Note: Descriptions are shown in the official language in which they were submitted.
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BACKG~OUND OF THE IN~IENTION
The present invention relates generally to electron
beam tubes having dual beams and associated deflection means,
and more particularly to single scan expansion mesh cathode
ray tubes having dual electron beam yuns that provide asymmetrical
~orizontal scanning.
In cathode-ray tubes having dual electron beams for
independent, multitrace operation, it has been a common practice
to provide a pair of electron guns mounted in a stacked
configuration such that one gun is disposed above the central
10 axis of the tube, and the other gun disposed below the central `
axis, both guns being mounted in the same vertical plane so that
the horizontal angles of the two electron beams swept horizontal-
ly across the tube screen are equal. Since the screen is
transverse to the central axis of the tube and the guns are
mounted off-axis, the guns are angled toward the central axis
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so that each gun can scan the entire screen. However, this
angling distorts the scanned display pattern from a rectangle
to a trapezoid, which can easily be corrected by adjusting the
horizontal deflection plates to be nonparallel from side to side
thereby affecting the horizontal sensitivity as the tube is
scanned vertically. If a divergent post deflection acceleration
(PDA1 field is used and full overlap of scan is desired, the
guns have to be angled quite steeply, resulting in a large
diameter cathode-ray tube which takes up useful space.
U.S. patent 3,819,984, assigned to assignee of the
present application, teaches the concept of mounting a pair
of electron guns parallel to each other in a horizontal plane
in order to reduce the tube nec~ diameter. However, the use
of a single scan expansion mesh in a cathode-ray tube having
parallel electron guns and associated deflection structures
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produces the undesirable ef~ect of causing the two electrical -
centers of the guns to be widely separated, for example, as ~ ;-
much as eight centimeters, and introduces a vertical trace
bowing problem at the center of the display screen.
SUMMARY OF THE INVENTION
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The present invention overcomes the disadvantages
of widely separated electrical centers mentioned hereinabove
by angling the horizontal deflection plates to direct the
electron beams toward the central axis of the tube, and
by disposing a set of beam-centering plates through which the
electron beam passes between each set of vertical deflection
plates and angled horizontal deflection plates to cause the
beams to converge before entering the space between the horizontal
de~lection plates. In addition, the beam centering plates
have radiussed edges to correct for vertical trace bowing
introduced by the mesh. Correction control to compensate for -~
part variations introduced by mass production is provided by
a bowing control plate adjacent each set of beam centering
plates to which a variahle voltage may be applied to change
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the apparent radius of the beam-centering plates as seen by the
electron beam.
An intergun shield is disposed between the closely
mounted horizontal deflection plates to mini~ize the electrical
capacitance therebetween, preventing high-frequency cross talk ~ -
between the two guns. This shield is wider than the horizontal ~ -
deflection plates and has scalloped edges to accommodate the
deflection-plate support legs while providing shielding therefor.
Separate inner-gun and outer-gun shields are additionally
provided to control horizontal keystone geometry and edge pattern ;
distortion. -
Features of various embodiments of the present invention ;
are:
~1) a dual-beam cathode-ray tube having parallel electron guns
dlsposed slde by side ln whlch the electrlcal centers for
the guns are colncident;
(2) a means for directing the electron beam of an off-center
electron gun in a cathode-ray tube toward the central axis
of such tube to preclude the need for a large diameter
tube neck;
(3) a bowing control means to correct vertical trace bowlng
caused by a scan expanslon mesh in a dual beam cathode-ray
tube;
~4) an intergun shield for use in a dual beam cathode-ray tube
ln which the hor~zontal deflection plates are mounted close
together; :
~5) an intergun shield assembly which includes inner-gun and ~ ~
outer-gun shield means for eliminating horizontal keystone ~ ;
and edge pattern distortion in a dual beam cathode-ray ; -
tube; and ~:
(6) improved dual-beam cathode-ray tube having a single scan ~
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expall.sion mcsll in which side-hy-sidc eloctron guns arc
control]cd to providc overlapping rcctangular display
patterns. .
In accordance with one aspect of the present invention
there lS provided an electron beam apparatus comprising:
an evacuated envelope having target means;
dual electron gun means disposed side-by-side in said
envelope on each side of a central axis of said envelope and
spaced from said target means for generating electron beams
therefrom; and :, .
deflection means for each of said dual electron gun :
.: .
means disposed between said electron gun means and said
target means for deflecting said clectron beams over said
target moans in accordance ~itll signal voltages applied
thereto to providc image displays thereover,
said deflection means including beam centering means :i :
for directing said electron beams toward said central sxis ~;
of said envelope so tllat the electrical center of said - . .
deflection means corresponds to the center of said target
means, said beam centering means including correction means
for correcting vertical trace bowing of said image displays.
In accordance with another aspect of the present invention
there is provided a cathode-ray tube comprising:
an evacuated envelope having target means; -
dual electron gun means disposed side-by-side in said
env~elope for generating electron beam means and being spaced -;
from said target means; : .
deflection means disposed in said envelope between said
target means and said electron gun means and including
independent vertical and horizontal deflection plate means
for each of said dual electron gun means for deflecting said '~
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electron bcam mcans ovcr said targct mcalls in accordancc
with s;gnal voltagcs applic~ to said vcrtical and horizontal
deflection plate means, said horizontal deflection plate
means being disposed at an angle with respect to said
vertical deflection plate means so that electron beam means ~ :
passing through the center of said deflection means corresponds
to the center of said target means, `~
said deflection means further including beam centering
plate means disposed between said vertical and horizontal ~ -
deflection plate means for diverting said electron beam
means through said horizontal deflection plate means; and
correction means provided by said beam centering plate
means for correction of vertical trace bowing of said
electron beam means.
BRI~F DESCRIPrlION OF TIIE DRAWINCS
The foregoing and other objects, features, and
advantages of this invention will become apparent from the
following detailed description of an illustrative embodiment -
which is to be read in conjunction with the accompanying `
drawings in which:
Figs. 1 and 2 are schematicized top and side views
respectively of a dual-beam cathode-ray tube according to the
present invention;
Fig. 3 shows a perspectlve view of an intergun shield
assembly for use in a dual-beam cathode-ray tube; ~
. Figs. 4 and 5 show side and top views respectively ~-
of an intergun shield assembly for use in a dual-beam
cathode-ray tube; and ~ ;
Figs. 6A, 6B, and 6C (appearing on the same sheet of
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drawings as Fig. 1) illustrate rectangular display patterns
formed by an electron beam on the fluorescent screen of a
cathode-ray tube.
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I)ETAILED DESCRIPTION
As shown in ~ig. 1, an elcctron dischargc which may ~ ;
be a cathode-ray tube 10 or other electron beam deElection
device has an evacuatecd envelope 12 of glass, ceramic, or
other suitable insulating material in which a fluorescent
screen 14 of phosphor material coated on the inner surface
of a light transparent faceplate 16 which is secured onto
the front end of such envelope. A thin metallic coating 18
preferably of aluminum is disposed on the gun side of screen 14.
Two separate electron guns of conventional design are
disposed in envelope 12 which include cathodes 20 and 21,
cntrol grids 24 and 25, and focusing anodes 28 and 29. In
addition, two separate electron beam deflection systems are
provided in onvelope lZ including a first pa:ir of vertical
clefloct:ion
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plates 32 and a second pair of vertical deflection plates 33,
a first pair of beam centering plates 36 and a second pair of
beam centering plates 37, and a first pair of horizontal
deflection plates 40 and a second pair of horizontal deflection
plates 41.
As can be discerned from Fig. 1 and Fig. 2, where
like elements have like reference numerals, cathode 20 has
associated therewith control grid 24, focusing anodes 28,
vertical deflection plates 32, beam centering plates 36, and
horizontal deflection plates 40 for controlling an electron
beam 44 produced by cathode 20, to which -3 kilovolts may be
applied. Similarly, cathode 21 may have -3 kL]ovolts applied
thereto, and has associated therewlth control grld 25, focusing
anodes 29, vertlcal deflectlon plates 33, beam centerlng plates
37, and horizontal deflection plates 41 for controlling the electron
beam 45 produced by cathode 21.
An annular mounting and shielding member 50 is disposed
in the envelope 12~so that the output ends of horizontal deflection ~ `
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means 40 and 41 are positioned therein, and it i8 operated at
near ground potential. Member 50 serves to shield the horizontal
deflection means from the high voltage of post deflection accelera-
tion anode 54 which may conaist of a conductive coatlng on the
interior surface of envelope 12 in electrical contac~ with
metallic coating 18 and has an operating potential of 20 to 24
kilovolts thereon. A scan expansion mesh 58 is secured on the
.... . .
member 50 which has an outwardly-directed hemispherical configura-
tion to provide diverging lens for scan expansion in the manner ~,
taught in a book entitled "Cathode-Ray Tubes," pp. 51-5~l, published
by Tektronix, Inc., in 1970. This mesh 58 causes the electron ~
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beams to be efeectively scanned over the screen in full overlap
operation, since both beams must be capable of coveri~g the same
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screen area.
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After leavlng the electron guns, the electron beams
44 and 45 first pass through the vertical deflcction plates 32
and 33 respectively. Conventional vertical de~lection pla~es
as shown in Figs. 1 and 2 will provide sa~isfactory operation
up to about 150 megahertz; however, for cathode-ray tube operation ~;
above this frequency, a vertical deflection means of the type
disclosed in U.S. Patent No. 3,694,689 will provide best operation.
Beam centering pla~es 36 and 37 are identical in
con~iguration and each pair comprises an outer planar plate
36a, 37a and an inner planar plate 36b, 37b, which are spaced
equidistant from each other and disposed parallel to th`e central
axis of the tube to receive the electron beams 44 and 45 passing
from ~he vertical de~lection pla~es 32 and 33 respectively. The
lnner beam centerlng plates 36b and 37b, which are closest to
the central axis oE the tube, are biased with an electrical
potential which is positive to the outer plates 36a and 37a -
respectively to cause the electron beams 44 and 45 to be directed
toward the central axis of the tube along the center lines of the
horizontal deflection plates 40 and 41 as shown in Fig. 1. The
beam entrance and exit portions of the beam centering plates may
20 be of an arcuate configuration as shown in Fig. 2 to correct ;
Eor vertical trace bowlng introduced by the mesh. ~s can be
dlscerned, a beam 44, 45 which is deflected upward or downward ;
by the vertical deflection plates 32, 33 must travel through a
longer path as ie passes through the beam centering plates 36, -~
37 and will be horizontally deflected more by the beam centering
plates than would a beam passing through the center thereof. ~ `
Hence, a bow is deliberately introduced into the ~ertical trace
which is opposite to that introduced by the mesh 58, resultlng in
a straight vertical center trace viewed on the screen 14.
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Compensator plates 70 and 71, which are planar plates
with straigh~ edges, are mounted adJacent the bea~ entrance edge
of the outer ~eam cente~ing plates 36a and 37a to provide a
control of the amount of vertical tracing bowing discussed in the
preceding paragraph to compensate for part tolerances and slight
misalignment of parts in the manufacture of the cathode-ray
tu~es. A variable electrical potential is applied to each
compensator plate 70 and 71 to produce an Plectrostatic field
whose equipotential lines interfere with the equipotential lines
at the extreme edge of each set of beam centering pla~es 36 and
37 respectively, thereby changlng the apparent curvature of
the entrance edge of the outer beam centering plates 36a and
37a to establish the requ:lred stralght vertical trace. ~ ~ ;
Horizontal deflection plates 40 and 4L are identical
in configuration and each pair comprises an outer plate 40a,
41a and an lnner plate 40b, 41b which are typically about 0.05 ;
inches apart at the entrance and about 0.35 inches apart at the
exit to form a wedge-shaped spacing therebetween. Each :et
of horizontal deflection plates is disposed at an angle within
the envelope 12 sa that the electron beams 44 and 45 directed
toward the central axis of the tube by the aforementioned beam , !
centering plate~ may enter and pass through without obstruction
along a line corresponding to the electrical center of the
viewing screen 14. The electric~l center of the screen is
defined as that point at which the beams 44 and 45 strike when
the vertical deflection plates 32, 33 and the horizontal ~ ~
deflection plates 40 and 41 are all grounded together, establish- ~ -
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~ng zero ~olts difference between the pairs of plates. The
effect of the ~eam centering plates 36 and 37, the horizontal -
30 deflection plates 40 and 41, and the scan expansion mesh 58
i8 to establlsh the electrical center of the screen at the ~-~
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physical center of the screen, even though the side-by-side
electron guns are physically several millimeters apart.
Plates 75 are mounted between the pairs of vertical
deflection plates to prevent the electrostatic fields of these
vertical aef~ection means from interfering with each other as
well as providing compensation so that the characteristic
impedance is constant therealong. Plates 75 are operated at
near the average potential of the vertical deflection means.
Intergun isolation shield 80 is disposed between
the pairs of horizontal deflection plates 40 and 41 to prevent
the electrostatic fields generated by the respective pairs of
horizontal deflection plates from affecting each other.
Shield 80 is operated at or near the average potential oE the
horizontal deflection means. This shield also serves to
mlnimize the capacitance between the sets of deflection plates,
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thus minimizing high-frequency crosstalk between the two gun :~
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systems.
Inner gun shield 82, and out gun shields 84 and 85
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are disposed ad~àcent the exit of horizontal deflection plates
40 and 41-~ and are operated at potentials sufficient to correct
overall display pattern distortion, particularly hori~ontal
keystone distor~ion, which will be further discussed later.
Further geometry correction can be effected by providing
the horizontal deflection plates 40 and 41 with arcuate, or
radiussed exit edges rather than the straight exit edge shown
in the drawings. :
Input signals are applied at input terminals 100 and
101, which are connected respectively to vertical amplifiers
- 106 and 107. Vertical amplifiers 106 and 107 develop push-pull
output signals which are connected respectively to ver~ical
def-lection means 32 and 33. Horizontal ramp g~nerators :L10 and
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111 are triggered in response to the receipt of inpu~ signals
at input terminals 100 and 101 ~y providing trigger circuits 116
and 117 having their inputs connected respectively to input
terminals 100 and 101 and having their outputs connected respectively
to the inputs of horizontal ramp generators 110 and 111.
Horizontal ramp generators develop push-pull sawtooth signals
suitable for driving dellection plates, and these signals are
applied respectively to horizontal deflection means 40 and 41. - -
Thus, electron ~eams 44 and 45 emitted respectively
from cathodes 20 and 21 are properly focused by focusing anodes
28 and 29, thereafter vertical deflection means 32 and 33 and
h~orizontal deflection means 40 and ~1 operate on the focused
electron beams to deflect the beams ln accordance wlth the
signals at input termin~ls 100 and 101 whereaEter the beams
are passed through scan expanslon mesh 58 whereby they are
accelerated about 2~i kilovolts before they strike the target j,
comprising phosphor layer 14 and metallic coating 17 which
produces light images of these electron beams, which under most
circumstances will be the signal waveform traces of the vertical
deflection signals. The thin film of aluminum, which is several
angstrom3 thick, is electron transparent and reElects the light
emitted,lby the phosphor layer 14 to increase the brightness of
the displays in a conventional manner.
Fig. 3 show8 a perspec~ive view of an intergun and ~
crosstalk shield assembly in accordance with the preferred ~;`
embodiment of the present invention, while Figs. 4 and 5 show -~
respectively side and top views of this preferred embodiment.
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Again9 like elements have like reference numerals to facilitate
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reference to the drawings. An isolation shield comprising
slotted half-discs 120 and 121 is insulatively attached to the
intergun isolation shield 80 on a plane transverse to the shield
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80 to provide isolation of the horizontal deflection means from `~
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the high-voltage field established by the post deflection anode
54 described earlier. The outer gun shields 84 and 85 are
insulatively attached to the shield 120 and 121 respectively.
The intergun shield 80, islolation shlelds 120 and 121, and outergun
shields 84 and ~5 are assembled by means of support legs 125, -
which may be wires spot-welded to the various members and
insulated from each other by glass beads 128.
Inner gun shield 82 comprises two separate shield
mem6ers 130 and 131 which are insulated from each other and `
insulatively mounted in the space provided in intergun shield 80.
The completed intergun shield assembly hereinabove
described i8 mounted in the tube between the two paLrs of
horizontal deflection plates 40 and 41, attached to the inner
horizontal deElection plate support rods 13~ and 136, which
may be suitably be fabricated of glass or other insulating material, '
by means of support legs 140 which are spot welded to isolation
shield 80 and embedded in the support rods 134 and 36 as shown
in Fig. 4.
The edges of shleld 80 are scalloped to permit the
inner horizontal deflection plate support legs 144 which are
~pot welded to the inner horizontal deflection plates 40b and
41b to be embedded in the support rods 134 and 136 without
touching the shield 80. This arrangement allows the two sets
of horizontal deflection plates 40 and 41 to be mounted as
close together as possible to achieve full scan overlap while
minimizing display distortion, and simultaneously reducing the
capacitance due to the dielectric mediums, i.e. the air and the
support rods, between the two sets of horizontal deflection plates.
As can be discerned, the deflection plate support
legs 144 are at the same electrical potential as their associated
deflection plates 40b and 41b, and to complete the shielding
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and further minimize capacitance in the support rods 13~ and
136, tfie outsi`de of the rods 134 and 136 are coated with an
electrically conductive paint 150 in bands connecting the
shield 80 support legs 140.
In the absence of the inner gun ~hields 82 and
outer gun shields 84 and 85, the display generated by th~ left --
electron gun means would provide a keystone-shaped display as ''~
shown in Fig. 6A whereby the horizontal lines above and below '' '~
the center horizontal line will deviate away therefrom in a
direction from left to right, whereas the display generated by
10 the right electron gun means would provide a keystone-shaped '";l";'~
display as shown in Fig. 6B wher'eby the horizontal lines above
and below the center horizontal llne will deviate away therefrom
in a directLon opposite ~o that of the display ~f the left
gun means as shown by Fig. 6A. Thus, the interaction of the ';
electrostatic fields of the vertical and horizontal deflection
means without the innergun shields 82 and outer gun shield '~
84 and 85 will provide displays having keystone distortion as
shown in Figs. 6A and 6B in a dual-beam cathode-ray tube wherein
the electron guns are disposed parallel to each other in side- '; '
by-side relationship. When the innergun shields 82 and outergun
shields 84 and 85 are provided for the horizontal defl~ction
means in accordance with the present invention, a true rectangular ~ -'
display as shown in Fi8. 6C 1s provided thereby correcting for ~' ;
ke~stone distor~ion. ' '
It will be obvious to those hav:Lng ordinary skill
in the'art that many changes may be made in the detaLls o~
the above-described preferred embodiment without departing '~
~rom the spirit of the invention. While a conventional cathode-
ray tube has been described, it is possible to employ t'he present
invention in a bistable charge image storage tube including the
s
type in which the phosphor layer also ~unctions as the storage
dielectric. T~ere~ore, the scope of the present invention is :~ .
to be determined by the ~ollowing claims.
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