Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-07-07
2002-11-12
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000, C313S432000, C313S460000
Reexamination Certificate
active
06479927
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube (CRT), and more particularly, to an electrode of an electron gun for forming a large-diameter electronic lens and an electron gun using the same.
2. Description of the Related Art
In general, spherical aberration and focusing characteristics in an electron gun for a CRT, are greatly affected by a main lens. Thus, in order to obtain good focusing characteristics, it is preferable to form a main lens having a diameter as large as possible.
However, in an in-line type electron gun, each three electron beam passing holes are formed in an in-line arrangement in at least two electrodes for forming an electron lens, and the diameter of a neck portion of a funnel in which the electron gun is mounted is limited. Thus, it is not possible to make the diameter of an electron beam passing hole larger than a distance between centers of two neighboring electron beam passing holes, which will be referred to as an “eccentricity distance” hereinafter.
Electrodes of an electron gun for improving spherical aberration in a conventional main lens are disclosed in U.S. Pat. No. 4,370,592, which is shown in FIG.
1
.
As shown in the drawing, burring portions
1
b
and
2
b
are formed at edges of an emitting surface
1
a
of a focusing electrode
1
and an entering surface
2
a
of a final accelerating electrode
2
, and large-diameter electron beam passing holes
1
H and
2
H having a predetermined depth, are formed in the central portion thereof, respectively. Also, small-diameter electron beam passing holes
1
H′ and
2
H′ through which R, G and B electron beams pass independently are formed in the large-diameter electron beam passing holes
1
H and
2
H.
When electron beams pass through a main lens formed by the focusing electrode
1
and the final accelerating electrode
2
, since the large-diameter electron beam passing holes
1
H and
2
H are horizontally elongated, the vertically and horizontally focused components of the electron beams having passed through the central small diameter electron beam passing hole and the side small-diameter electron beam passing holes are different. Thus, it is not possible to obtain uniformity in the spot size of electron beams landing on a phosphor screen. In other words, as shown in
FIG. 2
, the side electron beams RB and BB having passed through the large-diameter electron beam passing hole
1
H or
2
H of the focusing electrode
1
or the final accelerating electrode
2
are close to the burring portions
1
b
and
2
b
, and the central electron beams GB is relatively far from the burring portions
1
b
and
2
b
. Therefore, the side electron beams RB and BB are relatively strongly focused and the central electron beam GB is relatively weakly focused.
Also, since the distances between the side electron beams RB and BB and the burring portions
1
b
and
2
b
are different according to direction, that is, horizontally or vertically, horizontal and vertical focusing powers of the side electron beams RB and BB are different. Also, since the vertical distances between the central electron beam GB and the burring portions
1
b
and
2
b
are shorter than the horizontal distances therebetween, the central electron beam GB is strongly focused in a vertical direction. Also, the central electron beam GB is diverged in a diagonal direction of the large-diameter electron beam passing hole
1
H or
2
H. Therefore, the side electron beams RB and BB having passed through the main lens have substantially triangular cross-sections and the central electron beam GB has a cross-section having radially projecting parts, so that a uniform shape in electron beam cross-sections cannot be obtained throughout the entire phosphor screen.
In particular, since the sizes of the small-diameter electron beam passing holes
1
H′ and
2
H′ are restricted by the diameter of the neck portion of a CRT, there is a limit in increasing the eccentricity distance between the small-diameter electron beam passing holes
1
H′ and
2
H′. Further, in recent years, there has been a tendency to reduce the diameter of the neck portion for reducing a deflection current, the distance between the small-diameter electron beam passing holes
1
H′ and
2
H′ is reduced accordingly, thereby degrading spherical aberration and focusing characteristics.
An electrode structure of an electron gun for solving the above-mentioned problem is disclosed in U.S. Pat. No. 5,414,323. As shown in
FIG. 3
, the electrode structure is constructed such that an electrode member
12
is disposed at the center of an outer electrode
11
having a large-diameter electron beam passing hole, a vertically elongated small-diameter electron beam passing hole
13
is formed in the center of the electrode member
12
and both edges of the electrode member
12
are recessed in a half-elliptical shape to form side electron beam passing holes
14
and
15
.
The central small-diameter electron beam passing hole
13
is vertically elongated to offset astigmatism generated by the large-diameter electron beam passing hole. However, this electrode structure cannot easily correct 8-pole coma aberration of a central electron beam passing hole and 6-pole coma aberration of side electron beam passing holes.
An example of another conventional large-diameter electrode is disclosed in U.S. Pat. No. 4,626,783. This electrode, as shown in
FIG. 4
, includes an outer electrode
21
having a large-diameter electron beam passing hole, and an inner electrode
22
installed within the outer electrode
21
and having polygonal small-diameter electron beam passing holes
22
R,
22
G and
22
B. Here, the aberration generated by the large-diameter electron beam passing hole can be corrected by the polygonal small-diameter electron beam passing holes
22
R,
22
G and
22
B. However, it is not easy to fabricate polygonal small-diameter electron beam passing holes.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide an electrode of an electron gun for a color cathode ray tube, which can easily correct aberration of an electronic lens caused by a large-diameter electron beam passing hole and can improve focusing characteristics.
It is another object of the present invention to provide an electron gun for a color cathode ray tube, which can reduce astigmatism by compensating for distortion of an electron beam due to a difference in the voltage applied to three electron beam passing holes disposed in an in-line arrangement.
To accomplish the first object of the present invention, there is provided an electrode of an electron gun for a color cathode ray tube including an outer-rim electrode having a large-diameter electron beam passing hole through which three electron beams pass, and an inner electrode installed inside the outer-rim electrode member, and having three electron beam passing holes disposed in an in-line arrangement and recesses formed at peripheries of the electron beam passing holes, the recesses having an eccentricity distance larger than an eccentricity distance between centers of the three electron beam passing holes.
In the present invention, the horizontal width of each of the recesses formed at peripheries of the electron beam passing holes is preferably smaller than the vertical width thereof.
According to another aspect of the present invention, there is provided an electron gun for a cathode ray tube, the electron gun having a cathode, a control electrode and a screen electrode together constituting a triode section, and focusing electrodes installed to be adjacent to the screen electrode and forming at least one electronic lens, wherein each of the focusing electrodes includes an outer-rim electrode having a large-diameter electron beam passing hole through which three electron beams pass, and an inner electrode installed inside the outer-rim electrode member, and having three electron beam passing holes disposed in an in-line arrangement an
Lowe Hauptman & Gilman & Berner LLP
Patel Ashok
Samsung SDI & Co., Ltd.
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