Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1999-10-22
2002-05-07
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000, C313S432000, C313S439000
Reexamination Certificate
active
06384524
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inline electron gun for a cathode ray tube (CRT), and, more particularly, to an inline electron gun that is structured to improve an astigmatism in a focus lens.
2. Description of the Prior Art
A inline electron gun is arranged to form red, green and blue electron beams which passes through converging paths to a converging spot of a shadow mask or of an adjacent display screen.
Typically, a convergence of the beams is performed by an electric field which is formed by a plurality of the electrodes. A beam forming region in the electron gun includes a convergence region and a divergence region depending upon a difference in potential between adjacent electrodes. The convergence of the electron beams has an important effect on spots on the display screen. If the difference in potential is higher, the beams are more intensively converged.
However, the excessive difference in potential is not desirable in the aspect of a gradient of voltage.
U.S. Pat. No. 3,873,879 discloses a focus lens with a large diameter comprising two cup type electrodes symmetrically disposed to enlarge the electric field. It is well known that when a diameter of the focus lens is increased in the electron gun, a spherical aberration is decreased. Furthermore, when a space between the adjacent electrodes is increased, the spherical aberration is decreased because of the decreased gradient of the voltage.
However, when the space between the adjacent electrodes is more than 1.27 mm, the electrostatic field applies the electron beams to be curved. Furthermore, it is desired to consider an astigmatism in the electron gun together with the spherical aberration. The astigmatism is that, when the red, green and blue electron beams produce a circular spot on the display screen of the CRT, the vertical diameter of the green spot on the display screen is shorter than those of the red and blue spots. This is caused by the structure of the inline electron gun in which the center green electron beam is disposed asymmetrically with respect to the adjacent red and blue electron beams. To compensate for the astigmatism, controlling of the voltage applied to the electrodes of the electron gun and disposing of a magnetic element on a neck of the CRT are proposed, but these proposals are not a fundamental solution.
U.S. Pat. No. 4,388,553 discloses the compensating of the astigmatism by the construction of horizontal slots formed at an outlet side of a second accelerating electrode and a focus electrode of the electron gun. However, such proposal needs additional parts to provide two parallel strips and assembling of them into the electron gun.
Furthermore, other proposals for decreasing the astigmatism without additional parts have been tried. On the one hand, a center aperture is elongated to enlarge the vertical diameter of the green spot corresponding to the other red and blue spots. On the other hand as shown in
FIG. 4
, a protrusion C is formed adjacent to the center aperture G of an anode electrode A. Due to the protrusion C, the green electron beam is subject to a more intensive electromagnetic field than the adjacent red and blue electron beams and wherein the green electron beam is diverged to compensate for a decreased diameter of the green spot by the astigmatism.
However, a deformation of the center aperture to a vertical elongated one has the problem that the green spot on the display screen is distorted and the design of the elongated aperture is difficult to completely remove the astigmatism. With respect to the electrode having the protrusion C, the selection of the proper height of the protrusion C is difficult. Furthermore, when the anode electrode is subject to a minute variance of the voltage, a variance of the vertical diameter of the green spot on the display screen is considerable (see FIG.
5
).
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the above described problems.
It is an objective of the present invention to provide an inline electron gun that is structured to improve an astigmatism so that a vertical diameter of a green spot on a display screen is equalized with those of adjacent blue and red spots and the design can be easily made.
To achieve the above objective, the present invention provides an inline electron gun including three inline cathodes arranged in a same plane, a prefocus lens and a main focus lens which include a plurality of electrodes for converging or diverging a thermion emitted by the cathodes to form electron beams.
The electrodes include a control grid as a first electrode, a screen electrode or second electrode, a third electrode, a fourth electrode, a fifth electrode as a focus electrode and a sixth electrode as an anode electrode aligned from the cathodes.
The focus lenses include a rim or a lip to form a large aperture. The main focus lens may include the focus electrode, the anode electrode and a subsidiary electrode arranged between the focus electrode and the anode electrode to define a beam course of respective red, green and blue electron beams.
As a feature of the present invention, the focus electrode has symmetrical rectangular slots in its wall to define a green aperture of the subsidiary electrode, whereby the slots decrease the influence of the electric field to the electron beam passing through the green aperture so that the red, green and blue spots on the screen have a uniform vertical diameter.
REFERENCES:
patent: 3873879 (1975-03-01), Hughes
patent: 4388553 (1983-06-01), Chen
patent: 5394053 (1995-02-01), Yun
patent: 5739630 (1998-04-01), Shirai et al.
patent: 5883463 (1999-03-01), Kikuchi et al.
Bushnell , Esq. Robert E.
Patel Ashok
Samsung SDI & Co., Ltd.
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