Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1998-10-20
2002-07-23
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000, C313S449000, C315S015000, C315S382000, C315S382100, C315S368270
Reexamination Certificate
active
06424084
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube applied to a color picture tube and the like and, more particularly, to a cathode ray tube including an electron gun assembly capable of dynamic astigmatism compensation.
A self-convergence in-line color picture tube comprises an in-line electron gun assembly for emitting three electron beams in line, i.e., a center beam and a pair of side beams passing through the same horizontal plane, and a deflection yoke for forming a nonuniform magnetic field for deflecting the electron beams emitted by the electron gun assembly. The three electron beams emitted by the electron gun assembly converge on the center of the screen by the action of a main lens portion included in the electron gun assembly, and at the same time self-converge on the entire screen due to a nonuniform magnetic field made up of a pincushion horizontal deflecting magnetic field and a barrel vertical deflecting magnetic field.
As shown in
FIG. 1A
, electron beams
6
passing through the nonuniform magnetic field are influenced by astigmatism, e.g., forces in the directions of arrows
11
H and
11
V by a pincushion magnetic field
10
. A beam spot
12
formed on a phosphor screen by the electron beams
6
landing on the peripheral portion of the phosphor screen is distorted as shown in FIG.
1
B. This distortion is caused by a deflection aberration or excessive focus of the electron beams
6
in the vertical, i.e., V axis direction.
As a result, the beam spot
12
forms a halo
13
A widening in the vertical direction and a core
13
B extending in the horizontal, i.e., H axis direction. This deflection aberration becomes more conspicuous as the tube size is larger or the deflection angle of the tube is wider, resulting in a very low resolution at the peripheral portion of the phosphor screen.
Examples of a means for solving a decrease in resolution due to the deflection aberration are disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 61-99249, 61-250934, and 2-72546. Each of these electron gun assemblies basically has a cathode K, and first to fifth grids G
1
to G
5
, as shown in FIG.
2
A. The electron gun assembly has an electron beam generating portion GE, a quadrupole lens portion QL, and a final focusing lens portion EL sequentially arranged along the direction in which the electron beam travels.
The third grid G
3
forming the quadrupole lens portion QL has three rectangular electron beam passage holes
14
a
,
14
b
, and
14
c
in a surface facing the fourth grid G
4
, as shown in FIG.
2
B. The fourth grid G
4
has three rectangular electron beam passage holes
15
a
,
15
b
, and
15
c
in a surface facing the third grid G
3
, as shown in FIG.
2
C. The electron beam passage hole
14
(
a, b, c
) is formed with a shape asymmetrical to the electron beam passage hole
15
(
a, b, c
).
In the electron gun assembly, the lens powers of the quadrupole lens portion QL and the final focusing lens portion EL change in accordance with the beam deflection amount of the electron beam to compensate for the influence of any deflection aberration produced by the deflecting magnetic field on the electron beam deflected to the screen periphery, and to correct distortion of the beam spot on the phosphor screen.
Even with this correction means, however, when the electron beam is deflected toward the peripheral portion of the screen, generation of a halo of the beam spot can be suppressed, but vertically collapsing distortion of the beam spot cannot be satisfactorily corrected.
FIG. 3
is a view for explaining the electron beam orbit and the lens operation in the electron gun assembly shown in FIG.
2
A. In
FIG. 3
, the solid lines represent the electron beam orbit and the lens operation when electron beams are not deflected and focus on the center of the screen. The broken lines represent the electron beam orbit and the lens operation when electron beams are deflected and focus on the peripheral portion of the screen.
As shown in
FIG. 3
, when electron beams are not deflected, the electron beams focus on the center of the phosphor screen by the action of only the main electron lens portion EL indicated by the solid lines. When electron beams are deflected, electron beams focus on the peripheral portion of the phosphor screen by the action of the quadrupole lens portion QL located on the cathode side of the main electron lens portion EL, the main electron lens portion EL, and a deflection yoke lens portion DYL, i.e., a deflection aberration component included in the deflecting magnetic field formed by a deflection yoke.
Since a color cathode ray tube generally has a self-convergence deflecting magnetic field, a focusing lens is formed in only the vertical direction V while the focusing force in the horizontal direction H remains unchanged. In
FIG. 3
, therefore, the lens action of the deflecting magnetic field in the horizontal direction H is not illustrated.
When electron beams are deflected, the lens power of the main electron lens portion EL weakens as indicated by the broken lines, and the quadrupole lens portion QL is formed as indicated by the broken lines so as to compensate the focusing action in the horizontal direction H. Consequently, electron beams pass through electron beam orbits indicated by the broken lines in
FIG. 3
to focus on the peripheral portion of the screen.
In the example of
FIG. 3
, when electron beams are focused on the phosphor screen, the principal plane of the lens, i.e., virtual lens center (cross point between the orbit of a beam emitted by the cathode and the orbit of a beam incident on the phosphor screen) is at position A when the electron beam is not deflected. To the contrary, when the electron beam is deflected, the principal plane of the lens in the horizontal direction H moves from position A to position B on an accordance with generation of the quadrupole lens portion QL. At this time, the principal plane of the lens in the vertical direction V moves from position A to position C on the phosphor screen side.
The principal plane in the horizontal direction H therefore moves back from position A to position B on the cathode side to increase the lens magnification. This increases the beam spot diameter on the phosphor screen in the horizontal direction. The principal plane in the vertical direction V moves forward from position A to position C on the phosphor screen side to decrease the lens magnification. This decreases the beam spot diameter on the phosphor screen in the vertical direction. As a result, the magnification becomes different between the horizontal and vertical directions, and a beam spot formed by the electron beam landing on the peripheral portion of the screen is elongated in the horizontal direction H.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and has as its object to provide a cathode ray tube capable of obtaining a high image quality over the entire screen by preventing distortion of the spot formed by the electron beam resulting from the difference in lens magnification between the horizontal and vertical directions when electron beams are focused on the peripheral portion of the screen.
According to the present invention, there is provided a cathode ray tube comprising:
an electron gun assembly having an electron beam forming portion for forming and emitting at least one electron beam and a main electron lens portion for accelerating and focusing the electron beam; and
a deflection yoke for generating a deflecting magnetic field for deflecting the electron beam emitted by the electron gun assembly and scanning a screen in vertical and horizontal directions,
the main electron lens portion having first, second, and third lens regions sequentially formed by a voltage distribution continuously increasing along a traveling direction of the electron beam, the second lens region having means for, assuming that horizontal and vertical directions be perpendicular to the traveling direction of a nondeflected electron beam traveling towa
Awano Takashi
Kimiya Junichi
Sugawara Shigeru
Haynes Mack
Patel Vip
Pillsbury & Winthrop LLP
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