Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2001-08-23
2003-09-02
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S413000, C313S426000, C315S370000, C315S382000, C315S382100
Reexamination Certificate
active
06614156
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-253882, filed Aug. 24, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode-ray tube (CRT) apparatus, and more particularly to a color cathode-ray tube apparatus with an electron gun assembly capable of performing dynamic astigmatism compensation.
2. Description of the Related Art
In these years, self-convergence in-line type color CRT apparatuses, each of which can self-converge three in-line electron beams on the entire area of a phosphor screen, have widely been used. In this type of color CRT apparatus, an electron beam, which has passed through a non-uniform magnetic field, suffers deflection aberration. As is shown in
FIG. 1A
, for example, an electron beam
12
receives a force in the direction of arrows
13
due to a pin-cushion-shaped horizontal deflection magnetic field
11
. Consequently, as shown in
FIG. 1B
, the beam spot
12
of the electron beam deflected onto a peripheral portion of the phosphor screen deforms, thus seriously degrading the resolution.
Owing to the deflection aberration suffered by the electron beam, the electron beam is vertically over-focused while it is horizontally spread. As a result, the beam spot on the peripheral portion of the phosphor screen has a horizontally deformed core portion
14
with high luminance and a vertically spread halo portion
15
with low luminance.
There are known some means for solving the problem of degradation in resolution. For example, electron gun assemblies have a common structure comprising first to fifth grids. The electron gun assembly includes an electron beam generating section, a quadrupole lens, and a main lens, which are formed along the axis of travel of electron beams. The quadrupole lens is composed of the third and fourth grids disposed adjacent to each other. The third and fourth grids, respectively, have three vertically elongated non-circular electron beam passage holes and three horizontally elongated non-circular electron beam passage holes in their mutually opposing surfaces.
FIG. 2
shows an equivalent optical model for illustrating correction of deflection aberration by the electron gun assembly. When the quadrupole lens is not made to function, an electron beam
800
travels through a main lens
803
and a deflection magnetic field
804
, as indicated by broken lines. The electron beam
800
deflected on a peripheral portion
805
of the phosphor screen is horizontally under-focused and vertically over-focused. Consequently, the resolution greatly deteriorates.
When the quadrupole lens is made to function, the effect of deflection aberration due to the deflection magnetic field
804
is decreased, as indicated by solid lines. An electron beam
801
deflected on the peripheral portion
805
of the phosphor screen creates a beam spot with a suppressed halo portion.
Even if the above correction means is provided, however, the deflection aberration due to the deflection magnetic field is very serious. Although the halo portion of the beam spot may be eliminated, the horizontal deformation of the core portion cannot be corrected. This occurs mainly due to the difference in incidence angle between horizontal and vertical directions of the electron beam that strikes the phosphor screen.
Specifically, the electron beam is affected differently in the horizontal and vertical directions owing to the quadrupole lens and deflection magnetic field. Thus, the horizontal incidence angle ax << the vertical incidence angle ay. As a result, the horizontal magnification Mx >> the vertical magnification My, according to the law of Lagrange-Helmholz. Consequently, the beam spot of the electron beam focused on the peripheral portion of the phosphor screen is horizontally deformed.
There are known some color CRT apparatuses capable of correcting the horizontal deformation. An electron gun assembly applied to these CRT apparatuses basically comprises first to seventh grids and includes an electron beam generating section, a first quadrupole lens, a second quadrupole lens and a main lens, which are arranged in the direction of travel of electron beams. The first quadrupole lens is formed by providing the third and fourth grids, which are disposed adjacent to each other, with three horizontally elongated non-circular electron beam passage holes and three vertically elongated noncircular electron beam passage holes in their mutually opposing surfaces. The second quadrupole lens is formed by providing the fifth and sixth grids, which are disposed adjacent to each other, with three vertically elongated non-circular electron beam passage holes and three horizontally elongated non-circular electron beam passage holes in their mutually opposing surfaces.
The lens action of the first quadrupole lens varies in synchronism with the variation in the deflection magnetic field, thereby correcting the image magnification of the electron beam incident on the main lens. The lens actions of the second quadrupole lens and the main lens vary in synchronism with the variation in the deflection magnetic field, thereby preventing the electron beam, which will ultimately be deflected on the peripheral portion of the phosphor screen, from being greatly deformed by the deflection aberration due to the deflection magnetic field.
FIG. 3
shows an equivalent optical model for illustrating correction of deflection aberration by the electron gun assembly. Specifically, a first quadrupole lens
901
controls the image magnification of an electron beam
900
incident on a main lens
903
. A second quadrupole lens
902
varies the focus condition of the main lens
903
, thus correcting deflection aberration due to a deflection magnetic field
904
and focusing the electron beam
900
on a peripheral portion
905
of the phosphor screen. Thereby, compared to a conventional dynamic focus electron gun assembly with a single quadrupole lens, the horizontal deformation can be eliminated and the electron beam can be focused on the peripheral portion of the phosphor screen more appropriately.
The use of the above-described double quadrupole lens structure, however, increases the incident angle in the horizontal direction, at which the electron beam to be focused on the peripheral portion of the phosphor screen enters the main lens section. Thus, the electron beams becomes more susceptible to the effect of spherical aberration of the main lens. In short, the beam spot at the peripheral portion of the phosphor screen has a horizontal halo portion.
Compared to the structure shown in
FIG. 2
wherein the quadrupole lens is disposed in front of the main lens, the structure shown in
FIG. 3
, wherein the double quadrupole lenses are disposed in front of the main lens, has the following problem: the trajectory of the electron beam varies both in the horizontal and vertical directions. This requires optimization of the shape of the first quadrupole lens, optimization of the shape of the second quadrupole lens, and re-designing of the main lens system.
In general terms, the dynamic focus electron gun assembly performs focus adjustment by adjusting an external voltage. In the case of the structure shown in
FIG. 2
, the optimal focus adjustment can be made by varying the quadrupole lens
802
and main lens
803
. However, in the case of the structure shown in
FIG. 3
, the focus adjustment is affected by the variation of the first quadrupole lens
901
, second quadrupole lens
902
and main lens
903
. As a result, the lens functions are complicated, and it is difficult to set an optimal focus voltage.
Moreover, in the case of the structure shown in
FIG. 3
, the shape of the electron beam passage hole formed in each of the electrodes constituting the first quadrupole lens differs from the shape of other holes. Consequently, in the electron gun assembling steps, center rods
52
,
Kimiya Junichi
Oda Hiroyuki
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Ashok
Phinney Jason R
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