Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2001-11-29
2004-06-01
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000, C315S382000
Reexamination Certificate
active
06744191
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-365927, filed Nov. 30, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a cathode ray tube (CRT) apparatus, and more particularly to a color cathode ray tube apparatus equipped with an in-line electron gun assembly for emitting three electron beams travelling in the same horizontal plane.
2. Description of the Related Art
In recent years, a self-convergence in-line type color cathode ray tube apparatus has widely been put to practical use. This CRT apparatus is characterized in that three in-line electron beams are self-converged on the entire area of a phosphor screen.
In this type of color CRT apparatus, a method of increasing a lens aperture of a main lens section created by an electron gun assembly is effective as means for obtaining good image characteristics. Typical means for increasing the lens aperture of the main lens section are an overlapping field type lens and an extended field type lens.
As is shown in
FIG. 1
, an overlapping field type lens
52
is created between two adjacent electrodes
50
a
and
50
b
, which have outer peripheral electrodes
51
a
and
51
b
at their opposing faces. The overlapping field type lens
52
is an electric field lens acting commonly on three electron beams passing through three electron beam passage holes formed in each of the electrodes
50
a
and
50
b
. Thereby, the lens diameter of the main electric filed is substantially increased.
As is shown in
FIG. 2
, an extended field type lens
65
is created by disposing an intermediate electrode
62
between a focus electrode
61
and an anode
63
. A focus voltage is applied to the focus electrode
61
, an anode voltage higher than the focus voltage is applied to the anode
63
, and a voltage of an intermediate level between the focus voltage and anode voltage is applied to the intermediate electrode
62
. In general, in consideration of breakdown voltage characteristics, a voltage obtained by resistor-dividing the anode voltage via a resistor
64
is applied to the intermediate electrode
62
. The extended field type lens
65
increases the lens diameter by extending the lens region in the tube axis direction.
Jpn. Pat. Appln. KOKAI Publication No. 9-320485, for instance, discloses that two lenses are combined to obtain more improved image characteristics.
On the other hand, the effect of deflection magnetic fields upon electron beams cannot be ignored. In the color CRT apparatus, electron beams, which have passed through non-uniform magnetic fields, are affected by deflection aberration components included in the deflection magnetic fields. Consequently, a beam spot deforms on a peripheral portion of the phosphor screen, and the resolution considerably deteriorates.
An electron beam
12
deflected onto a peripheral portion of the phosphor screen is affected by a force exerted by a pincushion type horizontal deflection magnetic field
11
in the direction of arrows
13
, as shown in, e.g. FIG.
3
A. As a result, as shown in
FIG. 3B
, the beam spot on the peripheral portion of the phosphor screen horizontally deforms, and the resolution greatly deteriorates.
The electron beam affected by the deflection aberration components is horizontally enlarged and vertically over-focused. The beam spot formed on the peripheral portion of the phosphor screen thus produces a high-luminance core portion
14
deformed in a horizontal direction X and a low-luminance halo portion
15
enlarged in a vertical direction Y.
Jpn. Pat. Appln. KOKAI Publication No. 61-99249, for instance, discloses structural means for solving the problem of deterioration in resolution. The electron gun assembly in this structural means basically comprises first to fifth grids. The electron gun assembly also includes an electron beam generating section, a quadrupole lens and a main lens, which are disposed in the direction of travel of electron beams. The third and fifth grids disposed adjacent to each other to create the quadrupole lens have, respectively, vertically and horizontally elongated non-circular electron beam passage holes in their mutually opposing faces.
The lens function of the quadrupole lens dynamically is varied by applying a dynamic focus voltage that varies in synchronism with deflection magnetic fields to the fourth grid. Thus, the quadrupole lens corrects the deformation due to deflection aberration of the electron beam deflected on the peripheral portion of the phosphor screen.
If the quadrupole lens is combined with the above-mentioned two lenses (overlapping field type lens and extended field type lens), good image characteristics can be obtained over the entire area of the screen.
The overlapping field type lens can increase the horizontal lens diameter relative to the electron beams, but it cannot increase the vertical lens diameter as much as the horizontal lens aperture. This results in a difference in lens diameter between the horizontal and vertical directions, and the focal distance in the vertical direction becomes shorter than that in the horizontal direction. Thus, this overlapping field type lens has a negative astigmatism. The electron beam, which has passed through the overlapping field type lens, is horizontally under-focused and vertically over-focused. In order to compensate the negative astigmatism, one of the electrodes which is arranged back from the overlapping field type lens is generally provided with vertically elongated electron beam passage holes.
However, this electrode structure makes the horizontal dimension of the electron beam passage hole less than the vertical dimension thereof. Consequently, the distance between the electron beam and the horizontal end portions of the electron beam passage hole in the electrode decreases, and local aberration occurs. In practice, even if the length of the outer peripheral electrode is to be extended in the tube axis direction to realize a large-aperture lens, the above-mentioned horizontal local aberration restricts the length of the outer peripheral electrode and makes it difficult to obtain a desired lens aperture.
The combination of the above-mentioned quadrupole lens and the extended field type lens will now be considered.
In an electron gun assembly as shown in
FIG. 4
, a quadrupole lens is formed between a first focus electrode
803
and a second focus electrode
804
to which a dynamic focus voltage is applied. The first focus electrode
803
, second focus electrode
804
, an intermediate electrode
805
and an anode
806
constitute an extended field type main lens. The intermediate electrode
805
is supplied with a voltage from the anode
806
via a resistor
807
.
In this structure, if a dynamic focus voltage is applied to the second focus electrode
804
, part of the AC component of the dynamic focus voltage is superimposed on the intermediate electrode
805
due to the electrostatic capacitance created among the second focus electrode
804
, intermediate electrode
805
and anode
806
. Thus, the potential of the intermediate electrode
805
increases.
As is shown in
FIG. 5
, a potential Vf of the second focus electrode, a potential Vgm of the intermediate electrode and a potential Eb of the anode are set to become higher in the named order. When an AC component of the dynamic focus voltage is not applied to the second focus electrode, the extended field type main lens has a potential distribution
904
. When an AC component of the dynamic focus voltage has been applied to the second focus electrode and a part of the AC component of the dynamic focus voltage is not superimposed on the intermediate electrode, the extended field type main lens has a potential distribution
905
. When an AC component of the dynamic focus voltage has been applied to the second focus electrode and a part of the AC component of the dynamic focus voltage has been s
Kimiya Junichi
Oda Hiroyuki
Guharay Karabi
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Ashok
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