Electron gun in CRT

Details Electron gun in CRT Electron gun in CRT

2001-08-15

2003-10-21

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Plural beam generating or control

C313S412000

Reexamination Certificate

active

06635982

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun in a cathode ray tube (CRT), and more particularly, to an electron gun in a CRT, in which electron beam pass through holes in an electrostatic field controlling body provided both to a focusing electrode and anode of a main lens electrode are changed, for improving a screen focusing characteristic.
2. Background of the Related Art
The CRT, a device for forming a picture by landing electron beams emitted from the electron gun on a screen, is illustrated in
FIG. 1
, schematically.
Referring to
FIG. 1
, the CRT is provided with a panel
2
fitted to a front for acting as a screen, a fluorescent surface
4
of red R, green G, and blue B fluorescent materials coated on an inside surface of the panel
2
, a shadow mask
8
for selecting a color as electron beams
6
incident on the fluorescent surface
4
pass therethrough, a funnel
10
fitted to rear of the panel
2
for sustaining an inner space of the CRT at a vacuum, and a deflection yoke
12
surrounding an outer circumference of a neck part
10
a
of the funnel
10
for deflecting the electron beams
6
.
The electron gun
20
is placed in the neck part
10
a
of the funnel
10
of the CRT, and provided with three independent cathodes
201
, a first electrode
21
spaced a distance away from the cathodes
201
, a second electrode
22
, a third electrode
23
, a fourth electrode
24
, a fifth electrode
25
, and a sixth electrode
26
spaced at fixed intervals from the first electrode
21
, and a shield cup
27
above the sixth electrode
26
having a bulb space contact (B.S.C)
28
fitted thereto for electrical connection of the electron gun
20
to the funnel
10
and fastening the electron gun
20
to the neck part
10
a
of the funnel
10
.
The electron gun
20
emits electrons as heaters
203
in the cathodes
201
are heated by a power supplied from respective stem pins
202
at rear end thereof, and the electrons form electron beams, which are controlled by the first electrode
21
, a controlling electrode, and accelerated by the second electrode
22
, an accelerating electrode. Then, the electron beams are partly focused and accelerated by a pre-focus lens formed between the second electrode
22
, the third electrode
23
, the fourth electrode
24
, the fifth electrode
25
(a focus electrode), finally focused and accelerated by the sixth electrode
26
(anode), a final accelerating electrode, pass through the shadow mask
8
, and land on the fluorescent surface
4
on an inside surface of the panel
2
, to make the fluorescent surface to emit a light.
The focus electrode
25
and the anode
26
collectively called as a main lens
200
, and a related art main lens
200
will be explained with reference to FIG.
2
.
FIG. 2
illustrates a perspective view with a partial cut away view of the focus electrode
25
and the anode
26
in the main lens electrode.
Referring to
FIG. 2
, the focus electrode
25
is provided with a drum formed housing
252
externally, having an fore end facing the anode
26
with an opened central part and a rim
252
a
in a form of a racing track in a periphery, and a plate of electrostatic field controlling body
254
spaced a distance away inward from rim
252
a
with three electron beam pass through holes
254
a,
254
b,
and
254
c
for passing the three electron beams from the cathodes. The anode
26
is also provided with a drum formed housing
262
having a rim
262
a
at one end, and an electrostatic field controlling body
264
with electron beam pass through holes
264
a,
264
b,
and
264
c
inside thereof.
FIGS. 3
a
and
3
b
illustrate a plan view of the electrostatic field controlling bodies
254
and
264
of the focus electrode
25
and the anode
26
, respectively.
Referring to
FIGS. 3
a
and
3
b
, it can be known that the electron beam pass through holes
254
a
,
254
b
, and
254
c
in the electrostatic field controlling body
254
of the focus electrode
25
are similar, or identical to the electron beam pass through holes
264
a
,
264
b
, and
264
c
, respectively.
One of the most important parameter to be taken into account in design of an electron gun is a spot diameter Dt on a screen. There are three factors that influence the spot diameter on the screen, i.e., a magnification of the lens, a spatial charge repulsive power, and a spherical aberration of the main lens. Since voltage conditions, focal distances, a length of the electron gun, and etc., are already defined basically, the influence of the magnification of the lens to the spot diameter Dx has a small portion for utilizing as design parameter of the electron gun, and minimal effect.
The spatial charge repulsive power is a phenomenon in which the collision and repulsion between the electrons in the electron beam enlarge the spot diameter. For reducing enlargement of the spot diameter Dst caused by the spatial charge repulsive power, it is favorable to design an angle (a diverging angle) of the electron beam travel greater.
The spherical aberration of the main lens can form the smaller spot diameter on the screen, as the diverging angle of the electron beams is the smaller. In general, the spot diameter Dt on the screen may be expressed as a sum of three factors as follows.
D
t
={square root over ((
D
x
+D
st
)
2
+D
ic
2
)}
The best method for reducing the spherical aberration as well as the spatial charge repulsive power is enlargement of the main lens diameter, which reduces enlargement of the spot caused by the spherical aberration even if electron beams with a great diverging angle are incident thereon, and reduces the spatial charge repulsive power after electron beams pass through the main lens, thereby forming a small diametered spot on the screen. However, an enlargement of the rim, and spacing the distance from the rim to the electrostatic field controlling body greater for enlargement of the main lens diameter form the spot to be almost triangular with partial halo as a focusing of the outer main lens is in a 45° direction, with a difference between a central main lens side and an opposite side.
FIG. 4
illustrates the foregoing triangular spots S
1
on the screen.
The rim
252
a
of the focus electrode
25
focuses the outer beam weak in a 45° direction on the central beam side, and strong in a 45° direction on an opposite side of the central beam side, to form a triangle greater vertically in the 45° direction on the central beam side, and smaller vertically in the 45° direction on an opposite side of the central beam side. There are halos on sides opposite to the central beam in 45° directions. Of course, though forms of the outer spots can be slightly corrected at the anode as the anode acts opposite to the focus electrode, since an action of the main lens is significantly greater at the focusing side than the acceleration side, eventually a state at the focusing side is maintained as it is, due to which, because spot is formed not circular at a periphery of a picture, realization of focusing for meeting requirements of high definition, large sized screen, flat screen, and wide angle is difficult.
Moreover, in comparison to the electron gun with circular outer spots, alignments between apertures of electrodes of electron gun and one sided halo inducing characteristic dependent on assembly of electron gun related to a flatness of the electrode are sensitive, assembly of the electron gun is unfavorable.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an electron gun in a CRT that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electron gun in a CRT, which can enlarge a main lens diameter and form an excellent spot that is almost circular and has a reduced size.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practic

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