Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-03-22
2002-12-10
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S47700R, C313S413000, C313S415000
Reexamination Certificate
active
06492766
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and more particularly to a color cathode ray tube having a wide deflection angle and which is equipped with an in-line type electron gun having excellent focusing characteristics.
The color cathode ray tube used as a monitor of a television receiver and an information terminal accommodates an electron gun which emits a plurality of electron beams in one end of a vacuum envelope and has a phosphor screen (image screen) on which phosphor films of a plurality of colors are coated on an inner surface of the other end of the vacuum envelope. The color cathode ray tube is also provided with a deflection yoke on an outer portion of the vacuum envelope, which the deflection yoke performs a two-dimensional scanning of electron beams from the electron gun on the phosphor screen so as to display a given image.
Further, in many color cathode ray tubes, a shadow mask which constitutes a color selection electrode is installed close to the phosphor screen and a plurality of electron beams emitted from the electron gun are made to pass through the color selection electrode and impinge on the respective phosphor films so as to form color images.
To improve the color image formed on the phosphor screen over the whole screen area, a color cathode ray tube equipped with an electron gun as part of a system which applies high voltages other than an anode voltage to a plurality of electrodes which focus the electron beams and form a multi-stage focusing lens is known.
As such an electron gun, a so-called in-line type electron gun which emits three electron beams in parallel on a plane is most common.
FIG.
8
A and
FIG. 8B
are schematic cross-sectional views illustrating the schematic structure of the conventional in-line type electron gun, wherein
FIG. 8A
is a horizontal cross-sectional view as seen from a direction perpendicular to the in-line direction and
FIG. 8B
is a vertical cross-sectional view as seen from the in-line direction.
This electron gun includes an electron beam generating portion which is comprised of three cathodes
1
arranged in the in-line direction, a first electrode (control electrode)
2
and a second electrode (accelerating electrode)
3
and a pre-focusing lens portion which is comprised of the first electrode
2
, the second electrode
3
and a third electrode
4
. Further, in the direction toward the phosphor screen from the third electrode
4
, a fourth electrode
5
and a fifth electrode
6
which is divided into a first fifth electrode
61
and a second fifth electrode
62
are arranged in sequence, and the fourth electrode
5
is electrically connected with the second electrode
3
so as to have the same potential and is sandwiched between the third electrode
4
and the fifth electrode
6
to which a high voltage is applied, thus forming a first-stage focusing lens (UPF: Uni-Potential Focusing).
Further, the electron gun includes the fifth electrode
6
and a sixth electrode
7
to which the anode voltage Eb which is the optimal voltage is applied, and a second-stage focusing lens (BPF: Bi-Potential Focusing) is constituted by the fifth electrode
6
and the sixth electrode
7
. That is, a main lens which is formed by combining a UPF lens and a BPF lens is called a U-B lens and is popularly used in a multistage focusing type electron gun.
Numeral
8
indicates a shield cup contiguously connected to the sixth electrode
7
. Further, the fifth electrode
6
is divided into two electrodes and is comprised of the first fifth electrode
61
which is electrically connected to the third electrode
4
and the second fifth electrode
62
which faces the sixth electrode
7
so as to form the second-stage focusing lens.
Further, vertical correction plates
6
V and horizontal correction plates
6
H are respectively mounted on the first fifth electrode
61
and the second fifth electrode
62
. That is, on the second fifth electrode
62
side of the first fifth electrode
61
, there are mounted the vertical correction plates
6
V which are arranged such that they sandwich three electron beams individually from the horizontal direction, while on the first fifth electrode
61
side of the second fifth electrode
62
, there are mounted horizontal correction plates
6
H which are arranged such that they sandwich three electron beams from the vertical direction. An electrostatic quadrupole lens is constituted by these vertical correction plates
6
V and the horizontal correction plates
6
H.
In the in-line type electron gun having the above-mentioned constitution, a constant focusing voltage Vfs is applied to the first fifth electrode
61
, and Vfd+dVf, which is obtained by superposing a dynamic voltage dVf which is increased corresponding to a deflection amount of electron beams to an optimal focusing voltage Vfd at the center of the screen, is applied to the second fifth electrode
62
.
This kind of electron gun is disclosed in Japanese Laid-open Publication 189842/1990.
In this electron gun, the electrostatic quadrupole lens constituted by the vertical correction plates
6
V and the horizontal correction plates
6
H are installed, Vfs is applied to the vertical correction plates
6
V, Vfd+dVf is applied to the horizontal correction plates
6
H, and Vfs<Vfd+dVf is established; and, hence, the quadrupole lens acts as a focusing lens for the horizontal direction of the electron beams an acts as a divergent lens for the vertical direction.
Due to such actions, the deflection aberration which becomes a cause of a lateral defocusing phenomenon or a horizontal crush of the beam spot generated around the periphery of the screen is corrected. Further, when the electron beams are focused at the center of the screen, a curvature-of-field (curvature-of-field aberration, curvature-of-field defocusing) which causes excessive focusing is generated.
With respect to this phenomenon, since the focusing voltage of the second fifth electrode
62
which faces the sixth electrode (anode)
7
becomes high due to the relationship of Vfs<Vfd+dVf, the focusing action of the above-mentioned second-stage focusing lens is weakened so that the curvature-of-field can be simultaneously corrected and excellent focusing characteristics can be obtained over the whole screen.
SUMMARY OF THE INVENTION
Here, corresponding to the widening of the deflection angle of the electron beams, the above-mentioned deflection aberration and the curvature-of-field are also increased so that in the color cathode ray tubes which have been popularly used as display monitors for personal computers or electronic computer terminals, the deflection angle of the electron beams has been set to approximately 90°.
In converting this deflection angle of 90° into the shape of the color cathode ray tube, by designating the diagonal size of an effective screen as De and the distance from the center of the phosphor screen to the end portion of the focusing electrode which forms the main lens of the electronic gun and faces the anode electrode as Lg, the ratio De/Lg becomes De/Lg ≅1.4.
To consider the mounting of such a color cathode ray tube in a display monitor device, it is preferable that the total length of the color cathode ray tube is short. In case the deflection angle is widened to 100°, for example, to make the color cathode ray tube short, with the same diagonal size of effective screen De of the color cathode ray tube having a deflection angle of 90°, the distance Lg from the center of the phosphor screen to the opposing end portion of the focusing electrode, which forms the main lens of the electron gun and faces the anode electrode in an opposed manner, can be shortened approximately inversely proportional to the tangent angle (expressed as tan (Amax/2) in case the maximum deflection angle is Amax).
Further, in case this deflection angle is increased, it becomes necessary to increase the above-mentioned dynamic voltage dVf. However, in view of the limitation imposed on the actual designing of a dynamic focusing
Kato Shin-ichi
Sakamoto Hirotsugu
Shirai Syouji
Tsuzurahara Mamoru
Uchida Go
Antonelli Terry Stout & Kraus LLP
Day Michael H.
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