JPH04259173A - Video input changeover circuit - Google Patents

Abstract

PURPOSE:To prevent crosstalk of a selected video signal by providing a mute circuit respectively to two video signals or over and interrupting the video signal other than the selected video signal. CONSTITUTION:Different 1st and 2nd video signals are inputted from video input terminals 1,2 and a selection switch 8 is opened. In this case, a transistor(TR) 15 is turned off and a TR 25 is turned on. Thus, a base potential of a TR 12 is a potential depending on resistors 13,14, and since the base potential is set so that the TR 12 is turned on, a video signal inputted from the terminal 1 is outputted to a processing circuit 10 via an IC switch 7. On the other hand, a TR 22 is turned off and since the input video signal from the terminal 2 is not inputted to the switch 7, no crosstalk is caused to the selected 1st video signal.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a video input switching circuit for selecting an input video signal in a video equipment equipped with a plurality of video signal input terminals. I tried to avoid it.

0002

2 is a diagram showing a conventional video input switching circuit, in which 1 is a first video signal input terminal, 2 is a second video signal input terminal, 3 and 4 are terminating resistors, and 5 and 6 are terminals. Input capacitor, 7 is video input switching IC switch (hereinafter referred to as "
8 is a video input selection switch (hereinafter referred to as ``selection switch''), 9 is a voltage control resistor, and 10 is a video signal processing circuit.

Next, the operation will be explained. First and second video signals input from video input terminals 1 and 2 are terminated by terminating resistors 3 and 4, and input to an IC switch 7 via input capacitors 5 and 6. When the selection switch 8 is ON, an "L" level switching signal is input to the IC switch, and the IC switch is switched to the second video signal input terminal 2 side, and the second video signal is sent to the next stage of video processing. When it is OFF, an "H" level switching signal is input, the signal is switched to the first video signal input terminal 1 side, and the first video signal is output to the video processing circuit 10.

0004

[Problems to be Solved by the Invention] Since the conventional video input switching circuit is configured as described above, when video signals are applied to both video signal input terminals 1 and 2, the video signals of each However, crosstalk occurs on the printed wiring board pattern and within the video input switching IC, causing interference on the screen, and in order to eliminate it, the printed wiring pattern around the video input switching IC switch must be designed. The problem was that there were restrictions. An object of the present invention is to obtain a video input switching circuit that does not cause crosstalk between input video signals.

[0005]

[Means for Solving the Problem] Each video signal input circuit is provided with a muse circuit, and the muse circuits of systems not selected are turned on by the switching signal output from the video signal selection switch, so that the input video signal is connected to the IC switch. This is to prevent it from being entered.

[0006]

[Operation] The muse circuit provided in the video signal input circuit cuts off the currently unselected signal input near the input terminal and does not apply it to the IC switch, so no crosstalk occurs.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 11 is a first muse circuit, which has a PN
It is composed of a P-type video buffer transistor 12, base bias resistors 13 and 14, an NPN-type blanking transistor 15, and the like, and a selection signal from a video input selection switch 8 is input to the base of the transistor 15 via the resistor. 21 is a second muse circuit, which includes an NPN type video buffer transistor 22 and a base bias resistor 2.
The selection signal is input to the base of the transistor 25 via a resistor.

Next, the operation will be explained. It is now assumed that different first and second video signals are being input from video input terminal 1 and video input terminal 2, respectively, and selection switch 8 is turned off. At this time, the bases of transistors 15 and 22 are both at "H" level, so transistor 15 is turned off and transistor 25 is turned off.
becomes ON. Therefore, the base potential of the transistor 12 becomes a potential determined by the resistors 13 and 14, and since this base potential is set so that the transistor 12 is turned on, the video signal input from the first input terminal 1 is
The signal is output to the processing circuit 10 via the C switch 7. On the other hand, the base potential of the transistor 22 becomes OV, so the transistor 22 is turned off, and the video signal input from the second input terminal 2 is grounded by the transistor 25 and connected to I.
Since it is not input to the C switch 7, no crosstalk occurs in the selected first video signal.

Next, the video input selection switch 8 is turned ON.
At this point, the bases of transistors 12 and 25 both go to "L" level, so transistor 15 is turned on and transistor 25 is turned off. Therefore, the transistor 12 is turned off and the transistor 22 is turned on, so that the second video signal input from the second video signal input terminal 2 is outputted to the video signal processing circuit 10 via the transistor 22 and the IC switch 7. Since the first video signal is grounded through the transistor 15 and is not input to the IC switch 7, no crosstalk occurs.

[0010]Although the above embodiment shows an example in which two video input signals are switched, the present invention can be similarly applied to a case in which three or more video input signals are switched.

[0011]

According to the present invention, a muse circuit is provided in each of the input systems of two or more video signals, and the muse circuits of the input systems other than the one selected by the video input selection signal are operated, and the input system of the selected video signal is activated. Video signals other than I
Since no input is made to the C switch, it is possible to obtain a video input switching circuit that does not cause crosstalk.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional video input switching circuit.

[Explanation of symbols]

1, 2 Video signal input terminal 7 IC switch for video input selection 8 Video input selection switch 11, 21 Muse circuit

Claims (1)

[Claims] 1. A video input switching circuit configured to switch a plurality of input video signals by a video input IC switch controlled by a video input selection signal, the circuit comprising: a video input switching circuit provided in each of the plurality of video signal systems; The video signal input to each video signal system is inputted to the video input IC switch by activating the plurality of muse circuits of the video signal system selected by the video input selection signal and the muse circuits of systems other than the video signal system selected by the video input selection signal. A video input switching circuit characterized in that it is provided with means for cutting off the input signal.