U.S. patent number 3,566,014 [Application Number 04/631,846] was granted by the patent office on 1971-02-23 for electroluminescent display systems.
This patent grant is currently assigned to Autotelic Industries Limited. Invention is credited to Philip C. Norem.
United States Patent |
3,566,014 |
|
February 23, 1971 |
ELECTROLUMINESCENT DISPLAY SYSTEMS
Abstract
A display system including a display screen having at least two
component panels, one of the panels having a plurality of elements
for emitting light when activated and the other panel having a
layer comprising strips of material between two sets of conductive
electrodes so that when an element of the first panel is caused to
emit light, a potential is applied to conductive elements in the
first and second electrodes of the second panel to activate the
corresponding portion of the layer and transmit light through that
portion whilst preventing light from passing through other portions
of the layer. Circuits are provided to operate the display
panel.
Inventors: |
Philip C. Norem (New York,
NY) |
Assignee: |
Autotelic Industries Limited
(Fort Erie, Ontario)
|
Family
ID: |
24533013 |
Appl.
No.: |
04/631,846 |
Filed: |
April 12, 1967 |
Current U.S.
Class: |
348/803; 313/507;
345/81; 345/4; 315/169.3 |
Current CPC
Class: |
H05B
33/12 (20130101) |
Current International
Class: |
H05B
33/12 (20060101); H04n 009/12 () |
Field of
Search: |
;178/5.4,5.4(8),5.4(EL),7.3(D),7.5(D),6(A),6(LMS) ;315/169(TV)
;313/108(B&D) ;250/213 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Robert L. Richardson
Attorney, Agent or Firm: Jacobi, Davidson & Kleeman
Claims
I claim:
1. A display screen comprising a first multielement component panel
in which each element thereof is capable of emitting light when
selectively activated, and a second component panel adapted to
transmit substantially only that light from a selected element and
to prevent the transmission of light from non-selected elements,
said second component panel comprising a transparent electrode
layer consisting of a plurality of conductive strips, a layer
comprising a plurality of associated strips of photoconductive
material, each extending substantially right across the respective
surface of the second component panel, an opaque conductive layer,
a layer of electroluminescent material, and a segmented electrode
layer.
2. A display screen according to claim 1 wherein the first
component panel comprises an electroluminescent layer, a first set
of conductors on one surface of said layer, a second set of
conductors on the opposite surface of said layer, said first and
second set forming a selection matrix to permit activation of
preselected elements of said electroluminescent material.
3. A display screen according to claim 1 including an optical
filter positioned on one side of said first component panel to
remove a predetermined portion of said light.
4. A display screen according to claim 1 including a third
component panel composed of a plurality of light amplifying
elements each of which is capable of emitting light when
simultaneously excited by light from the respective one of said
elected element in said second component panel and an electric
field.
5. A display screen according to claim 3 wherein the third
component panel comprises a layer of photoconductive material, an
opaque conductive layer, an unbroken layer of electroluminescent
material, and an unbroken electrode layer.
6. A display screen according to claim 4 wherein the second
component panel is a sandwich light amplifier for amplifying light
produced by a fully selected element of the first component panel,
said second component panel having a plurality of diagonally
extending, electrically conductive strips passing across the face
of the panel whereby, in use, only the light from a selected
element in the first component panel is transmitted by the second
component panel.
7. A display screen according to claim 6 wherein said conductive
strips each comprise a series of substantially square-shaped areas,
said areas being each connected to adjacent areas in the same
conductive strip at diagonally opposite corners.
8. A display screen according to claim 6 wherein the second
component panel comprises a glass substrate on which are etched tin
oxide electrodes to constitute a first set of said conductive
strips, a photoconductive layer, an opaque conductive layer, a
layer of electroluminescent material, a second set of tin oxide
electrodes to constitute a second set of said conductive strips,
and a layer of glass, whereby the first and second sets of
conductive strips are parallel and on opposite sides of said layer
of electroluminescent material to permit selective activation of
said strip portions of the electroluminescent material in the
second component panel.
9. A display screen according to claim 1 wherein said
electroluminescent layer is a segmented zinc sulfide layer.
10. A display screen according to claim 1 wherein said opaque
conductive layer is adapted to conduct in one direction only.
11. A display screen for producing a color image comprising a first
multielement component panel in which each element thereof is
capable of emitting light when selectively activated, a second
component panel adapted to transmit substantially only that light
from a selected element and to prevent the transmission of light
from nonselected elements, said second component panel comprising a
transparent electrode layer consisting of a plurality of conductive
strips, a layer comprising a plurality of associated strips of
photoconductive material, an opaque conductive layer, a layer of
electroluminescent material, and a segmented electrode layer, and a
third component panel comprising a transparent continuous electrode
layer, a layer of strips of photoconductive material, an opaque
conductive layer, an electroluminescent layer segmented into
strips, and a segmented electrode layer, adjacent strips of said
electroluminescent layer being capable of producing different
colors on excitation whereby a composite color image may be
produced by the display screen.
12. A display screen according to claim 11 wherein the strips of
electroluminescent material in the electroluminescent layer are
strips of zinc sulfide doped with impurities whereby adjacent
strips produce said different colors.
13. A display screen according to claim 11 wherein the strips of
electroluminescent material in the electroluminescent layer are
strips of zinc sulfide doped with impurities whereby adjacent
strips stimulate phosphorescent elements which, in turn, provide
the required colors.
14. A display system including a display screen comprising a first
multielement component panel including an electroluminescent layer
in which each element thereof is capable of emitting light when
selectively activated and a second component panel adapted to
transmit substantially only that light from a selected element and
to prevent the transmission of light from nonselected elements,
said second component panel comprising a sandwich of materials
capable of transmitting light from said first component panel on
activation of a respective element thereof, said first component
panel including a first set of conductors located on one side of
said layer and a second set of conductors located on the opposite
sides of said layer whereby a selection matrix is formed to
selectively develop an electric potential across any required
element of said first component panel so that light is transmitted
therefrom on activation of the respective element by said
potential, said second component panel comprises a glass substrate
on which are etched tin oxide electrodes to constitute a first set
of said conductive strips, a photoconductive layer, an opaque
conductive layer, a layer of electroluminescent material, a second
set of tin oxide electrodes to constitute a second set of said
conductive strips, and a layer of glass, whereby the first and
second sets of conductive strips are parallel and on opposite sides
of said layer of electroluminescent material to permit selective
activation of said strip portions of the electroluminescent
material in the second component panel, circuit means associated
with said second component panel to select that conductor in its
respective first set and that conductor in its respective second
set corresponding to the required portion of the second component
panel whereby a potential may be applied thereacross to activate
that portion whilst all other portions of the second component
panel are retained inactive and means for applying a potential
across said portion at the instant that light is emitted from the
corresponding element in the first component panel.
15. A system according to claim 14 wherein said circuits include
semiconductor gating circuits.
16. A color image presentation system comprising a composite panel
composed of a first component panel of a luminescent material which
when excited to luminescence emits light radiation, a second
component panel composed of a plurality of elements each of which
will transmit said radiation only when simultaneously excited by
the excitation of said first component panel layer and an electric
field, a third component panel composed of a plurality of light
amplifying elements each of which emits a primary color emission
when simultaneously excited by the emission of said first component
layer and an electric field, said light amplifying elements being
arranged in groups whereby on excitation of respective light
amplifying elements in the same group a different primary color
emission occurs.
Description
This invention relates to information display systems and to
improved display screens therefor.
In radar display consoles and television display sets, high vacuum
cathode ray tubes have been used extensively together with
associated high potentials. Solid state circuits have been
incorporated in many television receiver sets but no satisfactory
substitute is known for the cathode ray tube requiring several
thousand volts of potential for operation.
One proposal for a display system is replace the above-mentioned
cathode ray tube and which does not utilize such high voltages is
disclosed in Canadian Pat. No. 627,213 to Ford E. Williams which
issued on Sept. 12th, 1961. However, the display system and display
screen disclosed in that patent utilizes light amplifying cells
which are made up of continuous, i.e. unbroken, layers and suffered
from the disadvantage that, when it was used, background
illumination was present and detracted from the overall picture
effect which is, of course, a disadvantage.
From one aspect of the present invention, it is an object to
provide an improved display screen in which the above-mentioned
disadvantage is reduced or substantially obviated.
Accordingly, there is provided a display screen comprising a first
multielement component panel in which each element thereof is
capable of emitting light when selectively activated, and a second
component panel adapted to transmit substantially only that light
from a selected element and to prevent the transmission of light
from nonselected elements.
In one construction according to my invention, I arrange for the
second component panel to transmit substantially only that light
from a selected element by constructing at least a part of the
second component panel in strip form.
According to another aspect of the invention, I provide a display
system including a display screen comprising a first multielement
component panel including an electroluminescent layer in which each
element thereof is capable of emitting light when selectively
activated and a second component panel adapted to transmit
substantially only that light from a selected element and to
prevent the transmission of light from nonselected elements, said
second component panel comprising a sandwich of materials capable
of transmitting light from said first component panel on activation
of a respective element thereof, said first component panel
including a first set of conductors located on one side of said
layer and a second set on conductors located on the opposite sides
of said layer whereby a selection matrix is formed to selectively
develop an electric potential across any required element of said
first component panel so that light is transmitted therefrom on
activation of the respective element by said potential, said second
component panel comprises a glass substrate on which are etched tin
oxide electrodes to constitute a first set of said conductive
strips, a photoconductive layer, an opaque conductive layer, a
layer of electroluminescent material, a second set of tin oxide
electrodes to constitute a second set of said conductive strips,
and a layer of glass, whereby the first and second sets of
conductive strips are parallel and on opposite sides of said layer
of electroluminescent material to permit selective activation of
said strip portions of the electroluminescent material in the
second component panel, circuit means associated with said second
component panel to select that conductor in its respective first
set and that conductor in its respective second set corresponding
to the required portion of the second component panel whereby a
potential may be applied thereacross to activate that portion
whilst all other portions of the second component panel are
retained inactive, and means for applying a potential across said
portion at the instant that light is emitted from the corresponding
element in the first component panel.
According to a further aspect of the invention, I provide a color
image presentation system comprising a composite panel composed of
a first component panel of a luminescent material which when
excited to luminescence emits light radiation, a second component
panel composed of a plurality of elements each of which will
transmit said radiation only when simultaneously excited by the
excitation of said first component panel layer and an electric
field, a third component panel composed of a plurality of light
amplifying elements each of which emits a primary color emission
when simultaneously excited by the emission of said first component
layer and an electric field, said light amplifying elements being
arranged in groups whereby an excitation of respective light
amplifying elements in the same group a different primary color
emission occurs.
According to yet another aspect of the invention, I provide a
method of providing a visible display in response to electrical
signals including the steps of providing a display screen
comprising a first multielement component panel in which each
element thereof is capable of emitting light when selectively
activated and a second component panel adapted to transmit
substantially only that light from a selected element and to
prevent the transmission of light from nonselected elements, said
second component panel being composed of a multielement layer
having a first set of conductors on one side and a second set of
conductors on the opposite side thereof whereby on application of a
potential between a conductor in the first set and a conductor in
the second set a respective element of said layer in said second
component panel is activated and if light from said first panel is
simultaneously incident thereon, then light is transmitted by said
element of the second component panel, and including the steps of
causing the respective elements of the first component panel to
emit light incident on corresponding elements of the second
component panel and simultaneously applying potential between
respective conductors of said first and second sets whereby the
respective element of the second component panel transmits the
light incident thereon from the first component panel whilst
preventing other elements of the second component panel from
transmitting a light therethrough.
According to yet a further aspect of the invention, I provide a
method of constructing a component panel for a display screen
including the steps of coating a first sheet of glass with a
transparent conductive electrode layer, then coating said first
sheet with a layer of photoconductive material, utilizing an
etching technique on said first sheet to form said conductive layer
and photoconductive material into strips, coating a second sheet of
glass with a transparent conductive electrode layer, then coating
said second sheet with a layer of photoconductive material,
utilizing an etching technique on said second sheet to form said
conductive layer and photoconductive layer into strips, coating the
strips on said first sheet with a conductive opaque glue, placing
the two glass sheets together with the strips in alignment and
facing each other whereby they adhere together to form said
component panel comprising the first and second sheets with said
strips between them.
The invention will now be described as applicable to a television
system and, by way of example, with reference to the accompanying
drawings in which:
FIG. 1 is a diagrammatic representation of a display screen for a
black and white television receiver according to the present
invention and including a first, second and third component
panel;
FIG. 2 is a cross-sectional view of the first component panel of
FIG. 1 taken on the line II-II of FIG. 4;
FIg. 3 is a cross-sectional view of a first component panel similar
to that shown in FIG. 2 but designed for use in a color television
receiver;
FIG. 4 is a frontal view of the display screen shown in FIG. 1 to
illustrate the crossed grid selection matrix;
FIG. 5 illustrates a horizontal scanning control circuit for use
with a display screen according to the present invention;
FIG. 6 illustrates a vertical scanning control circuit for use with
a display screen according to the present invention;
FIG. 7 is a diagrammatic representation showing the connection of
control circuits to a part of the display screen in a color
television system;
FIG. 8 shows an additional control circuit;
FIG. 9 is a detailed cross-sectional view of a display screen in
accordance with the present invention for use in a color television
system;
FIG. 10 illustrates a modification to the display screen of FIG. 9
for a black and white television system;
FIG. 11 is a diagrammatic representation of the second component
panel according to a further embodiment of the present
invention;
FIG. 12 is an enlarged view of the panel shown in FIG. 11 so as to
illustrate the formation of conductive strips thereon;
FIG. 13 is a cross-sectional view to illustrate the construction of
the component panel of FIG. 11;
FIG. 14 shows a further horizontal scanning control circuit;
FIG. 15 shows a further vertical scanning control circuit;
FIG. 16 is a diagrammatic representation of a control circuit
incorporating a clock pulse counter;
FIG. 17 illustrates a further control circuit;
FIG. 18 shows a further control gating circuit which may be used in
a color television system according to the present invention;
and
FIG. 19 is a diagrammatic representation of certain pulses present
in a part of the described circuits.
In FIG. 1, there is shown a display screen, i.e. panel, in
accordance with the present invention and it will be seen to
comprise three component panels 1, 2 and 3. A cross-sectional view
of the first panel on line II-II of FIG. 4 is shown in FIG. 2 and
the panel will be seen to consist of a glass plate 4 which is
designed to support a strip panel 5 of electroluminescent material
and an associated electrical grid comprising a first set 6 of tin
oxide conducting strips extending in one direction, e.g.
vertically, and a second set 7 of conducting strips extending at
right angles to the first set, e. g. horizontally. The second set 7
of conducting strips is deposited, for example by chemical or other
means, on the glass plate 4 whilst each of the conducting strips in
the first set 6 is deposited on the outer surface of a respective
strip of electroluminescent material 5. In this way, a selection
matrix is provided so that by applying a potential between a
conductive strip of the first set and a conductive strip of the
second set, any particular element of the electroluminescent strip
panel can be selected and activated by the potential
thereacross.
It will be appreciated that when the display screen of FIG. 1 is
used, the first set 6 of conducting strips will extend vertically
and the second set 7 will extend horizontally. Each set may
conveniently include 256 conductive strips. The display screen may
be used alone or may be inserted in an envelope including an
electron gun whereby elements of the first component panel may be
activated by an electron beam instead of, or as well as, by a
selection matrix.
In a television receiver, three information signals are produced
which may be utilized in a display system according to the present
invention. These comprise the vertical synchronizing pulses, the
horizontal synchronizing pulses, and a representation of the signal
amplitude at each point. A color television receiver also provided
information as to the signal amplitudes of the three color signals
and therefore, a display screen for a color television receiver
according to the present invention will utilize the synchronizing
pulses in the same way as one for a black and white television
receiver but, in addition, will utilize the color signal amplitudes
to produce a color image.
FIG. 2 is a cross-sectional view of a first component panel 1
designed for black and white television. For color television, it
is necessary to provide three parallel conducting strips, i.e.
electrodes, for each of the electrodes of the first set 7 of FIG. 1
so that the normal three colour signals from the colour circuits of
the television set may each be fed to a separate conducting
strip.
A component panel 1 for color television is shown in FIG. 3 and is
substantially identical to that shown in FIG. 1 except that three
parallel conductive strips 8, 9 and 10 (i.e. three vertical
electrodes, respectively the red, green and yellow electrodes) are
provided in place of each conductive strip 6 in FIG. 2. However,
the total overall size of the electrodes 8, 9 and 10 will be the
same as that of each vertical electrode 6. The electroluminescent
layers 5 under the electrodes are similarly split as shown in FIG.
3. In use, the three parallel electrodes 8, 9 and 10 are supplied
with the three different signals from the three amplified color
signals derived from the conventional circuits of the color
television receiver.
FIG. 4 is a plan view of the component panel 1 of FIG. 2 to
illustrate the selection matrix. One conductive strip 11 of the
first set is especially indicated as also is one conductive strip
12 of the second set of conductive strips. In this way, it can be
clearly seen how selection occurs of that element of the
electroluminescent layer 5 which is positioned between, and at the
intersection of, the two conductive strips 11 and 12. The first
component panel 1, when operating, generates a moving point of
light as each element is activated and each point is of constant
brightness. Sequential illumination of the elements causes the
point of light to move across the panel.
The second component panel 2 of the display screen is a light
amplifier panel which is arranged to truncate, i.e. cutoff, the
light pulses from the electroluminescent layer in the first
component panel 1 when they would blur the picture. The truncation
is achieved by momentarily disconnecting the second component panel
2 and this is equivalent to a truncation pulse sweeping across the
second component light amplifier panel. This disconnection, i.e.
truncation pulse, is accomplished by interrupting the high voltage
supply to the respective vertical strip of the light amplifier
panel 2 just as the electroluminescent layer elements associated
with, and adjacent, that strip are activated.
A circuit for supplying an activating voltage to an
electroluminescent layer conductive strip of the first set 6 is
shown in FIG. 5 and includes a circuit for interrupting the high
voltage supply to the respective vertical strip of the second
component light amplifier panel. If the electroluminescent layer
is, as mentioned above, provided with 256 vertical conductive
strips in the first set and similarly 256 vertical strips are
provided in the light amplifier, then 256 circuits as shown in FIG.
5 will be required to scan horizontally across the television
screen.
The circuit shown in FIG. 5 may be referred to as the horizontal
scanning circuit and comprises a transistor 200 having associated
resistors 21 and 22 and capacitor 23. A positive voltage of
substantially 80 volts is applied to terminal 24 of the transistor
circuit whilst a control gating voltage may be applied through
capacitor 23 to the base electrode of transistor 200 by means of a
gate circuit 25.
The transistor 200 is normally cutoff and no potential is developed
across resistor 21. However, as soon as the correct combination of
gating inputs is applied to gate circuit 25, transistor 200 is
caused to conduct and a voltage is developed across resistor 21.
This voltage is applied along wire 26 to the respective vertical
conductive strip of the first set 6, for example strip 11 in FIG.
4, and if a voltage is simultaneously applied to a horizontal
conductive strip, such as 12 in FIG. 4, then that element of the
electroluminescent first component panel at their intersection will
be activated so that a spot of light is generated-- the brightness
of the light spot, i.e. light pulse, is the same for each element
of the electroluminescent panel. The other elements of the
electroluminescent panel 1 which are under the strips 11 and 12 are
actually half-selected and, therefore, an unwanted background
illumination may be emitted by those strip elements which are not
actually selected since they are not at the intersection of strips
11 and 12. The way in which at least part of this unwanted
background illumination may be reduced is as follows.
At the same time as a voltage is applied along wire 26, a
truncating voltage is also applied along wire 27 to the electrode
28 of transistor 29 which is normally cutoff. Transistor 29 thus
conducts and the voltage on line 27 is applied through a diode 31
to a particular vertical strip of the second component light
amplifier panel 2 (FIG. 1). That particular vertical strip is the
strip corresponding to that strip of the first component panel
which has just been deactivated. Therefore, for example, wire 26 in
FIG. 5 may be connected to the 12th strip then the output of diode
31 will be applied to the 11th strip. Therefore, unwanted
background illumination from unselected elements, especially the
immediately preceding activated elements, of the electroluminescent
panel is reduced to a minimum. The light from the selected element
of the electroluminescent panel is, therefore, passed without
interference. In this way, a better and more acceptable display can
be obtained, for example in a television receiver.
A vertical scanning circuit for selecting the horizontal conductive
strips of the electroluminescent first component panel 1 (i.e. the
conductive strips of the second set 7 in FIG. 4) is shown in FIG. 6
which consists of a transistor 32 which is supplied with a negative
voltage of substantially 60 volts at terminal 33. A control gating
input may be applied to the base of transistor 32 from a gate 34
through a resistor-capacitor network 35. When transistor 32 is
caused to conduct, the resulting voltage developed across resistor
36 is applied to a horizontal conductive strip, such as 12, of the
second set 7 via lead 37 in FIG. 6 and vertical scan lead 47 in
FIGS. 1 and 4. If the second set 7 includes 256 horizontal
conductive strips, then 256 vertical scanning circuits, as in FIG.
5, will be provided so that selection of any element of the
electroluminescent panel 1 may be made by means of the logic gating
circuits.
In order to build up a complete picture frame, the elements of the
electroluminescent panel are activated in sequence so that a moving
point of light appears to pass over the panel to form a picture
roster-- the shape of the raster will, of course, be determined by
the controlling circuits in a well known manner.
The light pulses which pass through the second component panel then
pass through the third component panel. An optical filter may be
interposed between the second and third component panels or between
the first and second component panels to reduce light from the
decay tail of the electroluminescent material whereby only photons
corresponding to electric dipole transitions (the first portion of
the pulse) are allowed to pass.
The third component panel 3 (FIG. 1) is a light amplifier, capable
of operating at least at frequencies above 20 mc./sec., which is so
designed that by varying its amplification as various segments of
the panel are illuminated, a coherent picture display is produced.
For a black and white television display, this panel may be of
one-piece construction with, preferably, five layers of material.
Referring to FIG. 1, these layers will be a transparent electrode
layer 40, a photoconductive material layer 41, an opaque conductive
layer 46, an electroluminescent material layer 42, and a second
transparent electrode layer 43. In use, a voltage signal of about
150 volts positive is applied between the two transparent
electrodes 40 and 43 by way of wires 44 and 45. This voltage signal
is amplitude-modulated in accordance with the signal strength of
the television signal. It will be appreciated that in some
arrangements, the opaque conductive layer 46 may be omitted.
In the case of a color television receiver, the third component
panel 3 is divided into numerous vertical strips of four layer
amplifiers. These vertical strips are in groups of three
corresponding to the three primary colors of the spectrum so that
activation by light from the electroluminescent panel 1 causes the
selected vertical strip of a selected group to emit the required
primary color.
The circuits required for the display panel are naturally more
complicated since a selection must also be achieved between the
three vertical color strips in each group and, for this purpose,
three appropriate signal connections must be provided for each
group. By feeding these three signals directly to each panel, I
believe that an unnecessarily large electrical load would be placed
on the system and would prevent it working. Therefore, according to
my invention, those vertical color strips which produce red light
are connected to the modulated 20 mc./sec. signal corresponding to
the red portion of the picture. Since this group of vertical colour
strips only contains between 5 to 10 strips too great a load is not
placed on the rest of the circuit.
Similar circuit connections are, of course, made for those groups
of vertical color strips which correspond to the green and yellow
primary colors of the television picture. In this way, the
appropriate signals can be supplied to the color strips of the
third component panel 3 to provide the required color television
picture.
The logic circuits for determining which of the third component
panel's vertical strips are supplied with an activating voltage at
any time may be similar to the circuits for vertical and horizontal
scanning of the electroluminescent panel 1 but may be much simpler
since only 10 to 20 circuits may be required.
FIG. 7 is a diagrammatic representation of the third component
light amplifier panel 3 showing the way in which the three signals
may be applied to the panel to select either the red, green or
yellow-producing vertical color strips of the light amplifier panel
3. The vertical color strips of the panel are actually divided up
into several main groups and, for convenience, one such group 50,
e.g. including 10 to 20 strips, is shown in FIG. 7.
All the vertical color strips capable of producing a red light are
connected to a lead 51, all the vertical color strips capable of
producing a green light are connected to a lead 52 and all the
vertical color strips in the main group 50 capable of producing a
yellow light are connected to a lead 53. Leads 51, 52 and 53 are
connected to the secondary windings 54, 55 and 56 of transformers
57, 58 and 59. Therefore, when a gated input pulse is applied to
one of the primary input terminals 60, 61 or 62, then the
respective red, green or yellow color strips are activated to
produce the corresponding color on the television screen. In this
way, the color television picture is formed.
In FIG. 8, an alternative logic circuit is shown comprising a
transistor 63, whose base electrode may be supplied with a gated
control signal along lead 64 from a gating circuit 65 having a
plurality of inputs 66, at least some of which are provided with
clock pulses from the central control clock pulse generator for the
display system. An input color signal modulating the 20 mc./sec.
carrier is applied to transistor 63 along lead 67. Thus, when
transistor 63 conducts, an output voltage may be obtained across
resistor 68 and fed through capacitor 69 to output terminal 70.
In FIG. 9, there is shown the detailed construction of a display
screen according to the present invention for use in a color
television set. The same reference numerals have been used in FIG.
9 as have been used in FIG. 1 and, therefore, the first component
panel 1 is shown as being made up of vertically extending
electrodes 6 which are, in use, connected to the horizontal
scanning circuits (i.e. the first set 6 of conductive strips
referred to above), a layer 5 of electroluminescent material (for
example, Zn S) and finally, the horizontally extending transparent
electrodes 7 which are in the form of tin oxide (SnO) formed on a
glass plate -- these comprise the second set 7 of conductive strips
referred to above and are, in use, connected to the vertical
scanning circuits.
The second component panel 2 consists of a plane transparent
electrode layer 80 made up of a plurality of conductive strips, an
unbroken layer 81 of photoconductive material either in strip form
or continuous, a, preferably, continuous opaque conductive layer
79, a layer 82 of electroluminescent material, and a segmented
(i.e. strip form) electrode layer 83. The electroluminescent layer
82 may, for example, be a segmented zinc sulfide (Zn S) layer and
preferably, the opaque conductive layer 79 should conduct only in
the vertical direction although it will be appreciated that a layer
which conducts equally in all directions would also be suitable and
probably more readily available.
The third component panel 3 consists of a plane transparent
continuous electrode layer 84, a continuous, unbroken layer 85 of
photoconductive material, an opaque, conductive layer 86, an
electroluminescent segmented layer 87 of zinc sulfide material (Zn
S), and a segmented electrode layer 88. The third component panel 3
is, therefore, similar to the second component panel 2-- the zinc
sulfide layer 87 is, however, much more finely segmented and each
strip is doped with impurities which result in the production of
different colors from adjacent strips. Alternatively, adjacent
strips may stimulate phosphorescent elements which, in turn,
provide the required colors.
For a black and white television receiver, the construction of the
display screen is similar to that shown in FIG. 9 but the third
component panel 3 is as shown in FIG. 10 and is identical in
composition and design to the second component panel 2 of FIG. 9
except that the electroluminescent layer 87A and the electrode
layer 88A are unbroken.
In a second embodiment according to the present invention, it is
proposed that a different orientation of the scanning shutter, i.e.
component panel 2 of FIG. 1, should be used. Instead of using a
constant intensity scan with variable light amplification in the
third stage, i.e. component panel 3 of FIG. 1, a variable intensity
scan with a constant third stage of light amplification is used.
For this purpose, the second component panel 2 of the display
screen is constructed as a sandwich light amplifier whose function
is to suppress light produced by the half-selected areas of the
electroluminescent layer and to provide some amplification for the
light produced by the fully selected element of the
electroluminescent layer. To achieve this, the second component
panel 2 is provided with diagonal, electrically independent strips
running from the lower left portions of the panel to the upper
right portions as shown in FIG. 11. The photoconductive strips each
comprise a series of substantially square-shaped areas, said areas
being each connected to adjacent areas in the same conductive strip
at diagonally opposite corners as shown in FIG. 12. Those strips
which terminate on the right side of the panel are connected by
wires to other strips starting on the left hand side of the panel
at substantially the same height. For example, conductive strip 90
is connected to conductive strip 91 by means of wire 92.
Nonconductive gaps, such as 93 and 94, are provided between the
conductive strips and the arrangement and shape of the conductive
strips is such as to ensure uniform amplification over each square
of electroluminescent element. 95 indicates a portion corresponding
to FIG. 12.
In FIG. 12, there is shown an enlarged view of a portion of the
panel of FIG. 11 and it will be seen that the conductive strips
such as 91 are not absolutely straight but are provided with a
wave-shape.
In FIG. 13, a cross section through the second component panel of
FIG. 11 is shown. The panel consists of a glass substrate 96 on
which are etched tin oxide electrodes 97. The panel also includes a
photoconductive layer 98, an opaque layer 99, a layer of
electroluminescent material 100, tin oxide electrodes 101 and a
layer of glass 102.
In FIG. 11, the external wires connecting the conductive strips of
the second component panel to external circuits are identified as
104. The wires 104 are actually shown opposite gaps between
conductive strips but are, of course, each connected to a
conductive strip, for example that one horizontally to the left in
FIG. 11. Suitable AND circuits and clock circuits are connected to
the wires 104 so as to control the operation of the second
component panel 2 in the required manner. It is arranged that the
conductive strips thereof are turned on one at a time only and in
such a way that that strip which is on at any time crosses directly
over the fully selected element of the electroluminescent layer 5
in component panel 1 of FIG. 1. Thus, the light emitted by that
electroluminescent layer is amplified whilst the unwanted
illumination from the half-selected elements of that
electroluminescent layer are, in contrast, opposite inactivated
portions of the light amplifier second component panel 2 and thus,
any light produced by them is prevented from passing through to
succeeding portions of the display screen and thus the unwanted
background illumination is reduced or substantially obviated.
A useful feature of the second component panel according to the
second embodiment of the present invention and as shown in FIG. 11,
is that the same type of construction can be used no matter the
second component panel is intended to be used in a display screen
for color television or for black and white television. Similarly,
if a display screen intended for black and white television is
converted for operation in a color television system, then the
second component panel as illustrated in FIG. 1 will not require
any alteration.
The electrical connections to the second component panel are
similar to the electrical connections to the electroluminescent
layer in the first component panel 1 as described below. Circuits
substantially identical to the clock circuits used for the
horizontal scanning may be used to switch a 20 mc./sec., 200 volts
oscillation from strip to strip, e.g. from strip 90 to 93, etc. in
FIG. 11. However, instead of being reset to zero at each
synchronization pulse, another square wave pulse is sent to the
counter. This ensures that the particular strip which is receiving
voltage will always pass over a fully selected electroluminescent
element. Resetting to zero takes place only with the occurrence of
a vertical scan synchronization pulse.
For convenience, alternative circuits for use with the first
component panel 1 of FIG. 1 will now be described.
In FIG. 14, there is shown a horizontal scanning circuit. 256 of
these circuits may be required for a television receiver system and
will be each connected to a different one of the first set 6 of
conductive strips shown in FIG. 4. Similarly, FIG. 15 is a
representation of a vertical scanning circuit and, for a television
receiver, 256 of these circuits may well be required, each for
connection to a different one of the second set 7 of conductive
strips in the first component panel illustrated in FIGS. 1 and
4.
The horizontal scanning circuit illustrated in FIG. 14 comprises
semiconductive diodes 110, 111 and 112 connected between respective
terminals 113, 114, 115 and a common line 116 to which is connected
an output terminal 117 and one end of a resistor 118. The other end
of resistor 118 is connected to a terminal 119. In use, the
terminal 113 is the signal input terminal for the scanning circuit,
terminals 114 and 115 are connected to a clock pulse counter
generator which is shown in FIG. 16. Terminal 119 is connected to a
positive voltage supply and in this way, the horizontal scanning
circuit operates substantially as a gate circuit and supplies an
output to the respective conductive strip in the first component
panel 1 via terminal 117 when the correct combination of input
voltages is present at terminals 113, 114 and 115.
The vertical scanning circuit illustrated in FIG. 15 is similar to
the circuit illustrated in FIG. 14 except that the diodes are
reversed and a negative voltage source is used. Semiconductive
diodes 120, 121 and 122 are connected between respective terminals
123, 124, 125 and a common line 126. An output terminal 127 is
connected to line 126 as also is one end of a resistor 128 whose
other end is connected to a terminal 129. Terminal 123 is the
signal input terminal for the vertical scanning circuit, terminals
124 and 125 are connected to a clock pulse counter circuit similar
to the one indicated in FIG. 16 except that it is designed to
operate with opposite polarities. Output terminal 127 is connected
to the respective conductive strip either directly or indirectly
whilst terminal 129 is connected to a negative voltage source
whereby the vertical scanning circuit operates substantially as a
gate circuit in a manner which is well known in the art.
In FIG. 16, there is shown a circuit for producing clock pulses for
supply to the terminals 114 and 115 of the horizontal scanning
circuit shown in FIG. 14. A similar circuit will, of course, be
provided for supplying the clock pulses to terminals 124 and 125 of
the vertical scanning circuit shown in FIG. 15. In FIG 16, an
electronic counter 130 is controlled by a square wave input,
referred to previously, on line 131 so as to provide timing pulses
on a first set of four leads 132, 133, 134 and 135. These timed
pulses are eventually effective to control the supply of the
required clock pulses to the respective terminals 114 of FIG. 14.
Counter 130 also supplies a series of timed pulses on a second set
of four leads 136, 137, 138 and 139. These pulses are eventually
effective to supply the required clock pulses to each of the
terminals 115 of all the 256 horizontal scanning circuits.
The leads 132, 133, 134 and 135 are all connected to the respective
inputs of 16 control circuits such as that identified as 140 in
FIG. 16. Circuit 140 includes a four input gating circuit 141 which
is adapted to receive an input from each of the lines 132, 133, 134
and 135. The output of gating circuit 141 is fed along line 142 to
the base electrode of a transistor 143 whose circuit incorporates a
resistor 144 connected to a positive voltage supply via terminal
145. An output is taken along lead 146 which eventually connects to
16 individual leads, identified generally as 147, which are each
connected to a terminal 114 in a different one of the horizontal
scanning circuits such as shown in FIG. 14.
Since each of the 16 circuits 140 includes 16 output leads 147,
there are thus 256 output leads 147, i.e. one for each of the 256
horizontal circuits of FIG. 14.
To obtain the necessary pulses for application to the terminals 115
in the 256 horizontal scanning circuits, 16 composite circuits 150
(FIG. 16) are provided. These are similar to the circuits 140 and
each of the leads 136, 137, 138 and 139 are connected to the inputs
of all the respective gating circuits 151 in each circuit 150. The
output of the gating circuit 151 is connected along lead 152 to the
base electrode of a transistor 153 whose circuit incorporates a
resistor 154 connected to a terminal 155 which is supplied with a
positive voltage. An output is obtained along lead 156 which is
connected to 16 output leads identified generally as 157. Each of
the output leads 157 is connected to a terminal 115 of a different
one of the horizontal scanning circuits. Thus, since there are 16
leads 157 and sixteen composite circuits 150, there is thus
provided a sufficient number of output leads 157 to supply the
required pulses to all the terminals 115 in the 256 horizontal
scanning circuits.
As mentioned above, circuits similar to FIG. 16 are provided for
the 256 vertical scanning circuits of FIG. 15.
The circuits which are provided for providing voltage inputs to all
the terminals 113 (FIG. 14) of the 256 horizontal scanning circuits
and to terminals 123 (FIG. 15) of the 256 vertical scanning
circuits are determined by an Equation I below.
As will be understood, the final output amplifying stage of
conventional electronic circuitry is usually linear. That is to
say, V out = .alpha. V in, where .alpha. is a numerical constant
expressing the average amplification of the circuit. In the
above-described embodiments of the present invention, it is
desirable to ensure that: so that the nonlinear effect of the
electroluminescent panel can be compensated. .beta. is used as a
numerical constant in the equation with a value (measured in volts)
dependent on the specific electroluminescent material used.
Having regard to Equation I, the input signals for terminals 113
and 123 may be provided by a circuit as shown in FIG. 17 which
provides an approximation to the ideal circuit required to satisfy
Equation I.
Referring to FIG. 17, the circuit consists of a transformer 160
whose primary winding 161 is connected via terminals 162 and 163 to
the output from an output amplifying stage (not shown). The
secondary winding 164 of transformer 160 is center-tapped with the
center tap being connected to earth, i.e. ground, potential.
Opposite outer ends of the secondary winding 164 are connected to
terminals 165 and 166. A positive voltage is supplied to terminal
165 through resistor 167 whilst a negative voltage is applied to
terminal 166 through resistor 168. A first output from the
transformer is taken from terminal 165 through lead 169 to terminal
113 of FIG. 14, whilst a second output is taken from terminal 166
through lead 170 to terminal 123 of FIG. 15.
To provide the necessary clock pulses for the horizontal and
vertical scanning of the display screen, electronic counters are
used comprising eight or nine bistable digital flip-flop circuits
which are interconnected in a well known manner. The input to these
counters is provided by one astable flip-flop circuit for the
vertical scanning circuits and one astable flip-flop circuit for
the horizontal scanning circuits. Timing pulses are thus set to the
vertical scan clock circuit every 70 microseconds, and to the
horizontal scan clock circuit every one half to one quarter
microsecond. The counting circuits themselves are, as mentioned
above, of the type well known in the art and are initialized at
zero, i.e. reset to zero, by the synchronization pulses referred to
above.
The third component panel 3 could well be a simple light amplifier
designed to brighten the image produced by the first two component
panels 1 and 2 of FIG. 1. The light amplifier component panel 3 may
well be similar to the second component panel 2 except that both
tin oxide electrode layers are solid and cover the entire area of
the panel without gaps. As will be clear from the above, and with
reference to FIG. 1, the construction of the third component panel
will be first a transparent conducting electrode layer 40, then a
photoconductive layer 41, an opaque conductive layer 46, followed
by an electroluminescent layer 42 covered by another plane
electrode layer 43 of transparent material. The voltage applied
between the two electrode layers 40 and 43 should preferably be an
alternating voltage of about 150 or 200 volts at a frequency of 20
mc./sec. However, it will be appreciated that the most desireable
voltage and frequency may well be determined by experiment.
It will be appreciated that in some arrangements, the opaque
conductive layer 46 may be omitted. Furthermore, the second
component panel may comprise a glass substrate on which are etched
tin oxide electrodes to constitute a first set of said conductive
strips, a photoconductive layer, an opaque conductive layer, a
layer of electroluminescent material, a second set of tin oxide
electrodes to constitute a second set of said conductive strips,
and a layer of glass, whereby the first and second sets of
conductive strips are parallel and on opposite sides of said layer
of electroluminescent material to permit selective activation of
said strip portions of the electroluminescent material in the
second component panel.
When the display screen is constructed for color television, the
third light amplifier panel will be slightly modified in that its
electroluminescent layer 42 will be divided into vertical strips of
electroluminescent material corresponding to the division in FIG. 3
for the first component panel 1. The vertical strips of
electroluminescent material in component panel 3 will each radiate
that color of the electroluminescent material they are intended to
amplify.
Some additional information will now be given as to the circuits
which could be used to operate the display screen illustrated in
FIGS. 9 and 10. It is to be appreciated that this information may
be considered as an elaboration of the information given above but
that, in certain instances, it will preferably be applicable to an
alternative embodiment as will be clear from the description
below.
The circuits illustrated in FIGS. 14 to 17 are advantageous in that
their cost is relatively low, their design is relatively simple and
the resultant arrangement is of relatively small size when compared
with vacuum tube circuits. Clock pulses from the clock counter
circuitry will be applicable, in a well known manner, to layers 7
and 6 of component panel 1 (FIGS. 9 and 10), and to layers 83 and
85 of component panels 2 and 3 respectively. For layers 7 and 6 of
component panel 1, there is no necessity to provide a corresponding
terminal 113 of FIG. 14, but a terminal 113 will be provided in
respect of layer 83. The voltage applied to that terminal 113 will
be the variable amplification potential having a DC bias whereby it
will vary between ground potential and 200 to 300 volts.
When the display screen of FIG. 9 is constructed for use in a color
television set, it is desirable that a more sophisticated diode
network be used in respect of layer 88 of component panel 3. Such a
diode network is shown in FIG. 18.
Referring to FIG. 18, the diode network comprises a first gating
circuit having diodes 180 and 181 supplied with the required
voltage pulses via terminals 114A and 115A respectively-- these
terminals corresponding to terminals 114 and 115 of FIG. 14. In a
well known manner the diodes 180 and 181 are connected to a common
line 182 which is connected to ground potential through resistor
183. A common lead 184 is taken from lead 182 and one diode of each
of a plurality of subsidiary diode and gating circuits is connected
to lead 184. The first subsidiary diode and gating circuit includes
diodes 185 and 186, diode 185 being supplied with a gating voltage
from the common line 184 and diode 186 being supplied with its
respective gating voltage by way of a terminal 187, which, in use,
is supplied with the respective "red" signal from the color
circuitry of the television receiver. As shown, the diodes 185 and
186 are connected to a common point 188 which is connected to
ground potential through a resistor 189 and is also connected to
output terminal 190. In use, terminal 190 is connected to a "red"
strip of the electroluminescent (SnO) layer of the component panel
1, i.e. to the "red" conductive strip electrode 8 of FIG. 3---- in
practice, it may be connected to several such strips 8.
For the "green" signals in a color television receiver, a similar
subsidiary gate circuit is provided consisting of diodes 191 and
192 associated with terminal 193, resistor 194 and terminal 195--
diode 191 is, of course, also connected to common lead 184. The
"green" signals from the circuits of the television receiver are
supplied to terminal 193 and the output from terminal 195 is
supplied to the conductive strip electrodes made of
electroluminescent material (SnO) material associated with the
color green in the television display, i.e. electrodes 9 in FIG.
3.
A subsidiary gating circuit is similarly provided for the yellow
signals of the color television receiver and this comprises diodes
196 and 197. Diode 196 is connected to the common lead 184 whilst
diode 197 is supplied with the appropriate "yellow" television
signals through terminal 198. The opposite terminals of the diodes
196 and 197 are connected to ground through a common resistor 199
and the output from this subsidiary gate is fed, through terminal
210 to the respective conductive electrode strip or strips 10 (FIG.
3) associated with strips of electroluminescent material (SnO)
designed to produce yellow light on activation.
Whilst in the above description, the color television receiver has
been referred to as supplying "red" signals, "green" signals and
"yellow" signals, it is to be appreciated that the receiver might
well supply "red" signals, "green" signals, and "blue" signals or
any combination of color signals, or number thereof as required in
the design of the television receiver or other display
apparatus.
It is also to be appreciated that the OR gates of the clock
circuits for layer 88 may be replaced by "AND" gate circuits as
required.
With the additional information given above and from a
consideration of the figures, the operation of the display screens
according to the present invention and the associated circuits will
be understood. As mentioned above, a signal is produced in the
first component panel 1 which is of constant amplitude. This is
truncated and modulated in the second component panel 2 and in a
black and white television system, the signal is then amplified in
component panel 3a of FIG. 10. For a color television system, the
signal from the second component panel is amplified separately for
the three colors in the third component panel 3, a different
amplification ratio normally being necessary for each color.
It should be mentioned here that the second component panel would
appear to utilize spatial integration of the time signals which is
achieved by selective amplification. FIG. 19 is a graphical
representation as to how this is achieved. The first, upper, graph
therein represents the input pulse plotted against time, whilst the
second, middle, graph is a representation of the amplification
which is provided. In the third, lower graph, the output pulse is
shown.
It will be appreciated, from the above, that differentiation of the
averaged color signals is a preferable method of accentuating the
variation and contrast of the picture when the differentiated
signal is applied to the strips of layer 83 in FIG. 9. However,
this may be investigated quite simply by experiment.
From the above description, it will be seen that the problem of
unwanted light which was found to be present in a display screen
constructed in accordance with Canadian Pat. No. 627,213 is reduced
or substantially obviated in a display screen in accordance with
the described embodiments of the present invention and the
resulting image is, therefore, clearer. As will be clear from the
above, the unwanted background illumination in the prior art
display screen referred to was due to light being produced by
electroluminescence which had only been half-selected. This light
was, of course, much fainter than that produced by the fully
selected electroluminescent element but there are usually one to
two thousand half-selected elements and only one fully selected
element. Thus, it will be evident that the half-selected elements
may well combine to produce as much as ten times the light from a
fully selected element. It is believed that efforts have been made
in the past to reduce this undesirable result by providing a
nonlinear resistivity layer. However, such a layer must work
extremely well for the total suppression of the unwanted light to
be satisfactory and this is difficult to achieve. Furthermore, such
a layer is difficult to fabricate.
As mentioned above, the display screen according to the present
invention which is shown in FIG. 11 includes a second component
panel 2 which is so constructed that its amplification is selective
and some of the horizontal half-selected elements are suppressed by
simply not amplifying the light produced by the respective
electroluminescent elements. The conductive strips of the second
component panel are, as shown, arranged at 45.degree. across the
panel and instead of all of the strips but one being on at any
given time, it is arranged that all of them are off except one.
This conductive strip is activated and selected by the electronic
circuitry in such a way that it is that strip which crosses over
the fully selected electroluminescent at the instant when it is
activated. Owing to the 45.degree. tilt, it does not cross over any
half-selected elements at all and so only the fully selected
electroluminescent element of the component panel 1 has its light
amplified, the half-selected elements being rendered ineffective by
the nonoperative portions of the amplifier.
As mentioned above, the second component panel 2 (FIG. 1) is a
light amplifier in composition but it functions as a light
suppressor. In fact, it would be satisfactory if that panel
provided no amplification whatsoever but only suppressed the
various forms of unwanted light. With this in mind, the panel is
divided physically in the manner described above. Each section is
activated only when it is required to amplify (or only transmit) a
true light signal as opposed to the various types of noise
encountered in display screens.
It will be apparent that the second component panel may be
activated by means of vertical conductive strips only so as to
activate strips of the panel or by means of vertical and horizontal
strips in the form of a selection matrix to active respective
elements to pass the beam of light from the first component
panel.
A second source of unwanted light noise is due to the
phosphorescent tail of the electroluminescent material. As will be
appreciated, two different components of this phosphorescence are
known although there may be others. The first is blue
phosphorescence while the second component is green
phosphorescence. Both these components are generally undesirable
because the light they make is not produced at the same instant in
time at which they are activated electrically but is produced at a
later time which may be from 5 microseconds to 1 millisecond. By
this time, the final color amplifier has been readjusted to amplify
light from another portion of the picture, this new amplification
having a different amplification factor. The unwanted light
components having a blue or green phosphorescence would also be
amplified by this factor but this would only produce a blurring
effect on the wanted picture. This blurring would be most effective
since it is possible for more than 95 percent of the light to be
either delayed blue or green phosphorescence so that the picture
seen on the display screen becomes 95 percent unwanted blur and
only 5 percent wanted picture signal. Furthermore, this blurring is
additional to the blurring resulting from the above-mentioned
half-selected elements.
A display screen according to the described embodiments of the
present invention overcomes the effect of the above-mentioned two
phosphorescent tails in two ways. The green phosphorescence is the
worst of the two unwanted components because it is produced up to
one-thousandth of a second later than the electrical pulse which
produced it. However, this unwanted component is also the easiest
to eliminate by merely providing a blue filter to remove it from
the optical system--see the blue filters 89 and 90 in FIG. 9. The
unwanted blue light component of phosphorescence is much more
compact (the average delay is often as much as 3 microseconds) but
it is still too slow for a good picture. Its effect is obviated by
switching the light amplifier strip off, i.e. not activating the
second component panel 2, after the arrival of the first half
microsecond of the blue pulse. It has been stated that the
amplification of the strips in the second component panel 2 should
be kept constant. However, in some instances, it may be desirable
to vary the amplification of these strips in the second component
panel as well as varying the amplification of the third component
panel 3 so as not to lose any of the definition obtained--since the
display screen and the circuits are designed to provide the best
possible definition, every effort should be made to retain it. The
precise manner in which the amplification is varied is not critical
but two methods are readily apparent. The first method of varying
the amplification is to make the variation the average of the three
color signals whilst the second method is to make the variation the
differential of that average of the three color signals. At first
sight, it would seem that the second method is preferable.
It will also be appreciated that stray light may well interfere
with the operation of a display screen constructed in accordance
with Canadian Pat. No. 627,213 as it would appear that the three
amplifier panels referred to in that patent can and will interact
with each other. More specifically, the light produced by the red
panel amplifier in that patent illuminates the green light
amplifier in addition to the light emanating from the
electroluminescent panel. If the light from the red panel is
bright, then the green light amplifier will also be caused to be
bright, or alternatively, if the red light is dim, then the green
light amplifier might also be reduced in its illumination. This
sort of feedback within the display screen may well produce effects
which are difficult to describe but it is to be appreciated that
all these effects are not necessarily bad. However, they may well
be unpredictable and, therefore, undesirable. To overcome them in
the described embodiments of the present invention, the parts of
the panels are separated into strips and the strips are placed in
vertical rows across the face of the third component panel three at
a time as indicated above. By using light amplifier panels with
opaque layers, the last trace of interference between the various
color amplifying strips may well be eliminated.
The component panel illustrated in FIG. 11 may be considered as a
scanning shutter light amplifier but even with this amplifier,
there may still be some loss in picture contrast due to the length
of the decay period for the shutter light amplifier (i.e. after it
has been switched off). This could result in some sort of
horizontal averaging, or spatial integration--reference should be
made to FIG. 19 on this point. Once measurements have been made
experimentally on a prototype screen and the parameters of this
type of distortion determined, electronic circuits can be
constructed to perform an inverse operation on the light amplitude
control signal which would, therefore, cancel the distortion. Such
a circuit for performing the inverse operation could be
incorporated into the display system if the distortion is
noticeable. It is to be appreciated that this modification would
only effect the picture amplitude control signal and the circuit
would perform a form of differentiation with respect to time in
order to compensate for the horizontal spatial integration. The
construction of the required circuits should present no difficulty
once the exact form of the horizontal averaging has been
measured.
As mentioned above, the electroluminescent panel may be a zinc
sulfide panel, the first light amplifier, i.e. the first component
panel 1, may be a sandwich of zinc sulfide (Zn S) and cadmium
selenide. The second light amplifier, i. e. component panel 3, may
contain a cadmium selenide layer with vertical strips of zinc
sulfide (Zn S) which has been doped with impurities so that the
strips radiate the required respective colors when energized, i.e.
activated. This type of third component panel 3 is, of course, only
required for a color television receiver system and not for a black
and white television receiver system wherein the second and third
component panels may well be similar or even identical. The third
component panel basically is a light amplifier added to increase
the brightness of the image to acceptable brilliance and, in the
case of a color television receiver system, to convert the black
and white image produced by the first two stages into its color
equivalent.
It will thus be seen that two "solid state" image display panels or
screens have been described wherein each is composed of three
components, and the difference between them is in the manner in
which the image is created. The three components are very similar
between the two systems and, for the black and white versions of
each, are interchangeable. In the first system, the image is
produced by the first component, and electroluminescent screen with
crossed electrodes, and the second component, a segmented light
amplifier, cleans up the image by removing the effect of
half-selected electroluminescent elements. In the second system,
the electroluminescent panel generates a moving spot of light which
is then amplified by the segmented amplifier in a time varying
manner so that an image is produced. The segmented amplifier also
acts to clean up the effect of half-selected elements in the
electroluminescent layer, though this task is less important in the
second configuration. The third component of each system is a light
amplifier added to increase the brightness of the image to
acceptable brilliance and, in the case of color, to convert the
black and white image produced by the first two stages into its
color equivalent.
Both of these panels should be capable of producing well defined
images free of distorting effects from either the
electroluminescent or photoconductive material response times. The
first system gives promise of greater intensity for the same input
energy. The final device may well be a combination of both
approaches.
In the first panel, all three colors receive equal amplification
whilst in the second, the amplification of each color is
different.
As has been explained, a solid stage image display panel according
to a described embodiment of the present invention employs a
segmented light amplifier selectively energized as a defining
filter. Optical filters are used to selectively absorb all but the
light produced most quickly by electrical stimulation of the
electroluminescent material. The adaption of the two stage logic
decoder circuit permits switching a variable voltage to any
vertical or horizontal electrode in the system.
An image of graduated intensity is generated by using the described
segmented light amplifier to suppress light from half-selected
elements of the electroluminescent panel even when the voltage used
to stimulate the panel is variable. Some prior art methods have
relied on giving the electroluminescent a cutoff voltage greater
than half the maximum to be expected, below which the panel will
produce no light. These methods have essentially prohibited the use
of variable stimulation voltages to generate graded intensity
electroluminescent images.
A known type of display screen is described in Canadian Pat. No.
627,213 and the examples of materials and construction given
therein may, where suitable, be used in a display screen
constructed according to the embodiments of the present invention
described above.
One method which could be used to construct the second and third
component panels in a display screen according to the embodiments
described above is to coat a sheet of glass with a transparent
conductive electrode layer, then with a layer of photoconductive
material, then etch out strips of said photoconductive material and
conductive electrode, then take another sheet of glass and coat it
also with a transparent conductive electrode layer and an
electroluminescent layer and using an etching technique to form
strips of electroluminescent material and conductive electrode.
Finally, take one of the two glass sheets, having the respective
strips, and place a conductive, opaque glue on said strips of
material, then place the two glass plates and their strips in
physical contact so that they adhere together with the strips in
alignment on facing each other between the glass sheets.
The described embodiments of the display system using the display
screen alone without an envelope have certain advantages over known
electron beam devices. It has a variety of applications. The
display screen can be constructed to be relatively light in weight,
of reduced size and requiring no high voltage power supply and
could conveniently be used for portable television receivers. The
display being essentially digital would lend itself directly to
computer display problems. In one preferred arrangement, the
elimination of the need for a continuously deflected electron beam
makes this system useable for realizing the arbitrary random and
pseudorandom scanning patterns which have been shown to reduce the
amount of information needed to generate an acceptable continuous
picture.
The present invention has been described in some detail with
reference to a number of particular embodiments. However, it will
be understood that the invention is not limited thereto but the
scope of the invention is defined by the claims.
* * * * *