Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2000-02-24
2002-06-11
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S015000, C315S368110, C313S412000, C313S414000, C313S437000, C313S449000
Reexamination Certificate
active
06404149
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-051476, filed Feb. 26, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube apparatus and, more particularly, to a color cathode ray tube apparatus which reduces the elliptic distortion of an electron beam spot shape at the periphery of a phosphor screen and stably provides a good image quality.
In general, a color cathode ray tube apparatus comprises an in-line type electron gun assembly for emitting three electron beams horizontally in a line, i.e., a center beam and a pair of side beams that pass through the same horizontal plane, and a deflection yoke for generating a nonuniform deflection magnetic field for deflecting the three electron beams horizontally and vertically. This nonuniform deflection magnetic field is formed from a pincushion type horizontal deflection magnetic field and barrel type vertical deflection magnetic field. Three electron beams emitted by the electron gun assembly are focused on corresponding phosphor layers on the phosphor screen by a nonuniform deflection magnetic field generated by the deflection yoke while they undergo self-convergence as they travel toward the phosphor screen. Then, a color image is displayed on the phosphor screen.
As the electron gun assembly for emitting three electron beams, an electron gun assembly of a QPF (Quadru-Potential Focus) dynamic astigmatism correction and focus type comprises an array of three cathodes K, and first to sixth grids G
1
to G
6
which are sequentially laid out toward the phosphor screen and integrally supported, as shown in FIG.
4
. Each of the grids G
1
to G
6
has three electron beam apertures corresponding to the three aligned cathodes K.
In this electron gun assembly, each cathode K receives a voltage of about 150 V, and the first grid G
1
is grounded. The second grid G
2
is connected to the fourth grid G
4
in the tube, and receives a voltage of about 700 V. The third grid G
3
is connected to a (
5
-
1
)th grid G
5
-
1
in the tube, and receives a voltage of about 6 kV. A (
5
-
2
)th grid G
5
-
2
receives a voltage of about 6 kV. The sixth grid G
6
receives a high voltage of about 26 kV.
These voltages are applied to the cathodes and grids to form an electron beam generator
8
, pre-focusing lens
9
, UPF (Uni-Potential Focus) type sub-lens
10
, and BPF (Bi-Potential Focus) type main lens
11
.
The electron beam generator
8
is made up of the cathodes K, and first and second grids G
1
and G
2
, generates an electron beam, and forms an object point with respect to the main lens
11
. The pre-focusing lens
9
is made up of the second and third grids G
2
and G
3
, and preliminarily focuses the electron beam emitted by the triode
8
. The sub-lens
10
is made up of the third, fourth, and (
5
-
1
)th grids G
3
, G
4
, and G
5
-
1
, and further preliminarily focuses the electron beam which was preliminarily focused by the pre-focusing lens
9
. The main lens
11
is made up of the (
5
-
2
)th and sixth grids G
5
-
2
and G
6
, and finally focuses the preliminarily focused electron beam on the phosphor screen. Note that a lens including the sub-lens
10
and main lens
11
will be called a main lens system
13
.
In deflecting an electron beam to the periphery of the phosphor screen by a nonuniform magnetic field generated by the deflection yoke, the (
5
-
2
)th grid G
5
-
2
receives a voltage set in advance in accordance with the deflection distance. This voltage parabolically changes depending on the electron beam deflection amount such that the voltage minimizes when the electron beam is focused on the center of the phosphor screen, and maximizes when the electron beam is deflected and focused on the corners of the phosphor screen.
When the electron beam is deflected to a corner of the phosphor screen, the potential difference between the (
5
-
2
)th and sixth grids G
5
-
2
and G
6
becomes smallest, and the lens power of the main lens
11
becomes weakest. At the same time, the (
5
-
1
)th and (
5
-
2
)th grids G
5
-
1
and G
5
-
2
form a potential difference to form a quadrupole lens
12
. The quadrupole lens
12
formed at this time has the highest lens power because of the largest potential difference between the grids G
5
-
1
and G
5
-
2
. The quadrupole lens
12
is set to achieve horizontal focusing action and vertical divergent action.
As the electron beam is deflected to increase the distance from the electron gun assembly to the phosphor screen, and set the object point apart, the main lens power weakens. At the same time, a quadrupole lens
12
for compensating for a deflection error caused by the horizontal and vertical deflection magnetic fields of the deflection yoke is generated. The lens power of the quadrupole lens
12
increases depending on the deflection amount.
To improve the image quality of the color cathode ray tube apparatus, the focusing characteristic on the phosphor screen must be improved. Particularly in a color cathode ray tube which incorporates an electron gun assembly for emitting three electron beams in a line, the beam spot on the phosphor screen generates an elliptic distortion core
1
and blur
2
owing to the deflection error, as shown in FIG.
5
A.
In general, as shown in
FIG. 5B
, the blur
2
can be prevented according to the deflection error compensation method by constituting a low-voltage electrode forming a main lens by a plurality of grids such as the (
5
-
1
)th and (
5
-
2
)th grids G
5
-
1
and G
5
-
2
, and generating a quadrupole lens in accordance with deflection of the electron beam between these grids, like a dynamic astigmatism correction and focus type electron gun assembly. However, as shown in
FIG. 5B
, the elliptic distortion of a horizontally expanded beam spot still remains at the ends of the horizontal and diagonal axes of the phosphor screen. This elliptic distortion generates moire or the like due to interference with a shadow mask, which makes it difficult to see, e.g., a character formed by an electron beam spot.
The elliptic distortion of the beam spot will be explained using an optical lens model.
FIG. 6A
shows a lens model in a no-deflection state in which an electron beam is focused on the center of the phosphor screen without any deflection.
FIG. 6B
shows a lens model in a deflection state in which an electron beam is deflected and focused on the periphery of the phosphor screen.
The beam spot size on a phosphor screen SCN depends on a magnification M. Let Mh be the horizontal magnification of the electron beam, and Mv be the vertical magnification. Then, M can be given by
M=
Divergent Angle &agr;
o
/Incident Angle &agr;
i
That is,
Mh
(Horizontal Magnification)=&agr;
oh
(Horizontal Divergent Angle)/&agr;
ih
(Horizontal Incident Angle)
Mv
(Vertical Magnification)=&agr;
ov
(Vertical Divergent Angle)/&agr;
iv
(Vertical Incident Angle)
For &agr;oh=&agr;ov, when the electron beam is not deflected as shown in
FIG. 6A
, the electron beam is influenced by almost the same focusing action both in horizontal and vertical directions H and V by the sub-lens
10
and main lens
11
. This yields &agr;ih=&agr;iv and Mh=Mv.
When the electron beam is deflected as shown in
FIG. 6B
, the quadrupole lens
12
having divergent action in the vertical direction V and focusing action in the horizontal direction H is formed between the sub-lens
10
and main lens
11
so as to compensate for the influence of a deflection error
14
having focusing action in the vertical direction V and divergent action in the horizontal direction H. This yields &agr;ih<&agr;iv and Mv<Mh.
As a result, the beam spot shape of the electron beam becomes circular at the center of the phosphor screen, but is horizontally elongated at the periphery of the phosphor screen.
To prevent this, an electron gun assembly having a so-called double quadrupo
Takekawa Tsutomu
Ueno Hirofumi
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Philogene Haissa
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