U.S. patent number 3,904,923 [Application Number 05/433,186] was granted by the patent office on 1975-09-09 for cathodo-luminescent display panel.
This patent grant is currently assigned to Zenith Radio Corporation. Invention is credited to James W. Schwartz.
United States Patent |
3,904,923 |
Schwartz |
September 9, 1975 |
Cathodo-luminescent display panel
Abstract
This disclosure depicts cathodo-luminescent devices and
luminescent panels employing X-Y matrices of such devices as the
display elements. The cathodo-luminescent devices are depicted as
each comprising a two-section cell containing an ionizable gas at
very low pressure. The first section comprises an
electron-multiplier serving as a controllable source of free
electrons. Free electrons are drawn from the electron-multiplier
and accelerated in the second section to high energies whereupon
they collide with a light-emissive phosphor screen. Other
structures including means for modulating the flow of electrons to
the screen are disclosed.
Inventors: |
Schwartz; James W. (Glenview,
IL) |
Assignee: |
Zenith Radio Corporation
(Chicago, IL)
|
Family
ID: |
23719163 |
Appl.
No.: |
05/433,186 |
Filed: |
January 14, 1974 |
Current U.S.
Class: |
348/797;
345/74.1; 250/214LA; 313/105R; 313/103R; 315/12.1; 348/739 |
Current CPC
Class: |
H01J
31/128 (20130101); H01J 43/10 (20130101); H01J
29/467 (20130101) |
Current International
Class: |
H01J
43/10 (20060101); H01J 43/00 (20060101); H01J
29/46 (20060101); H01J 31/12 (20060101); H01J
043/10 (); H01J 043/30 () |
Field of
Search: |
;313/103-105,68,204
;315/11,12,169R,169TV ;178/7.3D,7.5D ;250/213R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: LaRoche; E. R.
Attorney, Agent or Firm: Coult; John H.
Claims
I claim:
1. A cathodo-luminescent device comprising:
wall means defining an enclosure containing an ionizable gas at a
predetermined low pressure;
an electron-multiplier located within said enclosure for creating
at an output end thereof a source of electrons, said
electron-multiplier including cathode means and electron-multiplier
anode means adapted to receive an applied potential different
thereacross, said electron-multiplier generating positive gas ions
as a result of collisions between electrons and the gas atoms, said
electron-multiplier being constructed to provide a clear path for
ions such that some of said ions feed back to said cathode to cause
said cathode to emit electrons;
phosphor means disposed at one end of said enclosure in spaced
relation to said output end of said electron-multiplier for
emitting light when bombarded by high energy electrons;
accelerating anode means disposed at said phosphor means and
adapted to receive a predetermined accelerating voltage
substantially more positive than the voltage applied to said
electron-multiplier means for drawing electrons from said
electron-multiplier when said electron-multiplier is on and for
accelerating them to high energies for impingement on said phosphor
means, the said predetermined gas pressure being sufficiently low
as to preclude the establishment of a gas discharge in said device;
and
activating means for selectively causing the feedback loop gain of
said electro-multiplier to be at least unity to drive said
electron-multiplier to an on state associated with a predetermined
high level of available electron-multiplier current and for
selectively causing the feedback loop gain of said
electron-multiplier to be less than unity to drive said
electron-multiplier to an off state associated with negligible
electron-multiplier current.
2. The device defined by claim 1 wherein said electron-multiplier
comprises a plurality of discrete, serially arranged,
secondary-electron-emissive dynodes disposed between said cathode
means and said electron-multiplier anode means and adapted to
receive applied voltages ever-increasing in positive polarity in a
direction away from said cathode, but substantially less than the
voltage applied to said accelerating anode means, said
electron-multiplier including an ion-generation region in which
said positive gas ions are generated, said dynodes being arranged
so as to permit some of said positive gas ions generated in said
electron-multiplier to be accelerated to said cathode means to
cause said cathode means to emit additional free electrons.
3. The device defined by claim 1 including control means responsive
to an applied control voltage for modulating the flow of electrons
to said phosphor means and thus the amplitude of the light emitted
by said phosphor means.
4. The device defined by claim 1 wherein said device includes
baffle means disposed between said electron-multiplier and said
accelerating anode means for blocking high energy electrons which
might be emitted by said electron-multiplier and for blocking the
passage to said cathode means of ions which might be generated in
the region between said baffle means and said accelerating anode
means.
5. A cathodo-luminescent device comprising:
wall means defining an enclosure containing an ionizable gas at a
predetermined low pressure;
an electron-multiplier located within said enclosure for creating
at an output end thereof a source of electrons, said
electron-multiplier comprising a cathode and an electron-multiplier
anode adapted to receive an applied potential difference
thereacross, said electron-multiplier including a plurality of
discrete, serially arranged, secondary-electron-emissive dynodes
disposed between said cathode and said anode and adapted to receive
applied voltages ever-increasing in a positive polarity in a
direction away from said cathode, said electron-multiplier
including an ion-generation region in which positive gas ions are
generated as a result of collisions between electrons and said gas,
said dynodes being arranged so as to permit said positive gas ions
to be accelerated to said cathode to cause said cathode to emit
additional free electrons and thereby complete a regenerate
electron-ion feedback loop;
phosphor means disposed at one end of said enclosure in spaced
relation to said output end of said electron-multiplier for
emitting light when bombarded by high energy electrons;
accelerating anode means disposed at said phosphor means and
adapted to receive a predetermined accelerating voltage
substantially higher than the voltage applied to said
electron-multiplier anode for drawing electrons from said
electron-multiplier when said electron-multiplier is on and for
accelerating them to high energies for impingement on said phosphor
means, the said predetermined gas pressure being sufficiently low
as to preclude the establishment of a gas discharge in said
device;
activating means for selectively causing the loop gain of said
electron-multiplier feedback loop to be less than unity to cause
said electron-multiplier to assume an inactive state or for turning
said electron-multiplier on by causing said loop gain to be unity
or greater wherein said electron-multiplier saturates at a
predetermined saturation current level; and
control means including a control electrode located within said
enclosure between said electron-multiplier and said accelerating
anode, said control means being responsive to an applied control
voltage for modulating the flow of electrons from said
electron-multiplier to said phosphor means and thus the amplitude
of the light emitted by said phosphor means.
6. The device defined by claim 5 wherein said device includes
baffle means disposed between said electron-multiplier and said
accelerating anode for blocking high energy electrons which might
be emitted by said electron-multiplier and for blocking the passage
to said cathode of ions which might be generated in the region
between said baffle means and said accelerating anode.
7. Television display panel for reproducing an image carried by an
input video signal, comprising:
an array of cathodo-luminescent elements discretely excitable by
row-column selective addressing, each element comprising:
wall means defining at least a portion of an enclosure containing
an ionizable gas at a predetermined low pressure,
an electron-multiplier located within said enclosure for creating
at an output end thereof a source of electrons, said
electron-multiplier comprising a cathode and an electron-multiplier
anode adapted to receive an applied potential difference
thereacross, said electron-multiplier including a plurality of
discrete, serially arranged, secondary-electron-emissive dynodes
disposed between said cathode and said anode and adapted to receive
applied voltages ever-increasing in a positive polarity in a
direction away from said cathode, said electron-multiplier
including an ion-generation region in which positive gas ions are
generated as a result of collisions between electrons and said gas,
said dynodes being arranged so as to permit said positive gas ions
to be accelerated to said cathode to cause said cathode to emit
additional free electrons and thereby complete a regenerate
electron-ion feedback loop,
phosphor means disposed at one end of said enclosure in spaced
relation to said output end of said electron-multiplier for
emitting light when bombarded by high energy electrons,
accelerating anode means adapted to receive a predetermined
accelerating voltage substantially higher than the voltage applied
to said electron-multiplier anode for drawing electrons from said
electron-multplier when said electron-multiplier is on and for
acccelerating them to high energies for impingement on said
phosphor means, the said predetermined gas pressure being
sufficiently low as to preclude the establishment of a gas
discharge in said device,
activating means for sectively causing the loop gain of said
electron-multiplier feedback loop to be less than unity to cause
said electron-multiplier to assume an inactive state or for turning
said electron-multiplier "on" by causing said loop gain to be unity
or greater wherein said electron-multiplier saturates at a
predetermined saturation current level, and
control means including a control electrode located within said
enclosure between said electron-multiplier and said accelerating
anode, said control means being responsive to an applied control
voltage for modulating the flow of electrons from said
electron-multiplier to said phosphor means and thus the amplitude
of the light emitted by said phosphor means; and
means responsive to the input signal and coupled to both said
control means and to said activating means associated with each of
said elements for storing a predetermined interval of said input
signal and for subsequently applying the stored information in
parallel to appropriate elements in said array of elements such
that said input signal is reproduced on the panel as a light image
spatially varying in amplitude.
8. The device defined by claim 7 wherein said panel includes baffle
means disposed between said electron-multiplier and said
accelerating anode for blocking high energy electrons which might
be emitted by said electron-multiplier and for blocking the passage
to said cathode of ions which might be generated in the region
between said baffle means and said accelerating anode.
9. A luminescent panel for displaying alpha-numeric characters or
other light representations carried by an input signal,
comprising:
an array of discretely excitable cathodo-luminescent elements, each
element comprising:
wall means defining at least a portion of an enclosure containing
an ionizable gas at a predetermined low pressure,
an electron-multiplier located within said enclosure for creating
at an output end thereof a source of electrons, said
electron-multiplier including cathode means and electron-multiplier
anode means adapted to receive an applied potential difference
thereacross, said electron-multiplier generating positive gas ions
as a result of collisions between electrons and the gas atoms, some
of which ions feed back to said cathode to cause said cathode to
emit electrons,
phosphor means disposed at one end of said enclosure in spaced
relation to said output end of said electron-multiplier for
emitting light when bombarded by high energy electrons,
accelerating anode means disposed at said phosphor means and
adapted to receive a predetermined accelerating voltage
substantially more positive than the voltage applied to said
electron-multiplier anode means for drawing electrons from said
electron-multiplier when said electron-multiplier is on and for
accelerating them to high energies for impingement on said phosphor
means, the said predetermined gas pressure being sufficiently low
as to preclude the establishment of a gas discharge in said device,
and
activating means for driving said electron-multiplier between an on
state associated with a predetermined maximum available
electron-multiplier current and an off state associated with
negligible electron-multiplier current; and
means responsive to the input signal and coupled to said
electron-multiplier of each of said elements for applying the input
signal to said array of elements to cause the input signal to be
reproduced on the panel as a light representation spatially varying
in amplitude.
10. A cathodo-luminescent device comprising:
wall means defining an enclosure containing an ionizable gas at a
predetermined low pressure;
an electron-multiplier located within said enclosure for creating
at an output end thereof a source of electrons, said
electron-multiplier including cathode means and
electrode-multiplier anode means adapted to receive an applied
potential difference thereacross, said electron-multiplier
generating positive gas ions as a result of collisions between
electrons and the gas atoms, said electron-multiplier being
constructed to provide a clear path for ions such that some of said
ions feed back to said cathode to cause said cathode to emit
electrons;
phosphor means disposed at one end of said enclosure in spaced
relation to said output end of said electron-multiplier for
emitting light when bombarded by high energy electrons;
accelerating anode means disposed at said phosphor means and
adapted to receive a predetermined accelerating voltage
substantially more positive than the voltage applied to said
electron-multiplier means for drawing electrons for said
electron-multiplier when said electron-multiplier is on and for
accelerating them to high energies for impingement on said phosphor
means, the said predetermined gas pressure being sufficiently low
as to preclude the establishment of a gas discharge in said
device;
activating means for selectively causing the feedback loop gain of
said electron-multiplier to be at least unity to drive said
electron-multiplier to an on state associated with a predetermined
high level of available electron-multiplier current and for
selectively causing the feedback loop gain of said
electron-multiplier to be less than unity to drive said
electron-multiplier to an off state associated with negligible
electron-multiplier current; and
beam deflecting means responsive to an applied deflection voltage
for vertically deflecting the electron beam to a different vertical
location on said phosphor means.
11. Television display panel for reproducing an image carried by an
input video signal, comprising:
an array of cathodo-luminescent elements discretely excitable by
row-column selective addressing, each element comprising:
wall means defining at least a portion of an enclosure containing
an ionizable gas at a predetermined low pressure,
an electron-multiplier located within said enclosure for creating
at an output end thereof a source of electrons, said
electron-multiplier comprising a cathode and an electron-multiplier
anode adapted to receive an applied potential difference
thereacross, said electron-multiplier including a plurality of
discrete, serially arranged, secondary-electron-emissive dynodes
disposed between said cathode and said anode and adapted to receive
applied voltages ever-increasing in a positive polarity in a
direction away from said cathode, said electron-multiplier
including an ion-generation region in which positive gas ions are
generated as a result of collisions between electrons and said gas,
said dynodes being arranged so as to permit said positive gas ions
to be accelerated to said cathode to cause said cathode to emit
additional free electrons and thereby complete a regenerate
electron-ion feedback loop,
phosphor means disposed at one end of said enclosure in spaced
relation to said output end of said electron-multiplier for
emitting light when bombarded by high energy electrons,
accelerating anode means adapted to receive a predetermined
accelerating voltage substantially higher than the voltage applied
to said electron-multiplier anode for drawing electrons from said
electron-multiplier when said electron-multiplier is on and for
accelerating them to high energies for impingement on said phosphor
means, the said predetermined gas pressure being sufficiently low
as to preclude the establishment of a gas discharge in said
device,
activating means for selectively causing the loop gain of said
electron-multiplier feedback loop to be less than unity to cause
said electron-multiplier to assume an inactive state or for turning
said electron-multiplier on by causing said loop gain to be unity
or greater wherein said electron-multiplier saturates at a
predetermined saturation current level,
control means including a control electrode located within said
enclosure between said electron-multiplier and said accelerating
anode, said control means being responsive to an applied control
voltage for modulating the flow of electrons from said
electron-multiplier to said phosphor means and thus the amplitude
of the light emitted by said phosphor means, and
beam deflecting means responsive to an applied interlace deflection
voltage for vertically deflecting the electron beam to a different
vertical location on said phosphor means to effect interlace of
successively displayed fields; and
means responsive to the input signal and coupled to both said
control means and to said activating means associated with each of
said elements for storing a predetermined interval of said input
signal and for subsequently applying the stored information in
parallel to appropriate elements in said array of elements such
that said input signal is reproduced on the panel as a light image
spatially varying in amplitude.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application relates to, but is in no way dependent upon,
copending application Ser. No. 538,486, filed Jan. 3, 1975,
assigned to the assignee of the present invention.
BACKGROUND OF THE INVENTION
The evolution of television and other displays has been toward
structures which are capable of reproducing ever larger and
brighter images, yet which are ever less bulky and lighter. Because
of seemingly inherent limitations of cathode ray tubes which
prevent attainment of compact large-screen television receivers,
other approaches, many of them radically different from cathode ray
tubes, have been investigated.
It has been recognized that other avenues of investigation, to be
viable, must potentially lead to display structures capable of
reproducing images having adequate brightness and luminous
efficiency and preferably having acceptable color rendition. A
popular and widely investigated approach has utilized
light-emissive elements arranged in X-Y matrices, selectively
energized by means of row and column selectors and drivers.
Light-emitting diodes, gas discharge devices and liquid crystal
devices have been explored as possible display elements for use in
such matrix-type devices. The utilization of display elements
arranged in an X-Y matrix for row-column selection has imposed its
own set of requirements, including the requirement that the
individual picture elements be capable of individual control
without partial energization of unselected elements.
PRIOR ART
2,868,994 Anderson 3,243,642 Gebel 3,262,010 Kazan 3,271,661
Goodrich et al 3,483,422 Novotny 3,492,523 Smith et al 3,519,870
Jensen 3,600,627 Goede et al 3,622,829 Watanabe 3,646,382 Goede et
al 3,693,004 Sanford 3,725,731 Kazan 3,771,008 Chen et al
OBJECTS OF THE INVENTION
It is a primary object of this invention to provide improved
light-emissive devices especially for use as the light producing
elements in image or alpha-numeric character display apparatus, or
the like, and to provide improved display panels incorporating such
devices.
It is a less general object to provide light-emissive devices
especially for use in television displays which are capable of high
luminous efficiency and brightness, which offer a wide selection in
the color characteristics of the emitted light, and which have a
threshold-switching characteristic useful to achieve element
selection in X-Y matrix television displays.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the invention which are believed to be novel are
set forth with particularity in the appended claims. The invention,
together with further objects and advantages thereof, may best be
understood, however, by reference to the following description
taken in conjunction with the accompanying drawings in which:
FIG. 1 is a highly schematic view of a gas discharge diode of a
type well known in the art;
FIG. 2 illustrates in highly schematic form a low pressure gas cell
containing an electron-multiplier;
FIG. 3 is a highly schematic view of a cathode-luminescent device
constructed in accordance with the principles of this
invention;
FIG. 4 is a fragmentary perspective view of a device similar to the
FIG. 3 device, shown in a more structural, less schematic
representation;
FIG. 5 shows in highly schematic form a television display panel
utilizing cathodo-luminescent devices constructed to implement the
teachings of this invention;
FIG. 6 is a schematic fragmentary perspective view, broken away, of
a display panel representing a preferred mode of execution of the
invention;
FIG. 7 is a sectioned elevational view of the panel shown in FIG.
6, taken along lines 7--7 in FIG. 6; and
FIG. 8 is an enlarged fragmentary sectional view taken along lines
8--8 in FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The principles of this invention are preferably implemented in
apparatus which employs a low pressure gas cell containing an
electron-multiplier which serves as an efficient source of free
electrons and which has a threshold switching capability to enable
mutually exclusive selection of elements in an X-Y matrix of
elements. The free electrons generated in the electron-multiplier
are accelerated in an accelerating stage into impingement with a
cathodo-luminescent phosphor screen. Before discussing the details
of a display panel constructed according to this invention, there
will be discussed certain basic principles underlying and employed
in cathodo-luminescent devices according to this invention.
In a simple gas diode (see FIG. 1), positive gas ions generated in
the gas impinge upon the cathode, releasing secondary electrons.
The electrons are accelerated toward the anode. The probability of
interaction with a gas atom in the intervening space depends upon
the density (pressure) of gas molecules in that space and the
length of the path. When an electron has gained sufficient energy
in falling through the electric field along the cathode-to-anode
path, it can ionize a gas atom, thus freeing an additional electron
and creating a "feedback" ion. The two electrons (the original one
plus the newly formed one) proceed toward the anode, perhaps
creating additional ion/electron pairs on the way. Some ions and
electrons will be lost to the walls. In general, each backwardly
accelerated ion impinging upon the cathode will free an average of
less than one electron -- perhaps as few as 1 electron per 10 ions
impinging. Hence, for a sustained discharge, each electron leaving
the cathode must initiate an avalanche of ion/electron pair
generating collisions such that enough ions are generated on the
average to satisfy wall losses and to generate collectively one new
secondary electrode at the cathode.
Obviously, if the density of gas is not sufficient to allow an
adequate number of collisions along the cathode-to-anode path, a
discharge cannot be maintained. Increasing the path length
increases the probability of a collision at a given pressure.
Raising the voltage difference helps in a marginal situation,
primarily because the electrons will be accelerated to the minimum
ionizing level sooner along the path (thus increasing the effective
path length), and because occasionally more than one electron may
be released per collision. On the other hand, high velocity
electrons may have reduced ionization probability. The net result
is that if a path is too short, for a given gas density, a
self-sustained discharge cannot be maintained even when very high
voltage differences exist in the field-containing space. This
circumstance is classically described by a Paschen curve. This
curve and other principles and details of gas discharge devices and
their operation are described in such works as "Gaseous
Conductors", by James Cobine, Dover Publications (1958).
The term "gas discharge cell" or "gas discharge device" is herein
intended to mean a cell or a device in which the electric fields
differ significantly between the "on" state wherein a plasma is
present and the "off" state wherein no current is flowing. Devices
constructed in accordance with this invention do not have the
described characteristics of a gas discharge device. Rather, they
may be aptly termed electrostatic devices in which the electric
fields established within by application of voltages to its
electrodes are not substantially and abruptly altered by the
presence of ions.
In a conventional gas discharge diode as shown in FIG. 1, the
design relationship between gas pressure "p" and the
cathode-to-anode spacing "d", for minimum operating voltage, is
given to excellent approximation by the Paschen similitude
expression: p .times. d = K, where K is a constant which depends on
cathode material, gas composition and tube geometry (but not tube
size). For usual discharge devices, K is generally equal to about
one-half torr cm.
In the FIG. 1 diode, electrons emitted from the cathode undergo
ionizing collisions in the gas, resulting in an electron
"avalanche" which multiplies the electron current as it approaches
the anode. If the ion-electron secondary emission ratio is 1/x
(typically about 0.1), a gas-electron-avalanche gain of at least x
(where x is typically about 10) must be developed to establish an
electron-ion loop gain of unity. Accordingly, the minimum breakdown
voltage characteristic for a given diode (revealed) by the
well-known Paschen curve) is a measure of the secondary emission
properties of the cathode of the diode, as well as a measure of the
electron-avalanche properties of the gas.
As will be explained in more detail hereinafter, in accordance with
the principles of this invention, an electron-multiplier, as shown
schematically in FIG. 2, is inserted between the cathode and the
region where ions are to be generated. The illustrated FIG. 2
device comprises an envelope 10 containing an ionizable gas such as
hydrogen, helium, neon or other suitable gases or gas mixtures. A
cathode 12 serves as an electron emitter. A plurality of serially
arranged, secondary-electron-emissive dynodes 14, 16, 18, 20, 22
and 24 receive applied voltages ever-increasing in positive
polarity in a direction away from the cathode 12. The voltages are
shown as being provided by a tapped voltage divider 26. A final
anode 28 collects the electrons from the last dynode 24.
Due to collisions between the electrons and the gas atoms within
the envelope 10, positive gas ions 30 are generated. In accordance
with this invention, as will be explained in more detail
hereinafter, the dynodes 14-24 are arranged so as to permit the
ions 30 to be accelerated directly to the cathode 12 to cause the
cathode to emit additional free electrons 32.
For the FIG. 2 device, the Paschen similitude expression takes the
general form:
p.sup.. l.sup.. g = K,
where "l" is the effective length of the ion generation region and
"g" is the gain of the electron-multiplier. The value of K depends
upon the efficiency with which positive ions are transported back
to the cathode and the ion-induced secondary electron emission
coefficient of the cathode. This is true whether or not an
electron-multiplier is included. K also depends upon the electron
velocity in the ion generation region. In appropriately designed
tubes, however, the value of K is not likely to differ greatly in
general magnitude whether a multiplier is present or not. Hence it
may be concluded that if an electron-multiplier of gain g is
interposed, a discharge may be initiated at a pressure which is
approximately l/g lower than if a multiplier is not interposed.
This principle is basic to this invention.
By operating a tube at sufficiently low gas pressure, ionizing
collisions between gas atoms and electrons becomes a negligible
effect so far as scattering of electrons is concerned. Under such
conditions a beam of electrons may be accelerated to high velocity
with no significant energy loss and no concern about initiating an
unwanted self-sustained discharge between the high voltage anode
and lower voltage electrodes in the tube.
FIG. 3 illustrates in highly schematic form a cathodo-luminescent
device containing basic components of devices constructed according
to this invention. The FIG. 3 device 34 is illustrated as
comprising wall means in the form of an envelope 36 (typically
glass) which defines an enclosure containing an ionizable gas such
as helium, hydrogen, neon or other suitable gases or gas mixtures
at a predetermined pressure sufficiently low to preclude
establishment of a gas discharge in the device.
An electron-multiplier 38 located within the enclosure creates at
an output end thereof a source of electrons. The
electron-multiplier 38 includes a cathode 40, which may comprise,
for example, an aluminum, magnesium or nickel strip. The
electron-multiplier 38 is depicted as including a plurality of
discrete dynodes 42, 44, 46, 48, 50 and 52. The dynodes 42-52 may
be composed, for example, of oxidized beryllium-copper alloy,
cesium-antimony alloy, silver-magnesium alloy, oxidized aluminum,
or other suitable materials. The last dynode in the FIG. 3
embodiment (52) and in later-described embodiments is also referred
to herein as the "electron-multiplier anode". As used, this term is
intended to mean the highest voltage dynode in an
electron-multiplier constituting a pair of a light-emissive device
constructed according to this invention, and is not intended to
mean a current-collecting electrode.
As in the FIG. 2 device, the dynodes are adapted to receive
voltages ever-increasing in positive polarity in a direction away
from the cathode 40, which pattern of voltages may be provided by a
voltage divider, as shown at 26 in FIG. 2. This invention
comprehends the use of an electron-multiplier of a type other than
as shown, such as a channel plate multiplier, a Weis mesh
multiplier, or a staggered plate multiplier; the illustrated shaped
dynode structure is preferred however.
The electron-multiplier 38, of whatever form, generates positive
gas ions 54 as a result of collisions between the electrons and gas
atoms within the multiplier. In accordance with this invention, as
will be explained in more detail hereinafter, the dynodes 42-52 are
arranged so as to permit the positive gas ions 54 to be accelerated
to the cathode 40 to cause the cathode to emit additional free
electrons 56. The additional electrons 56 emitted from the cathode
40 as a result of the ion bombardment are in turn multiplied in the
electron-multiplier 38. The electron-multiplier 38 thus constitutes
part of a regenerative electron-ion feedback loop.
Phosphor means in the form of a phosphor screen 58 is disposed at
one end of the enclosure in spaced relation to the output end of
the electron-multiplier 38 for emitting light when bombarded by
high energy electrons. As will become evident as this description
proceeds, the phosphor material may be selected to emit white light
for use in a one-color display device or panel, or may be, for
example, red-emissive, blue-emissive and green-emissive in arrays
of devices designed to form color television pictures or other
color displays. It should be noted that only a small percentage of
the multiplied electron beam is utilized to create positive gas
ions, a very substantial part of the beam being available for
acceleration to the phosphor screen 58.
An accelerating anode 60 is disposed at the phosphor screen 58 and
is adapted to receive a predetermined accelerating voltage which is
substantially higher than the voltage impressed on the last dynode
52 (the electron-multiplier anode) of the electron-multiplier 38.
The accelerating anode 60 draws electrons from the
electron-multiplier when the electron-multiplier is in an active
state and accelerates the electrons to high energies for
impingement upon the phosphor screen 58.
In the illustrated form of the invention, an ion generation region
or stage 62 is provided between the last dynode 52 and the
accelerating anode 60 to provide a maximized electron-gas
interaction probability. Additional field-forming electrodes may be
provided in such a special ion-generating region to optimize the
field characteristics for maximum ion generation. As described
hereinafter with respect to another embodiment of the invention,
ion generation may, alternatively, be accomplished within the
compass of the dynodes 42-52, thus obviating a separate ion
generation region within the device. The provision of a separate
ion generation region improves the efficiency of ion generation and
ion feedback efficiency, but adds to the length of the
cathodo-luminescent device and thus increases the front-to-back
depth of a display panel made up of such devices.
In accordance with this invention, activating means are provided
for selectively causing the loop gain of the electron-multiplier
feedback loop to be less than unity when it is desired to cause the
electron-multiplier to assume an inactive state, or for turning the
electron-multiplier on by causing the said loop gain to be unity or
greater. In the illustrated preferred embodiment, the
electron-multiplier is self-saturating due to space charge and
other effects. Thus when the electron-multiplier is turned on, it
is done so by causing the loop gain to momentarily exceed unity
wherein the electron-multiplier saturates at a predetermined
saturation current level and the gain becomes exactly unity. It is
contemplated that devices may be built, however, which follow the
teachings of this invention but which are not driven to saturation
in the on state.
By way of background, the "loop gain" is taken to be the average
number of electrons ultimately released from the cathode in a
complete cycle by the action of a single electron starting from the
cathode. The loop gain is thus equal to the product of the
following:
1. the gain of the electron-multiplier 38,
2. the gas ionization probability due to a single output
electron,
3. the probability that an ion generated in the ion generation
region will fall back to the cathode, and
4. the secondary-electron-emission coefficient of the cathode upon
ion bombardment.
If the loop gain exceeds unity, the current in the loop builds up
exponentially until some saturation effect such as space charge
alters the electrical fields within the electron-multiplier and
reduces the gain to unity. The loop current then stabilizes at that
level. If the loop gain is caused to fall below unity, the current
exponentially falls towards zero.
Thus in the context of the preferred FIG. 3 self-saturating device,
the device may be bi-stably driven between an off state and an
activated on state by selectively causing the loop gain to be
either less than unity or, alternatively, unity or greater than
unity. In FIG. 3, the device activating means is illustrated as a
switching means for applying to the cathode 40 a positive voltage
of such a value that the electron-multiplier gain drops below that
level necessary to establish a loop gain of unity or greater. To
turn the device on, a cathode voltage is selected which, in
combination with the voltages applied to the dynodes 42-52,
establishes a gain in the multiplier 38 which is adequate to cause
the loop gain of the device to be unity or greater.
It is manifest that by the expedient of a bi-stable switching
mechanism which switches the loop gain between less than unity and
unity or greater, the electron-multiplier 38 can be switched
between off and on states in a highly non-linear fashion.
It is contemplated that cathodo-luminescent devices constructed
according to this invention may be employed as a self-contained
cathodo-luminescent cell. Alternatively, the cells may be arrayed
in a display panel having one output level, that is, a panel which
is not capable of yielding a gray scale, but rather is either fully
on or fully off. An example of a commercially useful panel having
one on level would be an alpha-numeric display panel, or the like,
wherein alpha-numeric characters are displayed at one intensity
level.
It is contemplated however that the invention may be more usefully
employed in applications wherein it is desired to have multiple
light level rendition, that is, wherein it is possible to display a
"gray scale". An example of an application contemplated in which a
gray scale capability is necessary is a black and white or color
television display panel. A television display panel may comprise
an array or matrix of cathodo-luminescent cells according to this
invention, each of which is capable of yielding a luminous output
at any of a selected number of discrete output levels, or in a
continuum of light output levels. To this end, it is desirable that
control means be provided which is responsive to an applied control
voltage for modulating the flow of electrons from the
electron-multiplier 38 to the phosphor screen 58 and thus the
amplitude of the light emitted by the screen. In the illustrated
FIG. 3 embodiment, control electrode means are shown schematically
as taking the form of a control grid 63 flanked by apertured
electrodes 64, 65. The electrodes 64, 65 serve to isolate the
control grid 63 from fields in the electron-multiplier 38 and in
the electron accelerating region of the device. The electrodes 64,
65 may have applied thereto a common voltage which is somewhat
greater than the voltage applied to the last dynode 52. As will
become evident hereinafter, electrodes 64, 65 may comprise
windowed, electrically conductive plates.
It is also deemed to be desirable to provide baffle means between
the electron-multiplier 38 and the accelerating anode 60 for
blocking high energy electrons which might be emitted by the
electron-multiplier 38 and for blocking passage to the cathode 40
of ions which might be generated in the region between the baffle
means and the accelerating anode 60. In the FIG. 3 representation,
baffle means are illustrated in highly schematic form as taking the
form of a secondary-electron-emissive plate 66 having a surface
angled with respect to the axis of the electron-multiplier 38 for
blocking high speed electrons and an ion-blocking plate 68 for
blocking the passage to the cathode 40 of ions generated in the
electron accelerating region. The function of the plates 66, 68
will become more apparent as other, more structural, embodiments
are described hereinafter.
FIG. 14 illustrates, in more structural form than FIG. 3,
cathodo-luminescent devices according to this invention
incorporated in a display panel 69. The panel 69 is illustrated as
being bounded by a rear wall 70 and a faceplate 71. In the panel
71, the cathodes are shown as horizontal cathode strips 72. Five
dynodes, constituting part of an electron-multiplier 74, are
depicted at 76, 78, 80, 82 and 84. Voltages of ever-increasing
potential are supplied to the dynodes 76-84 from a voltage divider
86.
Beam control means are illustrated as comprising a pair of
electrically conductive grid-isolating electrodes 88, 90. Windows
89 are provided for passing the electron beams. Sandwiched between
the electrodes 88, 90 is a control grid 91. The control grid 91 may
take the form of a dielectric support plate 92 containing
conductively metalized apertured grid strips 93. The discrete grid
strips 93 are individually controlled by signals developed in
signal processing and scan control circuitry, represented
schematically at 94.
The FIG. 4 embodiment includes baffle means for blocking the
passage of high energy electrons from the electron-multiplier 74
into the accelerating region of the device and for preventing
feedback of high energy ions to the cathode from the electron
accelerating region of the device. The accelerating region is the
region between the beam control means and the accelerating
electrode, preferably located on the back of the faceplate 71. In
the illustrated FIG. 4 embodiment, the first-described baffling
function is accomplished by a secondary-electron-emissive baffle
plate 95. The latter baffling function is performed by
electron-opaque areas 96 on the grid-isolating plate 90.
As noted above, it is contemplated that cathodo-luminescent devices
constructed according to this invention may be incorporated in an
image display panel such as a television reproducer. FIG. 5 is a
highly schematic perspective view of a television display panel 112
constituting a part of a television receiver. The panel 112
incorporates an X-Y matrix of cathodo-luminescent devices according
to this invention. The display panel 112 is illustrated as
comprising a rear panel wall 114 on which is disposed an array of
horizontally oriented line or strip cathodes 116. At the forward
end of the panel 112 there is provided a transparent faceplate 118
on the back surface of which is disposed an array of sequentially
repetitive, vertically oriented red-emissive, blue-emissive and
green-emissive phosphor strips (not shown).
In FIG. 5 there is illustrated a series of column leads 120 which
lead from column current control circuitry 122 to control means
such as the grid strips 93 in the FIG. 4 embodiment. Row selection
and drive circuitry, shown schematically at 124, along with the
column control circuitry 122, provide a modulated raster scan of
the panel 112. The row selection and drive circuitry 124 and the
column circuitry 122 may be constructed following principles well
known to those skilled in the art.
In operation, the uppermost horizontally extending line of the
cathode-luminescent devices is activated by application of
appropriate potentials on the uppermost cathode 116. A line of
video information which has, for example, been received by an
antenna 126, been processed appropriately in a processor 128 and
been stored in a line storage memory 130, is applied in parallel to
a full row or a portion of a full row of cathodo-luminescent
devices. The video information is applied, as described, to control
grids within the cathodo-luminescent devices. The line of video
information is maintained for a horizontal line display period. In
an allotted retrace time, typically 10 microseconds of the 63
microsecond line time, the first video line is deactivated and the
next successive line or the line after that (depending upon the
means for effecting vertical raster interlace) is energized. A
second line of video information which has been stored in the
memory 130 is applied to the second video line. A complete vertical
scan of the panel to display a full video image is accomplished in
this manner.
If satisfactory luminous intensity is developed in the
cathodo-luminescent devices, the line of stored information can be
displayed during the retrace interval. This mode of operation would
require one, rather than two, video storage memories. If
insufficient intensity is obtained, the video information must be
simultaneously written into one set of storage elements while
another memory controls the display. Vertical commutation may be
accomplished using discrete or multi-phase scanning signals.
FIGS. 6-8 illustrate a color television display panel representing
a preferred embodiment of the principles of this invention. The
FIGS. 6-8 embodiment is illustrated as comprising a faceplate 134
on the rear surface of which is disposed a vertically oriented,
periodically repetitive sequence of red-emissive, blue-emissive and
green-emissive phosphor strips 136. An accelerating anode 138
comprising a layer of electrically conductive material (aluminum,
for example) is deposited over the phosphor strips 136 and is
adapted to receive a relatively high applied voltage for
accelerating the electron beams 139 (to be described) to high
energies for impingement on the phosphor strips 136.
The FIGS. 6-8 panel includes a rear enclosure plate 140 which may
be composed of glass or other suitable material, on which is
deposited a series of horizontally arranged cathode strips 141. The
cathode strips 141 function as cold cathodes and may be composed of
a material such as aluminum or other suitable materials, certain of
which are suggested above. Each cathode strip 141 forms part of an
electron-multiplier which includes a plurality of discrete,
serially arranged, secondary-electron-emissive dynodes 142, 144,
146, 148, 150, 152, 154 and 155 for multiplying electrons emitted
from the cathode strips 141.
In the illustrated preferred FIGS. 6-8 embodiment, the dynodes
142-155 are illustrated as being formed from a series of spaced
pairs of dynode sheets 156, 158. The dynode sheets 156, 158 each
comprise a sheet of electrically conductive material, preferably
beryllium-copper, in which is integrally formed from the sheet
material a matrix of flaps 160. The flaps 160 may be formed by
photo-etching away the flap boundaries and then stamping or
pressing out the flaps. The dynode sheets 156, 158 are preferably
formed similar to each other except that the dynode flaps are
deflected in opposite directions.
A dynode structure in the form of sheets with flaps bent out to
form the secondary-electron-emissive elements and certain other
structural and fabrication principles embodied and revealed in the
FIGS. 6-8 embodiment do not, per se, constitute a part of this
invention but are described and claimed in the referent copending
application Ser. No. 538,486, filed Jan. 3, 1975, assigned to the
assignee of the present invention.
Whereas each of the flaps 160 may be formed to act as a dynode
element for a single horizontal image line element, as shown, it is
preferable the flaps be wider so as to embrace a number of image
line elements -- six for example. By this approach, fabrication of
the flaps is vastly simplified, yet interstices are created between
flaps for increasing the mechanical integrity of the panel
structure.
The pairs of dynode sheets 156, 158 receive applied voltages
ever-increasing in positive polarity in a direction away from the
cathode strips 141, which pattern of voltages may be developed by
the use of voltage divider means as shown at 86 in FIG. 4. As shown
by the electron paths in FIG. 7, the first dynode 142 is not
actually an electron-multiplying element, but rather serves as a
field-forming electrode which deflects the electrons emitted by the
cathode strips to the second dynode 144. The pairs of dynode sheets
156, 158 are held in electrical union but are spaced each from each
adjacent pair of sheets by means of spacers 162 which may, for
example, be composed of glass or other suitable insulating
material. The spacers 162 may be fabricated as the vertically
spaced bridges between panel-wide slit windows (aligned with the
windows in sheets 156, 158) etched in a glass plate. The spacers
are shielded from the electron beams by the dynodes 142, 155 such
that fields due to surface charges on the insulators do not
substantially alter the charged particle trajectories. The spacers
162 serve a number of functions. They control the spacing of the
dynode sheets 156, 158 from neighboring dynode sheets. Secondly,
they provide periodic front-to-back support across the expanse of
the panel. Thirdly, the spacers 162 prevent buckling or bending of
the sheets to prevent electrical short circuiting between adjacent
sheet pairs.
A field-forming output electrode 164, including flaps 165, 166, is
spaced beyond the last dynode sheet 158a and serves to form an
electric field which guides the electron beam through the window
formed between the flaps 165, 166 and into an electron control
section or region of the panel, described below. The FIGS. 6-8
electron-multiplier is illustrated as having the capability of a
gain of approximately 1000. Suitable potentials which may be
applied to the dynodes 142-155 and other electrodes in the panel
are shown in FIG. 7. By fabricating the electron-multiplier dynodes
for the entire panel as flaps bent from electrically conductive
sheets stacked to form a multiple dynode electron-multiplier, very
substantial economies in panel fabrication are effected.
As in the above-described embodiments, the electron-multiplier
serves to establish a source of electrons for acceleration to high
energies for bombarding the phosphor strips 136. Control means for
controlling the flow of electrons from the electron-multiplier to
the phosphor strips 136 is illustrated in the preferred FIGS. 6-8
embodiment as taking the form of a stack of vertically oriented
electrodes 168, 170, 171, 172, 174, 175 and 176. The electrodes
168-176 are divided into three functional groups by vertically
oriented, horizontally spaced insulators 178, 180, which may, for
example, comprise windowed glass plates. The first group of
electrodes, comprising electrode 168, and the third group,
comprising electrodes 174, 175 and 176, receive potentials
effective to isolate the central group of control electrodes 170,
171, 172 from stray fields. See the exemplary potentials
illustrated in FIG. 7. The control electrodes receive a bias
voltage on which is superimposed a modulating signal voltage which
may, as shown in FIG. 7, for the illustrated embodiment, take the
form of a 1900 volt bias modulated by a signal having a maximum
peak-to-peak swing of 40 volts. The control electrodes 170-172 are
insulated from horizontally adjacent control electrodes by
insulators 181.
The electrodes 168, 174, 175 and 176 may be formed as physically
and electrically united conductive plates (metalized glass plates
or sheets of conductive materials, e.g.) having windows for passing
the electron beams. One of such windows is shown in electrons 168
as 184. These electrodes preferably extend horizontally and
vertically across the entire panel.
The insulators 178, 180 are also preferably formed as plates having
beam-passing windows, except, of course, the insulators are formed
of an electrically non-conductive material such as glass. In
outward appearance, the electrodes 168, 174, 175 and 176 and the
insulators 178, 180 closely resemble the grid-isolating plates 188
and 190 constituting part of the FIG. 4 embodiment.
The beam control electrodes 170-172 must be individually
controllable, column-by-column, since signal information to be
imparted on the individual electron beams reaching the phosphor
strips 136 is carried on these electrodes. The three electrodes
170-172 are preferably electrically conductive strips which are
physically and electrically united to act as a single control
element. The electrodes 170-172 also have windows for passing the
electron beams. The electrodes 170-172 thus have the same function
as the grid strips 93 in the FIG. 4 embodiment and a similar
construction, except for having three united electrodes operating
as a single electrode, rather than a single electrode.
In order to insure that each of the triads of tied electrodes
170-172 are each isolated from their horizontally spaced neighbors,
vertically oriented insulators 181 are provided (see FIG. 8). The
insulators 181 preferably extend continuously from the top to the
bottom of the panel and may be composed of glass or other suitable
insulating material.
The beam-passing windows in the electrodes 168, 170-172, 174-176
and insulators 178, 180 are successively vertically offset such
that they aggregatively define angled beam-conducting channels
through the beam control means. The opaque portions 186 of the
electrode 184 act as a baffle which precludes entry into the beam
accelerating region of high speed electrons generated in the
electron-multiplier. Areas such as shown at 182 on the
field-forming electrode 164 act to block the rearward passage of
positive ions which might be generated in the beam acceleration
region. Such baffling may not be necessary in all applications.
The electrodes are spaced from the faceplate 62 by horizontally
oriented, electrically insulative (glass, for example) spacers 198.
The spacers 198 are preferably disposed between every other line
(i.e., between each lace-interlace pair). Alternatively, other
vertical separation distances may be employed, depending on the
size of the panel and other electrical or structural
considerations. In a small panel, simplified support structures may
be employed.
Alternatively, vertically oriented, horizontally separated spacers
may be used to provide the necessary structural rigidity for the
panel. These would preferably be disposed in the location of and in
substitution for every other blue-emissive phosphor strip. Since
the resolving ability of the human eye to blue-wavelength light
images is relatively poor, the elimination of alternate
blue-emissive phosphor strips will have a negligible effect on the
perceived overall picture quality. These spacers 198 serve also to
periodically support the faceplate, preventing bending or breakage
due to atmospheric forces.
In order to precisely control the acceleration field in the
acceleration region, it may be necessary to provide a series of
electrically conductive ribbons, as shown at 202, on the sidewalls
of the spacers 198. The ribbons 202 are adapted to receive a
progression of voltages effective to achieve a satisfactory beam
acceleration characteristic and to preclude interference with the
beam by stray charge-generated fields or the like. An example of a
voltage pattern suitable for application to the ribbons 202 is
shown in FIG. 7.
In accordance with an aspect of this invention, beam deflecting
means may be provided for controlling the vertical position of the
electron beams in the panel, for example to effect interlace of
successive display fields. In the illustrated embodiment, to
deflect the electron beams for interlace purposes, a deflection
voltage, generated, e.g., by deflection signal generator 203, may
be applied to the first ribbons 202a, 202b. See FIG. 6. By
application of an appropriate negative deflection voltage to
ribbons 202a (a few hundred volts, for example) and a complementary
positive deflection voltage to ribbons 202b, the electron beams may
be deflected downward during raster interlace. The interlace
deflection signals must, of course, by synchronized with panel scan
signals and synchronization signals.
FIG. 8 is a view of the control and acccelerating regions of the
device taken along section lines 8--8 in FIG. 6. Electric fields
which are established in the control and accelerating regions cause
the electron beams to be converged or pinched horizontally such
that the ultimate beam cross-sectional configuration upon
impingement with the phosphor strips 136 is horizontally
narrowed.
FIG. 8 illustrates a triad of luminescent devices or cells 204,
206, 208, taken by way of example to be associated, respectively,
with a red signal picture element, a blue signal picture element
and a green signal picture element. In the illustrated FIG. 8
embodiment, by way of example, the control electrodes 170, 171, 172
controlling the red-associated cell 204 carry a signal voltage of
minus 30 volts which is effective to completely shut off the
red-associated electron beam and thus prevent the luminescence of
the red-emissive phosphor strip 136R. The control signal associated
with blue information is applied to the electrodes 170, 171, 172
controlling the blue-associated cell 206 and, in the illustrated
embodiment, is shown as being of such a value (minus 25 volts,
e.g.) as to admit passage of a relatively low intensity electron
beam 139B to the blue-emissive phosphor strip 136B. The green
information is shown as being a signal of greater value positive
than that applied to either the red-associated or blue-associated
cells 204, 206 (minus 20 volts, e.g.), permitting a relatively
intense green-associated electron beam 139G to impinge upon the
green-emissive phosphor strip 136G. Thus the integrated luminous
output of the triad of cells would be perceived as a predominantly
green image somewhat desaturated by blue light.
The invention is not limited to the particular details of
construction of the embodiments depicted and other modifications
and applications are contemplated. For example, rather than using
control electrodes in the acceleration region, such as electrodes
170-172 in FIGS. 6-8 to modulate the flow of electrons to the
phosphor strips 136, control structures of other types in the same
or different regions of the device may be employed to control the
flow of electrons from the electron-multiplier or to control the
output of the electron-multiplier itself. Rather than operating the
electron-multiplier in a mode wherein it is either off or driven to
saturation, the electron-multiplier may be activated in a
non-saturated state at a predetermined intermediate level of
output. If operated in a maximum output mode, it may be possible to
avoid storing all or part of a line interval of information and
display only in the retrace interval. Rather than switching the
electron-multiplier by application of a switching voltage to the
cathode, a switching voltage may be applied to other suitable
electrodes within the device such as one of the dynodes. It is
contemplated that the output beam may be deflected on the phosphor
screen, as by means of suitably structured and excited deflection
electrodes, for purposes other than interlace scanning. Certain
other changes may be made in the above-described apparatus without
departing from the true spirit and scope of the invention herein
involved and it is intended that the subject matter in the above
depiction shall be interpreted as illustrative and not in a
limiting sense.
* * * * *