Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
2001-01-25
2003-10-07
Oen, William (Department: 2855)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
Reexamination Certificate
active
06630777
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color cathode-ray tube, and more particularly, to an electron gun having an improved shield cup to improve the deflection (defocusing or aberration) or coma, and a color cathode-ray tube using the same.
2. Description of the Related Art
FIG. 1
shows a cathode-ray tube employing a deflection yoke of self-convergence, the cathode-ray tube used for televisions and monitors. As shown in
FIG. 1
, a color cathode-ray tube
10
includes a panel
12
having a phosphor screen
11
, on which red, green and blue phosphor materials are provided in a dotted or striped pattern, in the inside; a funnel
13
which includes a neck portion
13
a
and a cone portion
13
b
and is fastened to the panel
12
; an electron gun
20
housed in the neck portion
13
a
of the funnel
13
; and a deflection yoke
15
provided throughout the cone portion
13
b
of the funnel
13
to deflect electron beams emitted from the electron gun
20
.
As shown in
FIG. 2
, the electron gun
20
includes three cathodes
21
arranged in line, a plurality of electrodes
22
which are spaced apart from the cathodes
21
by a predetermined distance and having three electron beam passages arranged in line, a final accelerating electrode
23
, and a shield cup
24
provided on the final accelerating electrode
23
.
In the color cathode-ray tube
10
having such a configuration, three electron beams emitted from the electron gun
20
are selectively deflected by the deflection yoke
15
and land on the phosphor screen
11
, exciting phosphor materials, so that an image is displayed.
During this procedure, a deflection magnetic field deflecting electron beams emitted from the electron gun
20
is composed of a pincushion-shaped horizontal deflection magnetic field HB and a barrel-shaped vertical deflection magnetic field VB, as shown in
FIG. 3
, so that it can converge the three beams arranged in line to the phosphor screen
11
without additional dynamic convergence. However, as shown in
FIG. 4
, the flux density of a magnetic field formed by a deflection yoke increases from the center toward the periphery in a horizontal direction, so the cross-sections of the red (R) and blue (B) electron beams, among the three electron beams (R, G and B electron beams) arranged in line, are distorted. In other words, as shown in
FIG. 5
, the R and B electron beams are subjected to forces in arrow headed directions by the pincushion magnetic field HB of a deflection yoke, so that halos are formed around the R and B electron beams. A halo phenomenon appearing in the R and B electron beams becomes worse toward the periphery of a phosphor screen, as shown in FIG.
6
. Accordingly, the magnitude of an electron beam landing on the periphery of the phosphor screen changes. The halo phenomenon of an electron beam and the non-uniformity of the cross-section of the electron beam degrade the resolution of an image formed by exciting the phosphor screen.
Examples of an electron gun for reducing the problem of a coma are disclosed in Japanese Patent Publication No. Hei 4-52586, Japanese Patent Laid-open No. Sho 51-61766, Japanese Patent Laid-open No. Sho 51-64368 and Japanese Patent Publication No. Hei 10-116569.
According to the disclosed technical configurations, upper and lower flat electrodes narrowing the paths of three electron beams are disposed on the bottom face of a shield cup of an in-line type electron gun, parallel to the in-line direction of the electron beams and extending toward a main lens or a phosphor screen. Alternatively, an electron gun is designed such that an electrostatic quadrupole lens is formed between some electrodes, and the strength of the electrostatic quadrupole lens varies with a deflection signal corresponding to the deflection of an electron beam, thereby achieving uniformity of an image over the entire screen. In another example, an astigmatic lens is provided in a region between electrodes forming a prefocus lens to achieve the uniformity of the cross-section of an electron beam over the entire phosphor screen. In still another example, the electron beam passages of first and second electrodes of an electron gun have different aspect ratios, thereby preventing the distortion of electron beams landing on the center and periphery of a phosphor screen.
Japanese Patent Publication No. Hei 10-116570 discloses a configuration for correcting the deflection of electron beams, in which magnetic pieces are partially disposed in electrodes forming an electron gun installed in the neck portion of a cathode-ray tube, and a magnetic field generating device is disposed on the outer surface of the neck portion, thereby generating a magnetic field synchronized with a deflection signal and exciting the magnetic pieces.
U.S. Pat. No. 5,912,530 discloses a configuration for correcting deflection using a deflection magnetic field, in which left and right magnetic pieces are disposed in one of the electrodes of an electron gun emitting three electron beams in line, and magnetic pieces are disposed between a center electron beam and peripheral electron beams.
U.S. Pat. No. 5,818,156 discloses a configuration for correcting deflection, in which magnetic materials are attached to the upper and lower portions of each of the side electron beam passages in a shield electrode within a deflection magnetic field.
As described above, when the shape of an electron beam passage is transformed or the magnifying power of an electron lens is varied in synchronization with a signal applied to a deflection yoke, to correct the deflection of an electron beam using a deflection magnetic field, it is difficult to manufacture an electron gun and control electron beams. In addition, when magnetic pieces are attached to both sides of each of the electron beam passages arranged on the bottom face of a shield cup in line and attached between the electron beam passages, the complexity of the shape of the magnetic pieces causes excessive dissemination depending on the shape of parts and result in difficult assembly, thereby disturbing the improvement of productivity.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide an in-line type electron gun for reducing deflection (defocusing or aberration) or coma due to the non-uniform magnetic field of a deflection yoke and reducing a voltage difference due to the deflection of side electron beams arranged in line, thereby improving the resolution of an image throughout a phosphor screen, and a color cathode-ray tube using the electron gun.
Accordingly, to achieve the above object of the invention, in first aspect, there is provided an electron gun for a color cathode-ray tube. The electron gun includes cathodes arranged in line, a plurality of electrodes sequentially disposed from the cathodes and having electron beam passages for passing three electron beams, a shield cup coupled to a last electrode among the plurality of electrodes and provided with three electron beam passages in line, and at least one coma correction portion disposed on the shield cup or one or more electrodes among the plurality of electrodes in such a manner of positioning the coma correction portion above and below the spaces between the center of a central electron beam passage and the centers of side electron beam passages.
In second aspect, there is provided an electron gun for a color cathode-ray is tube. The electron gun includes three cathodes arranged in line, a control electrode, a screen electrode, a plurality of focus electrodes sequentially disposed from the screen electrode and forming an auxiliary lens and a main lens, a final accelerating electrode, a shield cup coupled to the final accelerating electrode and provided with three electron beam passages arranged in line, and at least a pair of coma correction portions which are disposed on the shield cup or one among the plurality of focus electrodes in such a manner of positioning the centers of magnetic pieces above and below the space
Kim Deog-ho
Kwon Yong-geol
Lee Yang-je
Yoon Young-jun
Yun Kwang-jin
Leydig , Voit & Mayer, Ltd.
Oen William
Samsung SDI & Co., Ltd.
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