Electron gun for cathode ray tube

Details Electron gun for cathode ray tube Electron gun for cathode ray tube

2003-02-05

2004-03-30

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Plural concentrating, accelerating, and/or de-accelerating...

C313S412000

Reexamination Certificate

active

06713964

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an electron gun for a cathode ray tube, and more particularly, to an electron gun for a cathode ray tube in which an efficiency of a main focus lens is maximized within a limited neck diameter such that high focus performance and resolution characteristics are obtained.
2. Related Art
A projection system that utilizes cathode ray tubes (CRTs) to realize large screen images typically includes as the main elements three monochrome cathode ray tubes, each for realizing an image of a single color, that is, a green image, a blue image, or a red image; and an optical lens system for enlarging and projecting each of the single color images onto a projection screen to combine the images as a full color image.
In the monochrome cathode ray tube, since the screen is scanned using a single electron beam, the focus performance of the electron beam directly affects the resolution of the display device. Further, because the image of each monochrome cathode ray tube is enlarged by approximately ten times before being projected onto the screen, it is necessary to increase screen brightness by emitting an electron beam of a high current density from each of the electron guns.
Accordingly, the electron gun provided in the monochrome cathode ray tube uses a unipotential focus or a hi-unipotential focus connecting structure that provides for high focus performance in a high current region, in addition to using an electrode structure that optimizes the performance of a main focus lens.
In the unipotential focus or hi-unipotential focus methods, the main focus lens of the electron gun is formed between focus and anode electrodes by a difference between a focus voltage applied to the focus electrode and an anode voltage applied to the anode electrode. The main focus lens focuses an electron beam emitted from a cathode to form an electron beam spot on a phosphor screen.
The performance of the main focus lens is affected by equivalent diameter and spherical aberration. Spherical aberration decreases with increases in the equivalent diameter of the main focus lens, and a spot size of an electron beam landing on the phosphor screen increases with increases in spherical aberration.
Therefore, there may be an effort to optimize a triode portion to limit the spherical aberration of the main focus lens, or to enlarge the diameter of the main focus lens to increase the efficiency of the same. In particular, to increase the diameter of the main focus lens, it is necessary to physically enlarge the focus electrode and the anode electrode.
However, efforts to physically increase the diameter of the focus and anode electrodes are constrained by the standardized diameter of the neck in present commercial use. As a result, there is a need for an electron gun structure that forms the main focus lens to a maximum diameter within the limited diameter of the neck.
SUMMARY OF THE INVENTION
The present invention provides an electron gun for a cathode ray tube, in which an electrode structure is improved to maximize an equivalent diameter of a main focus lens within a neck of a limited diameter such that exceptional focus performance and resolution characteristics are realized.
The present invention provides an electron gun for a cathode ray tube including a single cathode emitting electrons; first and second grid electrodes forming a triode portion with the cathode; a third grid electrode provided subsequent to the second grid electrode; a fourth grid electrode provided subsequent to the third grid electrode and to which a focus voltage is applied, the fourth grid electrode including an input section positioned opposing the third grid electrode and an output section connected to the input section; a fifth grid electrode mounted surrounding part of the fourth grid electrode with a predetermined gap therebetween and to which an anode voltage is applied; and a connector electrically interconnecting the third grid electrode and the fifth grid electrode. The fifth grid electrode is positioned surrounding the fourth grid electrode in such a manner to expose the output section of the fourth grid electrode.
Preferably, the fourth grid electrode is cylindrical, and a diameter of the output section Is greater than a diameter of the input section; and the fifth grid electrode is also cylindrical and includes an input section and an output section, the output section having a diameter that is larger than a diameter of the input section.
The fourth grid electrode and the fifth grid electrode satisfy the following condition,
1.08
<D
2
/D
1
<2.0  (1)
where D
1
is an outer diameter of the input section of the fourth grid electrode and D
2
is an outer diameter of the input section of the fifth grid electrode, and it is assumed that a thickness of the fifth grid electrode does not exceed 500 micrometers (&mgr;m).
The fourth grid electrode and the fifth grid electrode satisfy the following condition,
 1.0
<D
4
/D
3
<1.2  (2)
where D
3
is an outer diameter of the output section of the fourth grid electrode and D
4
is an outer diameter of the output section of the fifth grid electrode, and it is assumed the thickness of the fifth grid electrode does not exceed 500 micrometers (&mgr;m).
The fourth grid electrode is preferably divided into at least two sub-electrodes mounted with a gap therebetween.
An angled section is formed between the input and output sections of the fourth grid electrode, the angled section being progressively enlarged in diameter starting from an end connected to the input section of the fourth grid electrode and in a direction toward an end connected to the output section of the fourth grid electrode.
As another option, the output section of the fourth grid electrode may be formed such that an end connected to the input section of the fourth grid electrode is substantially identical in diameter to the input section, then is progressively enlarged from this end connected to the input section in a direction away from the cathode.
In accordance with the principles of the present invention, as embodied and broadly described, the present invention provides an electron gun for a cathode ray tube, the electron gun comprising: a cathode emitting electrons; first and second grid electrodes forming a triode portion with said cathode; a third grid electrode; a fourth grid electrode receiving a focus voltage, said third grid electrode being disposed between said cathode and said fourth grid electrode, said fourth grid electrode including an input section and an output section, the input section being disposed between the output section and said third grid electrode; a fifth grid electrode encircling a portion of said fourth grid electrode, at least a part of the output section of said fourth grid electrode being not encircled by said fifth grid electrode, said fifth grid electrode being spaced apart from said fourth grid electrode by a predetermined gap, said fifth grid electrode receiving an anode voltage; and a connector electrically connecting said third and fifth grid electrodes.
In accordance with the principles of the present invention, as embodied and broadly described, the present invention provides an electron gun for a cathode ray tube, the electron gun comprising: a single cathode emitting electrons; first and second grid electrodes forming a triode portion with said cathode; a third grid electrode; a fourth grid electrode receiving a focus voltage, said third grid electrode being disposed between said cathode and said fourth grid electrode, said fourth grid electrode including an input section and an output section, the input section being disposed between the output section and said third grid electrode, the output section of said fourth grid electrode having an edge facing away from said cathode; a fifth grid electrode receiving an anode voltage, said fifth grid electrode encircling a portion of said fourth grid electrode, at least a part of the output section of said fourth grid electrode being n

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