Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1999-03-02
2001-10-16
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S415000, C313S409000, C315S382000, C315S015000
Reexamination Certificate
active
06304026
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube, and particularly to a color cathode ray tube having an in-line type electron gun configured so as to project three electron beams arranged horizontally in a line toward a phosphor screen.
Cathode ray tubes for use in TV receiver sets or information terminal display monitors have at least an electron gun comprised of plural electrodes and a phosphor screen and is provided with a deflection device for scanning plural electron beams emitted from the electron gun on the phosphor screen.
For these cathode ray tubes, the following technologies have been known for reproducing a good image over the entire phosphor screen.
An electrostatic quadrupole lens is formed of electrodes in an electron gun, and the strength of the electrostatic quadrupole lens is varied dynamically with deflection of the electron beam to obtain uniform display image over the phosphor screen as disclosed in Japanese Patent Application Laid-Open No. Sho 61-250933 (Application No. Sho 60-90830, laid-open on Nov. 8, 1986), for example.
FIG. 11
is a schematic plan view of a color cathode ray tube having a electron gun employing the prior art electrostatic quadrupole lens. Reference numeral
1
denotes a glass envelope,
2
is a faceplate portion,
3
is a phosphor screen for displaying an image,
4
is a shadow mask,
5
is an internal conductive coating,
6
,
7
and
8
are cathodes,
9
is a first grid electrode (a beam control grid electrode or G1 electrode, hereinafter grid electrodes are abbreviated as G electrodes),
10
is a G2 electrode (an accelerating electrode),
11
is a G3 electrode,
12
is a G4 electrode,
13
is a first G5 sub-electrode,
14
is a vertical electrode piece,
15
is a horizontal electrode piece,
16
is a second G5 sub-electrode,
17
is a G6 electrode (an anode),
18
is a shield cup,
19
is a deflection yoke (a deflection device),
20
,
21
and
22
are center axes of the respective cathodes
6
,
7
and
8
,
23
and
24
are center axes of respective outer apertures in the G6 electrode
17
. In
FIG. 11
, the phosphor screen
3
comprising alternate lines of three color emitting phosphors is coated on the inner surface of the faceplate portion
2
of the glass envelope
1
.
The center axes
20
,
21
,
22
of the cathodes
6
,
7
,
8
are aligned with those of apertures corresponding to the respective cathodes in the G1 electrode
9
, the G2 electrode
10
, the G3 electrode
11
, the G4 electrode
12
for forming a pre-main lens in cooperation with the G3 electrode
11
, the first G5 sub-electrode
13
and the second G5 sub-electrode
16
of the focus electrode serving as one lens component of a main lens and the shield cup
18
, and arranged approximately parallel with each other in a common horizontal plane.
The center axis of the center aperture in the G6 electrode
17
serving as the other lens component, an anode, of the main lens is aligned with the center axis
21
, but the center axes
23
,
24
of two outer apertures in the G6 electrode
17
are displaced slightly outwardly with respect to the corresponding center axes
20
,
22
in the common horizontal plane.
The four vertical electrode pieces
14
are attached to the end of the first G5 sub-electrode
13
which is one on the cathode side of the two G5 sub-electrodes into which the focus electrode is divided such that the four vertical electrode pieces
14
sandwich the respective apertures in the end of the first G5 sub-electrodes
13
horizontally.
A pair of horizontal electrode pieces
15
are attached to the end of the second G5 sub-electrode
16
on the first G5 sub-electrode
13
side thereof such that the horizontal electrode pieces
15
sandwich three apertures in the end of the second G5 sub-electrode
16
vertically. These electrode pieces
14
,
15
form an electrostatic quadrupole lens therebetween.
A plurality (usually three) of electron beams emitted from the cathodes
6
,
7
,
8
enter the main lens along the center axes
20
,
21
,
22
of the corresponding cathodes. The second G5 sub-electrode
16
serving as the focusing electrode is supplied with a focus voltage of about 5 kV to about 10 kV, the G6 electrode
17
serving as the anode is supplied with an accelerating voltage of about 20 to about 30 kV, and the G6 electrode
17
is at the same potential with the shield cup
18
and the internal conductive coating
5
coated on the inner surface of the glass envelope
1
.
The center apertures in the first and second G5 sub-electrodes
13
,
16
of the focusing electrode and the G6 electrode
17
are coaxial with each other and aligned with the center axis
21
, and consequently the main lens in the center is axially-symmetrical, the center electron beam travels straight along the center axis after being focused by the main lens.
The center axes of the two outer apertures in the end of the G6 electrode
17
facing the second G5 sub-electrode
16
are displaced horizontally outwardly with respect to those of the two outer apertures in the second G5 sub-electrode
16
and non-axially symmetrical main lenses are formed in the paths of the two outer electron beams.
The outer electron beams traverse a portion displaced toward the center electron beam from the lens axis in a diverging lens formed in the G6 electrode
17
(the anode) side portion of the main lens region and receive a focusing action by the main lens and a force converging the outer electron beams toward the center electron beam at the same time. The three electron beams are converged at a point on the shadow mask
4
. This convergence of three electron beams at the central portion of the phosphor screen is called static convergence (hereinafter abbreviated to “STC”).
The three electron beams are subjected to color selection by the shadow mask
4
such that portions of each electron beam passed by the apertures in the shadow mask
4
excite only phosphor elements of its corresponding color on the phosphor screen
3
to luminescence.
The deflection yoke
19
for scanning the electron beams on the phosphor screen
3
is mounted around the funnel portion
32
for connecting the faceplate
2
and the neck portion
31
housing the electron gun. The deflection yoke
19
for use in color cathode ray tubes for monitors of information terminals employs a so-called saddle-saddle type deflection yoke having horizontal and vertical deflection windings wound in a saddle configuration so as to prevent leakage of magnetic fields from the monitor sets.
It is known that the three electron beams are converged at all points of the phosphor screen when the three electron beams are initially converged at the center of the phosphor screen, by combination of a so-called in-line type electron gun having initially three electron beam paths in a horizontal plane and a so-called self-converging deflection yoke generating specific non-homogeneous magnetic fields.
In general, there is a problem with the self-converging deflection yoke in that resolution at the periphery of the screen is degraded due to deflection defocusing increased by its non-homogeneous magnetic fields.
To solve this problem, the electrostatic quadrupole lens is employed. The first G5 sub-electrode
13
is supplied with a fixed focus voltage Vf, and the second G5 sub-electrode
16
is supplied with the fixed focus Vf superposed with a dynamic voltage dVf synchronized with deflection currents supplied to the deflection yoke.
With increase in deflection of the electron beams, the voltage difference between the first and second G5 sub-electrodes
13
and
16
increases and the lens strength of the electrostatic quadrupole lens formed by the vertical and horizontal electrode pieces
14
and
15
increases and provides a greatly astigmatic shape to the electron beam spots.
When the potential of the second G5 sub-electrode
16
is higher than that of the first G5 sub-electrode
13
, the astigmatism produced is such that an intense core of an electron beam spot is elongated vertically and a low intensity halo of the electron b
Nakamura Tomoki
Shirai Shoji
Yatsu Yasuharu
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Patel Nimeshkumar D.
Santiago Mariceli
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