Electron gun in color cathode ray tube

Details Electron gun in color cathode ray tube Electron gun in color cathode ray tube

2000-08-11

2003-09-16

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Ray generating or control

C313S414000, C313S460000

Reexamination Certificate

active

06621205

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun in a color cathode ray tube or a high definition industrial monitor, and more particularly, to an electron gun in a color cathode ray tube which can form a large sized main focusing electrostatic lens.
2. Background of the Related Art
FIG. 1
illustrates a cross section of a related art color cathode ray tube.
Referring to
FIG. 1
, the related art color cathode ray tube is provided with a panel
1
having red, green, and blue fluorescent materials coated on an inside surface thereof, a funnel
2
fixed to a rear of the panel
1
, an electron gun
5
in a neck part
3
of the funnel
2
for emitting electron beams
4
toward a screen, a deflection yoke
6
mounted around an outer circumferential surface of the neck part
3
for deflecting the electron beams
4
emitted from the electron gun
5
in up, down, left, right directions, and subjecting the electron beams to self convergence, and a shadow mask
7
provided close to the inside surface of the panel
1
for selective pass of the electron beams
4
. The electron gun
5
has three independent cathodes
8
arranged on a horizontal line for emission of the electron beams, a control electrode
9
, an acceleration electrode
10
, a pre-focusing electrode
11
, a first focusing electrode
12
, a second focusing electrode
13
having horizontal electrodes
133
b
on upper and lower sides of electron beam through holes
133
a
; an anode
14
, and a shield cup
15
for shielding a geomagnetism.
When the aforementioned cathode ray tube is put into operation, the electron beams are emitted from the cathode
8
, and controlled, accelerated, and pre-focused as the electron beams pass through the control electrode
9
, the acceleration electrode
10
, and the pre-focusing electrode
11
. Then, the electron beams are converged in a horizontal direction and diverged in a vertical direction by a dynamic quardrupole lens formed by a voltage difference of the first and second focusing lenses
12
and
13
and a horizontal lens
131
b
, focused mainly by a main focusing electrostatic lens formed by a voltage difference of the second focusing electrode
13
and the anode
14
, and accelerated into an inside of the cathode ray tube by the anode. In continuation, the electron beams are deflected in up, down, left, right directions and subjected to self convergence on the same time by a deflection signal from the deflection yoke
6
. While the deflection yoke
6
subjects the electron beams to self convergence, it has a drawback in that the electron beams are converged in up and down directions and diverged in left and right directions. However, as the electron beams are pre-corrected by the dynamic quardrupole lens, the electron beams
4
passed through the deflection yoke
6
are directed to the shadow mask
7
without any distortion, selectively pass through the shadow mask
7
, land on a fluorescent surface
16
of the fluorescent materials, to form a picture. A quality of the picture formed thus can be made the better as a spot diameter of the electron beam landed on the fluorescent surface are made the smaller.
In general, the spot diameter of the electron beams on a screen is influenced from a magnification of a lens, a spatial charge repulsive force, a spherical aberration of the main focusing electrostatic lens, and the like. Since the influence of the lens magnification on the spot diameter Dx of the electron beams is defined by a basic voltage condition, a focus distance, a length of the electron gun, and the like, it is of little use, and has very little significance as a design parameter of the electron gun. The spatial charge repulsive force is a phenomenon in which the spot diameter of the electron beams are enlarged as the electrons in the electron beams repulse and collide to one another. Therefore, for reducing enlargement of the spot diameter Dst of the electron beams caused by the spatial charge repulsive force, it is favorable that a travelling angle of the electron beams(called “a diverging angle”) is designed to be great. Different from the spatial charge repulsive force, the spherical aberration of the main focusing electrostatic lens implies an enlarged spot diameter Dic of the electron beams caused by a difference of focus distances of electrons passed through a radical axis of the lens and electrons passed through a protaxis of the lens. Therefore, the smaller the diverging angle of the electron beams incident to the main focusing electrostatic lens, the smaller spot diameter of the electron beams can be obtained on the screen. In general, a spot diameter Dt of the electron beams on the screen can be expressed as the following equation.
Dt
={square root over ((
Dx+Dst
)
2
+Dic
2
)}
Both the spatial charge repulsive force and the spherical aberration can be reduced by enlargement of a diameter of the main focusing electrostatic lens. That is, the enlargement of the main focusing electrostatic lens diameter can reduce the spatial charge repulsive force because the diverging angle is made great, and can also reduce the spherical aberration because the electron beams can pass a radical axis of the main focusing electrostatic lens.
FIG. 2
illustrates a graph showing a diameter of a main focusing electrostatic lens vs. a spot diameter.
Referring to
FIG. 2
, it can be known that the greater the diameter of the main focusing electrostatic lens, the less the enlargement of the spot diameter caused by the spherical aberration of the main focusing electrostatic lens, resulting to reduce the spot diameter of the electron beams on the screen. In general, a size of the diameter of the main focusing electrostatic lens is proportional to sizes of electron beam pass through holes formed in opposite surfaces of the second focusing electrode
13
and the anode
14
. Therefore, for maximizing the diameter of the main focusing electrostatic lens, it is known that single electron beam pass through hole for passing of the three electron beams in common is formed in each of the opposite second focusing electrode
13
and the anode
14
.
FIG. 3
illustrates a half section of a second focusing electrode
13
and an anode
14
for forming a large sized main focusing electrostatic lens in a related art electron gun, and
FIG. 4
illustrates a perspective view of the second focusing electrode
13
and the anode
14
shown in
FIG. 3
with a partial cut away view.
Referring to
FIGS. 3 and 4
, the second focusing electrode
13
is provided with a first cup formed electrode
131
having one end opened to the cathode
8
, and the other end with a rim part
131
b
of a horizontally elongated track form as a unit therewith to form single electron beam pass through hole for passing the three electron beams in common, an electrostatic field electrode
132
having one side fixed to the one end of the first cup formed electrode
131
and three electron beam pass through holes
132
a
formed therein, and a second cup formed electrode
133
having one opened end fixed to the other side of the electrostatic field electrode
132
, three electron beam pass through holes
133
a
, and horizontal electrodes
133
b
fitted to an upper portion and a lower portion of respective electron beam pass through holes
133
a
. The anode
14
is provided with a third cup formed electrode
141
having one end opened to the panel
1
, and the other end opposite to the rim part
131
b
of the second focusing electrode
13
with a rim part
141
b
of a horizontally elongated track form as a unit therewith to form a thermal electron beam pass through hole
141
a
for passing of the three electron-beams in common, an electrostatic field electrode
142
having one side fixed to the one end of the third cup formed electrode
141
and three electron beam pass through holes
142
a
, a fourth cup formed electrode
143
having one opened end fixed to the other side of the electrostatic field electrode
142
, and the other end with single electron beam pass through ho

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