JPH09135395A - Video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the tracking performance with respect to the change in an input signal by controlling the system under the premises that a frequency is unstable for a prescribed time after an input frequency becomes unstable. SOLUTION: A micro control unit 6 judges whether or not a frequency of an input signal is stable and provides a mute signal to a video signal processing circuit 3 when not stable to interrupt a video signal fed from the video signal processing circuit 3 to a CRT 4. Thus, there is no possibility of displaying a disturbed video image onto the CRT. When a horizontal synchronizing signal H and a vertical synchronizing signal V fed from a synchronizing separator circuit 5 to the micro control unit 6 as input frequency information and a horizontal flyback signal and a vertical retrace signal fed from a deflection circuit 7 to the micro control unit 6 as oscillated frequency information are stable, the mute signal fed from the micro control unit 6 to the processing circuit 3 is released.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video display device capable of synchronizing with two or more types of input signal frequencies.

[0002]

2. Description of the Related Art In recent years, for example, in the field of multi-scan display devices having an input signal discriminating function, the diversification of input sources has been brought about with the development of media, and images mainly on personal computers have been introduced. With the improvement in performance of signal output devices and the improvement of software technology for driving them, switching of input signals to a multi-scan display has been frequently and rapidly performed.

Therefore, it is desired for the video display device to appropriately follow an input signal which is switched at high speed without causing a malfunction. From this situation,
Conventionally, the input signal is discriminated by microcomputer software and signal processing by various circuits.

[0004]

As described above, for example, in a multi-scan display device having an input signal discriminating function, it is required to properly follow an input signal that switches at high speed without malfunction. Has been done. However, the actual device may erroneously determine the change in the input signal, and as a result, malfunction may occur, for example, displaying an image before the input signal stabilizes, or vice versa. .

Therefore, the present invention has been invented in view of the conventional situation, and an object thereof is to provide an image display device capable of appropriately following a change in an input signal. .

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that when the frequency is switched, the input frequency becomes unstable for a proper time. Found that the frequency is unstable regardless of the state of the frequency of the input signal and controlling the system by controlling the system to improve the followability to the change of the input signal, thus completing the present invention. Came to.

That is, the video display device of the present invention is a video display device which can be synchronized with two or more types of input frequencies, and when the input frequency becomes unstable at the time of frequency switching, From that point onwards, the frequency is considered to be unstable regardless of the input frequency and the system is controlled. By doing so, the followability to changes in the input signal is improved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a video display device of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, a personal computer (PC) 1 is connected to the input of the video display device 2, and a horizontal synchronizing signal H, a vertical synchronizing signal V, a video signal (color signals R, G, B The video signal shown) is supplied.

In the present embodiment, the video display device 2
Is equipped with a video signal processing circuit 3, a CRT 4, a sync signal / separation circuit 5, a micro control unit 6 and a deflection circuit 7, and is supplied from the personal computer 1.
The color signals of (red), G (green), and B (blue) are input to the video signal processing circuit 3, and the micro control unit 6
According to the mute signal from, the signal is supplied to the CRT 4 or stopped.

The horizontal synchronizing signal H and the vertical synchronizing signal V supplied from the personal computer 1 may be sent as a composite video signal together with the video signal (superposed on the G signal). In 1, the sync signal is sent on the input lines indicated by H and V, and the sync signal and the video signal may be separated. Then, when they are not separated, they are separated in the sync signal / separation circuit 5, and the horizontal and vertical input frequency information H and V and the polarity information signal are output.
The input frequency information H and V are supplied to the micro control unit 6 and also to the deflection circuit 7.

The deflection circuit 7 has an oscillator inside and operates to lock the oscillation frequency of the oscillator to the input frequency based on the input frequency information. Based on the output of this oscillator, a horizontal deflection voltage and a vertical deflection voltage are generated and supplied to the deflection yoke.
The oscillation frequency information including the horizontal flyback signal and the vertical retrace signal is sent to the unit 6.

The polarity information signal has a plurality of bits (for example, 3 bits).
Bit) signal, which indicates what the input signal from the personal computer is, that is, whether it is a composite video signal or a signal in which the sync signal is separated, and also determines whether the frequency of the input signal is stable. Is a signal that gives.

The micro control unit 6 judges whether or not the frequency of the input signal is stable, and if it is not stable, it outputs a mute signal to the video signal processing circuit 3 and the video signal processing circuit 3 3 to CRT 4
The video signal supplied to is cut off. As a result, the distorted image is not displayed on the screen of the CRT.

Thereafter, the horizontal H and vertical V sync signals supplied from the sync signal / separation circuit 5 to the micro control unit 6 as input frequency information and the deflection circuit 7 to the micro control unit 6 as oscillation frequency information. When the supplied horizontal flyback signal and vertical retrace signal become stable, the mute signal sent from the micro control unit 6 to the video signal processing circuit 3 is released, and the video signal is displayed on the screen of the CRT.

In the image display device of this embodiment, when the input frequency at that time is switched to another signal having a very close frequency and a different polarity, for example,
Since the horizontal synchronizing signal H and the vertical synchronizing signal V are locked in a short time, the change of the polarity information is not yet sent from the synchronizing signal / separation circuit 5 at this time.
In the unit 6, H and V are locked, and it is judged that there is no polarity change, and the mute is released. However, after that, the sync signal / separation circuit 5 outputs the information of the polarity change and mutes again.

The second mute is released again after a short time, but the image is displayed or disappeared on the screen during this time, which is annoying to the user, and in some cases, the device is mistakenly operated or mistaken. There is a fear. Therefore, in the image display device of the present invention, the time for canceling the mute is delayed so that, if there is a change in the polarity signal, the mute is canceled after the change occurs.

Next, the operation of the apparatus shown in FIG. 1 will be described with reference to FIG. The micro control unit 6 starts the operation in step S1, checks the elapsed time of 33 ms in step S2, and if it does not reach 33 ms, this operation is repeated. When it reaches 33 ms, the process proceeds to step S3, and it is determined whether or not the input frequency is stable.

At this time, if there is a change in one or more of the horizontal synchronizing signal H, the vertical synchronizing signal V, or the polarity information, it is determined to be unstable and the process proceeds to step S4 to execute mute. After muting, return to step S2, 33ms from the previous operation
It stays in this state until it passes. When this time elapses, the process proceeds to step S3. If the input frequency is not stable, the process proceeds to step S4 and the same operation as the previous time is performed.

When it is determined in step S3 that the input frequency is stable, the process proceeds to step S5, and it is determined whether or not the mute is being performed. If it is not in the mute state, the process returns to step S2, and the operation is performed once every 33 ms.

If it is determined in step S5 that the mute is being performed, the process proceeds to step S6 and 1 is added to the count value of the counter. Subsequently, in step S7, it is determined whether or not the count value has reached a predetermined value, for example, 20. If it has not reached the predetermined value, the process returns to step S2 to check whether 33 ms has elapsed. When 33 ms have elapsed, the process proceeds to step S3 again and the same operation as described above is continued.

In step S7, the count value is 20.
When it is determined that the counter has reached, the process proceeds to step S8, the mute is released, and the counter is cleared to zero. After the mute is released, the process returns to step S2, and it is monitored again every 33 ms whether or not the input frequency is stable.

By counting the number of state monitoring by the counter and maintaining the previous state until the number of times reaches a predetermined number, the time for canceling the mute can be delayed, so that the mute may be canceled by mistake. Disappears. In addition, since the mute time can be set to be constant, it is easy to determine whether the mute is in progress or a failure has occurred.

Next, with reference to FIG. 3, a second embodiment of the image display device of the present invention will be described. In the figure, a personal computer 1, a video display device 2, a video signal processing device 3, a CRT 4, a sync signal / separation circuit 5, a micro control unit 6 and a deflection circuit 7 are the same circuits as those shown in FIG. Therefore, detailed description is omitted here.

In the figure, the image display device 2 has a changeover switch circuit 8 so that another personal computer 9 can be changed over and connected by this switch circuit. In this way, when switching and connecting two PCs,
Compared to the case described above with reference to FIG. 1, since the input signal is stable from the beginning, the frequency stability at the time of frequency switching is faster.

This means that the frequency lock of the variable frequency oscillator in the deflection circuit is fast, and as described above, it is judged that the circuit is stable before the polarity information signal is sent and the mute is released. The inconvenience of being lost occurs.
Therefore, in the same manner as described above, when muting is performed, the mute is released after waiting a fixed period of time. This makes it possible to keep the time until the mute is released.

[0026]

As is apparent from the above description, in the image display device of the present invention, the input signal frequency is kept constant for a certain period of time after the input frequency becomes unstable, such as when the frequency is switched. Regardless of the state, the frequency is considered to be unstable and the system is controlled to improve the followability to changes in the input signal.

Therefore, in the multi-scan display device adopting the present invention, the effect is exerted in order to properly mute the video signal when the signal is unstable when the frequency of the input signal changes, and the change of the input signal. Can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an embodiment of a video display device of the present invention.

FIG. 2 is an operation flowchart of a mute circuit portion of the device shown in FIG.

FIG. 3 is a circuit block diagram of another embodiment of the video display device of the present invention.

[Explanation of symbols] 1 PC 2 Video display device 3 Video signal processing circuit 4 CRT 5 Sync signal / separation circuit 6 Micro control unit 7 Deflection circuit

Claims (2)

[Claims] 1. A video display device capable of synchronizing with two or more types of input signal frequencies, when the input signal becomes unstable, during a predetermined time, regardless of the state of the input signal. An image display device, characterized in that means for controlling the system is considered to be unstable. 2. The video display device according to claim 1, wherein the means for controlling the system by regarding the input signal as being unstable during the predetermined time is a video signal mute means, and the input signal is A video display device, wherein mute is started when it becomes unstable, and the mute is released after a lapse of a predetermined period.