Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-03-15
2002-01-15
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C313S414000, C313S415000, C313S467000
Reexamination Certificate
active
06339300
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and particularly to a color cathode ray tube having a three beam in-line, dynamic focus type electron gun capable of providing good focus characteristics over the entire screen area and good display contrast with a reduced dynamic focus voltage for its electrostatic quadrupole lens.
Color cathode ray tubes having an in-line type electron gun for use in TV receivers or display monitors have a phosphor screen formed on the inner surface of a faceplate of its panel portion, a shadow mask closely spaced from the phosphor screen within the panel portion, a deflection yoke mounted around its funnel portion, and an in-line type electron gun housed in its neck portion. The in-line type electron gun includes three cathodes arranged in line, and at least the first grid (G1) electrode, the second grid (G2) electrode, the third grid (G3) electrode and an anode, and projects three electron beams toward the phosphor screen.
To obtain good display image at the periphery of the phosphor screen as well as the center of the phosphor screen, that is, uniform resolution over the entire phosphor screen by using a color cathode ray tube having an in-line type electron gun, it is known to employ an electron gun of the dynamic focus type in which an electrostatic quadrupole lens is formed between two adjacent ones among electrodes of the in-line type electron gun and one of the two is supplied with a fixed focus voltage and the other of the two is supplied with-a fixed focus voltage superposed with a dynamic voltage varying with deflection of the electron beams.
FIG. 4
is a cross-sectional view of a prior color cathode ray tube employing an in-line type electron gun of the dynamic focus type (hereinafter referred to as a DF type in-line electron gun).
In
FIG. 4
, reference numeral
41
denotes a panel portion,
41
F is a faceplate,
42
is a neck portion,
43
is a funnel portion,
44
is a phosphor screen,
45
is a shadow mask,
46
is an internal conductive coating,
47
is a DF type in-line electron gun,
48
is a deflection yoke.
A grid electrode occupying the nth position counting from a cathode is called a grid n electrode in this specification.
A grid occupying the nth position counting from a cathode is called a Gn in this specification.
In the DF type in-line electron gun
47
, reference numerals
501
,
502
and
503
denote cathodes,
51
is a G1 electrode,
52
is a G2 electrode,
53
is a G3 electrode,
54
is a G4 electrode,
55
(
1
) is a first G
5
sub-electrode,
55
(
2
) is a second G5 sub-electrode,
56
is a G6 electrode (an anode),
57
is a shield cup,
58
are vertical electrode pieces, and
59
are horizontal electrode pieces.
The glass bulb of the color cathode ray tube comprises a panel portion
41
, a neck portion
42
and a funnel portion
43
. The panel portion
41
is provided with the phosphor screen
44
coated on the inner surface of its faceplate
41
F and the shadow mask
45
closely spaced from the phosphor screen
44
within the panel portion
41
. The funnel portion
43
is provided with the internal conductive coating
46
in its inner surface and the deflection yoke
48
mounted on the outer surface. The neck portion
42
houses the DF type in-line electron gun
47
therein.
The DF type in-line electron gun
47
comprises three cathodes
50
1
,
50
2
and
50
3
arranged in line in a horizontal plane, and following the cathodes, the G1 electrode
51
, the G2 electrode
52
, the G3 electrode
53
, the G4 electrode
54
, the first G5 sub-electrode
55
(
1
), the second G5 sub-electrode
55
(
2
) the G6 electrode
56
, the shield cup
57
, arranged along the axis of the cathode ray tube in the order named. One center and two side electron beam apertures in each of the G1 electrode
51
, the G2 electrode
52
, the G
3
electrode
53
, the G4 electrode
54
, the first G5 sub-electrode
55
(
1
), the second G5 sub-electrode
55
(
2
), the G6 electrode
56
, and the shield cup
57
are aligned with center lines O
2
, O
1
and O
3
of the cathodes
50
2
,
50
1
and
50
3
, respectively.
In the G6 electrode
56
, the center line of the center electron beam aperture is aligned with the center line O
2
of the corresponding cathode
50
2
, and the respective center lines of the two side electron beam apertures are slightly displaced outwardly with respect to the center lines O
1
and O
3
of the corresponding cathodes
50
1
and
50
3
, respectively. The first G5 sub-electrode
55
(
1
) is provided with the vertical electrode pieces
58
sandwiching horizontally each of the three electron beam apertures in its end facing the second G5 sub-electrode
55
(
2
), and the second G5 sub-electrode
55
(
2
) is provided with a pair of the horizontal electrode-pieces
59
sandwiching vertically the three electron beam apertures in common in its end facing the first G5 sub-electrode
55
(
1
). The vertical electrode pieces
58
and the horizontal electrode-pieces
59
form an electrostatic quadrupole lens between the first and second G5 sub-electrodes
55
(
1
),
55
(
2
).
In operation, the first G5 sub-electrode
55
(
1
) is supplied with a fixed-focus voltage, the second G5 sub-electrode
55
(
2
) is supplied with a fixed focus voltage superposed with a dynamic voltage varying with deflection of the electron beams, and the G6 electrode
56
serving as an anode, the shield cup
57
and the internal conductive coating
46
are supplied with an accelerating voltage (an anode voltage).
In the prior art color cathode ray tube, three electron beams emitted from the three cathodes
50
1
,
50
2
,
50
3
of the DF type in-line electron gun
47
travel accelerated and focused along the respective center lines O
1
, O
2
, O
3
through the electron beam apertures in each of the G1 electrode
51
, the G2 electrode
52
, the G3 electrode
53
, the G4 grid electrode
54
, the first G5 sub-electrode
55
(
1
), the second G5 sub-electrode
55
(
2
), the G6 electrode
56
, the shield cup
57
, and are projected from the electron gun
47
toward the phosphor screen
44
. The three electron beams projected from the electron gun
47
are properly deflected horizontally and vertically by the deflection yoke
48
, then pass through an electron beam aperture in the shadow mask
45
and impinge upon the phosphor screen
44
to produce a desired image on the phosphor screen
44
.
Color cathode ray tubes for use in color display monitors and the like usually employ a self-converging deflection yoke
48
of the type having both horizontal and vertical deflection windings wound in a saddle configuration (hereinafter referred to as the saddle/saddle type) to prevent magnetic fields generated by the deflection yoke
48
from radiating from the monitor to its outside.
The self-converging deflection yoke
48
increases deflection defocusing on the phosphor screen
44
due to the inherent non-uniformity in its deflection magnetic fields, deteriorates image resolution at the periphery of the phosphor screen
44
and therefore an electrostatic quadrupole lens is employed in the in-line type electron gun
47
with a dynamic focus voltage varying with deflection of the electron beams.
When the deflection of the electron beams is zero or very small, that is, when the electron beams scan the central portion of the phosphor screen
44
, a dynamic voltage becomes zero or very small, a focus voltage applied to the first G5 sub-electrode
55
(
1
) becomes equal or nearly equal to a focus voltage applied to the second G5 sub-electrode
55
(
2
), the strength of the electrostatic quadrupole lens is weakened and consequently no astigmatism is produced in the electron beam spot at the center of the phosphor screen
44
.
When the deflection of the electron beams is large, that is, when the electron beams scan the periphery of the phosphor screen
44
, the dynamic voltage becomes large, the focus voltage applied to the second G5 sub-electrode
55
(
2
) becomes higher than the focus voltage applied to the first G5 sub-electrode
55
(
1
) a
Nakamura Tomoki
Shirai Shoji
Yatsu Yasuharu
Tran Thuy Vinh
Wong Don
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