JPH06209442A - Picture display device - Google Patents

Abstract

PURPOSE:To effectively compensate a leakage alternate electric field at an ELF band caused by a cathode ray tube by sampling a voltage waveform of an opposite phase and that of a leaked electric field generated in the display device and adding the sampled voltage to a compensation electrode of the display device. CONSTITUTION:The picture display device 2 which outputs a display picture signal periodically to a display device 1 via a random access device stored in a frame buffer 4 for each prescribed period to display a picture is provided with a leaked electric field compensation voltage generator 7. The generator 7 is made up of an arithmetic operation circuit 5 and a voltage generating circuit 6, and the frame buffer 4 transfers picture data to the circuit 5 a little before a time when the frame buffer 4 outputs picture data of one frame to the cathode ray tube for a prescribed period. Then fluctuation of a cathode current is read and the waveform is sampled and the circuit 6 inverts the phase and the resulting voltage is given to a compensation electrode provided to the cathode ray tube of the display device 1. Thus, a leakage alternate electric filed at an ELF band generated from the cathode ray tube is effectively suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device, and more particularly to suppression of a leakage electric field of an image display device using a cathode ray tube as a display device of a terminal device or a computer.

[0002]

2. Description of the Related Art With the recent remarkable development of OA equipment, various OA equipments are becoming familiar in offices and homes. In such a situation, a technique related to leakage electromagnetic field shielding is important from the viewpoint of preventing noise of electronic devices and preventing influence of electromagnetic fields on the human body. For example, in Europe, the allowable values of alternating electric fields and alternating magnetic fields have already been specified as standards in some countries, and standardization is spreading to advanced countries. Regarding the alternating electric field, the frequency band in question is ELF
(5-2000Hz) and VLF (2-400KHz)
It is in the obi.

As a conventional technique for suppressing this leakage electric field, in the case of an image display device using a cathode ray tube, it is relatively easy to electrically shield the cabinet except in the direction of leakage to the front surface of the display surface. The leakage electromagnetic field can be shielded. However, for the front surface of the display surface, there is a means for forming a conductive film on the front display panel of the cathode ray tube as, for example, a transparent electromagnetic field shielding means, but the shielding effect is still insufficient. Regarding the VLF band, it is considered that the cause is the leakage of the horizontal deflection voltage added to the deflection device of the cathode ray tube, and the voltage of the opposite phase is applied to the compensation electrode of the leakage electric field from the flyback transformer or the like to suppress the leakage electric field. There is a way to do it.

Further, it is considered that the cause of the ELF band is the leakage of voltage fluctuation depending on the cathode current change of the cathode voltage of the cathode ray tube. Therefore, a copper plate or the like is arranged around the front display panel of the cathode ray tube, and its charge due to the leakage electric field is generated. There is a method of obtaining the potential change from the change of the amount and applying it to the leakage electric field compensation electrode to suppress the leakage electric field.

[0005]

As described above, the conventional technique is still insufficient for suppressing the leakage electric field of the image display device using the cathode ray tube, particularly for suppressing the leakage electric field in the front direction of the display surface. is there.

The present invention has been made in view of the above problems, and it is possible to effectively suppress an alternating electric field generated from an image display apparatus using a cathode ray tube, particularly a leakage alternating electric field in an ELF band which is a low frequency band. It is an object of the present invention to provide an image display device that can be used.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an image display device for periodically outputting a display image signal to a display device via a random access device that stores a display image signal in a frame buffer at regular intervals to display an image. Means for calculating sampling generation of a voltage waveform having a phase opposite to the leakage electric field generated in the display device by outputting the display image signal to the display device based on the display image signal stored in the buffer, and the calculating device. The leaky alternating electric field can be effectively suppressed by providing means for generating the voltage waveform calculated by the above and means for adding the voltage waveform generated by the voltage waveform generating means to the compensation electrode of the display device. It is an image display device.

[0008]

According to various experimental measurements, it has been found that the leakage alternating electric field in the cathode ray tube does not depend on the cathode potential and the deflection voltage, but depends on the current generated in the cathode ray tube when the display signal is input. . Therefore, it is considered that the cause of the leakage alternating electric field in the ELF band is not the deflection device mounted on the cathode ray tube but the cathode ray tube itself. It is considered that this is because a change in the electron beam caused by the input of the display signal to the cathode ray tube causes a potential fluctuation inside the cathode ray tube, and an alternating electric field is formed between the cathode ray tube and the ground potential.

In this regard, for example, there is a method in which a copper plate or the like is arranged around the front display panel of the cathode ray tube, and the change in the amount of charge due to the leakage electric field is utilized to obtain the voltage waveform applied to the compensation electrode by the inverting amplifier circuit. . However, in this method, the noise component of the external electric field generated from other than the cathode ray tube is also added to the compensation electrode, which may cause a case where the leakage electric field is not sufficiently suppressed or a malfunction of the device depending on the environment in which the cathode ray tube is placed. there is a possibility.

The present invention, in an image display device using a cathode ray tube as a terminal display or a display device of a computer, has a frame buffer which is a storage area for storing an information signal of a display image, and is stored in the frame buffer. A calculation means and a voltage generation means are provided based on the image information, the voltage waveform applied to the compensation electrode for the leakage electric field is sampled, and the leakage alternating electric field in the ELF band generated from the cathode ray tube is affected by the influence of external noise. Not effectively suppress.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an image display device to which the present invention is applied. In FIG. 1, a computer 2 has a central controller 3 (CPU) and a frame buffer 4 for storing video signal data of a display image, and a display device 1 using a cathode ray tube.
It is connected to the. Further, the frame buffer 4 is connected to the cathode ray tube of the display device 1 via a leakage electric field compensation voltage generator 7 including an arithmetic circuit 5 and a voltage generator 6.

In the computer 2 which uses a cathode ray tube or the like as the display device 1, the information of the display image is stored frame by frame in the frame buffer 4 which is a random access device and periodically output to the display device.

Elements representing the color of a color image have chromaticity, saturation and lightness. Generally, in the case of a color image display device,
The information for each element forming an image is as follows. That is, one is lightness and the other is R, G,
The chromaticity and the saturation are the types of colors that are determined by the mixing ratio of the colors according to the B primary color addition method. On the frame buffer, an address is provided to uniquely correspond to the information for each pixel,
CPU with fixed size of 1 to 8 bits CPU
The image information including the type of color for each pixel transferred from the above is stored.

FIG. 2 shows an example of a memory image of the frame buffer. In the method of forming an image with 640 dots in the horizontal direction and 400 dots in the vertical direction, the same number of memory areas are provided for each dot and they are arranged in raster scanning order. The numbers written in the boxes are address numbers in hexadecimal notation, and data indicating the type of color is stored in the area indicated by each address.

FIG. 3 shows an example of a video signal of one frame obtained from the frame buffer, and the horizontal axis represents the raster scanning order of each dot. The vertical axis is shown as the sum of the magnitudes of the brightness of the three primary colors corresponding to each dot, the type of color is expressed by the mixing ratio of the three primary colors, and the amount thereof is proportional to the cathode current amount of the cathode ray tube. There is.

Since the ELF generated from the cathode ray tube is considered to be the leakage of the variation of the anode voltage depending on the variation of the amount of the cathode current, the image data of one frame transferred from the frame buffer 4 to the cathode ray tube at a constant period. Immediately before the output timing, the image data is transferred to the arithmetic circuit 5, the fluctuation of the cathode current is read, the waveform is sampled and generated, the waveform is sent to the voltage generation circuit 6, the phase is inverted, and the amplification is performed appropriately. , Is added to the compensation electrode installed in the cathode ray tube of the display device 1. Further, when the central control unit 3 of the computer 2 has a multitasking function capable of executing a plurality of programs, a method of operating the arithmetic circuit 5 by software and controlling the voltage generating circuit 6 is also possible.

FIG. 4 is a schematic diagram showing an example of a compensation electrode installed in a cathode ray tube. Although the cathode ray tube 10 has a general structure, it has a substantially rectangular panel 11 and this panel 11.
A glass envelope consisting of a funnel 12 connected to
An electron gun (not shown) arranged inside the neck 13 of the funnel 12 to face a phosphor screen (not shown) formed on the inner surface of the panel 11 and emit an electron beam for exciting and emitting the phosphor screen. Is equipped with. Furthermore, a pair of compensation electrodes 20 are installed on the upper and lower side surfaces of the panel 11 of the cathode ray tube 10.

Next, the leakage electric field compensating action of the compensating electrode will be described with reference to FIGS. FIG. 5 schematically shows an electric field of an AC electric field generated from a cathode ray tube at an arbitrary time. That is, the electric field generated by the cathode ray tube is roughly approximated to show the potential distribution formed between the electric field and the ground potential. In the example shown in FIG. 5, the equipotential lines 30a spread radially from the center of the cathode ray tube 31, and the potential becomes lower as the distance from the center increases, and the electric force lines 32 shown by arrows are formed.
The direction of a is also radially outward from the center.

FIG. 6 schematically shows an electric field at a given time among the AC electric fields generated by the pair of compensation electrodes 33 provided on the upper and lower side surfaces of the panel of the cathode ray tube 31. As described above, the voltage of the opposite polarity to the voltage due to the leakage electric field generated in the cathode ray tube 31 is applied to the compensation electrode 33. In the case of FIG. 6, the equipotential line 30b spreads around the pair of upper and lower compensation electrodes 33, and the electric force line 32
The direction of b is toward the compensation electrode 33 above and below the cathode ray tube, and is toward the panel on the front surface of the panel. Figure 7
The leakage electric field shown in FIG. 5 and the compensating electric field for wetting shown in FIG. 6 are combined. That is, as in the present invention, by providing the compensating electrode 33 to which a voltage having a polarity opposite to the voltage due to the leakage electric field generated in the cathode ray tube is applied, the leakage electric field spreading around the cathode ray tube, particularly on the front surface of the panel is effective. It can be seen that it can be suppressed.

FIG. 8 is a sectional view taken along the line AA ′ of FIGS.
The electric potential distributions in the cross sections BB ′ and CC ′ are shown by calculating the electric field as the inclination of the electric potential. It can be seen from FIG. 8 that the leakage electric field generated in the cathode ray tube, particularly the leakage electric field spreading on the front surface of the panel is effectively suppressed.

[0021]

As described above, according to the present invention, data is transferred from the frame buffer to the cathode ray tube at a constant period.
Immediately before the frame image data is output, the image data is transferred to the arithmetic circuit, the fluctuation of the cathode current is read, the waveform is sampled and generated, and the waveform is sent to the voltage generation circuit to invert the phase, ELF generated due to the cathode ray tube by amplifying and adding to the compensation electrode installed in the cathode ray tube of the display device.
It is possible to effectively compensate for the leakage alternating electric field that spreads in the band, especially on the front surface of the panel.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image display device of the present invention.

FIG. 2 is a configuration diagram showing an example of a memory image of the frame buffer of FIG.

3 is a distribution diagram showing an example of signal data obtained from the frame buffer of FIG.

FIG. 4 is a schematic configuration diagram showing a cathode ray tube as the display device of FIG.

FIG. 5 is a schematic diagram showing distribution of an electric field leaking from a cathode ray tube as a display device.

6 is a schematic diagram showing distribution of an electric field leaking from a cathode ray tube as the display device of FIG.

FIG. 7 is a schematic diagram showing the leakage electric field distributions of FIGS. 5 and 6 in combination.

FIG. 8 is a sectional view taken along line AA ′, BB ′, and CC ′ of FIGS. 5 to 7;
It is a distribution diagram which shows each electric potential distribution in a cross section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Display device 2 ... Computer 3 ... Central control unit (CPU) 4 ... Frame buffer 5 ... Arithmetic circuit 6 ... Voltage generation circuit 7 ... Leakage electric field compensation voltage generator, 20, 33 ... Compensation electrode.

Claims (1)

[Claims] 1. An image display device for periodically outputting a display image signal to a display device via a random access device which stores a display image signal in a frame buffer at regular intervals to display an image, the display stored in the frame buffer. Means for computing sampling generation of a voltage waveform having a phase opposite to the leakage electric field generated in the display device by outputting the display image signal to the display device based on the image signal, and the voltage computed by the computing device. An image display device comprising: means for generating a waveform; and means for adding the voltage waveform generated by the voltage waveform generating means to a compensation electrode of the display device.