Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-01-31
2002-10-22
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C313S414000
Reexamination Certificate
active
06469459
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-022651, filed Jan. 31, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube apparatus comprising an electron gun assembly which emits one or more electron beams, and particularly to a cathode ray tube apparatus in which focus characteristics of the electron beam or beams are improved so that high resolution is obtained for the entire screen.
In general, in a color cathode ray tube apparatus, the three-electron beams emitted from an electron gun assembly is deflected by horizontal and vertical deflection magnetic fields. The deflected beams are oriented to a fluorescent screen made of a three-color fluorescent layers which are scanned horizontally and vertically by the electron beams so that a color image is displayed on the fluorescent screen.
Particularly, in this cathode ray tube apparatus, there is a trend as follows. That is, the electron gun assembly is constructed as an in-line type electron gun assembly which emits three electron beams arranged in line and including one center beam and a pair of side beams which penetrate in one same horizontal plane. On the other hand, its deflection yoke generates a horizontal deflection magnetic field of a pincushion type and a vertical deflection magnetic field of a barrel type, thereby to converge the three electron beams emitted from the electron gun assembly and arranged in line, onto a phosphor screen.
In this kind of cathode ray tube apparatus, the deflection magnetic field described above is not uniform, and therefore, the electron beam spot receives a diverging effect in the horizontal direction, causing an under-focused state even if the electron beam spot formed on the center part of the phosphor screen is a true circle. In the vertical direction, the electron-beam spot receives a focusing effect, causing an over-focused state.
Further, the distance from the electron gun assembly to the phosphor screen increases with the deflection amount of the electron beam. Accordingly, even if the electron beams spot is formed to be a true circle at the center part of the phosphor screen, the beam spot becomes over-focused at the peripheral portion of the phosphor screen.
As a result of this, the electron spot at the periphery part of the phosphor screen becomes remarkably over-focused in the vertical direction due to the two effects described above, and the above two effects compensate for each other in the horizontal direction to cause a substantially focused state. That is, in the peripheral part of the phosphor screen, astigmatic aberration caused due to a difference in the focus state between the vertical and horizontal directions. As shown in
FIG. 1
, the electron beam spot
2
is deformed into an asymmetric shape composed of a core part
3
as a high-luminance part and a halo part
4
as a low-luminance part, so that the resolution is remarkably degraded at the peripheral part of the phosphor screen. In addition, deflection aberration received by the electron beam increases as the scale of the cathode ray tube apparatus increases and the deflection angle increases. In this case, the resolution at the peripheral part of the phosphor screen is deteriorated much more.
To modify the electron beam spot, it is also important that the electrode forming the main lens of the electron gun assembly is formed with a large hole diameter so as to reduce the spherical aberration. Therefore, the mutual distance between the three electron beams must be set large. However, if the electron gun assembly is designed to have a large mutual distance between the three electron beams, there is a problem that the convergence characteristic of the three electron beams is deteriorated. Also, the hole diameter of the electrode forming the main lens part is limited by the inner diameter of the neck where electron gun assembly is provided. That is in order to attain an excellent resolution of the color cathode ray tube apparatus, it is necessary to enlarge the effective diameter of the main lens without increasing the mutual distance between the three electron beams, and to improve deformation of the electron beam spot at the peripheral part of the screen.
As a method of achieving improvements for an enlarged diameter and a deflection deformation of the main lens, Japanese Patent Application KOKAI Publication No. 64-38947 proposes an electron gun assembly having a structure as follows. In this electron gun assembly, the main lens is comprised of a focus electrode G
5
, two intermediate electrodes Gm
1
and Gm
2
, and a final acceleration electrode G
6
. In the electron gun assembly shown in these
FIGS. 2A and 2B
, a high voltage applied to the final acceleration electrode G
6
is divided by a resistor T provided along the electrode of the electron gun assembly, and predetermined divided voltages are applied to the intermediate electrodes Gm
1
and Gm
2
. In addition, a dynamic voltage having a parabola shape which changes in accordance with deflection of the electron beam is applied to the focus electrode G
5
, superposed into a constant direct current voltage. All the beam-passing holes of the focus electrode G
5
, intermediate electrodes Gm
1
and Gm
2
, and the final acceleration electrode G
6
are each formed to be a true circular shape. In addition, no side wall part, i.e., no bar ring is formed on the side surface of each electron-beam-passing hole, in the focus electrode G
5
and the final acceleration electrode G
6
. Therefore, an electric field common to three electron beams is formed in the horizontal direction inside the focus electrode G
5
and the final acceleration electrode G
6
. As a result of this, a first quadrapole lens having a strong focusing effect in the relatively vertical direction is formed near the focus electrode G
5
, and a second quadrapole lens having a strong diverging effect in the relatively vertical direction is formed near the final acceleration electrode G
6
.
Accordingly, in the electron gun assembly having a structure as described above, an enhanced electric field lens in which the main lens is enhanced by the intermediate electrodes Gm
1
and Gm
2
can be formed. Further, if the electron beam is deflected at the peripheral parts of the screen, the focus electrode G
5
is supplied with a higher voltage (dynamic voltage) in accordance with the deflection of the electron beam, so that the voltage difference is decreased between the focus electrode G
5
and the intermediate electrode Gm
1
. Therefore, the effect of the first quadrapole lens is weakened. Accordingly, the electron beam is diverged in the vertical direction while the focused state of the electron beam is not substantially changed in the horizontal direction. As a result, it is possible to compensate for the over-focusing in the vertical direction, which is caused by the non-uniform magnetic field generated from the deflection yoke. In the horizontal direction, deterioration of the magnification is smaller compared with a dynamic electron gun assembly in which a quadrapole lens is provided in the side closer to the cathode side than the main lens. Therefore, the electron-beam spot can have a smaller diameter.
By the electron gun assembly having a structure as described above, it is possible to solve two problems, i.e., the enlarged effective diameter described above and improvement concerning the deterioration of the resolution due to deflection aberration described above.
However, in case of the electron gun assembly having the structure described above, no side wall part (bar ring) is formed on the side surface of each of the electron-beam-passing holes, and therefore, the effective diameter is smaller in the vertical direction than in the horizontal direction. Consequently, the lens magnification and spherical aberration are enlarged so much that the diameter of the electron beam spot in the vertical
Kabushiki Kaisha Toshiba
Vu David
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