Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
1999-03-12
2001-09-25
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S309000, C313S414000, C315S005000, C315S005330
Reexamination Certificate
active
06294868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron gun with a cold cathode for use in a microwave electron tube such as a traveling-wave tube or the like, and more particularly to an electron gun for an electron tube with a cold cathode, which has at least two electrodes extending from a surface of the cold electrode.
2. Description of the Related Art
There has been known mounting of a cold cathode in an electron-beam device represented by a traveling-wave tube. However, no previous instance of mounting a cold cathode with a focusing electrode in such an electronbeam device as disclosed in the present invention is found in the art.
First, various conventional examples of mounting a cold cathode with no focusing electrode will be described below. Then, device mounting manners which could generally be derived from the conventional processes in order to mount a cold cathode with a focusing electrode will be described below.
1. Japanese unexamined patent publication No. 129144/97 discloses a linear beam microwave tube. As shown in
FIG. 1
of the accompanying drawings, the disclosed linear beam microwave tube has cathode tip
52
with cold cathode
51
disposed on a surface thereof. Cathode tip
52
is joined by silver paste to a joint of mount support
53
which is supported by a package. Mount support
53
and cathode tip
52
are joined such that cathode tip
52
has end
55
abutting against reference surface
54
of mount support
53
and an opposite end spaced slight gap
56
from mount support
53
. Cold cathode
51
can thus be accurately positioned with respect to reference surface
54
. Wehnelt electrode
57
for focusing electron beam
50
emitted from cold cathode
51
is installed as follows: after Wehnelt electrode
57
has been shaped to a desired configuration, it is secured by heat-pressing to a gate electrode of cathode tip
52
so that the center of an opening of Wehnelt electrode
57
is aligned with the central axis of cold cathode
51
. In operation, a predetermined potential is supplied to the gate electrode through Wehnelt electrode
57
.
2. Japanese unexamined patent publication No. 115453/97 reveals an electron gun with a cold cathode. As shown in
FIG. 2
of the accompanying drawings, the disclosed electron gun has first cylindrical insulator
61
and metal conductor
62
extending through a central hole in first cylindrical insulator
61
in an axial direction of the electron gun. Cold cathode
63
is mounted on emitter electrode
60
disposed on a tip end of metal conductor
62
. An emitter potential of cold cathode
63
is led out of a vacuum space through metal conductor
62
. First cylindrical insulator
61
and second cylindrical metal sleeve
64
disposed and abutting around first cylindrical insulator
61
are held respectively against gate electrode cylindrical metal sleeve
66
concentrically disposed around a shank of the metal conductor
62
and second cylindrical insulator
67
through conductive layer
65
, abutting around gate electrode cylindrical metal sleeve
66
. An end of second cylindrical metal sleeve
64
remote from conductive layer
65
is connected to a gate electrode of cold cathode
63
by metal bonding wire
68
. A gate potential is thus taken out of the gate electrode through metal bonding wire
68
, second cylindrical metal sleeve
64
, conductive layer
65
, and gate electrode cylindrical metal sleeve
66
.
3.
FIG. 3
of the accompanying drawings shows another conventional arrangement. As shown in
FIG. 3
, cold cathode emitter device
71
is fitted in a complementary recess defined in emitter electrode support
72
. Cold cathode emitter device
71
is pressed against Wehnelt electrode
75
under the bias of spring
74
which acts between emitter electrode support
72
and another support
73
which is fixed in place and by which emitter electrode support
72
is supported. A gate electrode of cold cathode emitter device
71
is electrically connected to Wehnelt electrode
75
.
Device mounting processes which could generally be derived from the above conventional processes in order to electrically draw out two independent electrodes, i.e., a gate electrode and a focusing electrode which are set up on a cold cathode emission surface will be described below with reference to FIGS.
4
(
a
),
4
(
b
), and
4
(
c
) of the accompanying drawings.
The device mounting processes may include a Wehnelt electrode pressing process, a brazing process, and a resiliently biased fixing process. FIGS.
4
(
a
),
4
(
b
), and
4
(
c
) show the resiliently biased fixing process.
For taking the potentials of two electrodes from the cold cathode emission surface, it is appropriate to take one electrode potential via the Wehnelt electrode. Specifically, as shown in FIG.
4
(
a
), an electrode connected to the Wehnelt electrode is of necessity a focusing electrode due to structural limitations imposed to a cold cathode with such a focusing electrode. This is because no feeder lines can be exposed between the Wehnelt electrode and an anode disposed in facing relation to the Wehnelt electrode since an axially symmetrical electron lens should be formed between the Wehnelt electrode and the anode.
A gate electrode is usually electrically connected by a bonding wire or tab for taking an electrode potential therefrom at an outer periphery of the focusing electrode according to an electronic device mounting process.
FIG.
4
(
a
) shows the use of a bonding wire for taking out a gate electrode potential, and FIG.
4
(
b
) shows the use of a tab for taking out a gate electrode potential. FIG.
4
(
c
) shows at enlarged scale structural details in the vicinity of a cold cathode illustrated in FIGS.
4
(
a
) and
4
(
b
).
For taking a potential from the gate electrode with a bonding wire, it is necessary that the bonding wire have a looped shape in order to keep its strength enough, and hence a space is required to accommodate such a looped shape. Furthermore, for maintaining a desired dielectric strength between the bonding wire and the Wehnelt electrode, the Wehnelt electrode needs to be large upwardly and diametrically, with the result that the electron gun cannot be reduced in size.
For connecting the bonding wire or tab to the cold cathode, it is necessary to exert forces to bonding wire or tag. At this time, dust particles are liable to stick between the gate electrode and the emitter electrode, developing an insulation failure therebetween which tends to cause the cold cathode to fail to operate.
Moreover, if the tab is used to connect the gate electrode, then the electron gun necessarily becomes large in outer dimensions because the electron gun needs to have a structure strong enough to withstand the driving of the tab.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electron gun for an electron tube with a cold cathode, which can be designed with increased freedom, can be reduced in size, can be assembled with ease when manufactured, has high dimensional accuracy, provides a high dielectric strength between a gate electrode and an emitter electrode, and is made highly resistant to vibrations.
An electron gun for an electron tube with a cold cathode according to the present invention has a cold cathode fixedly sandwiched between a Wehnelt electrode and an emitter electrode, and feeder path structures are connected respectively to at least two electrodes disposed on a surface of the cold cathode. Specifically, a ceramic plate is interposed between the cold cathode and the Wehnelt electrode, and at least two metallized layers associated respectively with the at least two electrodes are disposed on the ceramic plate. The metallized layers serve as the respective feeder path structures and are connected to external power supplies. The ceramic plate and the Wehnelt electrode have respective central holes aligned coaxially with the central axis of the electron gun. The central holes jointly have a tapered wall surface which spreads outwardly and through which an e
Imura Hironori
Seko Nobuya
Guharay Karabi
NEC Corporation
Patel Nimeshkumar D.
Young & Thompson
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