Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2002-07-12
2004-11-09
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S382000, C315S382100, C313S412000, C313S414000, C313S446000, C313S447000, C313S448000, C313S449000, C313S458000, C313S460000
Reexamination Certificate
active
06815913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube which enhances a speed modulation effect.
2. Description of the Related Art
A color cathode ray tube, particularly a high brightness cathode ray tube such as a projection-type cathode ray tube forms images of high brightness and high definition on a phosphor screen by increasing electron beams (current) projected to a phosphor screen, by increasing an acceleration voltage applied to a final acceleration electrode (anode), and by elevating a potential of a focusing electrode.
Further, there has been known a method which changes a scanning speed of electron beams in response to a contrast level of images to display images having an excellent contrast (speed modulation method).
In this method, the scanning of electron beams is controlled such that when the electron beams perform horizontal scanning from a black level to a white level in response to a differential output of image signals, the scanning speed is temporarily accelerated and thereafter the scanning is temporarily stopped, while when the electron beams perform horizontal scanning from the white level to the black level in response to a differential output of image signals, the scanning is temporarily stopped and thereafter is temporarily accelerated.
A portion where the scanning speed is fast exhibits low electron beam density and hence, the portion is dark, while a portion where the scanning is stopped exhibits the high electron beam density and hence, the portion is bright. Accordingly, a region of black level is increased and, at the same time, a region of white level is narrowed so that the current density is increased where by the brightness is increased. Accordingly, the contrast is enhanced so that an image display of high quality is obtained.
An evacuated envelope of a cathode ray tube is constituted of a panel portion on which a phosphor screen is formed, a neck portion which houses an electron gun and a funnel portion which connects the panel portion and the neck portion.
FIG. 15
is a cross-sectional view of a neighborhood of a neck portion of a conventional cathode ray tube. An electron gun is housed in the neck portion
23
. The electron gun is constituted of a cathode K, a first grid electrode (control electrode)
11
, a second grid electrode (accelerating electrode)
12
, a third grid electrode (front-stage anode electrode)
13
, a fourth grid electrode (focus electrode)
14
and a fifth grid electrode (anode electrode)
15
. A deflection yoke
6
is exteriorly mounted on a transitional region between the neck portion
23
and the funnel portion
22
. Further, on an outside of the neck portion
23
, a correction magnetic device
7
for convergence adjustment and color purity adjustment and a speed modulation coil
8
are exteriorly mounted.
Electron beams temporarily receive a positive deflection action (scanning direction) or a negative deflection action (direction opposite to scanning direction) in the horizontal scanning direction due to a magnetic field generated by the speed modulation coil
8
.
An electric current which flows in the speed modulation coil
8
has a high frequency and the fourth electrode
14
is constituted of nonmagnetic metal material such as stainless steel in the same manner as other electrodes and hence, when the magnetic field generated by the speed modulation coil
8
acts on the electrode
14
, an eddy current is generated in the inside of the electrode
14
.
The generation of a magnetic flux which acts in an inner space of the fourth electrode
14
is suppressed by this eddy current so that the speed modulation effect is reduced.
To make the speed modulation magnetic field effectively act on the electron beams, it has been known to divide the fourth electrode
14
into halves along an electron beam path. The divided halves of the fourth electrode
14
are electrically connected by a connection line.
Due to such a constitution, it is possible to perform the speed modulation by inserting the magnetic field of the speed modulation coil in the space of the fourth electrode
14
so that the highly efficient speed modulation can be realized.
Further, by elongating an interval in the tube axis direction of the two-split fourth electrode
14
, the speed modulation magnetic field acts on the electron beams more effectively.
FIG. 16
is a side view of an electron gun adopting a speed modulation method. In the electron gun shown in
FIG. 16
, a portion of the fourth grid electrode
14
is inserted into the fifth grid electrode
15
. In
FIG. 16
, parts which perform the same actions as the parts shown in
FIG. 15
are indicated by the same numerals.
As publications which disclose the prior art related to this type of cathode ray tubes, for example, Japanese Laid-open Patent Publication 334824/1998, Japanese Laid-open Patent Publication 74465/1998 and Japanese Accepted Patent Publication 21216/1987 are named.
Further, a structure in which a coil-shaped portion is formed in a portion of a third grid electrode is disclosed in Japanese Laid-open Patent Publication 188067/2000.
In an electron gun which divides a focus electrode into halves in the tube axis direction, there exists a limit with respect to the expansion of a gap between the divided halves. When the gap between the divided halves of the electrode is excessively large, it is impossible to maintain the potential in the inside of the fourth electrode at an equal potential. That is, when the gap between the divided halves of the electrode is increased, the electron beams receive the influence of an electric field other than the electric field generated by electrodes of the electron gun or an external magnetic field. For example, the influence of electric fields from a charged with the front-stage anode electrode
13
by means of a connection line
181
.
Since the front-stage anode
13
and the focus electrode
14
are respectively divided, an eddy current which is generated in the focus electrode
14
due to a magnetic field generated by the speed modulation coil
8
is reduced. Further, the magnetic field generated by the speed modulation coil
8
can easily enter the electron beam passing region so that a sufficient speed modulation effect can be obtained. Accordingly, a contrast of displayed images can be enhanced.
In
FIG. 2
, the front-stage anode electrode
13
has one gap and the focus electrode
14
has three gaps. However, the anode electrode
13
may have a plurality of gaps and the focus electrode
14
may have a single gap. In this embodiment, to make the speed modulation magnetic field permeate into the inside of the focus electrode
14
where the diameter of the electron beam becomes bold as much as possible, three gaps are formed in the inside of the focus electrode
14
.
The third focus electrode
143
uses parts having the same shape as those of the second focus electrode
142
.
In
FIG. 2
, A
1
indicates a total length of the first front-stage anode
131
, A
2
indicates a total length of the second front-stage anode
132
, B
1
indicates a total length of the first focus electrode
141
, B
2
indicates a total length of the second focus electrode
142
, B
3
indicates a total length of the third focus electrode
143
, B
4
indicates a total length of the fourth focus electrode
144
, C
1
indicates the gap between the first front-stage anode
131
and the second front-stage anode
132
, D
1
indicates the gap between the first focus electrode
141
and the second focus electrode
142
, D
2
indicates the gap between the second focus electrode
142
and the third focus electrode
143
, D
3
indicates the gap between the third focus electrode
143
and the fourth focus electrode
144
, E
1
indicates an interval between the second front-stage anode
132
and the first focus electrode
141
, &phgr;
1
indicates an inner diameter of the second front-stage anode electrode
132
and an inner diameter of the first focus electrode
141
, and &phgr;
2
indicates an inner diameter of the large-diameter portion of the
Harasaka Kouichi
Nakayama Toshio
Suzuki Nobuyuki
Tanaka Yasuo
Wakita Syoichi
Leurig Sharlene
Milbank Tweed Hadley & McCloy LLP
Patel Nimeshkumar D.
LandOfFree
Cathode ray tube does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cathode ray tube, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cathode ray tube will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3292915