U.S. patent number 3,786,307 [Application Number 05/265,772] was granted by the patent office on 1974-01-15 for solid state electroluminescent x-y display panels.
This patent grant is currently assigned to Atronics Corporation. Invention is credited to Thomas L. Robinson.
United States Patent |
3,786,307 |
Robinson |
January 15, 1974 |
SOLID STATE ELECTROLUMINESCENT X-Y DISPLAY PANELS
Abstract
One or more EL electrodes in the form of wire mesh strips coated
with electroluminescent phosphor are sandwiched between a rigid,
transparent cover and a sheet of dielectric insulation. This panel
is removably secured above a printed circuit board which carries a
plurality of metal electrode strips that extend transversely to the
EL electrode or electrodes. A plurality of spaced, non-linear
electrical elements are secured between the panel and board to
register with, for example, points where the EL electrode(s)
intersect the printed circuit electrodes. In one embodiment, when
an AC or pulsating voltage is applied across a selected EL
electrode and an intersecting circuit board electrode, the
non-linear element at the intersection of these electrodes conducts
and causes the phosphor coating on the registering portion of the
energized EL electrode to glow with a regulated intensity. If the
non-linear elements are SCR's, the conduction of each SCR may be
controlled by a pair of triggering signals arranged to be applied
selectively as an X and Y coordinate, respectively, for each SCR.
One or more spots, each registering with one of the non-linear
elements, may thus be made to glow at selected points on the face
of the panel, and with different colors, if desired.
Inventors: |
Robinson; Thomas L. (East
Aurora, NY) |
Assignee: |
Atronics Corporation (Buffalo,
NY)
|
Family
ID: |
23011831 |
Appl.
No.: |
05/265,772 |
Filed: |
June 23, 1972 |
Current U.S.
Class: |
345/80;
348/E3.016; 313/505 |
Current CPC
Class: |
H05B
33/12 (20130101); H04N 3/14 (20130101); G09G
3/30 (20130101); G09G 2360/148 (20130101); G09G
2300/0885 (20130101); G09G 2300/08 (20130101) |
Current International
Class: |
G09G
3/30 (20060101); H05B 33/12 (20060101); H04N
3/14 (20060101); H05b 037/00 () |
Field of
Search: |
;313/18B ;315/169R,169TV
;340/166EL |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Saalbach; Herman Karl
Assistant Examiner: Dahl; Lawrence J.
Attorney, Agent or Firm: Shlesinger, Fitzsimmons &
Shlesinger
Claims
Having thus described my invention, what I claim is:
1. An electroluminescent display panel, comprising
a pair of electrodes, one of which is coated on one side with
electroluminescent material,
a layer of dielectric material disposed at the opposite side of
said one electrode,
means for releasably securing said electrodes together with said
layer of dielectric material positioned between and separating said
electrodes, and with the coated side of said one electrode facing
outwardly,
means for applying a pulsating voltage across said electrodes to
excite said electroluminescent material,
a non-linear electrical element removably positioned between said
layer of dielectric material and the other of said two electrodes
with one end of said non-linear element releasably engaging said
dielectric material and with its opposite end releasably and
electrically connected to said other electrode,
said element having an impedance operative normally to prevent
significant current flow between said ends thereof and thereby to
prevent the portion of electroluminescent material registering with
said element from glowing, and
control means operable during application of said pulsating
exciting voltage selectively to reduce said impedance sufficiently
to cause said registering portion of the electro-luminescent
material to glow.
2. An electroluminescent display panel as defined in claim 1,
wherein said control means is operative for increasing and
decreasing, selectively, the impedance of said non-linear element
during application of said exciting voltage thereby to vary the
intensity with which said registering portion of said
electroluminescent material glows.
3. An electroluminescent display panel as defined in claim 1,
wherein
said element comprises a solid state switching device normally
disposed in a non-conductive mode to present a high impedance to
current flow between opposite ends of said element, and
said impedance control means comprises means for selectively
switching said device to its conductive mode, when said exciting
voltage is applied across said electrodes.
4. An electroluminescent display panel as defined in claim 3,
wherein said impedance control means comprises
means for applying a pair of voltage signals to said device,
means responsive to said signals to switch said device from its
non-conductive to its conductive mode, and
means for causing said registering portion of said
electroluminescent material to glow with an intensity and duration
proportionate to the intensity and duration of one of said
signals.
5. An electroluminescent display panel as defined in claim 4,
including means operative, once said device has been switched to
its conductive mode, to maintain said device in the last-named mode
while said exciting voltage is applied across said electrodes.
6. An electroluminescent display panel, comprising
a first electrode having on one side a layer of dielectric
insulation, and on its opposite side a layer of electroluminescent
material,
a substrate having thereon a second electrode,
means for releasably securing said first electrode to said
substrate with said insulation disposed in spaced, confronting
relation to said substrate,
a plurality of spaced, electrically conductive back electrodes
disposed between said insulation and said substrate, and seated
against the underside of said insulation to register with spaced
portions of said electroluminescent material on said first
electrode,
a plurality of non-linear and normally non-conducting electrical
elements connecting said back electrodes to said second
electrode,
means for applying a pulsating voltage across said first and second
electrodes, and
means for selectively switching said elements to conducting modes
selectively to apply the potential on said second electrode to
selected ones of said back electrodes thereby to cause only the
portions of said electro-luminescent material in registry with said
selected back electrodes to excite and glow, when said pulsating
voltage is applied across said first and second electrodes.
7. An electroluminescent display panel as defined in claim 6,
wherein
the last-named means includes means for simultaneously switching a
plurality of said elements to their conductive modes thereby to
cause registering portions of said electroluminescent material to
be excited by said pulsating voltage, and
certain of said registering portions of said material are tinted
differently in color from other portions thereby to cause said
display panel to glow in different colors, when excited.
8. An electroluminescent display panel as defined in claim 6,
including
a section of electrically conductive wire mesh connected to each of
said elements and coated with a layer of electro-luminescent
material and illuminable by said pulsating voltage when the
non-linear element associated therewith is in its conducting mode,
and
a photoconductive member confronting each of said mesh sections and
responsive to the illumination of the electroluminescent material
thereon to maintain the associated element in its conductive mode
until said pulsating voltage is removed from said first and second
electrodes.
9. An electroluminescent display panel as defined in claim 8,
wherein
a diode is connected in parallel with each of said photoconductive
members between said second electrode and one of said wire mesh
sections normally to prevent illumination of the said
electroluminescent material on the last-named section, and said
registering portion of the first-named electro-luminescent
material, and
said switching means includes means for selectively applying a
forward bias to said diodes to switch the latter from
non-conducting to conducting modes thereby to effect selective
illumination of the associated electroluminescent material.
10. An electroluminescent display panel as defined in claim 6,
wherein
said back electrodes are arranged in parallel rows and intersecting
columns beneath said insulation, and
said elements comprise a plurality of solid state switches normally
disposed in non-conducting modes to impede current flow between
said back electrodes and said second electrode, but operative, when
conducting, to cause the voltage on said second electrode to be
applied to the associated back electrode.
11. An electroluminescent display panel as defined in claim 10,
wherein said switching means comprises
a first plurality of terminals corresponding in number to the
number of rows of said back electrodes and arranged at spaced
points along a first axis,
a second plurality of terminals corresponding in number to the
number of columns of said back electrodes and arranged at spaced
points along a second axis transverse to said first axis, and
means connecting each of said switches to at least one of said
terminals to be switched thereby to a conducting mode, when a
predetermined signal appears at said one terminal.
12. An electroluminescent display panel as defined in claim 11,
wherein each of said switches is connected to one each of said
first and second terminals to be switched selectively to a
conducting mode upon the appearance of predetermined signals
simultaneously at the two terminals to which the switch is
connected.
13. An electroluminescent display panel as defined in claim 11,
wherein
a plurality of said first electrodes are secured on said substrate
in parallel rows to register with said rows of said back
electrodes,
said means for applying said pulsating voltage across said first
and second electrodes comprises an AC voltage source and a further
plurality of solid state switches interposed between said first
electrodes and said AC voltage source and normally disposed in a
first mode to block AC current flow between said first and second
electrodes, and
means connecting each of said further switches to another of said
terminals to be switched thereby to a second mode to allow AC
current flow between the last-named electrodes, when a
predetermined signal appears at said other terminal.
14. An electroluminescent display panel as defined in claim 13,
wherein
each of the first-named solid state switches comprises an SCR
element connected between one of said back electrodes and said
second electrode with its gating terminal connected to one of said
second plurality of terminals, and
each of said further plurality of switches is connected to one of
said first plurality of terminals to be controlled thereby.
15. An electroluminescent display panel as defined in claim 13,
wherein
each row of said first electrodes has the electro-luminescent
material thereon tinted a color different from that of the two
adjacent rows thereof, and
said columns of said back electrodes are arranged so the back
electrodes in each column register with rows of said first
electrodes having electroluminescent material of the same color,
and so that the back electrodes of adjacent columns register with
different rows of said first electrodes.
16. An electroluminescent display panel as defined in claim 12,
including light sensitive means operative, when one of said
switches is switched to its conducting mode, to maintain the
last-named switch in its conducting mode after the disappearance of
said predetermined signals from said one each of said first and
second terminals, as long as said pulsating voltage is applied
across said first and second electrodes.
17. An electroluminescent display panel as defined in claim 16,
wherein said light-sensitive means comprises
a further plurality of spaced electrodes secured to the underside
of said insulation adjacent said back electrodes and coated with
electroluminescent material which is caused to glow whenever the
adjacent back electrode is energized by the switching of one of
said switches to its conducting mode, and
a photoconductor interposed between each of said back electrodes
and said second electrode and responsive to the light emitted by
the electroluminescent on the adjacent one of said further
electrodes to conduct and apply the voltage on said second
electrode to the associated back electrode.
18. An electroluminescent display panel comprising
a first plurality of spaced electrodes coated with
electroluminescent material,
a layer of dielectric material on which said electrodes are
mounted,
a substrate disposed below said layer of dielectric material and
having a second plurality of spaced electrodes mounted thereon and
angularly disposed transverse to the first-named electrodes, so
that portions of the second-named electrodes register vertically
with portions of said first-named electrodes,
a plurality of non-linear, electrically-conductive elements
releasably disposed between said substrate and said dielectric
material at the points of registry of the first-named and
second-named electrodes, and each being in contact at one end with
said dielectric material and at its opposite end with one of said
second-named electrodes, and
means for selectively applying to one each of said first and said
second pluralities of electrodes, respectively, and across the
associated conductive element disposed between the registering
portions of the selected electrodes, a pulsating voltage operative
to cause the electroluminescent material on the registering portion
of the selected first-named electrode to excite and glow.
19. An electroluminescent display panel as claimed in claim 18,
wherein said first plurality of electrodes extend at right angles
to said second plurality of electrodes.
20. An electroluminescent display panel as claimed in claim 18,
wherein the electrodes of one of said two pluralities of electrodes
are circular and concentric of one another and the electrodes of
the other of said pluralities of electrodes are arranged radially
of the center of said circular electrodes.
21. An electroluminescent display panel as claimed in claim 18,
wherein
each of said electrically conductive elements includes a solid
state switching device normally disposed in a non-conducting state
to prevent excitation of said electroluminescent material on said
registering portion of the selected first-named electrode, and
said voltage applying means including means for selectively
switching a plurality of said devices to their conducting states to
enable excitation of said electro-luminescent portions thereof by
said pulsating voltage.
22. An electroluminescent display panel comprising
a transparent cover,
an electrically conductive grid, comprising a first plurality of
spaced electrodes, mounted on one side of said cover and coated on
one side with an electroluminescent material facing said cover,
a dielectric sheet disposed on the side of said grid remote from
said cover,
a substrate, having a second plurality of electrodes mounted
thereon in spaced relation,
means releasably securing said cover, grid and sheet on said
substrate with said sheet disposed in spaced relation to said
substrate, and with said second electrodes disposed in angular
relation to said first electrodes,
a plurality of spaced, non-linear and normally non-conducting
electrical elements removably mounted in the space between said
sheet and said substrate, and contacting at opposite ends with said
sheet and the last-named electrodes, respectively,
said elements being disposed between registering portions of said
first and second pluralities of electrodes, and
means for simultaneously applying a pulsating voltage to selected
electrodes in each of said first and second pluralities selectively
to switch the elements between the registering portions of the
selected electrodes to their conducting modes thereby to cause the
portions of the electroluminescent material registering with said
conducting elements to excite and glow.
Description
This invention relates to electroluminescent display panels, and
more particularly to the "X-Y" or "cross-grid" variety in which
electrical inputs are applied coincidentally to electrodes along
selected X and Y axes to produce a spot of light on the panel at
the cross point of the energized electrodes.
Cross-grid display panels have been manufactured with the
intersecting X and Y strip electrodes on a glass panel in the form
of either rectangular or polar coordinates. In such panels one of
the X-Y set of electrodes is made of transparent material in order
to transmit electroluminescent (EL) light, when proper voltage is
applied to the selected pairs of intersecting electrodes. However,
a very high ohmic resistance is present along the narrow,
transparent, strip electrodes, and due to the fragility of the
glass substrate, and to the highly resistive electrodes, the
displays are generally limited in size to areas under one square
foot. Furthermore, fabrication techniques do not lend themselves to
mass production; and hence the unit cost per display is far too
high for commercial use. In addition, the useful display life of
this known type of X-Y panel is short, because the
electroluminescent (EL) phosphors, which are integral parts of this
type of panel, diminish in light output as a function of time and
excitation conditions, and when the light output falls below
acceptable levels, the whole monolithic assembly must be discarded,
even though other parts of the panel may still be in satisfactory
condition.
It is an object of this invention to provide an improved EL display
panel which is capable of being manufactured economically in
substantially larger sizes than heretofore practical.
Another object of this invention is to provide a panel of the type
described which will have a substantially longer operating life
than prior such panels. To this end it is an object also to provide
an improved EL panel that has a removable EL face, which can
readily be replaced when necessary to prolong the useful life of
the panel.
Still another object of this invention is to provide an improved
panel of the type described which can be assembled in various sizes
by using standard stock materials, such as printed circuit board
laminates and pre-tested circuit components.
A further object of the invention is to provide an EL, X-Y
coordinate display which is adjustable in degree as to light
persistence or "memory".
Still another object of the invention is to provide an EL, X-Y
display that can be controlled by low level logic signals.
A further object of this invention is to provide an improved EL
panel of the cross-grid variety, which through the use of high
quality non-linear components, has a high discrimination ratio
between its energized and de-energized light emitting elements or
electrodes.
Another object of this invention is to provide an improved EL panel
of the cross grid variety, which may be constructed with memory
characteristics for maintaining selected cross point electrodes
energized for intervals following removal of enabling signals
therefrom, thus permitting more rapid operation of the panel.
Another object of the invention is to provide a flat panel display
in which the light-emitting surface is a separate part of the
device so that it can easily be assembled to, and disasssembled
from, the parts that make up the total display without detriment to
the display, thereby enabling indefinite extension of the life of
the display;
Still a further object is to provide an improved EL panel capable
of emitting light of various colors and patterns.
Other objects of the invention will be apparent hereinafter from
the specification and from the recital of the appended claims,
particularly when read in conjunction with the accompanying
drawings.
In the drawings:
FIG. 1 is a fragmentary plan view of a rectangular, planar,
electroluminescent display panel made in accordance with one
embodiment of this invention, portions of the panel being cut away
for purposes of illustration:
FIG. 2 is a fragmentary sectional view taken along the line 2--2 in
FIG. 1 looking in the direction of the arrows, and with the
thickness of certain portions of the panel exaggerated for purposes
of illustration;
FIG. 3 is a schematic wiring diagram fragmentarily illustrating one
manner in which the panel of FIGS. 1 and 2 may be wired for
operation.
FIG. 4 is a fragmentary plan view of a modified form of panel, a
polar coordinate display;
FIG. 5 is a fragmentary sectional view taken along the line 5--5 in
FIG. 4 looking in the direction of the arrows;
FIG. 6 is a fragmentary plan view of a display panel made in
accordance with still another embodiment of this invention,
portions of the panel being broken away, and certain of the
electrical components thereof being illustrated schematically;
FIG. 7 is a fragmentary sectional view of this panel taken along
the line 7--7 in FIG. 6 with portions of its electrical components
again being illustrated schematically;
FIG. 8 is a wiring diagram illustrating fragmentarily one manner in
which the electrical components of the panel of FIGS. 6 and 7 may
be wired for operation;
FIG. 9 illustrates fragmentarily a modification of the wiring
diagram shown in FIG. 8;
FIG. 10 is a schematic plan view of still another modification of
this panel, portions of its electrical components again being
illustrated schematically;
FIG. 11 is a fragmentary plan view of a display panel made in
accordance with still another embodiment of this invention,
portions thereof being cut away for purposes of illustration;
FIG. 12 is an enlarged, fragmentary sectional view taken along the
line 12--12 in FIG. 11 looking in the direction of the arrows, part
of the electrical components of the panel being illustrated
schematically;
FIG. 13 is a wiring diagram illustrating fragmentarily one manner
in which the components of the embodiment shown in FIGS. 11 and 12
may be wired for operation;
FIG. 14 is a fragmentary, schematic plan view of a modification of
the display panel of FIG. 11;
FIG. 15 is a diagrammatic view, partly a sectional view of a panel
such as shown in FIG. 14; and
FIG. 16 is a wiring diagram showing the circuit for one of the
display elements of this panel.
The X-Y panel of this invention is based on a unique method of EL
light generation. Light-emitting phosphor is placed on top of a
screen electrode, where a fringe field, formed between the screen
and a bottom electrode, traverse it. The EL phosphor is excited to
luminescence on top of the screen and at its edge openings by the
fringing electrostatic flux field. One main advantage of this
light-emitting system is that the EL portion can be a separate
detachable part of the display assembly by making the bottom
electrode part of another assembly.
Each embodiment of the invention comprises three principal
elements: an electroluminescent light emitting sheet, a plurality
of non-linear electrical components, and a printed circuit board
substrate. The light emitting sheet comprises an electrically
conductive screen or grid fastened beneath a transparent cover on a
layer of dielectric insulating material, and coated with a layer of
electroluminescent phosphor, or the like. This sheet is releasably
secured on the substrate, with the non-linear electrical components
interposed between the sheet and the substrate. The coated grid may
be in the form of a plurality of spaced, parallel strips, which
extend at right angles over spaced, parallel conductors in the
substrate, or radially over concentric, circular conductors in the
substrate. The non-linear components are positioned between the
sheet and substrate to register with the intersections of the EL
electrodes (the phosphor coated grids) and the conductors in the
substrate. When an AC voltage is applied between an EL electrode
and a conductor in the substrate, the non-linear component located
at the intersection of the energized electrodes may be utilized to
control the intensity and duration of light that is emitted from
the registering portion of the phosphor on the energized EL
electrode.
Referring now to the drawings by numerals of reference, and first
to the embodiment illustrated in FIGS. 1 to 3, 20 denotes generally
an electroluminescent display panel comprising a plurality of
spaced, parallel electroluminescent (EL) strips or electrodes 22,
which are fastened to the upper surface of a rectangular sheet 23
of transparent dielectric insulating material. Each EL electrode 22
comprises an electrically conductive screen or grid 24, which is
coated in known manner with a layer 25 of electroluminescent
material, such as phosphor.
At one end (the right end in FIGS. 1 and 2) a marginal portion of
each electrode 22 is secured beneath one of a plurality of solid,
electrically-conductive metal terminals 27, which are secured to
the face of the insulator sheet 23 adjacent its edge. Laminated or
otherwise adhered to this assembly to cover the electrodes 22 is a
transparent stiffener, or cover panel 29, which may be made from a
clear sheet of polycarbonate, such as sold under the trademark
"Lexan", or polymethylacrylate.
This assembly, comprising the insulator 23, the EL electrodes 22
and the transparent cover 29, is releasably secured on a printed
circuit board or substrate 30 by screw and nut combinations 32.
Spacers 33 are interposed between sheet 23 and the substrate 30 to
maintain these members in spaced, parallel relation.
Secured on the upper face of the circuit board 30 are a plurality
of spaced, parallel metal strips or conductors 35, which extend at
right angles to the EL electrodes 22. Removably mounted between
electrodes 35 and the insulator 23 to register with the
intersections of the electrodes 22 and 35 are a plurality of
pellet-shaped, non-linear electrical components 37. Many materials
possess the property of non-linearity when inserted in an
electrical circuit. Some of these materials are silicon carbide,
selenium, copper oxide, cadimium sulfide, cadmium selenide, barium
titanate, strontium titanate, etc. These non-linear materials can
be coin pressed and processed into various shapes, such as pellets,
discs, rods, spheres etc. At its lower end each component 37 has an
electrically-conductive terminal 38, which is seated on one of the
electrodes 35; and at its upper end each component has another
electrically-conductive terminal 39, which is seated against the
underside of the insulator 23.
In the illustrated embodiment, seven EL electrodes 22 are disposed
in intersecting relation to five substrate electrodes 35, thereby
forming thirty-five intersections (FIG. 1), with each of which a
different non-linear component 37 registers. By connecting the EL
electrodes 22 through conductors 27 to the terminals X.sub.1
through X.sub.7, and one end of each of the substrate electrodes 35
to the terminals Y.sub.1 through Y.sub.5 (FIGS. 1 and 2), the exact
location of each component 37 in the panel 20 may be represented by
a specific X and Y coordinate.
As illustrated schematically in FIG. 3, each component 37 may
comprise a non-linear resistive element that is operatively
connected in series between its associated substrate conductor 35,
and the registering, insulated portion 23 of the associated EL
electrode 22. The portion of the EL electrode that registers with a
respective component 37 depends upon the diameter of the upper
electrode 39, which is seated against the dielectric insulator
23.
When a pulsed or alternating voltage (Excitation Voltage in FIG. 3)
is applied between any two X and Y terminals (X.sub.1 and Y.sub.1
in FIG. 3), the component 37 located at the intersection of the two
associated electrodes 22 and 35 will conduct sufficienty to cause a
changing electric field to be generated between its upper terminal
39 and the energized screen electrode 22. Electric field fringe
lines will traverse the EL phosphor particles and excite them to
luminescence, and the portion of the EL electrode that registers
with the terminal 39 on the conducting component 37 located at the
intersection of the two energized electrodes will be caused to
glow, or emit light. The remaining components 37, which are not
located at the intersection of two energized electrodes, will
operate to supress the application of voltage to their terminals 39
at this time, thereby preventing any cross effect or undesirable
illumination of any portions of the electroluminescent material
adjacent to the intersection of the energized electrodes.
It will be apparent that one or more spots on the panel 20, which
register with components 37, may be caused to glow selectively
merely by selective application of an AC or intermittent voltage to
selected pairs of X and Y terminals of the panel. These spots will
remain illuminated, however, only so long as the excitation voltage
is applied to their associated X and Y coordinates.
It should be noted that the EL sheet may be replaced at will, and
so may any non-linear resistor element. Further, the display can be
driven from a computer or integrated circuit logic via a buffer
stage which switches the voltage levels needed to light the EL
display elements.
In the modified display panel shown in FIGS. 4 and 5, wherein like
numerals are employed to denote elements similar to those employed
in the first embodiment, the EL electrodes 22 are positioned
between the insulator 23 and transparent cover 29 in equi-angularly
spaced relation about a screw and nut combination 32 that is
employed to secure the light emitting assembly to a printed circuit
substrate 42. On its upper face, substrate 42 has three, circular,
concentric, radially spaced electrodes 43, which are disposed
coaxially of the center screw 32. Each radial EL electrode 22 is
disposed in registering, intersecting relation to the two outermost
substrate electrodes 43, while only the alternate EL electrodes 22
are disposed in intersecting relation to all three of the substrate
electrodes 43.
As in the first embodiment, non-linear electrodes 37 are positioned
between the insulator 23 and substrate 42 to register with the
intersections of the substrate electrodes 43 and the radial
electrodes 22. The outer ends of the radial electrodes 22 are
connected to different terminals, respectively, denoted in FIG. 4
as terminals X.sub.1, X.sub.2, etc.; while the circular substrate
electrodes 43 are connected to three electrodes Y.sub.1, Y.sub.2
and Y.sub.3, respectively.
Panel 40 thus provides a polar coordinate array, wherein by
application of an AC or pulsating voltage across any two
preselected X and Y terminals, a spot of light may be produced on
the face of the panel at any one of a plurality of different
angularly and radially spaced points about the axis of the central
mounting screw 32. In this embodiment, as in the first embodiment,
a given spot on the panel 40 will be caused to glow only so long as
the AC or pulsating voltage is applied across its associated X and
Y terminals.
If a control element, such as an SCR or a transistor is inserted in
the circuit, the EL light elements may be switched on and off
electronically. When a number of these circuit elements are
arranged in an X-Y array, or in a polar coordinate array, a
multi-function, flat-screen diplay can be achieved by switching
selected EL light elements on and off in accordance with a
programmed signal. Such an arrangement is shown in FIGS. 6 to 8,
wherein like numerals are again employed to denote elements similar
to those incorporated in the preceding embodiments, and where 50
denotes a modified light panel having short term memory
capabilities which enable the intensity and duration of
illumination of selected spots on the panel to be controlled. As in
the embodiment of FIGS. 1 to 3, the light emitting assembly
comprises a plurality of spaced, parallel electrodes 22 that are
sandwiched between the insulator sheet 23 and a transparent cover
29. This assembly is secured by screws 32 and spacers (not
illustrated) to a printed circuit substate 52. Secured on the upper
face of substrate 52 is a ground bus electrode 53 having a base
portion that extends along one side of the substrate, and a
plurality of spaced, laterally projecting, parallel leg portions
53-1, 53-2, 53-3, etc., which extend beneath and at right angles to
the EL electrodes 22. A further plurality of electrodes 54 are
secured on the underside of substrate 52 in parallel relation to
the ground bus projections 53-1, 53-2, 53-3, etc.
Arrayed in spaced rows and columns between insulator 23 and the
substrate 52 are a plurality of non-linear components 57, each of
which contains a silicon controlled rectifier (SCR) of the type
shown schematically in FIGS. 7 and 8. At its lower end, each
component 57 has the cathode of its SCR connected to an
electrically conductive plate 58, which is seated on one of the
ground bus projections 53-1, etc., overlapping one of the substrate
conductors 54. Each component 57 has the anode of its SCR connected
to an electrically conductive plate 59 that is seated against the
underside of the insulator 23. As shown schematically in FIG. 7,
the triggering or gating terminal of each SCR is electrically
connected with the adjacent substate electrode 54 by a probe 56,
which projects through registering openings in the substrate 52 and
the cathode end 58 of each component 57. This construction enables
each component 57 to be removed and replaced, if necessary.
Along one side of the circuit board 52 (lower side in FIG. 6) each
electrode 54 is connected through a resistor R.sub.1 to one of a
plurality of column-selecting terminals Y.sub.1, Y.sub.2, Y.sub.3,
etc. (FIGS. 6 and 8). Each of these terminals is also connected to
the ground bus 53 through a condenser C1, which functions with the
associated resistor R.sub.1 to form a time delay circuit between
the respective column-selecting terminal Y.sub.1 - Y.sub.2, etc.
and the ground bus 53.
Each of the terminals 27 of the EL electrodes 22 of panel 50, only
four of which are illustrated in FIG. 6, is connected by a line 61
to the collector of one of four PNP transistors denoted
schematically at Q.sub.1, Q.sub.2, Q.sub.3 and Q.sub.4,
respectively. The emitters of these transistors are connected by a
line 62 to the ground bus 53. Each collector lead 61 is also
connected through a separate load resistor R.sub.3 and a line 64 to
one side of an AC or pulsating excitation voltage, the opposite
side of which is connected through the line 62 to the ground bus
53. The base of each transistor Q.sub.1, Q.sub.2, Q.sub.3 and
Q.sub.4 is connected through a resistor R.sub.2 and a line 65 to
one of four row-selecting terminals located adjacent one end of the
circuit board 52 and denoted in FIG. 6 at X.sub.1, X.sub.2, X.sub.3
and X.sub.4, respectively. Each row-selecting terminal X.sub.1,
X.sub.2, etc., is also connected to ground through a condenser
C.sub. 2, which is connected between the associated terminal lead
65 and the bus 53.
In operation, one side of an AC or pulsating excitation voltage is
applied through the line 64 and load resistors R.sub.3 to each of
the EL electrodes 22, and to the collector terminals of the
transistors Q.sub.1 through Q.sub.4 ; and the opposite side of this
voltage is applied by line 62 to the ground bus 53, and through
each of the time delay circuits R.sub.2 - C.sub.2 to the base of
each transistor. Unlike the preceding embodiments, the excitation
voltage is connected at all times across all of the EL electrodes
22 of panel 50, so that whenever a positive DC triggering signal is
applied to any one of the column-selecting terminals Y, for example
terminal Y.sub.1, this signal is applied through a resistor R.sub.1
simultaneously to all of the gating terminals 56 of the SCR
components 57 in this column, so that the latter are gated or
caused to conduct, thereby placing their associated anode terminals
59 at approximately ground potential. This tends normally to cause
portions of each of the registering EL electrodes 22 to glow,
thereby to form a column of glowing spots on the face of the panel
50. However, at this time the transistors Q.sub.1, Q.sub.2 etc. are
also conducting, thereby effectively shunting out all of the SCR
components 57 so that virtually all of the excitation voltage
appears across the load resistors R.sub.3. As a result, only a
small fraction of the excitation voltage appears across the EL
electrodes 22, and this voltage is not sufficient to cause the
portions of the EL electrodes 22, that register with the
now-conducting SCR components 57 -- i.e., the components controlled
by terminal Y.sub.1 in the example under consideration, to
glow.
If at this time a sufficient positive DC signal is applied also to
one of the X or row-selecting terminals, then the associated
transistor Q.sub.1, Q.sub.2, etc. is switched to a blocking or
substantially non-conductive state. This will increase the AC
voltage drop across the intersecting X and Y coordinates
sufficiently to cause the registering portion of the EL electrode
to glow. For example, assuming that positive DC signals are applied
simultaneously to the terminals X.sub.1 and Y.sub.1 of panel 50,
the transistor Q.sub.1 is switched to a blocking or non-conductive
mode so that current ceases to flow in its collector-emitter
circuit. Since the SCR component 57 illustrated in the lower right
hand corner of FIG. 8 (in column Y.sub.1) is now conducting,
substantially all of the excitation voltage applied to this
component is dropped across the component and the registering
portion of the associated EL electrode 22, so that the
electroluminescent phosphor on this portion only of this EL
electrode is made to glow, while the remaining EL sectors
registering with the column Y.sub.1 do not glow because their
associated transistors Q.sub.2, Q.sub.3, etc. are still conducting
and shunting the excitation voltage which otherwise would be
applied across their associated SCR components 57.
From the foregoing it will be apparent that, by selectively
applying positive triggering signals to selected X and Y terminals
in the panel 50, selected portions of the grid represented by the
spaced electrodes 57 may be caused to glow in a manner generally
similar to that in the previously described embodiments. However,
panel 50 has the additional advantage that triggering signals
applied to its X and Y terminals can be made to persist for periods
of time after the voltages have been removed from the terminals.
For example, when a positive DC signal is applied to terminal
Y.sub.1, the condenser C.sub.1 immediately charges, so that upon
subsequent removal of the signal, the condenser discharges through
the associated resistor R.sub.1, and thus maintains the triggering
terminal of each SCR 57 in the associated column at a positive
potential for the period of time that it takes for the condenser to
discharge. Similarly, when a positive DC signal is applied to one
of the X terminals, the associated condenser C.sub.2 immediately
charges, and upon subsequent removal of the signal this condenser
maintains the base of the associated transistor Q.sub.1 positive
until the condenser C.sub.2 discharges through the associated
resistor R.sub.2.
This short term memory feature allows panel 50 to be employed in
conjunction with conventional scanning apparatus which may operate,
for example, to keep all of the EL sectors associated with row
X.sub.1 enabled or energized for a predetermined period after a
triggering signal has been removed from terminal X.sub.1. During
this interval the column terminals Y.sub.1, Y.sub.2, etc. may be
scanned or triggered successively. Under these circumstances, of
course, the time delay period provided by the column delay circuits
C.sub.1, R.sub.1 would have to be shorter than that afforded by a
respective row selecting delay circuit R.sub.2, C.sub.2.
Moreover, since the ratio of the light intensity developed at each
spot on the panel 50 is a function of the current flowing through
the associated blocking transistor Q.sub.1, Q.sub.2, Q.sub.3, etc;
the circuitry of panel 50 enables the intensity of the light
emitted at each spot on the panel to be controlled merely by
modulating the control voltage applied to the row-selecting
terminals X.sub.1, X.sub.2, etc. For example, instead of applying
to the terminal X.sub.1 a DC voltage large enough completely to
shut off transistor Q.sub.1, the triggering voltage at X.sub.1 may
be selected merely to reduce the current flow in the
collector-emitter circuit of this transistor, thus to shunt part
only of the excitation voltage across the associated load resistor
R3, and to allow the remainder of this voltage to be applied across
the selected SCR component 57. This causes the registering portion
of the associated EL electrode 22 to glow with an intensity less
than that which would occur if this transistor Q.sub.1 were to be
switched completely to a non-conductive mode.
If control of light intensity for the panel 50 is not desired, its
circuit may be modified, as illustrated fragmentarily in FIG. 9, by
substituting an SCR element 68 for each of the transistors Q.sub.1,
Q.sub.2, Q.sub.3, etc. Each such element 68 has its anode connected
through one of the lines 61 (FIGS. 8 and 9) to the associated load
resistor R.sub.3, and its cathode connected directly through line
62 to the ground bus 53. The gating terminal 69 of each element 68
is connected through a resistor R.sub.2 and condenser C.sub.2 to
ground, and through the same resistor R.sub.2 to one of the
row-selecting terminals X.sub.1, X.sub.2, etc. Thus, whenever a
positive DC signal is applied to one of these terminals, the
associated element 68 is rendered conductive to shunt the
excitation voltage through the SCR 68 to ground, thereby preventing
illumination of any portion of the EL electrode 22 that is
connected by line 61 to the anode of this element. In this
embodiment, then, in order selectively to illuminate a particular
spot on the panel 50, assuming one of its column-selecting
terminals Y is energized, it is necessary also to apply gating or
shunting signals to all but one of the row-selecting terminals
X.
FIG. 10 illustrates schematically still a further modification of
the invention. FIG. 10 shows an array of red, blue and green EL
elements which make up a three-color X-Y display. The physical
arrangement and electrical connections are very similar to those
shown in FIGS. 6, 7 and 8. The difference is that all red elements
are in discreet rows and columns as well as are the blue and green
elements. If it is desired to display a green image alone, signal
voltages are applied only to row and column gates containing the
green EL light-emitting elements. So it is similarly where a
totally blue or a totally red display is desired; the control
signals are applied to the appropriate control gates in the blue
rows and columns or in the red rows and columns. Three separate
display colors may also be presented simultaneously but
independently, one screen in red, one in blue, one in green by
feeding the color signals to corresponding row and column gates in
sequence.
In the embodiment of FIG. 10 the horizontally disposed EL
electrodes 22 are positioned closer to one another; and adjacent
electrodes 22 are tinted differently to produce differently colored
light, when energized. For example, starting with the lowermost
electrode 22, the phosphor layer on the first is tinted blue, the
second red, and the third green. This pattern is repeated, the
fourth row from the bottom being tinted blue, the fifth red, and
the sixth green, etc. Positioned closely adjacent each other
beneath each electrode 22 with their anode plates 59 (broken line
rectangles in FIG. 10) seated against the insulator 23 (not
illustrated) are a plurality of SCR components 57 of the type
employed in panel 50. Also as in panel 50 an AC or pulsating
excitation voltage is connected at one side by load resistors R3
and line 61 to the EL electrodes 22, and through the
collector-emitter circuit of a transistor Q to ground 62, the base
of each of these transistors being connected through a time delay
circuit R.sub.2 -C.sub.2 to ground.
Since in the embodiment of FIG. 10 there are three differently
colored electroluminescent electrodes, the bases of the transistors
Q that control the blue electrodes 22 are connected to the
row-selecting terminals X.sub.B1, X.sub.B2, X.sub.B3 ; the bases of
the transistors controlling the red electrodes 22 are connected
through the row-selecting terminals denoted X.sub.R1, X.sub.R2,
X.sub.R3 ; and the bases of the transistors controlling the green
electrodes 22 are connected to the row-selecting terminals
X.sub.G1, X.sub.G2, etc. The SCR elements 57 of adjacent EL
electrodes 22 are offset horizontally from each other, so that
those beneath every third row of electrodes 22 register vertically
to form columns of vertically spaced components 57. The anodes of
all components 57 in each column thereof are connected to one of a
plurality of column-selecting terminals denoted as Y.sub.G1,
Y.sub.R1, Y.sub.B1, Y.sub.G2 etc. In FIG. 10 each column of
components 57 is illustrated schematically by the representation of
a single SCR element; but it will be understood that there is one
such SCR element for each illuminable spot of light on this
cross-grid type panel. Also, although only one time delay circuit
C.sub.1 - R.sub.1 is illustrated in this figure between the
Y.sub.R5 column-selecting terminal and ground, it will be
understood that one such time delay circuit is interposed between
each column-selecting terminal and ground.
When a positive gating signal is applied to any one of the Y
terminals of the panel of FIG. 10, for example to terminal
Y.sub.G1, the SCR's that register with the right ends of the green
electrodes 22 will conduct, so that if a positive blocking signal
is applied at the same time to one of the row-selecting terminals
X.sub.G1, X.sub.G2, etc., a green spot will be caused to glow at
the right end of the green electrode 22 which registers with the
selective, or energized, X and Y coordinates. Selected red or blue
spots on the panel may be caused to glow in a similar manner by
proper selection of the associated X and Y coordinates; or a
plurality of differently colored spots, or spots all of the same
color, may be caused to glow on the panel by the application of
positive DC signals to selected pairs of the X and Y coordinates of
this panel. Thus, either a solid color or a multi-colored display
can be produced; and by incorporating electroluminescent electrodes
22 having still differently tinted electroluminescent material,
additional colors may be incorporated in the panel, provided that
their associated non-linear components 57 are properly arranged in
separate or offset columns as described above in connection with
the red, blue and green colors.
In any such multi-color display, of course, it is necessary that
each EL element and its associated control component 57 be made
relatively small, so that sufficient resolution can be achieved. In
the embodiment illustrated in FIG. 10, a multi-color display can be
achieved by addressing a group of red, green and blue EL elements
22 in much the same manner as is done in color TV tubes, where the
red, green and blue dots are mixed to produce the colored images.
Moreover, as in the embodiment illustrated in FIGS. 6 to 8, the
time delay circuits (R.sub.2 -C.sub.2) interposed between the X
coordinates and the bases of the associated transistors Q may be
utilized to cause the signals supplied to successive groups of
three of the X coordinates, for example, to persist or remain "on"
for a time duration equal to the time it takes to scan three of the
Y coordinates. Moreover the intensity of each of the color EL
elements 22 may be controlled by the amplitude of the DC signal
applied through the corresponding X terminal to the base of its
associated transistor Q, as described in connection with the
embodiment of FIGS. 6 to 8.
FIGS. 11 to 13 illustrate a modified panel 70 which has latching
memory capabilities, in the sense that once a spot on the panel has
been illuminated it will remain illuminated indefinitely after the
removal of the triggering signals from its associated X and Y
coordinates. This embodiment employs a single, large
electroluminescent screen electrode 22, which is common to all
electronic elements in the components section. The screen is
sandwiched between a layer of insulation 23 and a transparent cover
29 to form a light emitting assembly that is removably secured on a
printed circuit substrate 72 in a manner similar to that of the
preceding embodiments. This light emitting assembly, however,
includes a plurality of small, rectangular, opaque light shields
26, which are secured in intersecting rows and columns beneath the
cover 29, and over the single electro-luminescent electrode 22.
Interposed between the insulator 23 and substrate 72 are a
plurality of rectangular, non-linear electrical components 77,
which also are arranged in intersecting rows and columns so that
each light shield 26 registers vertically with part of one of the
electrodes 77.
On its upper face substrate 72 has a plurality of spaced, parallel
conductors 73, which are connected adjacent one end of panel 70 to
row-selecting terminals X.sub.1, X.sub.2, X.sub.3. A ground bus or
electrode 74 on the underside of substrate 72 has a base portion
that extends along one edge of the substrate, and a plurality of
spaced, parallel leg portions 74-1, 74-2, 74-3, etc., each of which
extends beneath a column of the components 77 in right angular,
intersecting registry with the conductors 73. On its underside
substrate 72 also has a plurality of spaced, parallel conductors
75, which extend beneath components 77 parallel to the legs of bus
74, and which are connected adjacent one side of panel 70 to the
column-selecting terminals Y.sub.1, Y.sub.2, Y.sub.3, etc.
As shown in FIG. 12, each component 77 has in its upper end two
chambers or recesses 78 and 79. Secured to the upper end of each
component 77 over its chamber 78 is a rectangular, electrically
conductive plate or back electrode 81. Secured in a rectangular
notch in one side of each plate 81 to register vertically with part
of the chamber 79 in the associated component 77, and with the
light shield 26 that is positioned above this component, is a small
rectangularly shaped EL electrode 82 similar in construction to the
electrode 22.
Encapsulated in the chamber 78 of each component 77 is an SCR
element (FIG. 12), which has its cathode connected directly to the
associated back electrode 81, and its anode connected through a
photoconductive cell PC to the same back electrode 81. The anode of
each such SCR is also removably connected, for example by a
conventional probe 83 (FIG. 12) that extends through a registering
opening in the substrate 72, to one of the ground bus legs 74-1,
74-2, etc. Its cathode is also connected in series with a diode Ds
and another probe 85 to a row-selecting conductor 73. The gating or
triggering terminal of each of these SCR's is connected, for
example by a conventional probe 84, with one of the
column-selecting conductors 75.
The back electrodes 81 of the EL sheet are isolated areas which
define the shape of the EL light. Each of the back electrodes is a
solid conducting area except for the small screen opening. This
opening is necessary for the EL light from a cell to shine through
the screen onto the photosensitive face of the associated
photoconductive component.
The single, upper EL electrode 22 is connected at one end by a
terminal 27 and line 86 to one side of an AC or pulsating
excitation voltage, which is connected at its opposite side to the
ground bus 74, so that the excitation voltage may be applied at all
times to electrode 22. The excitation current is designed to follow
a series path through the EL cell, and through a parallel connected
photoconductive cell with SCR and thence back to the excitation
source at ground potential. Note that the entire array of
light-emitting elements are connected in parallel across the
excitation voltage source.
Normally, when the SCR's of the components 77 are not conducting,
this excitation voltage is divided between the capacitive reactance
of electrode 22, and the parallel impedance presented by each
non-conducting SCR and its associated photo conductor PC. The photo
conductors and SCR's are selected so that, when no triggering
voltages are applied to the associated X and Y terminals, the
capacitive reactance of electrode 22 is less than the parallel
impedance of the photoconductor PC and the SCR of each component
77, so that substantially all of the exciting voltage is dropped
across the PC-SCR combinations. Therefore, at this time not enough
of the exciting voltage is dropped across the EL cell to cause it
to glow.
When a positive DC gating signal is applied to one or more of the
column-selecting terminals Y, and a negative DC triggering voltage
is applied to a like number of the row-selecting terminals X to
bias the associated series diodes Ds forwardly, then the SCR's
located at the intersections of these energized X and Y terminals
will be gated and will conduct. This has the effect of causing the
associated back electrode 81 of each conducting SCR to be brought
substantially to ground potential, so that the portions of the
upper EL electrode 22 that register with these electrodes 81, and
also the adjacent lower EL electrodes 82, are caused to glow.
Whenever one of the lower EL electrodes 82 is energized and caused
to glow, light therefrom is directed onto the PC element in the
recess 79 of its associated component 77, causing the
photoconducting to increase to a point where resistance of this PC
element falls to a very low value, thereby producing a shunt
circuit across the associated SCR from ground to its back electrode
81. Consequently, when the triggering voltages are removed from the
X and Y terminals of an SCR to switch it back to its blocking or
non-conductive state, the associated back electrode 81 will remain
substantially at ground potential because of the hunting effect of
the adjacent PC element, so that the associated portions of the
upper and lower EL electrodes 22 and 82 continue to glow as long as
the excitation voltage is maintained between the upper electrode
22, and the ground bus 74. This is so because of the low resistance
state of the photoconductive unit which now is the controlling
element. The SCR unit is the first member of the electronic module
to turn "on" the EL cell. After the triggering voltage has been
removed, the EL radiation from an energized electrode 82 activates
the adjacent photoconductor PC to a low resistance state; and the
associated SCR then reverts back to its "off" state of high
resistance. The diodes Ds at this time prevent any unselected EL
cell from receiving excitation voltage from adjacent lit, or
energized cells, on the same row selecting line 73.
In panel 70 opaque masks 26 are employed to prevent any ambient or
external light from entering the recesses 79 in the components 77,
thus assuring that the resistance of each PC element will be
controlled solely by radiation from the adjacent EL element 82. In
this embodiment, therefore, whenever one or more X-Y coordinates or
terminals are energized with the necessary positive and negative
potentials, the selected portions of the upper electrode 22, and
the associated lower EL electrodes 82, will remain "on" or lighted
for as long as the excitation source voltage is maintained.
In order to "erase" the display, the excitation voltage must be
removed. Lack of radiation impinging on the photoconductor will
cause it to change from a low resistance state back to its normal
high resistance state. The speed of the response of the display 70
will depend on the type of the photosensitive element employed.
Some of the materials used for making such elements are: silicon,
germanium, lead sulphide, selenium, cadmium sulphide, cadmium
selenide, etc. These materials may be in the form of
photo-resistors or phototransistors.
The latching display panel 90 of FIGS. 14 to 16 differs from the
latching memory display 70 in FIGS. 11 to 13 in that only diodes Ds
and Dt and photoconductors PC are employed as non-linear elements.
As in panel 70, a single upper screen electrode 22 is common to all
non-linear elements, while the lower (back) screen electrodes 82
are isolated, discreet areas positioned to direct light onto
adjacent photoconductors PC, when illuminated. The dielectric film
23, which contains the upper and lower screen electrodes 22 and 82
is opaque, so as to prevent the ambient light on the upper or
observer's side of panel 90 from triggering the photoconductors PC
into their low-resistance states.
For panel 90 the excitation voltage comprises a unidirectional,
pulsating positive voltage having a wave form generally similar to
that shown in FIGS. 14 to 16. This voltage supply maintains bus 94
at zero potential, and applies the positive signal through line 96
and separate load resistors R.sub.L and lines 92 to each of the Y
or column selecting terminals Y.sub.1, Y.sub.2, Y.sub.3, etc. Each
Y terminal is also connected through a separate coupling diode
D.sub.C to the zero potential bus 94; through series connected
diodes D.sub.T and D.sub.S to one of the row selecting conductors
93 that are connected, respectively, to the row selecting terminals
X.sub.1, X.sub.2, X.sub.3, etc.; and through a photoconductor PC
with one of the back electrodes 82, each such photoconductor PC
being connected in parallel with its associated triggering diode
D.sub.T. As in the case of the preceding embodiments, the
non-linear elements D.sub.S, D.sub.T and PC for each back electrode
82 may be enclosed in a dielectric housing that is removably
mounted as a replaceable component between the insulation layer 23
and a printed circuit board containing the zero bus 94 and X and Y
selecting electrodes 93 and 92, in a manner that will be readily
apparent to one skilled in the art from the above disclosure.
Referring to the equivalent circuit in FIG. 16, when the excitation
source voltage is applied between lines 94 and 96, a
unidirectional, pulsating positive voltage appears across the upper
EL cell 22, and each back EL cell 82 and its associated non-linear
elements. When these EL cells (FIG. 16) are illuminated, the
excitation current flow I.sub.E (electron flow) is in a direction
through the coupling diode D.sub.C, through the parallel connected
photoconductor PC and trigger diode D.sub.T, through the EL cells
and thence to line 96 and the positive excitation terminal. High
value load resistor R.sub.L shunts the EL cells and provides a
discharge path through the low impedance of the photoconductor PC
between pulses.
The trigger current I.sub.t, shown in FIG. 16 by the dotted arrows,
flows from a battery or direct current power supply B through
switch SW.sub.X, through the series blocking diode D.sub.S, through
the trigger diode D.sub.T and thence through the Y-axis switch
SW.sub.Y and back to the trigger voltage source B, thus completing
the circuit.
When excitation voltage is applied across the display terminals,
(and in the absence of triggering voltage), most of the pulsating
excitation voltage appears across the high impedance of the "back
biased" junction of the triggering diode D.sub.T which is in
parallel with the high dark resistance of the photoconductor PC. In
other words, the a.c. impedance of the EL cells is lower than the
impedance of the parallel PC-D.sub.T combination, and due to the
relation, E = IZ., most of the excitation voltage will be developed
across the higher of the two impedances in series. Thus the EL
cells will not light because of insufficient voltage across
them.
If now an X-Y coordinate trigger voltage is applied from source B,
triggering current I.sub.t will flow through triggering diode
D.sub.T in the forward direction, causing the impedance of the
diode to instantaneously drop to a very low value. At this instant
of time, the greater part of the excitation voltage is shifted
across the EL cells, whose a.c. impedance is now higher than that
of the PC-D.sub.T parallel combination. The EL cells therefore emit
light at the chosen X-Y point.
EL light generated at the upper screen shines toward the observer
while EL light from the back screen sector 82 shines on the
photoconductor PC, whose high impedance instantly falls to a very
low value.
When the triggering voltage is removed, the diode D.sub.T reverts
back to its high resistance state, but the EL cell will remain lit
because of its optical coupling to the photoconductor PC, keeping
it in its low-resistance state. The EL cell will remain lit as long
as the excitation voltage is maintained across the display.
The function of the series diode D.sub.s is to prevent any
unselected EL cell from receiving excitation voltage from adjacent
lit cells on the same X-axis feed line. If the diodes D.sub.s were
not there, all cells in the selected X-axis row would light up. In
order to "erase" the display on panel 90, the excitation voltage
must be interrupted for a time long enough for the photoconductors
to change back to their high "dark" resistance. Dark resistance is
defined as the internal impedance of the photoconductor in the
absence of radiation impinging upon it.
From the foregoing it will be apparent that the instant invention
provides a novel EL electroluminescent display panel that is
substantially sturdier and more versatile than prior such
panels.
While the invention has been described in connection with several
different embodiments thereof and various uses therefor, it will be
understood that it is capable of further modification and use, and
this application is intended to cover any embodiment or use of the
invention that comes within the invention and the disclosure or the
limits of the appended claims.
* * * * *