Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-05-10
2002-06-11
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C313S306000, C313S309000, C313S351000
Reexamination Certificate
active
06404138
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of driving an electric field emission type cold cathode element having at least one electric field emission type cold cathode. Further, the present invention relates to a display apparatus for using the electric field emission type cold cathode element as an electron-generating source.
2. Description of the Related Art
In an electric field emission type cold cathode element, a gate electrode is arranged adjacently to a flat type emitter or a cone-shaped sharp emitter, and a high electric field is concentrated on the emitter through the gate electrode to emit electrons from the emitter.
In this electric field emission type cold cathode element, a current density can be made higher than that of a hot (thermionic) cathode element. The electric field emission type cold cathode element can be applied to a display apparatus needing a high current density, for example, such as a Braun tube and the like. There is a merit that a constant voltage driving and a heater are unnecessary, if the cold cathode element is used as a source of electrons, such as the Braun tube and the like, instead of the hot cathode.
In the display apparatus, the electrons emitted from the emitter are passed in vacuum through an electron lens (including a main lens) mounted above the emitter, and are sent to a (display) screen as an electron beam while deflected by a magnet field provided by a deflection yoke, between the electron lens and the screen. Especially, a color display apparatus usually uses three cold cathodes corresponding to the three primary colors of a red (R), a green (G) and a blue (B). It is required to superimpose three electron beams from the three cold cathodes of R, G and B on the screen to further make a diameter of a beam spot thinner (smaller).
In a usual case, such a color display apparatus employs an in-line structure, namely, a structure in which the three cold cathodes (electron guns) corresponding to the three primary colors are aligned in one lateral row. In such structure, beams emitted from the three electron guns arrive at the screen in the magnetic field. However, the beams are not usually concentrated into one point on the screen under an uniform magnet field. So, in order to concentrate the three electron beams so that they are superimposed on the screen, a magnetic field for the concentration is applied from external portion. That is to say, the beam passed through an outer side is passed through the high-strength magnetic field to be deflected largely. The beam passed through an inner side is passed through the low-strength magnetic field to be deflected small. As a result, the three beams are concentrated into one point on the screen.
A technique of self-convergence has been used for attaining such concentration of the beams on the screen without adjustment. This technique contrives the deflection yoke so that a horizontal deflection magnetic distribution is pincushion-shaped and a vertical deflection magnetic distribution is barrel-shaped to generate a magnetic field combined by the distorted deflection magnetic fields. However, when the electron beams are passed through such magnetic field, the respective beams are distorted by the strongly distorted deflection magnetic field. This distortion causes the generation of aberration referred to as astigmatism or spot coma, which further causes a beam diameter to be larger, and also causes a spot form to be distorted. The following method is proposed with regard to a control to avoid such beam form from being distorted.
That is, for example, Japanese Laid Open Patent Application (JP-A-Heisei, 7-147129) (Patent Publication No.2737616) discloses a technique that divides an emitter array constituting an electric field emission type cold cathode into a plurality of areas, and when a beam spot is located at a center of a display screen which is not distorted, drives only a circular emitter array area, and when the spot is located around a circumference of the display screen, drives the circular emitter array area and a sub emitter array area around it at the same time, and then sets them at a longitudinally long form, and accordingly suppresses the generation of the distortion in the beam spot. However, in this technique, the sizes of the spots of electron beams are different between the center and the circumference of the display screen. This results in a problem that a uniform resolution can not be obtained.
Also, for example, Japanese Laid Open Patent Application (JP-A-Heisei, 9-115426) discloses a technique that mounts a plurality of convergence electrodes around a gate electrode, and corrects a spot form laterally crashed because of distortion of a magnetic field, when electrons are passed through a self-convergence deflection magnetic field. However, this technique generates the magnetic field combined by deflection magnetic fields distorted by making a horizontal deflection magnetic distortion in a pincushion-shaped state and making a vertical deflection magnetic distortion in a barrel-shaped state. Thus, this technique requires a complex deflection yoke. Also, the yoke must be designed for each type of display apparatus. Also, a development method based on an adjustment in an actual sample is used, which leads to the increase of a development period and a development cost. Moreover, the variations between the individual display apparatuses and the mounting ways cause a difference between samples, which easily brings about defective samples having larger beam diameters, and results in a drop of yield.
SUMMARY OF THE INVENTION
The present invention is accomplished in view of the above mentioned problems. Therefore, an object of the present invention is to provide a method of driving an electric field emission type cold cathode element that can disuse the horizontal deflection magnetic distribution and the vertical deflection magnetic distribution or can make them smaller, and can suppress the distortion in the beam form caused by the magnetic distribution and the larger (thicker) diameter of the beam spot on the screen, and a display apparatus using this method.
In order to achieve an aspect of the present invention, a method of driving a cold cathode element, includes: (a) providing a plurality of cold cathodes; (b) deflecting a plurality of electron beams respectively emitted from the plurality of cold cathodes; (c) providing at least one control electrode for at least one of the plurality of cold cathodes, wherein an electric field above the control electrode is change d when a voltage is applied to the control electrode; and (d) controlling the voltage applied to the control electrode such that the plurality of electron beams are concentrated on a fluorescent surface.
In this case, the (d) step includes controlling the voltage to be a value close to a voltage applied to one of gate electrodes of the plurality of cold cathodes.
In order to achieve another aspect of the present invention, a method of driving a cold cathode element, includes: (e) providing a plurality of cold cathodes including a first cold cathode and a second cold cathode; (f) deflecting in a deflecting direction a plurality of electron beams respectively emitted from the plurality of cold cathodes; (g) providing at least one control electrode for at least one of the plurality of cold cathodes; and (h) controlling a voltage applied to the control electrode such that a first potential of the first cold cathode is different from a second potential of the second cold cathode, wherein the first potential is a potential difference between a first deflecting side in the deflecting direction and a first opposite side opposite to the first deflecting side above the first cold cathode, and the second potential is a potential difference between a second deflecting side in the deflecting direction and a second opposite side opposite to the second deflecting side above the second cold cathode.
In this case, the (g) step includes providing the control electrode such that an
Konuma Kazuo
Okamoto Akihiko
NEC Corporation
Tran Thuy Vinh
Wong Don
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