Cathode-ray tube

Details Cathode-ray tube Cathode-ray tube

2002-03-12

2003-09-02

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Beam deflecting means

C313S414000, C313S439000

Reexamination Certificate

active

06614157

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a cathode ray tube device, and it relates, in particular, to a structure near an electron gun and a velocity modulation coil.
BACKGROUND ART
FIG. 3
is a lateral cross-sectional view showing a cathode ray tube device. As shown in
FIG. 3
, the cathode ray tube device includes a cathode ray tube, a deflection yoke
5
, a convergence yoke
7
and velocity modulation coils
6
. The cathode ray tube has a front panel
1
whose inner surface is provided with a phosphor screen
8
, a funnel
2
and an electron gun
4
provided inside a neck portion
3
of the funnel
2
. The deflection yoke
5
has horizontal deflection coils and vertical deflection coils that are mounted on an outer surface of the funnel
2
and positioned on the side of the front panel
1
with respect to the electron gun
4
. The convergence yoke
7
is provided on an outer surface of the neck portion
3
.
FIG. 11
is a lateral cross-sectional view of the neck portion
3
. The electron gun
4
(shown not as a cross-sectional view) has a structure in which a cathode
21
, a control electrode (a G1 electrode)
22
, an accelerating electrode (a G2 electrode)
23
, a focusing electrode (a G3 electrode)
24
and an anode
25
having a G4 electrode
26
and a top unit
27
are arranged sequentially. The top unit
27
is a cup-shaped member having a cylindrical portion and a bottom portion that is provided with an electron beam passing hole. Until electron beams
9
(shown in
FIG. 3
) emitted from the cathode
21
reach the phosphor screen
8
formed on the inner surface of the front panel
1
, their paths are deflected by an ac magnetic field generated by the deflection yoke
5
, the velocity modulation coils
6
(which are not true to life in
FIG. 11
for the sake of convenience, but actually are formed as shown in
FIG. 2
) and the convergence yoke
7
. The deflection yoke
5
includes horizontal deflection coils
51
for deflecting the paths horizontally and vertical deflection coils
52
for deflecting the paths vertically and is mounted on a cone portion of the funnel
2
. The deflection yoke
5
generates the ac magnetic field so as to deflect the paths of the electron beams, thereby scanning the phosphor screen with the electron beams. The convergence yoke
7
is mounted outside the neck portion
3
and focuses the three electron beams on one point by its magnetic field.
In a current advanced display technology, the magnetic field is modulated by the velocity modulation coils
6
so as to perform what is called a velocity modulation of electron beams, thereby improving the focus performance (see JP 10(1998)-74465 A). The velocity modulation coils
6
are each arranged between the convergence yoke
7
and the neck portion
3
and at a position where the G3 electrode
24
and the G4 electrode
26
are located. The velocity modulation coils
6
generate an ac magnetic field
28
(shown as “a barrel shape” with dashed lines) so as to modulate a scanning velocity of the electron beams, thereby realizing a high-brightness portion and a low-brightness portion on the phosphor screen, thus achieving a sharp image.
The frequency of the ac magnetic field
28
for modulating the electron beams is of the order of a megahertz, as high as a video frequency. Therefore, when the velocity modulation coils
6
are provided at the position shown in
FIG. 11
, the ac magnetic field
28
is attenuated by the G3 electrode
24
and the G4 electrode
26
, which are formed of a metallic material such as stainless steel, causing a problem in that the electron beams cannot be modulated in a desired manner. In other words, the ac magnetic field
28
generates eddy currents in the G3 electrode
24
and the G4 electrode
26
, causing a loss of the ac magnetic field
28
.
Conventionally, it has been suggested that an electrode formed by deep-drawing should be divided into several parts, which are then spaced away from each other so as to improve magnetic permeability (see JP 8(1996)-115684 A). However, when the distance between the electrodes in the electron gun are designed to be great, an electric potential permeating into the neck portion separates the three electron beams that have been focused on one point on the phosphor screen, causing a problem in practical use. There also have been problems in that an assembling accuracy lowers, costs increase, and the magnetic permeability cannot be improved considerably because the size of each component should not be reduced too much in order to maintain a mechanical strength of each of the divided electrodes.
In addition, it is suggested in JP 5(1993)-347131 A that velocity modulation coils should be provided to overlap horizontal deflection coils, thus forming a portion in which an electrode of an electron gun and the velocity modulation coil do not overlap each other, thereby improving a modulation sensitivity of the velocity modulation coil. In this case, the frequency of an ac magnetic field from the velocity modulation coils is of the order of a megahertz and higher than the video frequency, and therefore, this ac magnetic field interferes with the magnetic field from the horizontal deflection coils, thus deteriorating signals of a television device. This leads to a poor image quality, becoming inappropriate for a practical use.
DISCLOSURE OF INVENTION
The present invention has been made in order to solve the problems described above, and it is an object of the present invention to provide a cathode ray tube device that can achieve a desired modulation effect on electron beams without blocking permeation of a velocity modulation magnetic field from an external side of a cathode ray tube.
A first cathode ray tube device of the present invention includes a cathode ray tube including a front panel, a funnel and an electron gun that is provided inside a neck portion of the funnel, a deflection yoke including a horizontal deflection coil and a vertical deflection coil that are mounted on an outer surface of the funnel and positioned on a side of the front panel with respect to the electron gun, and a velocity modulation coil that is mounted on an outer surface of the neck portion. An end of the velocity modulation coil on the side of the front panel is positioned on a side of the electron gun with respect to an end of the horizontal deflection coil on the side of the electron gun and is positioned on the side of the front panel with respect to an end of the electron gun on the side of the front panel.
With the above structure, since the horizontal deflection coil of the deflection yoke and the velocity modulation coil do not overlap in a direction perpendicular to a tube axis of the cathode ray tube, no interference from these coils deteriorates signals of a television device so as to cause a poor image quality. Also, because at least a part of the velocity modulation coil on the side of the front panel does not overlap a screen-side end of an electrode of the electron gun in the direction perpendicular to the tube axis of the cathode ray tube, it is possible to reduce a loss of an ac magnetic field from the velocity modulation coil owing to eddy currents, thereby achieving a desired modulation effect on electron beams.
It also is preferable that a distance along a tube axis direction of the cathode ray tube between the end of the velocity modulation coil on the side of the front panel and the end of the electron gun on the side of the front panel is at least 10% of a length of the velocity modulation coil along the tube axis direction. With this structure, it is possible to reduce the loss of the ac magnetic field from the velocity modulation coil owing to the eddy currents, thereby achieving a desired modulation effect on electron beams.
Furthermore, it is preferable that a distance along a tube axis direction of the cathode ray tube between the end of the velocity modulation coil on the side of the front panel and the end of the electron gun on the side of the front panel is at least 1 mm and not greater than 10 mm. With this structure, it is

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