Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1998-04-17
2001-07-17
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C335S210000, C348S805000
Reexamination Certificate
active
06262524
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun for a color cathode ray tube. More particularly the invention relates to an electron gun for a color cathode ray tube provided with a mechanism for deflecting the electron beams from cathodes to make the beams cross at the downstream side of a quadrupole lens and a cathode ray tube using the same.
2. Description of the Related Art
FIG. 4
is a cross-sectional view for explaining the internal structure of a Trinitron electron gun
1
, while
FIG. 5
is an enlarged view of the portion of
FIG. 4
surrounded by the broken line. Note that, a half side to the left of the center axis is shown in FIG.
5
.
As shown in FIG.
4
and
FIG. 5
, the Trinitron gun
1
is provided with cathodes
2
comprising a red cathode
2
R and a blue cathode
2
B arranged in-line around a green cathode
2
G. The cathodes
2
R,
2
G, and
2
B respectively emit a red, green, and blue electron beam.
From the cathodes
2
to the downstream emission of the electron the beams successively encounter a G
1
electrode, G
2
electrode, GMA electrode, GMB electrode, G
3
electrode, G
4
electrode, convergence electrode CONV, aperture grille (not shown), and three-color phosphor screen stripes (not shown). The electrodes are each provided with three openings (beam through holes) through which the red, blue, and green electron beams pass. For example, as shown in
FIG. 5
the GMA electrode and the GMB electrode are each provided with beam through holes
9
A and
9
B through which the red electron beam passes, beam through holes
10
A and
10
B through which the green electron beam passes, and the beam through holes (not shown) through which the blue electron beam passes.
Here, the G
1
electrode is for example supplied with a voltage of 0V. To simplify the structure, it is formed integrally with the cathodes
2
. Further, the cathodes
2
are supplied with a voltage of 40 to 170V.
The G
2
electrode, GNA electrode, GMB electrode, and G
3
electrode cooperate to form a focus lens which bends the electron beams slightly inward around the green electron beam. Note that the G
2
electrode is supplied with a voltage of 500V, the GMA electrode is supplied with a voltage of 7000V, the GMB electrode is supplied with a voltage of 7000V, and the G
3
electrode is supplied with a voltage of 29000V.
Here, the voltage applied to either the GMA electrode and the GMB electrode is fixed, while the voltage applied to the other is variable.
Note that the distance L
1
between the emission surface of the cathode
2
G and the G
1
electrode is about 0.1 mm, the distance L
2
between the G
1
electrode and the G
2
electrode is about 0.4 mm, the distance L
3
between the G
2
electrode and the GMA electrode is about 1 mm, the distance L
4
between the center of the GMA electrode and the center of the GMB electrode is about 0.5 mm, and the distance L
5
between the GMB electrode and the left side end of the G
3
electrode in the figure is about 2.0 mm.
The GMA electrode and the GMB electrode form a quadrupole lens for correcting the aspect ratio of the cross-section of the electron beam spot In order to obtain a good electron beam spot over the entire region of the phosphor s creen, that is, a good focus characteristic.
The G
3
electrode, G
4
electrode, and G
5
electrode form a larg e diameter main focus lens (main lens) about which the beams cross. The red and blue electron beams cross, then spread out toward the outside and are deflected by the convergence electrode CONV to pass through the aperture grille and converge at the three-color phosphor screen.
In this way, the Trinitron electron gun
1
is configured with a single main lens for the three electron beams.
In the conventional Trinitron electron gun
1
, however, with only the prefocus lens composed of the G
2
electrode, GMA electrode, GMB electrode, and G
3
electrode, it is not possible to sufficiently bend the electron beams so as to cross the beams in the main focus lens, so as shown in FIG.
1
and
FIG. 2
, the cathodes
2
R and
2
B are provided inclined by a predetermined angle toward the center axis Z.
Alternatively, instead of inclining the cathodes
2
R and
2
B, it is possible to arrange them in parallel with the cathode
2
G (center axis Z) and use the voltage occurring at a cup-shaped wall surface provided in the vicinity of the outer circumference of the G
2
electrode to bend the red and blue electron beams toward the center axis Z.
In the above Trinitron electron gun
1
, however, If the cathodes
2
R and
2
B are arranged at an angle, the red and blue electron beams will strike the quadrupole lens composed the GMA electrode and the GMB electrode at an angle in accordance with that, so there will be the problem that the clearance between the beam through holes provided at the GMA electrode and GMB electrode and the beam paths will become small and, due to optical aberration, a sufficient focus characteristic will not be obtained. Further, if the clearance between the beam through holes and the beam paths is small in this way, there will be the problem of a low freedom of design. Further, it will be necessary to use a sophisticated and expensive manufacturing apparatus to arrange the cathodes
2
R and
2
B inclined precisely by a predetermined angle with respect to the center axis Z in the manufacturing process-resulting in the problem of a high cost.
Further, in the method of providing a cup-shaped wall surface in the vicinity of the outer circumference of the G
2
electrode, in addition to the problem of the inability to obtain a sufficient focus characteristic, due to the effect of the medium voltage electrodes provided between the G
2
electrode and the G
3
electrode, that is, the GNA electrode and the GMB electrode, there will be the problem of a difficulty in obtaining a sufficient potential difference for bending the electron beams to cross them.
SUMMARY OF THE INVENTION
The present invention was made in consideration of the above related art and has as its object the provision of a cathode ray tube having a superior focus characteristic and an electron gun of the same.
Another object of the present invention is to provide a color cathode ray tube having a high design freedom with its electron gun.
According to a first aspect of the present invention, there is provided an electron gun for a color cathode ray tube, comprising an electron beam emitter for emitting three electron beams an, intermediate voltage electrode for forming a quadrupole lens, an electron beam orienting means and high voltage electrodes forming a main lens. The electron beam orienting means is disposed between the quadrupole lens and main lens, and redirects two side electron beams from the emitter toward a center electron beam so that three electron beams emitted from the emitter cross in the main lens.
Preferably, the electron beam emitter is comprised of three cathodes arranged side by side so as to emit the three electron beams parallel to each other. Further, preferably, the orienting means is a conductive member to which a predetermined voltage is supplied and orients the electron beams by a potential difference with the high voltage electrodes of the main lens.
Preferably, the quadrupole lens is formed by at least a first intermediate voltage electrode and a second intermediate voltage electrode provided at a downstream side of the path of the electron beams from the first intermediate voltage electrode.
Preferably, the orienting means is a conductive tube provided so as to surround the beam through holes at a downstream side of the second intermediate voltage electrode.
Preferably, a single electron gun emits the three electron beams.
According to a second aspect of the present invention, there is provided a cathode ray tube with such an electron gun.
REFERENCES:
patent: 4703223 (1987-10-01), Iguchi et al.
patent: 4922166 (1990-05-01), Ichida et al.
patent: 5488264 (1996-01-01), Ota et al.
patent: 5751100 (1998-05-01), Kim
Gerike Matthew J.
Kananen Ronald P.
Patel Nimeshkumar D.
Rader Fishman & Grauer
Sony Corporation
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