JPH03190384A - Video signal switching circuit - Google Patents

Abstract

PURPOSE:To obtain excellent picture quality by providing a switch comprising a transistor(TR) further to a switch input and turning on the input TR when the switch is turned off so as to fix a video signal to an L level. CONSTITUTION:A switch comprising a TR 8(9) is provided respectively to an input of switches 5, 6. Thus, a video signal not selected by using a switching signal (c) and its inverting switching signal (d) is fixed to an L level at the input of the switch. Thus, a signal being a cause to crosstalk is not inputted to a switch of the post-stage. Thus, crosstalk between the switches 5, 6 is avoided to prevent deterioration in the picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal switching circuit for switching video signals of a television receiver.

BACKGROUND OF THE INVENTION In recent years, video signal switching circuits have been widely used as television receivers have become AV systems.

An example of the conventional video signal switching circuit mentioned above will be described below with reference to the drawings.

FIG. 3 shows a circuit diagram of a conventional video signal switching circuit. In FIG. 3, 1 is a video signal input terminal to which a video signal a is input. 2 is a video signal input terminal for inputting a video signal. 3 is a switching signal input terminal to which a switching signal C is input. 4 is an inverter,
The switching signal C is inverted to generate an inverted switching signal d. A switch 5 turns on and off the video signal a using a switching signal C. b is a switch that turns on and off the video signal with an inverted switching signal d; A video signal output terminal 7 outputs the video signal e switched by the switch 5.6.

The operation of the video signal switching circuit configured as described above will be explained below.

First, FIG. 4 shows a timing chart corresponding to the circuit diagram of FIG. 3. When the switching signal C is "H", the inverted switching signal d becomes "L", the ONL video signal a passes through the switch 5, and the switch 6 is 0FFII, and the video signal does not pass, so the video signal e is video signal a is output.

On the other hand, when the switching signal C is "L", the inverted switching signal d becomes "°H", the switch 5 is turned off and the video signal a does not pass, and the switch 6 passes only the ONL video signal. Therefore, the video signal S is output as the video signal e. In this way, the switching signal C °°H","
L", only one of the switches 5 and 6 switches between ONL, video signal a, and video signal S.

Problems to be Solved by the Invention However, in the above configuration, the degree of separation between the switches 5 and 6 is not sufficient, so crosstalk occurs between signals containing high frequency components such as video signals, which deteriorates the image quality. There was a problem.

In view of the above problems, the present invention provides a video signal switching circuit that suppresses the occurrence of video signal crosstalk between two switches and prevents deterioration of image quality.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention is designed so that a signal that is a source of video signals is not input to a subsequent switch.

According to the present invention, with the above-described configuration, a signal that causes crosstalk is not inputted to a subsequent switch, so that crosstalk does not occur and image quality does not deteriorate.

Embodiment Hereinafter, a video signal switching circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a circuit diagram of a video signal switching circuit in one embodiment of the present invention.

In FIG. 1, 1 is a video signal 1 input terminal, 2 is a video signal 2 input terminal, 3 is a switching signal input terminal, 4 is an inverter, 5.6 is a switch, 7 is a video signal output terminal, and the above is a third video signal input terminal. The configuration is the same as the one shown in the figure. A transistor 8 turns on and off the video signal a. 9 is a transistor that turns on and off the video signal. Reference numeral 10 denotes a base resistor of the transistor 8, which converts the inverted switching signal d into the base current of the transistor 8. Reference numeral 11 denotes a base resistor of the transistor 9, which converts the switching signal C into the base current of the transistor 9. 12 is a collector resistor of the transistor 8, which acts as a load for the transistor 8, and absorbs the video signal a when the transistor 8 is turned on. A collector resistor 13 serves as a load for the transistor 9, and absorbs the video signal when the transistor 9 is on.

The operation of the video signal switching circuit configured as described above will be described below with reference to FIGS. 1 and 2.

First, FIG. 2 shows a timing chart corresponding to the circuit diagram of FIG. 1, in which when the switching signal C is "H",
Switch 5 is ONL, and inversion switching signal d is “L”
, and turns off the transistor 8ε. As a result, the video signal a is input to the switch 5 and passes through the switch 5. Further, since the inverted switching signal d is "L", the switch 6 is 0FFL, and the transistor 9 is turned on. As a result, the video signal g2 is absorbed by the collector resistor 13 and is not input to the switch 6.
It is fixed at "L" and the switch 6 is OFF, so it does not pass through. Therefore, the video signal a is output as the video signal e. Conversely, when the switching signal C is "L", the switch 5 is set to 0FFL, or is inverted. The switching signal d becomes "H" and turns on the transistor 8. As a result, the video signal a
is absorbed by the collector resistor 12, and is not input to the switch 5, but is fixed at "L", and since the switch 5 is OFF, it does not pass through, and the switch 6 is ON, and the transistor 9 is OFF. As a result, the video signal is switched 6
g and passes through switch 6. Therefore, the video signal S is output as the video signal e.

As described above, according to this embodiment, by further providing switches using transistors 8 and 9 at the inputs of the switches 5 and 6, unselected video signals can be input to the switches using the switching signal C and its inverted switching signal d. The crosstalk between the switches 5 and 6 can be fixed at 0.degree.L'', and the image quality can be prevented from deteriorating.

Effects of the Invention As described above, according to the present invention, a switch using a transistor is further provided at the input of the switch, and when the switch is OFF, the input transistor is turned ON and the video signal is fixed at "L". Good image quality can be obtained without crosstalk to the video signal passing through the path where the switch is ON.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a video signal switching circuit in an embodiment of the present invention, FIG. 2 is a timing chart of FIG. 1,
Figure 3 is a circuit diagram of a conventional video signal switching circuit; Figure 4 is a circuit diagram of a conventional video signal switching circuit;
The figure is a timing chart of FIG. 3. 1... Video signal a input terminal, 2... Video signal input terminal, 3... Switching signal input terminal, 4... Inverter, 5.6... Switch, 7... Video signal output Terminal, 8.9... Transistor, 10.11...
・Base resistance, 12.13...Collector resistance.

Claims (1)

[Claims] a first switch that turns on and off a first video signal using a switching signal, an inverter that inverts the switching signal, and a second video signal that turns on and off using the inverted switching signal;
, a second switch that turns off the first video signal; a first transistor that turns off the second video signal at the input side of the second switch when the first switch of the first video signal is on; a second transistor that turns off the first video signal at the input side of the first switch when the second signal switch is ON, and the output ends of the first and second switches are connected in common. A video signal switching circuit characterized in that: