Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
1999-11-04
2001-12-18
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S414000, C313S412000, C315S015000, C315S382000
Reexamination Certificate
active
06331752
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube and more particularly to a color cathode ray tube having an electron gun providing a satisfactory resolution over the entire picture with a comparatively low dynamic focus voltage.
In a color cathode ray tube used as a color picture tube or a display tube, it is necessary to control the focus characteristic of the electron gun properly according to the angle of deflection of electron beams so as to provide a satisfactory resolution always over the entire screen.
FIG. 3
is a cross sectional schematic view illustrating the structure of this kind of conventional color cathode ray tube. Numeral
1
indicates an evacuated glass envelope,
2
a faceplate portion constituting a screen,
3
a phosphor screen,
4
a shadow mask,
5
an internal conductive coating,
6
,
7
, and
8
cathodes,
9
a first grid electrode (G1 electrode),
10
a second grid electrode (G2 electrode),
11
a third grid electrode (G3 electrode),
12
a fourth grid electrode (G4 electrode),
13
a fifth grid electrode (G5 electrode),
14
an accelerating electrode (G6 electrode),
15
a shield cup,
16
a deflection yoke,
17
,
18
, and
19
initial paths of electron beams, and
20
and
21
center lines of passage aperture of outer electron beams (hereinafter referred to as apertures) formed in the accelerating electrode
14
.
In the figure, a phosphor screen
3
comprising an alternate line pattern of red, green, and blue emitting phosphors is supported on the inner wall of the faceplate portion
2
of the evacuated glass envelope
1
. The center lines (the initial paths of electron beams)
17
,
18
, and
19
of the cathodes
6
,
7
, and
8
coincide with the center lines of apertures associated with corresponding cathodes, of the G1 electrode
9
, the G2 electrode
10
, and the G3 electrode
11
, the G4 electrode
12
, and the G5 electrode (focus electrode)
13
, these three constituting the main lens, and the shield cup
15
and are arranged almost in parallel with each other in a common plane (inline arrangement).
The center line of the aperture at the center of the G6 electrode (accelerating electrode)
14
which is another electrode constituting the main lens coincides with the center line
18
. However, the center lines
20
and
21
of both the apertures on the outer side do not coincide with the center lines
17
and
19
corresponding to them but are slightly displaced outwardly.
Three electron beams emitted from the cathodes
6
,
7
, and
8
enter the final lens (main lens) formed between the G5 electrode
13
and the G6 electrode
14
along the center lines
17
,
18
, and
19
.
A focus voltage V
f
of about 5 to 10 kV is applied on the G3 electrode
11
and the G5 electrode
13
and an accelerating voltage Eb which is the highest voltage of about 20 to 30 kV is applied on the G6 electrode
14
via the conductive coating
5
and the shield cup
15
placed in the evacuated glass envelope
1
.
The center lines of the apertures at the centers of both of the G5 electrode
13
and the G6 electrode
14
constituting the final lens for focusing electron beams on the phosphor screen
3
are coaxial, so that a lens formed in the aperture portion at the center is axially symmetric and an electron beam (center beam) passing through the aperture at the center is focused by the final lens and goes straight along the axis.
On the other hand, the center lines of the outer apertures of both the electrodes constituting the final lens are displaced from each other, so that a non-axially-symmetric lens is formed in the outer aperture portion. As a result, an electron beam (outer beam) passing through the outer apertures passes through a portion displaced toward the center beam from the center line of the lens in the diverging lens region formed on the side of the accelerating electrode (G6 electrode)
14
in the lens region, so that it is subjected to the focusing action by the lens and the converging force toward the center beam at the same time.
Also known is a type of an electron gun in which each of two electrodes constituting a final lens has a single horizontally elongated opening at their opposing ends and has a plate electrode therein having beam passage apertures retracted inwardly from the opposing ends.
Also in this type of an electron gun, a non-axially-symmetric lens is formed in the outer aperture portion of both the electrodes and the outer electron beams are given the converging force toward the center beam, and the three electron beams are converged so as to be superposed in the plane of the shadow mask
4
.
An operation for converging each electron beam by an electrode structure like this is referred to as a static convergence (STC).
Furthermore, each electron beam is subjected to color selection by the shadow mask
4
and only a portion of each electron beam passes through an aperture of the shadow mask
4
for exciting the phosphor of a color corresponding to the electron beam on the phosphor screen
3
to luminescence and reaches the phosphor screen
3
.
A magnetic deflection yoke
16
for scanning electron beams on the phosphor screen
3
is mounted outside the funnel portion of the evacuated glass envelope
1
.
As mentioned above, it is known that when an inline electron gun in which three electron beam passage apertures are arranged in a horizontal plane and a so-called selfconverging type deflection yoke for forming a special nonhomogeneous magnetic field distribution are combined, by adjusting a self-convergence of the three beams at the center of the picture, the convergence can be adjusted over the entire remaining picture at the same time. However, when the self-converging type deflection yoke is used, a problem arises that large aberration due to deflection are generated by non-uniformity of the magnetic field and the resolution at the corners of the screen lowers.
FIG. 4
is a schematic view illustrating beam spots on the screen by an electron beam subjected to aberrations due to deflection. Numeral
3
indicates a phosphor screen (hereinafter may be referred to as a screen) and
3
a
,
3
b
, and
3
c
beam spots.
In the figure, the beam spot
3
a
is almost circular at the center of the screen
3
. However, at the corners of the screen, as indicated by the beam spots
3
b
and
3
c
, a high brightness portion indicated by hatching (core) c widens in the horizontal direction (X—X direction) and a low brightness portion (halo) h widens in the vertical direction (Y—Y direction) and the resolution lowers. Conventionally, as an example for solving such a problem, an electron gun is disclosed in U.S. Pat. No. 5,212,423 (corresponding Japanese Patent Application Laid-Open Hei 4-43532).
FIG. 5
is an illustration for the constitution of an electron gun of the prior art for reducing the lowering of the resolution at the corners of the screen.
In the figure, the G5 electrode
13
is divided into four parts such as a first member
13
h
, a second member
13
i
, a third member
13
j
, and a fourth member
13
k
toward the phosphor screen from the cathode.
A single opening is provided in the end face of the third member
13
j
opposite to the fourth member
13
k
and a plate electrode
131
having an electron beam passage aperture is located therein.
Plate correction electrodes
13
m
are located at the end face of the fourth member
13
k
opposite to the third member
13
j
so as to sandwich the electron beam passage aperture vertically and extend into the third member
13
j
through the single opening of the third member.
A voltage V
d
varying dynamically in synchronization with the deflection current supplied to the deflection yoke is applied on the second member
13
i
and the fourth member
13
k
and a fixed voltage V
o
is applied on the first member
13
h
and the third member
13
j.
By using such a constitution, an electrostatic quadrupole lens having a function for changing the cross sectional shape of an electron beam into a non-axially symmetrical one in accordance with the amount of deflection o
Kato Shin-ichi
Shirai Shoji
Tojyou Tutomu
Antonelli Terry Stout & Kraus LLP
Haynes Mack
Hitachi , Ltd.
Patel Nimeshkumar D.
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