15 become high level, the output terminal 16 of the AND circuit 15 becomes high level, and the terminal 9 of the switching circuit 5 also becomes high level.

When the terminal 9 of the switching circuit 6 becomes high level, the contacts 6 and 8 of the switching circuit 6 are connected. Therefore, the signal connected to the video input terminal 4 is transmitted to the contact 8. of the switching circuit 5. Contact 6
．． The image passes through the color demodulation circuit 10 and is displayed on the CRT II.

When there is no video signal at the video input terminal 4, the output terminal 14 of the video signal detector 12 is at a low level, and the terminal 17 of the AND circuit 16 is also at a low level. Even if the terminal 18 is at a high level, the output terminal 16 is at a low level, and the terminal 9 of the switching circuit 5 is also at a low level, so the switching circuit 6 connects contacts 6 and 7 and switches to the TV side, so the video input is switched to the TV side. It is not connected to the terminal 4 side. Therefore, no noise appears on the CRT screen.

Effects of the Invention As described above, according to the present invention, the switch is made to the video side only when there is a video signal at the video input terminal.
Even if the CRT is operating, it will not switch to the video side when no video signal is being output, so it can only be switched so that the image is always displayed on the CRT, thereby preventing a noise screen. This means that you can always receive television.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a television receiver according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional television with a video signal switching function. 4...Video input terminal, 6...Signal switching circuit, 12...Video signal detector, 15...
...AND circuit, 19...changeover switch. Name of agent: Patent attorney Toshio Nakao and one other person
1 figure
4-11-15-・Duto J East 1 Yoe ξ Figure 2

Claims (1)

[Claims] a video input terminal, a video signal detector that detects the presence or absence of a video signal applied to the video input terminal, and a switching circuit that switches between the video signal obtained from the antenna and the video signal applied to the video input terminal and outputs it to the cathode ray tube. and means for controlling the switching circuit to select the video signal applied to the video input terminal by the output of the video signal detector when the video signal is applied to the video input terminal.