JPH10271390A - Signal switching device - Google Patents

Abstract

(57) [Problem] To prevent interference to an adjacent monitor when a video signal is lost and a monitor enters a free-run state. A video signal is supplied to an input video detection circuit and a switch via an input terminal. The system SYNC signal is supplied to the switch 15 via the minute power supply extracting circuit 18 via the input terminal 12 and the resistor 16. The input video detection circuit 13 detects whether a video signal is being input. The switches 14 and 15 are controlled based on the detection result. When a video signal is detected, the switch 14 is turned on, the switch 15 is turned off, and a video signal is output from the output terminal 19. If no video signal is detected, the switch 14 is turned off, the switch 15 is turned on, and the output terminal 19 outputs the system SYNC signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal switching method for preventing a screen of an adjacent monitor from being disturbed even if one of a plurality of adjacent monitors to which the video signal is supplied is interrupted. Related to the device.

[0002]

2. Description of the Related Art In a system in which a large number of monitors (monitor TVs) for video, such as a video studio and a broadcast van, are used side by side, electromagnetic interference occurs between adjacent monitors in each video monitor. In other words, there is no problem when monitoring various synchronized images, but when the input signal of one monitor is lost, the monitor goes into a free-run state and is connected to an adjacent operating monitor. It is known to cause horizontal line disturbances in the vertical synchronization period.

[0003]

In order to solve this problem, the electromagnetic shield between monitors has been strengthened, and the connection of the input circuit has been devised so as not to be in a non-input state. Did not become.

Accordingly, it is an object of the present invention to provide a signal switching device capable of preventing a monitor from going into a free-run state even when a video signal supplied to the monitor is lost.

[0005]

According to a first aspect of the present invention, in a signal switching device for outputting a signal to a monitor, a first input terminal to which a video signal is supplied; A video signal detecting means having a second input terminal to which a synchronizing signal for synchronizing is supplied, and an output terminal for outputting a signal to a monitor, and detecting whether or not a video signal is input; Switching means for switching between a video signal and a synchronizing signal based on the detection result of the means and outputting the signal to an output terminal; and power supply extracting means for extracting a power supply voltage for operating the video signal detecting means from the synchronizing signal. Signal switching device.

When the video signal input to the monitor is interrupted, the signal input to the monitor is switched from the video signal to the system sync signal (composite sync signal), whereby the free-run state can be suppressed. By extracting a power supply voltage from a signal, an operation of switching a signal can be performed without power.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an example to which the present invention is applied. A video signal is input to the switching circuit 3 to which the present invention is applied via the input terminal 1, and a system sync signal (composite sync signal) synchronized with the video signal is input to the switching circuit 3 via the input terminal 2. . The signal selected by the switching circuit 3 is transmitted to the monitor 4 for video.
Supplied to The supplied signal is displayed on the monitor 4. The basic operation of FIG. 1 is as follows. When an input video signal is present, the input video signal is supplied to the monitor 4 via the switching circuit 3, and when there is no input video signal, the input video signal is automatically transmitted via the switching circuit 3. The system sync signal is supplied to the monitor 4.

FIG. 2 is a block diagram showing one embodiment of the switching circuit 3. As shown in FIG. A video signal is supplied from an input terminal 11, and a system sync signal is supplied from an input terminal 12. The input video signal is supplied to an input video signal detection circuit 13 and a switch 14. The input video signal detection circuit 13 detects whether a video signal is input. When it is detected that a video signal is being input, the switch 14 is turned on and the switch 15 is turned off. Thereby, the video signal is output from the output terminal 19.
Output from When the input video signal detection circuit 13 detects that no video signal is input, the switch 14 is turned off and the switch 15 is turned on, so that the system sync signal is output from the output terminal 19.

[0009] The system sync signal supplied from the input terminal 12 is supplied to the switch 15 via the minute power supply extracting circuit 18 and the attenuator 16. The minute power supply extracting circuit 18 extracts a minute power supply (for example, −3 V) from the supplied system sync signal, and the extracted minute power supply is supplied to the input video signal detection circuit 13. The resistor 17 is connected to the input terminal 12 and the minute extraction circuit 18.
Is connected between the connection point and the ground.

The operation of the switching circuit 3 will be described. When only the video signal is input to the switching circuit 3, the video signal is output as it is. When the video signal and the system sync signal are input to the switching circuit 3, the video signal is selected and output. Input video signal detection circuit 1
When the video signal is not supplied by the detection of 3 and only the system sync signal is input to the switching circuit 3, the system sync signal is reduced by the attenuator 16 to the SYNC signal level of the video signal and output.

As described above, when the video signal and the system sync signal are input to the switching circuit 3, it is necessary to select the video signal. Therefore, an active circuit for selecting a video signal and a power supply for operating this active circuit are required. The minute power supply extracting circuit 18 converts the system sync signal (4Vp-p) into, for example, -3.
A V power supply is created. FETs that operate with very low power as more basic circuit conditions to satisfy these conditions
The circuit must be composed of (field-effect transistors) and CMOS circuit elements.

FIG. 3 shows an embodiment of the circuit configuration. The video signal supplied from the input terminal 11 is supplied to a switch 14 composed of an N-channel type FET 21 and
When T21 is turned on, the signal is output from the output terminal 19. Further, the system sync signal supplied from the input terminal 12 is supplied to the switch 15 including the P-channel type FET 22, and when the FET 22 is turned on,
Output from the output terminal 19. FETs 21 and 22
Is turned on / off in response to a control signal supplied from the input video detection circuit 13. The control signal is supplied to the FETs 21 and 22 via the resistors 39 and 40.

The minute power supply extracting circuit 18 comprising a resistor 41, capacitors 42, 43 and diodes 44, 45 constituting a rectifier circuit extracts a power supply voltage of -3V from a system sync signal of 4Vp-p. In the rectifier circuit of the minute power supply extracting circuit 18, the + side of the capacitor 42, the anode of the diode 44 and the cathode of the diode 45 are connected, and the capacitor 43 is connected between the cathode of the diode 44 and the anode of the diode 45. The connection point between the cathode of the diode 44 and the + side of the capacitor 43 is grounded.

The extracted power supply voltage of -3 V is supplied to the input video detection circuit 13. Input video detection circuit 1
3 is a resistor 25 for detecting the input video signal, 2
8, a capacitor 26 and an IC 27, capacitors 29, 30, 31, and 32, diodes 33, 34, 35, and 36, which constitute a voltage doubler rectifier circuit, and a resistor 37.

The double rectifier circuit of the input video detection circuit 13
Diodes 33, 34, 35, 36 are connected in series,
The anode of the diode 33 is connected to the anode of the diode 45, and the cathode of the diode 36 is connected to the resistor 39.
And 40 connection points. One of the capacitors 29, one of which is connected to the output of the IC 27, is connected to the cathode of the diode 35, and the other of the capacitor 30, one of which is connected to the output of the IC 27, is also connected to the cathode of the diode 33. . Further, the other of the capacitor 31, one of which is connected to the anode of the diode 45,
The other end of the capacitor 32, which is connected to the cathode of the diode 36 and one of which is also connected to the anode of the diode 45, is connected to the cathode of the diode 34.

The operation of this circuit configuration will be described. When a video signal is input to the input terminal 21 and a system sync signal is not input from the input terminal 12, the FET 21
Is turned on because the gate voltage becomes 0V. Therefore, a video signal is output from the output terminal 19. FE
T22 is turned off because the gate voltage is 0V. The resistor 25 extracts a video signal, but has no effect because the impedance is high.

When both the video signal and the system sync signal are input, the system sync signal (composite SYNC signal, 4Vp-p) is first composed of capacitors 42 and 43 and diodes 44 and 45 via a resistor 41. In the rectifier circuit, −3 V is output to the − terminal of the capacitor 43. This output is connected to a FET through a resistor 37.
21 and 22 and the IC 27
It is also supplied as a power source. Although the IC 27 is an unbuffered CMOS logic IC, it operates as an analog inverting amplifier for a small current operation, and
1 is applied to the input terminal of this IC 27 via the resistor 25 and the capacitor 26. IC2
The output of 7 is a rectangular wave with a horizontal synchronization period.

The rectangular wave output from the IC 27 is provided by diodes 33, 34, 35, 36 and capacitors 29, 30,
It is rectified by a voltage doubler rectifier circuit composed of 31, 32. The rectified signal is taken out and supplied to a connection point between the cathode of the diode 36 and the resistor 37. That is, F
The voltage supplied to the gates of ET21 and ET22 is +1 to
2V. Thus, the FET 21 is turned on and the FET 22 is turned off. As a result, a video signal is output to the output terminal 19.

When the video signal is not supplied after the video signal and the system sync signal are supplied, the rectangular wave output of the IC 27 is lost.
About -3 V is supplied to the gates of 1 and 22 via the resistor 37, whereby the FET 21 is turned off and the FET 22 is turned on. as a result,
The output terminal 19 outputs a system sync signal. The output system sync signal is connected to the resistors 23 and 2
Since the voltage is divided by 4, a signal of 0.3 Vp-p and 75Ω is output. As a result, the monitor 4 is in a state synchronized with the system sync signal.

As shown in FIG. 4, the external appearance of an example of the switching circuit 3 is about 54 mm in width, about 50 mm in depth, and about 23 mm in height. On one side, two BNC terminals for inputting a video signal and a system sync signal are arranged, and on the opposite side, one BNC terminal for outputting a selected signal is arranged. Further, as described above, no power supply is required, the phase stability is extremely high,
Both input and output are 75Ω, making it compact and lightweight.

[0021]

According to the present invention, by attaching a small switching circuit for switching between a video signal and a system sync signal to the input side of a monitor, one of a plurality of adjacent monitors to which a video signal is supplied is provided. Even if the video signal is interrupted, the system sync signal is automatically switched so that the system sync signal is supplied, so that the monitor does not go into a free-run state, so that it is possible to prevent the occurrence of interference on the screen of an adjacent monitor.

Further, according to the present invention, the power supply voltage can be extracted from the supplied system sink signal, so that the cost can be reduced and the power supply is unnecessary, so that energy is saved and the effect is great. When the system sync signal is no longer input, the switching circuit does not operate, but can output a video signal.

[Brief description of the drawings]

FIG. 1 is a schematic diagram to which the present invention is applied.

FIG. 2 is a block diagram of an embodiment of an image signal switching device according to the present invention.

FIG. 3 is a circuit diagram of an embodiment of an image signal switching device according to the present invention.

FIG. 4 is an external view of an example of an image signal switching device according to the present invention.

[Explanation of symbols]

13: input video detection circuit, 14, 15: switch, 16: attenuator, 17: resistor, 18
... Micropower supply circuit

Claims (2)

[Claims] 1. A signal switching device for outputting a signal to a monitor, wherein a first input terminal to which a video signal is supplied and a second input to which a synchronization signal synchronized with the video signal are supplied. A video signal detection means for detecting whether or not the video signal has been input; and a video signal detection means for detecting whether or not the video signal has been input. A switching means for switching between the synchronizing signal and the synchronizing signal and outputting the signal to the output terminal; and a power supply extracting means for extracting a power supply voltage for operating the video signal detecting means from the synchronizing signal. . 2. The signal switching device according to claim 1, wherein the video signal is output when the video signal is detected from the detection result of the video signal detection means, and the video signal is not detected. In the case, the signal switching device controls the switching means so as to output the synchronization signal.