Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2002-09-17
2004-02-17
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S382000, C315S015000, C315S017000, C313S414000, C313S449000
Reexamination Certificate
active
06693398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an electron gun for a cathode ray tube, and more particularly to an electron gun for a cathode ray tube to achieve an excellent focus characteristic on the whole screen by forming a dynamic quadruple lens in the electron gun used for a transpose scan type cathode ray tube.
2. Description of the Related Art
FIG. 1
is a view of showing a structure of a general related cathode ray tube and electron gun, and
FIG. 2
is a view of showing a structure of a general related electron gun.
As shown in FIG.
1
and
FIG. 2
, the general cathode ray tube (CRT) and an in-line type electron gun for the CRT includes three cathodes
3
that are independent from each other; a first electrode
4
that is separated from the cathode
3
at a specific interval; a second electrode
5
, a third electrode
6
and a fourth electrode
7
that are positioned at regular intervals from the first electrode
4
; a fifth electrode
8
-
1
,
8
-
2
,
8
-
3
that are divided into three electrodes; a sixth electrode
9
; and a shield cup
10
to which a B.S.C
11
is attached at its upper part.
Additionally, a deflection yoke
12
that allows electron beams
13
to be deflected onto a whole screen
15
is mounted on an outside of the electron gun. The general cathode ray tube further includes a shadow mask
14
, which is an electrode to distinguish colors, and a screen
15
having a fluorescent material.
An operation of the electron gun constructed as above is described as follows. The electrodes forming the electron gun are respectively provided with different voltages in order to obtain an uniform current and allow their cut off voltages to be same.
In detail, the sixth electrode
9
that is an anode is provided with a constant voltage Eb of about 26000V, and a first electrode
8
-
1
, and a third electrode
8
-
3
of the fifth electrode and the third electrode
6
are provided with a dynamic voltage Vdf that varies simultaneously according to a deflection force of the deflection yoke
12
.
Additionally, a second electrode
8
-
2
of the fifth electrode is applied by a focus voltage Vsf, and the second electrode
5
and the fourth electrode
7
are applied with a constant voltage Ec2 of about 600V. The first electrode
4
that is a control electrode is applied by a ground voltage.
As a heater
2
that is mounted in the cathode
3
of the electron gun is heated, electrons are emitted from a stem pin
1
, and an amount of the emitted electrons are controlled by the first electrode
4
. The controlled electron beams
13
is accelerated by the second electrode
5
, and the accelerated electron beams
13
are partly converged by the third electrode
6
, the fourth electrode
7
and the third electrode
8
-
3
of the fifth electrode. The converged electron beams
13
pass the third electrode
8
-
3
and the second electrode
8
-
2
of the fifth electrode that form a MQ lens for circularizing shapes of spots around the screen.
Additionally, the electron beams
13
pass the second electrode
8
-
2
and the first electrode
8
-
1
of the fifth electrode which form a dynamic quadruple DQ lens for eliminating a Halo phenomenon that occurs at the spots around the screen.
Additionally, the electron beams
13
pass the sixth electrode
9
and are deflected onto the whole screen
15
by the deflection yoke
12
mounted on the outside of the electron gun.
The deflected electron beams
13
pass a shadow mask
14
, and collide with the screen having the fluorescent material to form a picture.
FIG. 3
a
and
FIG. 3
b
are views of describing shapes of holes for passing the electron beams in the related electron gun.
With respect to
FIG. 3
a
, in the related in-line type electron gun, a surface
27
of the third electrode
8
-
3
of the fifth electrode for forming the MQ lens, which is opposite to the second electrode
8
-
2
, and a surface
29
of the second electrode
8
-
2
of the fifth electrode forming the dynamic quadruple lens, which is opposite to the first electrode
8
-
1
, are provided a passage hole
18
for the electron beams having a longitudinal keyhole shape combining a circle and a rectangular having its width smaller than its length.
Additionally, a surface
28
of the second electrode
8
-
2
of the fifth electrode for forming the MQ lens, which is opposite to the third electrode
8
-
3
, and a surface
30
of the first electrode
8
-
1
of the fifth electrode forming the dynamic quadruple lens, which is opposite to the second electrode
8
-
2
, are provided a passage hole
19
for the electron beams having a transversal keyhole shape combining a circle and a rectangular having its width longer than its length.
FIG. 4
shows a scan configuration
16
on the screen of the related CRT and positions
17
of
3
color electron beams of the electron gun.
As shown in this figure, in the related CRT, the electron beams are shot on the screen from its upper part to its lower part and from the left to the right, and the
3
color electron beams of the electron gun are horizontally arranged in an in-line shape.
FIG. 5
a
and
FIG. 5
b
are views of describing lenses of the electron gun.
In a related CRT, asymmetric lenses are arranged between the separated
3
electrodes of the fifth electrode, and the asymmetric lenses have intensities that are varied by the dynamic voltage synchronized by the deflection current.
A detail explanation of an operation of the asymmetric lenses is as follows.
The dynamic quadruple lens DQ formed between the first electrode
8
-
1
and the second electrode
8
-
2
of the fifth electrode performs an asymmetric operation in the largest at comers of the screen where the deflection current is highest, that is, where the deflection force of the deflection yoke
12
is largest.
On the other hand, the lens performs a smallest asymmetric operation at a center of the screen where there is little deflection current, that is, where there is little deflection force.
In the related in-line type electron guns without the dynamic quadruple lens, a horizontal spotting magnification and a vertical spotting over-convergence occur around the screen because of an non-uniform magnetic field DL of a self-convergence deflection yoke, thus causing a Halo phenomenon and focus deterioration around the screen.
This phenomenon means that a horizontal convergence force for the electron beams is weakened by the non-uniform magnetic field for the deflection and a vertical convergence force for the electron beams is intensified. A dynamic lens for overcoming the problem as above weakens the vertical convergence force around the screen to achieve an excellent focus characteristic over the whole screen as shown in
FIG. 5
a.
Additionally, a dynamic voltage is applied to the first electrode
8
-
1
of the fifth electrode to change, according to the deflection, an intensity of the main lens ML that performs the most important action for the convergence of the electron beams, thus compensating a focus distance, which increases in the case of the deflection of the electron beams around the screen, by weakening the intensity of the main lens.
As shown in
FIG. 5
b
, the MQ lens formed between the second electrode
8
-
2
and the third electrode
8
-
3
of the fifth electrode allows the horizontal convergence force to be weaken according to an increase of the deflection force, unlike the dynamic quadruple lens.
On the other hand, as shown in
23
of the
FIG. 6
b
, the MQ lens has an action to intensify the convergence force to compensate a longitudinal extension phenomenon
20
of spots around the screen in the case of having only the dynamic quadruple lens DQ as shown in
20
of
FIG. 6
a
Meanwhile, a spot diameter can be calculated by a multiplication of a object space size and a lens magnification, which is determined by a start angle (&thgr;o) of an electron beam and an incidence angel (&thgr;i) of the electron beam, as shown in a following formula
The spot diameter is inversely proportional to the incidence angle (&thgr; i)
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