Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-01-06
2001-12-11
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000, C313S460000
Reexamination Certificate
active
06329747
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube, and particularly to a cathode ray tube having its overall length shortened with its deflection angle increased, but without increasing deflection power consumption or degrading display resolution.
Cathode ray tubes such as color cathode ray tubes used as TV picture tubes and monitor tubes for information terminals house an electron gun for emitting a plurality (usually three) of electron beams at one end of an evacuated envelope, a phosphor screen (a viewing screen) formed of phosphors coated on an inner surface of the evacuated envelope at the other end thereof for emitting light of a plurality (usually three) of colors, and a shadow mask which serves as a color selection electrode and is closely spaced from the phosphor screen.
The electron beams emitted from the electron gun are deflected to scan the phosphor screen horizontally and vertically in two dimensions, by magnetic fields generated by a deflection yoke mounted externally of the evacuated envelope and display a desired image on the phosphor screen.
FIG. 16
is a schematic cross-sectional view of a shadow mask type color cathode ray tube as an example of a cathode ray tube to which the present invention is applicable, and
FIG. 17
is a front view of a panel portion of the color cathode ray tube of FIG.
16
.
In
FIG. 16
, reference numeral
1
denotes the panel portion forming a viewing screen,
2
is a neck portion,
3
is a funnel portion,
4
is a phosphor screen,
5
is a shadow mask,
6
is a mask frame,
7
is a magnetic shield,
8
is a mask suspension mechanism,
9
is an in-line type electron gun,
10
is a deflection yoke,
11
is an internal conductive coating,
12
is a shield cup,
13
is a contact spring,
14
is a getter,
15
is a stem,
16
are stem pins,
17
is an implosion protection band,
18
is a magnetic beam adjusting device, and
19
is a usable display area.
In
FIG. 16
, a dimension L is a distance from the phosphor screen
4
to the end of the anode on the focus electrode side thereof, of the in-line beam type electron gun
9
, and a dimension d is an outside diameter of the neck portion
2
. In
FIG. 17
, a dimension D is a diagonal length of the usable display area
19
.
The evacuated envelope of this color cathode ray tube is comprised of the panel portion
1
, the neck portion
2
and the funnel portion
3
. Three electron beams (one center electron beam Bc and two side electron beams Bs) emitted from the in-line type electron gun housed in the neck portion
2
is scanned over the phosphor screen
4
two-dimensionally by the horizontal and vertical deflection magnetic fields generated by the deflection yoke
10
mounted around the transition region between the funnel portion
3
and the neck portion.
The highest voltage (an anode voltage) to the electron gun is supplied by the contact springs
13
attached to the shield cup
12
via the internal conductive coating
11
coated on the inner surface of the funnel portion
3
from an anode button (not shown) embedded in a wall of the funnel portion
3
.
The deflection yoke
10
is of a self-converging type which provides a pin cushion-like horizontal deflection magnetic field and a barrel-like vertical deflection magnetic field to converge a plurality of electron beams over the entire phosphor screen.
The electron beams Bc, Bs are modulated in amount by modulating signals such as video signals supplied via the stem pins
1
6
, are color-selected by the shadow mask
5
disposed immediately in front of the phosphor screen
4
, and impinge upon the phosphors of the corresponding colors to reproduce a desired image. Color purity of the reproduced color image and static convergence of the three electron beams are adjusted by the magnetic beam adjusting device
18
mounted around the neck portion
2
.
In color cathode ray tubes of this type, a large-diameter non-axially-symmetric lens formed between an anode and a focus electrode are extensively used as a main lens system of the electron gun to provide sufficiently small electron beam spots over the entire phosphor screen.
FIG. 18
is a schematic side elevation view of a prior art electron gun employing the large-diameter non-axially-symmetric lens system viewed in a direction perpendicular to the in-line direction of the electron beams. In this electron gun, an electron beam generating section is comprised of a cathode
21
, the first grid electrode
22
and the second grid electrode
23
, and an accelerating and focusing section is comprised of the third grid electrode
24
serving as a focus electrode and the fourth electrode
25
serving as an anode. The cathode and electrodes are fixed on a pair of insulating rods
26
made of glass in the predetermined order and the predetermined spaced relationship.
The contact springs
13
are attached to the front end of the shield cup
12
which in turn is attached to the anode
25
. The highest voltage is applied to the anode
15
by the resilient contact springs
13
pressed against the internal conductive coating
11
on the inner wall of the funnel portion
3
.
FIG. 19
is a plan view of the third grid electrode
24
viewed from an anode side thereof and
FIG. 20
is a cross-sectional side view of the third grid electrode
24
viewed in a direction perpendicular to the in-line direction of the three electron beams. Reference
31
denotes an electric field correction plate having three vertically elongated electron beam apertures with their minor diameters in the in-line direction of the electron beams and disposed within the third grid electrode
24
, and reference numeral
32
denotes an electrode having the configuration of the outer periphery of a racetrack shape (hereinafter referred to as a racetrack electrode) and formed with a single opening with its major diameter in the in-line direction of the electron beams.
FIG. 21
is a plan view of the anode
25
viewed from the third grid electrode
24
side thereof and
FIG. 22
is a cross-sectional side view of the anode
25
viewed in the direction perpendicular to the in-line direction of the three electron beams. Reference
33
denotes an electric field correction plate having a vertically elongated electron beam aperture at the center with its minor diameter in the in-line direction of the electron beams and cutouts on opposite sides of the electron beam aperture and disposed within the anode
25
, and reference numeral
34
denotes a racetrack electrode formed with a single opening with its major diameter in the in-line direction of the electron beams. With such an electrode structure, an effectively large-diameter electron lens is formed between the grid electrode
24
and the anode to provide a high definition image display.
SUMMARY OF THE INVENTION
While cathode ray tubes presently used as a monitor tube in the information terminals increases in the size of the viewing screen, there is a demand for reduction of their overall length with a view to improving the efficiency of utilization of the space.
The overall length of cathode ray tubes without changing the size of the viewing screen can be shortened by increasing the maximum deflection angle of the electron beams so as to decrease the distance from the phosphor screen to the end of the anode on its focus electrode (the third grid electrode).
In this specification, the ratio D/L is used instead of a deflection angle, where D (mm) is a diagonal length of the usable display area of the viewing screen, and L (mm) is a distance from the center of the phosphor screen to the end of the anode on its focus electrode side in a cathode ray tube.
A 90° deflection angle is extensively employed in presently-used monitor tubes for information terminals and this corresponds to the D/L of about 1.35. If the ratio D/L is increased without changing the overall length of an electron gun, the overall length of the cathode ray tube decreases correspondingly.
If the ratio is selected to be at least 1.55, for example, the overall length of a cathode ray tube having the D of 460
Nakamura Tomoki
Noguchi Kazunari
Shirai Shoji
Yatsu Yasuharu
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Patel Ashok
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