Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2001-01-11
2002-05-07
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
Reexamination Certificate
active
06384546
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a deflection yoke attached to an inline type color cathode-ray tube and a mis-convergence correction method for a color cathode-ray tube correcting mis-convergence on the Y-axis of a screen. The present invention particularly relates to a deflection yoke and a mis-convergence correction method capable of simultaneously correcting comatic aberration and mis-convergence.
2. Description of the Related Art
There exists a color display device provided with an inline type color cathode-ray tube (to be referred to as “color CRT” hereinafter). In the inline type color CRT, electron beams are produced in a vacuum valve from electron guns for blue, green, and red, respectively. The electron beams are deflected in X and Y-axes directions by a deflection yoke made up of an electromagnetic coil and the like and reach a phosphor film through a shadow mask.
In the inline type color CRT stated above, electron beams pass into a heavily distorted deflecting magnetic field at the time of deflecting the electron beams in the X and Y-axes directions by means of the deflection yoke. Due to this, three electron beams disadvantageously, poorly converge. This phenomenon is called mis-convergence.
To solve the disadvantage, there is provided a color CRT which adopts a system called inline self-convergence system.
FIGS. 1A and 1B
are typical views showing the inline self-convergence system. In the inline self convergence system, a deflecting magnetic field
101
(
FIG. 1A
) having a pin cushion type, horizontally deflecting magnetic field distribution, and a deflecting magnetic field
102
(
FIG. 2B
) having a barrel type, vertically deflecting magnetic field distribution are formed. Three electron beams
10
B,
10
G and
10
R emitted from three inline electron guns aligned in the same horizontal plane are deflected by these deflecting magnetic fields
101
and
102
and converge at arbitrary points on a screen, respectively.
The inline self-convergence system has advantages in that it suffices to provide a small number of electrical circuits, adjustment is required infrequently and the like to converge the three electron beams
10
B,
10
G and
10
R and in that the highly accurate convergence can be realized.
Nevertheless, a focus voltage Vfh capable of minimizing a horizontal diameter of a spot and a focus voltage Vfv capable of minimizing a vertical diameter of a spot differ from each other and the difference between the both focus voltages &Dgr;Vf=Vfh−Vfv is negative. Namely, the convergence state of the electron beams in the vertical direction is an over-focus state. For that reason, if the distortions of the shapes of the electron beams on the periphery of the screen are finely observed, it is found that halos occur in vertical direction because of astigmatism.
FIG. 2
is a typical view showing electron beam spots on a conventional screen. Electron beams
10
B,
10
G and
10
R are influenced by the magnetic field distortions of the self convergence deflecting magnetic fields
101
and
102
when passing into the fields
101
and
102
. As a result, the shapes of the electron beam spots become round at the center of the screen, which is free from deflection. However, if the electron beams are deflected to the peripheral portions of the screen, the shape of each electron beam spot becomes one having an oblong beam core
111
and a radial halo
112
generated above and below the beam core
111
, i.e., a distorted shape. The diameter of each of the distorted electron beam spots on the peripheral portions of the screen is, therefore, larger than that of the completely round spot at the center of the screen, with the result that resolution on the peripheral portions of the screen considerably deteriorates.
Further, because of the asymmetry of deflecting magnetic fields, comatic aberration, which causes mis-convergence occurring between the center beam (G) and the side beams (B, R) among the three electron beams as deflection frequency is higher. It is, therefore, necessary to eliminate the comatic aberration, as well.
FIGS. 3A
to
3
D are typical views showing mis-convergence.
FIG. 4
is a typical view showing one example of a lateral raster distortion. The mis-convergence caused by the comatic aberration includes an arc distortion, as shown in
FIG. 3A
, in which a red line
20
R and a blue line
20
B separate from each other in lateral direction on the upper and lower ends of the screen, a distortion, as shown in
FIG. 3B
, in which a red line
21
R and a blue line
21
G separate from each other in longitudinal direction on the upper and lower ends of the screen, and a distortion, as shown in
FIG. 3C
, in which a red line
21
R and a blue line
21
B separate from a green line
21
G in longitudinal direction. Further, as shown in
FIG. 3D
, if a figure which should be originally a rectangle is distorted into a trapezoid
30
due to the influence of a pin cushion type magnetic field distribution and a barrel type magnetic field distribution, the distorted figure is visually inappropriate particularly for CAD, CAM or the like and causes much deficiency. Moreover, as shown in
FIG. 4
, if there is a parallel distortion in which a red line
21
R and a blue line
21
B are deviated from a green line
21
G in the lateral direction of the screen, a resultant image is difficult to view.
The mis-convergence stated above is normally considered to derive from the deviation between the mechanical center of three electron beams and that of a deflecting magnetic field from the viewpoint of the electron guns of a color CRT. Further, the mis-convergence is considered to derive from a design in which a variable resistor for deflecting current control provided on a deflection coil simultaneously corrects comatic aberration and the distortion of an image from the viewpoint of a deflection yoke.
To solve the above-stated disadvantages, there has been conventionally proposed a mis-convergence correction method using a deflection yoke provided with a pair of E-shaped magnetic members (Japanese Patent Application Laid-Open No. 9-17355).
FIG. 5
is a typical view showing a conventional deflection device disclosed by Japanese Patent Application Laid-Open No. 9-17355.
FIG. 6
is a typical view showing magnetic fields generated by the conventional deflection device.
This conventional deflection device has a pair of E-shaped magnetic members
41
and
42
provided on a deflection yoke bobbin attached to the neck portion
40
of a color CRT. Coma correction coils
51
a
and
51
c
are wound around the leg portions
41
a
and
41
c
of the E-shaped magnetic member
41
on both ends thereof, respectively. A coma correction coil
51
b
is wound around the central leg portion
41
b
of the E-shaped magnetic member
41
. Likewise, coma correction coils
52
a
and
52
c
are wound around the leg portions
42
a
and
42
c
of the E-shaped magnetic member
42
on the both ends thereof, respectively. A coma correction coil
52
b
is wound around the central leg portion
42
b
of the E-shaped magnetic member
42
.
In the conventional deflection device constituted as stated above, a pin cushion type deflecting magnetic field
60
a
is generated between the leg portions
41
a
and
42
a,
and a pin cushion type deflecting magnetic field
60
c
is generated between the leg portions
41
c
and
42
c
as shown in
FIG. 6. A
barrel type deflecting magnetic field
61
b
is generated between the leg portions
41
b
and
42
b.
As a result, astigmatism and mis-convergence can be simultaneously corrected.
Although the conventional mis-convergence correction method stated above has an advantage in that astigmatism and mis-convergence can be simultaneously corrected by simple means relatively easily, the following disadvantages are still to be solved.
Since three coma correction coils are provided for each E-shaped magnetic member, the mold structure of a supporter for an E-shaped magnetic member becomes complicated. Consequently, production co
McGinn & Gibb PLLC
NEC Corporation
Vu David
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