Cathode ray tube

Details Cathode ray tube Cathode ray tube

2000-07-20

2002-10-29

Philogene, Haissa (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

C315S015000, C313S414000, C313S449000

Reexamination Certificate

active

06472832

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube, and more particularly to a cathode ray tube provided with an electron gun assembly that suppresses resolution deterioration on the periphery of a screen.
An in-line color cathode ray tube of self-convergence type is provided with an in-line electron gun assembly for emitting three in-line electron beams traveling in the same horizontal plane. One of the beams is a center beam, and the others are side beams traveling along the center beam. The cathode ray tube is also provided with a deflection yoke for generating a non-uniform magnetic field, with which the electron beams emitted from the electron gun assembly are deflected. The three electron beams emitted from the electron gun assembly are converged by the main lens portion incorporated in the electron gun assembly and then self-converge on the entire screen by the action of a non-uniform magnetic field. This magnetic field is made by a pincushion-type horizontal deflecting magnetic field and a barrel-type vertical magnetic field.
Electron beams
6
passing through this non-uniform magnetic field undergo astigmatism. As shown in
FIG. 1A
, each electron beam is applied with the forces acting in the directions of arrows
11
H and
11
V by the pincushion-type magnetic field
10
. When the electron beam
6
falls on the periphery of the phosphor screen, it forms a distorted beam spot
12
on the phosphor screen, as shown in FIG.
1
B. This distortion is due to the deflection aberration that causes the electron beam
6
to excessively focus in the vertical direction, i.e., in the V-axis direction.
Hence, the beam spot
12
includes a halo portion
13
A extended in the vertical direction and a core portion
13
B extended in the horizontal direction, i.e., in the H-axis direction. This deflection aberration becomes significantly marked in accordance with an increase in the size of the tube or the deflection angle thereof, and results in a marked deterioration of the resolution on the periphery of the phosphor screen.
In order to provide a solution to the resolution deterioration that is due to the deflection aberration, a high-performance electron gun assembly has been developed. This electron gun assembly corrects the deflection aberration on the periphery of the screen by varying the lens power of an electron lens inside the electron gun assembly in accordance with the amount of deflection of an electron beam directed toward the screen periphery.
An example of such an electron gun assembly is described in Jpn. Pat. Appln. KOKAI Publication No. 64-38947. This electron gun assembly comprises a first grid G
1
, a second grid G
2
, a third grid G
3
, a fourth grid G
4
, a fifth grid G
5
, a first intermediate electrode GM
1
, a second intermediate electrode GM
2
, and a sixth grid G
6
. These elements are arranged from the side of a cathode K(R,G,B) to the side of a phosphor screen in the order mentioned, as shown in FIG.
2
. The third to sixth grids are applied with voltages shown in FIG.
3
.
Referring to
FIG. 3
, the solid line in the graph represents the voltage that is used in the non-deflection mode, i.e., in the mode wherein an electron beam is focused on the center of the phosphor screen. The broken line in the graph represents the voltage that is used in the deflection mode, i.e., in the mode wherein an electron beam is focused on the periphery of the phosphor screen. The axis of abscissa Z represents the positions of the electrodes arranged on the tube axis, which is substantially the central axis of a cylindrical neck portion in which the electron gun assembly is arranged. The increasing direction of the Z axis is a direction approaching the phosphor screen, while the decreasing direction is a direction approaching the cathode. The axis of ordinate V represents the voltage levels applied to the grids.
As shown in
FIG. 3
, the third and fifth grids are applied with a dynamic focusing voltage obtained by superimposing a variation voltage on a predetermined DC voltage Vf. The variation voltage varies in accordance with the amount of deflection of an electron beam.
When the voltage described above is applied to each grid, a quadrupole lens section QL
2
is formed between the fifth grid G
5
and the first intermediate electrode GM
1
, a cylindrical lens section CL between the fifth grid G
5
and the sixth grid G
6
, and a quadrupole lens section QL
1
between the second intermediate electrode GM
2
and the sixth grid G
6
. The quadrupole lens section QL
2
includes a vertical-direction component with a relatively focusing function and a horizontal-direction component with a relatively divergent function. The quadrupole lens section QL
1
includes a vertical-direction component with a relatively divergent function and horizontal-direction component with a relatively focusing function. The main lens section ML of the electron gun assembly is constituted by the quadrupole lens sections QL
1
and QL
2
and the cylindrical lens section CL.
In the deflection mode, the voltages applied to the third and fifth grids are raised from the level indicated by the solid line to the level indicated by the broken line, as shown in FIG.
3
. As shown in
FIG. 4B
, the power of the quadrupole lens section QL
2
and that of the cylindrical lens section CL are suppressed. As a result, the diverging effect is maintained only in the vertical direction, with the focusing effect in the horizontal direction being unchanged. In this manner, an electron beam is prevented from being excessively focused in the vertical direction by the deflecting magnetic field.
However, the dynamic focusing voltage, which is synchronously related to the-horizontally-deflecting magnetic field, may fluctuate in synchronism with a deflecting frequency of 15 kHz or higher. When this fluctuation occurs, the capacitance between the fifth grid and the first intermediate electrode, that between the first and second intermediate electrodes and that between the second intermediate electrode and the sixth grid serve to conduct AC components. As a result, the first and second intermediate electrodes are applied with part of the dynamic focusing voltage acting in the horizontal direction. This being so, not only the quadrupole lens section QL
2
and the cylindrical lens section CL but also the quadrupole lens section QL
1
vary in lens power.
Owing to this, the divergence in the vertical direction may not be sufficient. In the case of a self-convergence type, the focusing force in the horizontal direction may abate though it must not. As a result, an electron beam spot on the periphery of the phosphor screen is excessively focused in the vertical direction, resulting in a halo portion, and is insufficiently focused in the horizontal direction.
To solve this problem, Jpn. Pat. Appln. KOKAI Publication No. 7-147146 proposes such an electron gun assembly as is shown in FIG.
5
. The fifth grid of this electron gun assembly is made up of a first segment G
51
and a second segment G
52
. As indicated by the broken lines in
FIG. 6
, a third grid and a second segment G
52
are applied with a voltage that rises in accordance with the amount of deflection of an electron beam. As indicated by the broken lines in
FIG. 7
, therefore, a quadrupole lens QL
3
having a diverging vertical component and a focusing horizontal component is formed between the first segment G
51
and the second segment G
52
in the deflection mode only.
If the auxiliary quadrupole lens section QL
3
is formed, however, the lens main plane, namely, the imaginary lens center used for focusing electron beams on the phosphor screen (i.e., the point where the path of a beam emitted from the cathode and the path of a beam incident on the phosphor screen cross each other) is shifted.
In the non-deflection mode, the lens main plane in the vertical direction is located substantially in the center of the main lens section ML. In the deflection mode wherein the quadrupole lens section QL
3
is used, the lens main plane in the vertical direction is

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