JPH03250871A - Video signal switching system - Google Patents

Abstract

PURPOSE:To avoid disturbance on a monitor screen by outputting only a synchronizing signal of a video signal to be switchingly outputted for a prescribed time after changeover when the video signal is switchingly outputted and outputting the video signal after lapse of a prescribed time. CONSTITUTION:When an input video signal A outputted at present is switched and outputted into an input video signal B, a low pass filter-(LPF) and limiter circuit 3 are acted by a signal from a microcomputer 5, a synchronizing signal of the input video signal B is extracted and sent to an output terminal via an amplifier 4. The function of the LPF limiter circuit 3 is active only for a predetermined time (time till a monitor is made stable in its operation) with a microcomputer 5, the function is separated after lapse of a prescribed time and the video signal B from a clamp circuit 2 is sent as it is to the amplifier 4. Only the synchronizing signal of the video signal is outputted for a prescribed time till a monitor is made stable at the switching of the video signal in this way and since the substantial video signal is displayed on the screen after the monitor is made stable (after a prescribed time), the disturbance of the monitor screen is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a video signal switching system, and more particularly to a video signal switching system that prevents disturbances in screen images that occur when switching video signals.

(Prior Art) With the recent appearance of video playback devices, a single TV monitor has come to be shared by multiple video playback devices.
A system is used in which video signals from each playback device are switched and output to the monitor TV.

Conventionally, such video signal switching has been performed using a configuration as shown in FIG.

In FIG. 4, input video signals A, B, and C are switched and outputted by an analog switch 1. In FIG. This switching output is
It is controlled by a switching signal from the microcomputer 5.

The switching output from analog switch 1 is the amplifier <6dB
) 4 and supplied to the output terminal connected to the monitor side.

(Problems to be Solved by the Invention) As mentioned above, conventional video signal switching was performed by operating the analog switch 1 under the control of the microcomputer 5, which caused the problem that the output video signal caused disturbances on the monitor screen. was there.

That is, for example, input video signals A and B (input video signal C is not shown) as shown in FIGS. 5(a) and 5(b) are
Considering the case where the input video signal B is input to the analog switch 1 and is switched and output while the input video signal A is being output, the output signal of the analog switch 1 is as shown in FIG.
), a timing difference occurs between the synchronization signal of the video signal before switching and the synchronization signal of the video signal after switching.

Therefore, it takes a certain amount of time for the monitor that reproduces and displays the video signal to pull in the synchronization signal that has been switched, resulting in the problem that the monitor screen is distorted when the video signal is switched.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video signal switching method that eliminates disturbances on a monitor screen when switching video signals.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the video signal switching method according to the present invention is a video signal switching method that selects and outputs one video signal from among a plurality of video signals. , when the switching output is performed, only the synchronization signal extracted from the video signal to be switched and output is output for a predetermined fixed time, and after the elapse of the fixed time, the video signal to be switched and output is outputted. has been done.

(Function) In the video signal switching method according to the present invention, when switching and outputting an input video signal, for a certain period of time immediately after switching, only a synchronization signal that is not extracted from the video signal to be switched and output is output,
A video signal that is switched and output after a certain period of time is supplied to the monitor side. Therefore, since a video signal containing disturbance is not supplied to the monitor screen at the time of switching, the disturbance on the screen is removed.

(Example) Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a video signal switching system according to the present invention.

In FIG. 1, input video signals A, B, and C are input to an analog switch 1 based on control of a switching signal from a microcomputer 5.
The output is switched from .

After the switching video signal output from the analog switch 1 is fixed at a DC level or a constant value by the clamp circuit 2,
LPF is supplied to the limiter circuit 3.

The LPF/limiter circuit 3 is a circuit that cuts the color signal of the video signal from the clamp circuit 2 and the luminance signal higher than the pedestal level.
The circuit function can be activated. Here, analog switch 1 is activated.
The video signal from the analog switch 1 is sent as it is to the amplifier 4 only within a certain period of time after the switching operation.

In the LPF limiter circuit 3, the color signal of the video signal is cut by the low pass filter (LPF) w&function,
Since the brightness signal is cut by the limiter circuit function, only the synchronization signal of the video signal B is output.

FIG. 2 shows examples of input and output video signals for specifically explaining the operation of the embodiment shown in FIG. 1.

The analog switch 1 switches the currently output input video signal A (see Fig. 2) based on the switching signal from the microcomputer 5.
a)) to the input video signal B (Fig. 2 (b)), the signal from the microcomputer 5 causes the LP
The F limiter circuit 3 functions, and a synchronizing signal of the input video signal B is taken out and sent to the output terminal via the amplifier 4.

The function of this LPF/limiter circuit 3 works for a predetermined period of time (until the monitor stabilizes) determined by the microcomputer 5, and after the period of time, the function is disconnected and the video signal B from the clamp circuit 2 is The signal is sent to the amplifier 4 as is.

In this way, when switching video signals, only the video signal synchronization signal is output for a certain period of time until the monitor stabilizes, and after the monitor stabilizes (after a certain period of time), the original video signal is displayed on the screen. Screen clutter can be prevented.

FIG. 3 is a block diagram showing an example of a configuration in which the present invention is applied to a video signal switching system having a function of superimposing a character signal on a video signal.

The analog switch 1, clamp circuit 2, and amplifier 4 have the same configuration as shown in FIG.

The switching video signal amplified by the amplifier 4 is sent to both synchronized circuits R6. The synchronization separation circuit 6 receives synchronization signals C and 5YNC from the video signal from the amplifier 4.

Horizontal synchronization signal H, 5YNC and vertical synchronization signal V, 5Y
It extracts the NC and supplies the synchronizing signals C and 5YNC to the analog switch 8.

The superimpose circuit 7 is a circuit for superimposing a character signal based on the signal sent from the microcomputer 5 on the video signal from the amplifier 4.
A character signal is superimposed using the C signal, V, and 5YNC signals, and is supplied to the analog switch 8.

The microcomputer 5 controls the analog switch 8 and outputs the synchronization signal C, 5YN from the synchronization separation circuit 6 for a certain period of time after switching.
After a certain period of time has elapsed, the video signal from the superimpose circuit 7 is outputted to the buffer amplifier 9.

The video signal from the buffer amplifier 9 is sent to an output terminal connected to the monitor side.

(Effects of the Invention) As explained above, the video signal switching method according to the present invention, when switching and outputting video signals, outputs only the synchronization signal of the video signal to be switched and output for a certain period of time after switching, and Since the video signal is output after a certain amount of time has elapsed, there will be no disturbance on the monitor screen.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the video signal switching system according to the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment of FIG. 1, and FIG. FIGS. 4 and 5 are block diagrams illustrating other embodiments of a conventional video signal switching method, and signal waveform diagrams for explaining its operation. 1.8. Analog switch, clamp circuit, 3.
・LPF limiter circuit, 4.9... amplifier, 5.
...Microcomputer, 6...Synchronization separation circuit, 7...Superimpose circuit. ＜−〇

Claims (1)

[Claims] In a video signal switching method in which one video signal is selected from a plurality of video signals for switching and outputting, when the switching output is performed, a predetermined period of time is from the video signal to be switched and output. A video signal switching method characterized in that only the extracted synchronization signal is output, and after the predetermined period of time has elapsed, the video signal to be switched and output is output.