Electron gun for cathode ray tube

Details Electron gun for cathode ray tube Electron gun for cathode ray tube

2000-10-10

2002-09-24

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

C315S382000, C315S368160, C313S412000, C313S428000

Reexamination Certificate

active

06456017

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun, and more particularly, to an electron gun for a cathode ray tube (CRT) having reshaped electron beam apertures.
2. Description of the Related Art
In general, an electron gun includes a triode consisting of a cathode structure, a control electrode and a screen electrode, a focusing electrode opposed to the screen electrode to form a pre-focusing lens and a final accelerating electrode opposed to the focusing electrode to form a main focusing lens.
If power is applied to a CRT, an electron gun emits electron beams from the cathode structure. The emitted electron beams pass through electron beam apertures of multiple electrodes and are focused and accelerated. The accelerated electron beams are selectively deflected by a deflection yoke installed at the cone portion of a bulb, and excite a phosphor screen on the inner surface of a panel, thereby displaying a picture image.
In the above-described CRT, in order to prevent enlargement or distortion of the spot of an electron beam landing on the phosphor screen due to a nonuniform magnetic field of a deflection yoke, a dynamic focusing method using a quadrupole lens, in which the cross section of an electron beam emitted from an electron gun is distorted in the opposite direction of the deflection magnetic field and the focus voltage applied to the electron gun is varied when the electron beam is scanned at the center or periphery of the phosphor screen, has been employed.
FIG. 1
shows the first embodiment of parts of electrodes of an electron gun based on the dynamic focusing method, and
FIG. 2
is a view in elevation and in section of FIG.
1
.
Referring to
FIGS. 1 and 2
, the focusing electrode of the electron gun includes a static electrode
10
to which a static focusing voltage VF
1
is applied, and a dynamic electrode
100
which faces the static electrode
10
and to which a dynamic voltage DF varying in synchronization with a deflection signal is applied.
The electrodes
10
and
100
include outer electrodes
12
and
120
having separate electron beam apertures
11
and
110
, and auxiliary electrodes
14
and
140
inside the outer electrodes
12
and
120
and arranged in-line, respectively. The auxiliary electrodes
14
and
140
have three separate apertures
13
b
/
13
a
/
13
c
and
130
b
/
130
a
/
130
c
for R, G and B electron beams so that electrons emitted from cathode structure are focused and accelerated by an electronic lens formed between each of the-respective electrodes according to application of a voltage.
Here, the diameters of the G electron beam apertures
13
a
and
130
a
formed in the center, among the three separate apertures
13
b
/
13
a
/
13
c
and
130
b
/
130
a
/
130
c
, are equal. However, the diameters of the R and B electron beam apertures
13
b
/
13
c
and
130
b
/
130
c
arranged at opposite sides of the G electron beam apertures
13
a
and
130
a
are different.
In other words, whereas the R and B electron beam apertures
13
b
and
13
c
are equal to the G electron beam aperture in diameter in the static electrode
10
, the diameter of the R or B electron beam aperture
130
b
or
130
c
is greater than that of the G electron beam aperture
130
a
in the dynamic electrode
100
.
Accordingly, the central axes of the R electron apertures
13
b
and
130
b
are spaced apart by a distance D, and the central axes of the B electron beam apertures
13
c
and
130
c
are also spaced apart by the same distance, as shown in FIG.
2
. As described above, asymmetry in electric fields of the electronic lens formed between each of various electrodes makes it easier to adjust convergence.
However, when a dynamic voltage is applied to the final focusing electrode, that is, the dynamic electrode
100
, since the focusing force of the final focusing electrode changes, the focusing force for converging three electron beams onto a phosphor screen changes accordingly. Thus, the capability of correcting convergence at the screen corner is deteriorated, thereby lowering picture quality.
In order to manufacture an electron gun having the electrodes
10
and
100
, electrodes are arranged on a zig rod for assembling the electron gun, and spacers for maintaining a gap between each of the respective electrodes are interposed and then assembled. The assembled electrodes are fusion-fixed within the neck portion of a bulb by pressing buried portions at edges of the electrodes when bead glass positioned at both sides of each electrode is semi-fused.
However, in the above-described electrodes
10
and
100
, the axis between centers of R electron beam apertures
13
b
and
130
b
and the axis between centers of B electron beam apertures
13
c
and
130
c
are spaced a predetermined distance D apart from each other. Thus, when the electrodes
10
and
100
are inserted into a zig, the R and B electron beam apertures
130
b
and
130
c
having relatively larger diameters become eccentrically disposed from the zig rod, which makes it difficult to attain alignment, resulting in poor assembling efficiency.
Although the electrode structure disclosed in U.S. Pat. No. 4,701,678 can easily adjust convergence, it is very difficult to fabricate.
In detail, as shown in
FIGS. 3 and 4
, facing electrodes
30
and
300
according to another conventional example are substantially trapezoidal laterally. In the electrodes
30
and
300
, R electron beam apertures
32
and
320
and B electron beam apertures
33
and
330
are tilted toward the edges of G electron beam apertures
31
and
310
at a predetermined angle.
In this case, a problem is encountered in controlling tolerance since the R electron beam apertures
32
and
320
and the B electron beam apertures
33
and
330
are tilted from the top surfaces of the electrodes
30
and
300
.
Also, the electrode structure disclosed in U.S. Pat. No. 5,027,043 exhibits deteriorated focusing characteristic.
In still another conventional electrode structure shown in
FIGS. 5 and 6
, outer electrodes
50
and
500
are provided and separate small, R, G and B electron beam apertures
52
and
520
are formed on top surfaces of the outer electrodes
50
and
500
.
Here, enlargement portions
530
protruding from the rims of the R and B electron beam apertures
520
b
and
520
c
toward a G electron beam aperture
520
a
, are formed in the static electrode
500
.
In this case, electron beams converge toward the enlargement portions
530
. Thus, in spite of relatively easy assembling work, electron beam spots are locally distorted, thereby degrading the quality of a picture. Accordingly, the above-described electrode structure is not suitable for a high resolution CRT to which high-current electron beams are applied.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an improved electron gun for a cathode ray tube (CRT) which can easily adjust convergence by changing the shape of electron beam apertures of electrodes, and which can reduce a position error when being assembled.
Accordingly, to achieve the above objective, there is provided an electron gun for a cathode ray tube having a triode consisting of a cathode structure, a control electrode and a screen electrode, a plurality of focusing electrodes for forming a pre-focusing lens unit for pre-focusing and accelerating R, G and B electron beams emitted from the triode, and a final accelerating electrode facing the focusing electrodes, for forming a main lens unit, wherein among R, G and B electron apertures of one of the focusing electrodes facing each other to form a quadrupole lens unit, to which an AC voltage having a relatively low peak, or a static voltage, is applied, enlargement portions which are asymmetrical with respect to the central axes of the respective electron beam apertures are formed into the rim of each of the R and B electron beams, so that the R, G and B electron beams are converged into one point even when the electron beams deviate to the corner of a sc

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