Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1998-10-30
2001-05-22
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S414000, C313S413000, C313S449000
Reexamination Certificate
active
06236152
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube apparatus, and more particularly to a color cathode ray tube apparatus that has a high-resolution electron gun.
Most color cathode ray tubes have a panel
1
and a funnel
2
that is formed integral with the panel
1
, as is illustrated in
FIG. 1. A
phosphor screen
3
is provided as a target, opposing the inner surface of the panel
1
. The phosphor screen
3
has a number of tricolor segments, each consisting of three stripes or dots of different colors. A shadow mask
4
having a number of apertures is provided, opposing the inner surface of the phosphor screen
3
. The funnel
2
has a neck
5
, in which an electron gun assembly
7
is arranged. The electron gun assembly
7
is designed to emit three electron beams
6
B,
6
G and
6
R. A deflection yoke
8
is provided outside the funnel
2
. The yoke
8
generates horizontal and vertical deflection magnetic fields. The magnetic fields deflect the electron beams
6
B,
6
G and
6
R emitted from the assembly
7
, in a horizontal direction and a vertical direction. The electron beams
6
B,
6
G and
6
R thus deflected are applied through the shadow mask
4
to the phosphor screen
3
. The screen
3
is thereby scanned in both the horizontal direction and the vertical direction. A color image is thereby displayed on the phosphor screen
3
.
A so-called inline color cathode ray tube of self-convergence type has been put to practical use. The inline color-receiving tube has an electron gun assembly
7
that emits a center beam
6
G and two side beams
6
B and
6
R, which have their axes extending in the same horizontal plane. The electron gun assembly has a main electron lens including a low-voltage grid and a high-voltage grid, each having three beam-guiding holes. The holes for guiding the side beams
6
B and
6
R, made in the low-voltage grid are eccentric to the holes for guiding the side beams
6
B and
6
R, made in the high-voltage grid. Thanks to this specific positioning of beam-guiding holes, the three electron beams are focused at a center part of the phosphor screen
3
. Further, the deflection yoke
8
is designed to generate a horizontal deflection magnetic field shaped like a pincushion and a vertical deflection magnetic field shaped like a barrel. The pincushion-shaped magnetic field and the barrel-shaped magnetic field focus the three electron beams
6
B,
6
G and
6
R at any part of the phosphor screen
3
.
An electron gun assembly for use in this type of a color cathode ray tube is known. It is called “extended electric-field type,” designed in order to improve the focusing of electron beams at any part of the phosphor screen. This electron gun assembly has a main electron lens having a long focal distance and a large aperture. The main electron lens is formed by such a method as is disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 61-39346 and 61-39347. That is, the focusing grid structure is not composed of only one grid but is comprised of segment grids, and the anode voltage is divided into partial voltages by a resistor arranged in the neck of the color cathode ray tube. The partial voltages, thus obtained, are applied to the segment grids of the focusing grid structure, which achieves moderate distribution of potential.
FIGS. 2A and 2B
show an electron gun assembly of the extended electric-field type described above. As shown in
FIG. 2A
, the electron gun assembly has three cathodes KB, KG and KR, first to fifth grids G
1
to G
5
, an intermediate electrode GM, sixth grid G
6
and a convergence cup
90
, which are arranged coaxial, in the order they are mentioned. The cathodes KB, KG and KR each incorporate a heater (not shown). The cathodes KB, KG and KR, girds G
1
to G
6
, electrodes GM and convergence cup
90
are supported by and secured to an insulating support (not shown).
As shown in
FIG. 2B
, a resistor
100
is provided near the electron gun assembly. One end
110
of the resistor
100
is connected to the sixth grid G
6
. The other end of the resistor
100
is connected to the fifth grid G
5
. The resistor
100
is connected, at its middle point
120
, to the intermediate electrodes GM. The end
110
of the resistor
100
is connected also to a voltage source
131
, which applies an operating voltage to the electron gun assembly.
The first grid G
1
is a thin-plate electrode and has three small beam-guiding holes. The second grid G
2
is also a thin-plate electrode and has three small beam-guiding holes. The third grid G
3
comprises a cups-shaped electrode
31
and a plate-shaped electrode
32
, which abut on each other. The cup-shaped electrode
31
opposes the second grid G
2
and has three beam-guiding holes slightly larger than the beam-guiding holes of the second grid G
2
. The holes for guiding one side beam, made in the first to third grids G
1
to G
3
, have a common axis. Similarly, the holes for guiding the other side beam, made in these grids G
1
to G
3
, have a common axis. The two side beams, therefore, travel along the common axes of the side beam guiding holes of the first to third girds G
1
to G
3
. The plate-shaped electrode
32
of the third grid G
3
, which opposes the fourth grid G
4
, has three beam-guiding holes having a large diameter.
The fourth grid G
4
comprises two cup-shaped electrodes,
41
and
42
, which abut on each other. The electrodes
41
and
42
each have three beam-guiding holes having a large diameter. The fifth grid G
5
comprises two cup-shaped electrodes
51
and
52
, a thin-plate electrode
53
, and a thick-plate electrode
54
. The cup-shaped electrodes
51
and
52
each have three beam-guiding holes having a large diameter. The thin-plate electrode
53
has three beam-guiding holes that are elongated in the inline direction. The thick-plate electrode
54
has three beam-guiding holes having a large diameter. The intermediate electrode GM is a thick-plate electrode having three large beam-guiding holes. The sixth grid G
6
comprises a thick-plate electrode
61
, a thin-plate electrode
62
and two cup-shaped electrodes
63
and
64
. The thick-plate electrode
61
has three beam-guiding holes. The thin-plate electrode
62
has three beam-guiding holes elongated in the inline direction. The cup-shaped electrodes
63
and
64
abut each other at their open ends. The convergence cup
90
is fastened to the bottom of the cup-shaped electrode
64
.
A DC voltage of, for example, about 100 to 150V is applied to the cathodes KB, KG and KR. A modulation signal corresponding to an image is supplied also to the cathodes KB, KG and KR. The first grid G
1
is connected to the ground. The second grid G
2
and the fourth gird G
4
are connected to each other in the tube. A DC voltage of about 600 to 800V is applied to the second and fourth grids G
2
and G
4
. The cathodes KB, KG and KR and the first and second grids G
1
and G
2
compose a three-pole section for emitting electron beams and forming a crossover. The third grid G
3
and the fifth grid G
5
are connected to each other in the tube. A voltage of about 6 to 9V is applied to the third and fifth grids G
3
and G
5
, serving as a focusing voltage. An anode voltage of about 25 to 30 kV is applied to the sixth grid G
6
.
The second grid G
2
and the third grid G
3
constitute a pre-focusing electron lens. The pre-focusing electron lens performs preliminary focusing on the electron beams emitted from the three-pole section. The third grid G
3
, fourth grid G
4
and fifth grid G
5
compose an auxiliary electron lens, which performs further preliminary focusing on the electron beams.
The resistor, provided near the electron gun assembly, applies a voltage to the intermediate grid GM. This voltage has a value almost halfway between the voltages applied to the fifth and sixth grids G
5
and G
6
. In the electron gun assembly, the fifth grid G
5
, intermediate electrode GM and sixth grid G
6
jointly form a main electron lens. The main electron lens focuses the electron beams finally on the phosphor screen of the c
Hoshino Fumitaka
Kimiya Junichi
Sugawara Shigeru
Guharay Karabi
Kabushiki Kaisha Toshiba
Patel Ashok
Pillsbury & Winthrop LLP
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