JPH0651729A - Automatic switching circuit for input signal path - Google Patents

Abstract

PURPOSE:To detect the frequency of the synchronizing signal of an input signal and automatically switching the path of the input signal so as to eliminate the trouble of manual switch switching as for a circuit which switches input signal paths from plural different signal terminals used for a display device. CONSTITUTION:This circuit is an automatic input signal switching circuit consisting of the input signal path switching circuit 4 equipped with plural signal input terminals 1-3, a synchronizing signal separating circuit 5 which separates a video signal and the synchronizing signal a synchronizing signal detecting means 6, a signal path switching control means 7 which operates according to the detection state of the synchronizing signal detecting means 6; and the input signal switching circuit switches the input signal paths in order by a signal switching means when the signal detecting means 6 detects the absence of the synchronizing signal or stops the sequential input switching operation when the synchronizing signal detecting means 6 detects the presence of the synchronizing signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having a plurality of signal input connection terminals.

[0002]

2. Description of the Related Art In recent years, due to the diversification of computers, a sync signal is an input signal of a display device, which is a green signal of a video signal plus a horizontal / vertical sync signal.
c On Green signal (hereinafter referred to as 3-wire type signal because three signals of red, green and blue are input), H / V Mixed in which vertical synchronizing signal is added to horizontal synchronizing signal
Sync signal (because there are four signal inputs of a synchronizing signal obtained by adding a vertical synchronizing signal to a horizontal synchronizing signal in addition to the three signals,
H / V Separated signal with independent horizontal / vertical sync signals (3 horizontal video signals and 5 vertical sync signals in addition to 3 video signals. There is a signal). The shape of the signal input connection terminal is also diverse, such as a BNC plug and a D-SUB connector.

A conventional input signal path switching circuit will be described below. 6 and 7 show the configuration of a conventional input signal path switching circuit.

In FIG. 6, 1 is a signal input connection terminal and 2 is a signal input connection terminal.
Is another signal input connection terminal, 4 is an input path switching circuit,
Reference numeral 5 is a sync signal separation circuit, 10 is a manual switch, 9 is a switch state detecting means for detecting and determining the state of the switch, and 7
Is composed of signal path switching control means. The operation of the input signal path switching circuit configured as shown in FIG. 6 will be described. First, the switch state detection means 9 detects the on / off state of the manual switch 10, determines which of the input signal paths of the signal input connection terminals 1 and 2 is to be switched, and the signal path switching control means 7 A control signal for switching the signal path is output to the input signal path switching circuit 4 according to the determination of the signal path to be switched. The other input signal paths of the signal input connection terminals 1 and 2 are switched by the control signal for switching the signal path in the input signal path switching circuit 4, and the input signal of the switched input signal path is converted into a 3-wire signal and a 4-wire signal. In this case, the video signal, the horizontal sync signal, and the vertical sync signal are input to the sync signal separation circuit 5, and the input signal path is manually switched.

In FIG. 7, 1 is a signal input connection terminal and 2 is a signal input connection terminal.
Is another signal input connection terminal, 11 is a manual switch, and 5 is a sync signal separation circuit. In the input signal switching circuit configured as shown in FIG. 7, the manual switch 1
The input signal paths of the signal input connection terminals 1 and 2 are switched by 1 to output the input signal to the synchronization signal separation circuit 5, and the input signal paths are manually switched.

[0006]

However, in the above-mentioned configuration, since the input signal path is switched by the manual switch, there is the trouble of switching the manual switch, and the signal path with no input signal is selected. Then
There was a problem that no signal was input to the display.

The present invention solves the above-mentioned conventional problems, and a display capable of automatically switching the input signal path by detecting the synchronizing signal frequency of the input signal and controlling the input signal path switching circuit. An object is to provide an input signal path automatic switching circuit of a device.

[0008]

In order to achieve this object, an input signal path automatic switching circuit of the present invention is an input signal switching circuit having a plurality of signal input connection terminals, a synchronizing signal detecting means, and a synchronizing signal. The input signal automatic switching circuit is provided with a signal path control unit that operates in the detection state of the detection unit, and the input path switching circuit, when the synchronization signal detection unit detects that there is no synchronization signal, the signal switching control unit. The input signal paths are controlled so that the input signal paths are switched sequentially, and when the synchronization detecting means detects that there is a synchronization signal, the operation of switching the input signal paths is stopped sequentially. It has a circuit configuration for automatic selection.

[0009]

With this configuration, even when a plurality of input signal connection terminals are provided, the input signal synchronization signal is detected,
The input signal path can be automatically switched by controlling the input signal path switching circuit to be sequentially switched.

[0010]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a signal input connection terminal and 2 is a signal input connection terminal.
Is another signal input connection terminal, 4 is an input signal path switching circuit, 5 is a sync signal separation circuit, 6 is a sync signal detection means, and 7
Is a signal path switching control means.

The synchronizing signal separation circuit 5 separates the Sync On Green signal into a green signal, a horizontal synchronizing signal and a vertical synchronizing signal in the case of a three-wire type signal, and outputs it, and in the case of a four-line type signal, the H / V Mixed Sync. The signal is separated into a horizontal synchronizing signal and a vertical synchronizing signal and output, and in the case of a 5-wire type signal, the horizontal synchronizing signal and the vertical synchronizing signal are output.

The operation of the input signal path automatic switching circuit configured as described above will be described below. First, in the initial state of the automatic input signal path switching circuit, the input signal path switching circuit 4 is used as the signal path of the signal input connection terminal 1. When you turn on the display device,
Since the input signal path switching circuit 4 is the signal circuit of the signal input connection terminal 1, it becomes as follows.

When there is an input signal at the signal input terminal 1, the sync signal separation circuit 5 performs the above-mentioned operation, and a horizontal sync signal appears at the output terminal. This horizontal synchronizing signal is detected by the synchronizing signal detecting means 6, and since there is a horizontal synchronizing signal, the signal input connection terminal 1 is left as it is.

When there is no signal at the input connection terminal 1, it is judged that there is no input signal because there is no horizontal synchronizing signal at the output terminal,
The signal path switching control means 7 sends a control signal to the input signal path switching circuit 4 to switch the signal path to the signal input connection terminal 2. If there is an input signal at the signal input connection terminal 2, a horizontal synchronizing signal appears at the output terminal, the synchronizing signal detecting means 6 judges that there is an input signal, and the input signal path remains connected to the input signal 2. Control so that

FIG. 4 shows a specific embodiment of the input signal path switching circuit 4 of FIG.

This circuit includes a capacitor C for separating a DC component.
1, C2, C3, C4 and transistors Tr1 and Tr2 for switching the DC level and diode D for switching the signal
1 and D2. When the Hi signal is output from the signal path switching control means of FIG. 1, Tr2 is turned off, the DC voltage is not superimposed on the point b of the input signal 2, the switching diode D2 is in the cutoff state, and the input signal 2 is It is electrically separated from the output. On the other hand, the Hi signal output from the signal path switching circuit is converted into a Low signal via the NOT gate and reaches Tr1. At this time, Tr1 is turned on, the DC voltage is superimposed on the point a of the input signal 1, D1 becomes conductive, and the input signal 1 is output. Similarly, when the Low signal is output from the signal path switching control means, the input signal 2 is output and the input signal 1 is electrically disconnected from the output.

As described above, if there is an input signal in the connected input signal path, the connection of that path is left as it is, and if there is no input signal, the input signal path is switched to the next input signal path. Here, in the sync signal separation circuit 5, not only in the 5-wire type signal but also in the 3-wire type signal and the 4-wire type signal, the sync signal is separated from the video signal, and the horizontal sync signal appears at the output terminal to synchronize. Signal detecting means 6
It is possible to detect the sync signal with, and determine the presence or absence of the input signal based on the presence or absence of the sync signal, and the input signal path automatic switching circuit can automatically switch the input signal path.

(Embodiment 2) A second embodiment of the present invention will be described with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a signal input connection terminal, 2
Is another signal input connection terminal, 3 is another signal input connection terminal,
4 is an input path switching circuit, 5 is a sync signal separation circuit, 6
Is a synchronization signal detecting means, and 7 is a signal path switching control means. The above is the same as the configuration of FIG.

The difference from the configuration of FIG. 1 is that another signal input connection terminal 3 is added. The input signal path automatic switching circuit configured as shown in FIG. 2 operates in the same manner as in FIG. 1 to determine the presence or absence of an input synchronizing signal. When there is no horizontal synchronizing signal, the input terminals are sequentially set to 1 , 2, 3, and control is performed so that the connection remains as it is in the input signal path determined to have the horizontal synchronizing signal. Here, in FIG.
A specific example of the input signal path switching circuit 2-4 will be described.

This circuit includes a capacitor C for separating a DC component.
1, C2, C3, C4, C5, C6 and transistors Tr1, Tr2, Tr3 for switching the DC level and diodes D1, D2, D3 for switching the signal. When a low signal is output to the control signal 1 and a Hi signal is output to the control signals 2 and 3 from the signal path switching control means of FIG.
The DC voltage is not superimposed on the point and the point C of the input signal 3, the switching diodes D2 and D3 are cut off, and the input signals 2 and 3 are electrically disconnected from the output. On the other hand, Tr1 is output by the Low signal output from the control signal 1.
Turns on, the DC voltage is superimposed on point a of input signal 1, and D1
Are conducted, and the input signal 1 is output. Similarly, a Low signal is output from the control signal 2, and Hi is output from the control signals 1 and 3.
When the signal is output, the input signal 2 is output and the input signals 1 and 3 are electrically separated from the output. Further, a Low signal is output from the control signal 3, and H is output from the control signals 1 and 2.
When the i signal is output, the input signal 3 is output and the input signals 1 and 2 are electrically separated from the output. As described above, in the configuration of FIG. 2, even when the number of input signal connection terminals is increased from two to three, the input signal path automatic switching circuit can automatically switch the input signal path.

(Embodiment 3) Next, a third embodiment of the present invention will be described with reference to the drawings.

In FIG. 3, 1 is a signal input connection terminal, 2
Is another signal input connection terminal, 3 is another signal input connection terminal,
Reference numeral 4 is an input signal path switching circuit, 6 is a synchronizing signal detecting means, and 7 is a signal path switching control means. The above is the same as the configuration of FIG.

The difference from the configuration of FIG. 2 is that the synchronizing signal detected by the synchronizing signal detecting means 6 is used as the output of the input signal switching circuit 4. Therefore, there is no function of separating the input signal into the video signal, the horizontal synchronizing signal, and the vertical synchronizing signal, and the input signal is a 5-wire signal that is independent of the video signal, the horizontal synchronizing signal, and the vertical synchronizing signal. Is effective in the case of. If the signal is a 5-wire type signal, the input signal path automatic switching circuit can automatically switch the input signal path.

The operation of the input signal path automatic switching circuit configured as shown in FIG. 3 is the same as that of FIG. 2, and the presence / absence of an input synchronizing signal is determined. Switch to a few.

The first embodiment, the second embodiment, the third embodiment
In the embodiment, the signal path of the signal input connection terminal 1 in the input signal path switching circuit 4 is set to the initial state of the input signal automatic switching circuit, but the signal input connection terminal 3 is also used as the signal path of the signal input connection terminal 2. It goes without saying that the signal path (excluding the second embodiment) may be used.

Further, the first embodiment, the second embodiment, the third embodiment
Needless to say, in the embodiment, the number of signal input connection terminals is set to 1 to 3, but a larger number of signal input terminals may be used.

Although the horizontal synchronizing signal is detected by the synchronizing signal detecting means 6, it goes without saying that the vertical synchronizing signal may be detected.

Further, as the method of the synchronizing signal detecting means 6, there is a method of judging the presence or absence of the synchronizing signal at the rising and falling edges of the synchronizing signal pulse, and how many times the synchronizing signal frequency is within a fixed time. It is also possible to use a method of detecting the frequency by counting and determining that there is no synchronizing signal when the frequency is zero.

[0031]

As described above, according to the input signal path automatic switching circuit of the present invention, if the input signal has the synchronizing signal, the input signal path of the display device can automatically switch the input signal path. It is possible to realize an automatic path switching circuit.

[Brief description of drawings]

FIG. 1 is a block diagram of an input signal path automatic switching circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an input signal path automatic switching circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram of an input signal automatic switching circuit according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of an input signal path switching circuit according to a first embodiment of the present invention.

FIG. 5 is a circuit diagram of an input signal path switching circuit according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a conventional input signal path switching circuit.

FIG. 7 is an explanatory diagram showing an example of a conventional input signal path switching circuit.

[Explanation of symbols]

 1 signal input connection terminal 1 2 signal input connection terminal 2 3 signal input connection terminal 3 4 input signal path switching circuit 5 sync signal separation circuit 6 sync signal detection means 7 signal path switching control means 8 function realizing means by a microcomputer 9 Switch status detecting means 10 Manual switch 11 Manual switch

Claims (1)

[Claims] 1. An input signal automatic switching circuit comprising an input signal path switch having a plurality of signal input terminals, a synchronization signal detection means, and a signal path control means operating in a detection state of the synchronization signal detection means, When the synchronizing signal detecting means detects that there is no synchronizing signal, the input signal path switching circuit controls the signal switching control means to sequentially switch the input signal paths so that the synchronizing signal detecting means has a synchronizing signal. An input signal path automatic switching circuit, which is controlled so as to sequentially stop the input signal path switching operation when detected.