Flat panel display with full color capability

A color capability flat panel display comprised of the combination of two mi-independent linear displays. One of the displays is an active light emitting linear display and the other display is a passive light modulating linear display wherein both of the linear displays are orthogonally aligned on opposite sides of an optically thin dielectric spacer. The active display may be an electroluminescent panel comprised of opaque linear electrodes on the back side and a common transparent electrode that is contiguous with the dielectric spacer on the front side. A plurality of vertical color electroluminescent phosphor stripes are sandwiched between the horizontal electrodes and the transparent electrode. The passive display is comprised of electronic birefringent electro-optical material having linear interdigital surface electrodes thereon sandwiched between two orthogonal dichroic polarizers.

BACKGROUND OF THE INVENTION 
The present invention is in the field of flat panel video type displays 
that have color capability. The present color capable flat panel video 
display may be altered and also used as a black and white display if the 
interdigital surface electrodes are individually connected to the outputs 
of each detector in a column of infrared detectors in an infrared viewing 
device without having additional light amplification. Prior art flat panel 
displays required additional electronics to enhance the incoming video 
signal. 
Presently known flat panel displays require active electronics at every 
picture element (PIXEL) site. An example of this is discussed in an 
article by M. N. Ernstoff of Hughes Aircraft Company, entitled "Liquid 
Crystal Pictorial Display," 1975 presented at SID Technical Meeting at 
Culver City, California on Nov. 6, 1975. Other flat panel displays depend 
on non-linear or thresholding phenomenon, such as an electroluminescent 
cross grid panel. An example of this phenomenon is discussed in an article 
entitled, "Computer Compatible Electroluminescent Techniques for the 
Achievement of Wide Angle Visual Displays," by W. Merel and H. Barkan in 
IEEE Inter. Conv. Record, 1963. 
The present display does not require non-linear thresholding nor 
electronics at every PIXEL site. 
SUMMARY OF THE INVENTION 
The present color display is comprised of four functional components. The 
first functional component is an active, or light emitting, linear 
electroluminescent display having a plurality of opaque horizontal stripe 
electrodes on the back side and a common transparent electrode on the 
front side. The combined horizontal stripe electrodes and the transparent 
electrode are positioned on opposite sides of vertical color phosphor 
columns. The columns may be comprised of alternating red, green, and blue 
colored phosphors. Functionally, when a voltage potential is applied to 
one horizontal electrode, one horizontal line will be illuminated which is 
composed of contiguous color spots, alternating between red, green, and 
blue. The second functional component is a passive, or light modulating, 
linear display, which is based on electronically induced birefringence in 
a material such as lanthanum-modified lead zirconate titanate (PLZT). 
Interdigital vertical surface electrodes may be placed on one, or both 
sides, of this electronically induced birefringence material. This 
material and the electrodes thereon are sandwiched between two orthogonal 
dichroic polarizers. The interdigital vertical electrodes are aligned with 
the vertical color phosphor columns of the electroluminescent display. The 
two dichroic polarizers are aligned respectively at +45.degree. and 
-45.degree. to the electric field produced by voltages applied to the 
interdigital electrodes. Therefore, when these electrodes are activated, 
the passive display will exibit light transmission that is uniform in the 
vertical direction and varying in the horizontal direction preportional to 
the square of the electric field produced by video signal voltages applied 
to the interdigitated electrodes. The third functional component is an 
optically thin dielectric spacer which separates the active and passive 
linear displays. The spacer is required to electrically isolate the two 
linear displays while at the same time maintaining approximate optical 
contact. For small format displays, of say 1 to 3 inches diameter, the 
above requirements may be satisfied by a flat fiber optic plate. However, 
for larger formats where the individual PIXELs are larger than a few 
thousands of an inch a thin glass, or transparent plastic, spacer can be 
used. In practice the electroluminescent linear display is viewed through 
both the spacer and the passive electro-birefringent linear display. At 
any instant in time, one horizontal electrode of the electroluminescent 
display is activated while the voltages on the vertical interdigital 
electrodes vary according to the intensity and color information along the 
corresponding scan line of the input image. By sequencing through all of 
the horizontal striped electrodes, a full frame of color video information 
is displayed. The fourth functional component is the electric circuitry 
necessary to process the incoming information and provide the appropriate 
electrical signals to the electrodes to produce a display as described 
above. The particular nature of the circuitry may vary according to the 
format of the incoming video signal.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present color capable display is comprised of a linear 
electroluminescent (EL) panel as an active light emitting portion and a 
passive portion comprised of electrically induced birefringence material 
having electrodes thereon aligned with various color phosphor columns in 
the EL panel with orthogonal dichroic polarizers positioned on opposite 
sides of the birefringence material. The birefringence material may be a 
lanthanum-modified lead zirconate titanate (PLZT) plate. An example of the 
present color capable flat panel display, depicted as having 5 by 5 
picture elements (PIXELs), is shown in the lone FIGURE. The FIGURE 
illustrates a television type input flat panel display having three color 
capability. However, the concept is not limited to color capability but 
may be used in the monochromatic, or black and white, area wherein the 
serial-to-parallel horizontal scan electronics 80 is not required to 
switch voltages on PLZT electrodes 40 and 41 on an individually 
corresponding color phosphor column to PLZT electrode basis. The EL panel 
is comprised of a phosphor screen 14, preferably a three component P-22 
tri-color phosphor that is sandwiched between a common transparent 
electrode 16 on a front side thereof and a plurality of opaque horizontal 
stripe electrodes 12 on the backside thereof. The vertical scan electronic 
means 10 activates one horizontal stripe electrode 12 one at a time. The 
sequence of activation follows the sequence of horizontal scan lines in 
the incoming video signal into the vertical scan electronic means 10. The 
phosphor in screen 14 is energized by a DC voltage applied to electrodes 
12. However, to maintain long life in the electroluminescent panel, the 
polarity of the activating voltages on electrodes 12 are preferably 
reversed in polarity each full frame to avoid electron drift within the 
phosphor. A typical voltage that is easiest to handle for the device is 30 
DC volts. Since a higher voltage for activation of the phosphor is 
preferable, peak-to-peak voltage of 30 volts negative to 30 volts positive 
may be used. The opaque electrodes 12 may be made from any convenient 
metal such as copper, aluminum, or nickel. The transparent electrode 16 
through which the phosphor light emission passes may be tin oxide, indium 
oxide, or a thin gold layer. The phosphor may be the three-component P-22 
phosphor for red, blue and green color operation, or P-4 phosphor for 
monochrome operation. In the color capable embodiment shown in the FIGURE 
the electroluminescent phosphor is divided into vertical stripes of 
different color phosphor, with each vertical strip 1/3 the horizontal 
width of a PIXEL. The vertical height of each horizontal stripes electrode 
12 is equal to the vertical dimension of a PIXEL. 
The second portion, supported on the opposite side of an optically thin 
dielectric spacer, such as a fiber optic substrate 18 on a thin glass, 
consists of an electronically induced birefrengent material plate 30, such 
as lanthanummodified lead zirconate titanate (PLZT) plate having PLZT 
electrodes 40 and 41 on each side thereof. Each of the PLZT electrodes 40 
and 41 are comprised of a common ground electrode and a plurality of 
interdigital surface electrodes interlaced and parallel with the common 
ground electrode. The PLZT plate 30 and electrodes 40 and 41 are 
sandwiched between the two orthogonal linear dichroic polarizers 20 and 
50, herein noted respectively as first and second dichroic polarizers. The 
polarizers may be Polaroid brand HN-32 sheets. Numeral 40a represents a 
common ground potential to the common electrode of each of the 
interdigital electrodes 40 and 41. All of the other electrodes have 
voltages applied thereto to induce a birefringence in the PLZT plate in 
the area lateral to the common ground electrode and the activated 
electrodes. Numeral 40c represents one common connection between two 
corresponding interdigital surface electrodes 40 and 41 that are both 
aligned with one of said plurality of vertical color phosphor stripes. 
Bracket 40b illustrates all of the corresponding interdigital surface 
electrodes of 40 and 41. Each of the plurality of activated interdigital 
surface electrodes of 40 are aligned with one of the plurality of active 
interdigital surface electrodes of 41 with both optically aligned with one 
of said plurality of vertical color phosphor stripes 14. Since only one 
opaque horizontal stripe electrode is activated at a time, the 
intersection of the horizontal EL electrode and vertical three consecutive 
set of PLZT electrodes defines one image element, or PIXEL. The relative 
voltages applied to each set (of three) of PLZT electrodes determines the 
color and the voltage applied across the EL phosphor stripe determines the 
overall intensity of a PIXEL. All PIXELs along one horizontal line are 
imaged in parallel by activating all the PLZT interdigital electrodes in 
one scan. The horizontal scan is fed from vertical scan electronic means 
10 directly to the serial-to-parallel electronic means 80 along lead 60. 
The information for the horizontal scan line is fed to all the PLZT 
electrodes after being converted to parallel by the serial-to-parallel 
electronic means 80. The sequence of activation of the active display 
horizontal electrodes 12 follows the sequence of horizontal scan lines in 
the incoming video signals. The PLZT electrodes 40 and 41 may be any 
convenient metal, such as gold. The serial-to-parallel electronic means 80 
may be comprised of two CCD shift registers with a sample and hold 
amplifier for each location. In practice, one CCD and its sample and hold 
amplifiers would determine the sequence of activation on each set of PLZT 
electrodes 40 and 41, while the video signal for the next horizontal scan 
line is being fed into the other set of sample and hold amplifiers by the 
other CCD shift register. An example of the video type, or TV type, sweep 
is that all odd numbered lines of, say the 515 lines, are swept and stored 
in the first register and are read out, and are activating the 
interdigital surface electrodes, while the even numbered lines are stored 
in the second register, and are then read out while the next odd numbered 
lines are being entered again, etc. During one frame, of both even and odd 
numbered lines, the common transparent electrode 16 is at ground potential 
and the activated opaque horizontal stripe electrodes 12 at any time is 
electrically positive relative to ground. During the following frame 
electrode 16 is still at ground potential but electrodes 12 are at a 
negative potential relative to ground. The voltages on the interdigital 
surface electrodes will preferably vary from zero potential when there is 
no signal from the serial-to-parallel electronic means 80 to approximately 
6,000 volts per centimeter for full transmission. For a typical format 
having 500 horizontal, full color, PIXELs, and with the distance between 
the interdigital surface electrodes and the common ground electrode of 40 
micrometers, this voltage reduces the signal voltages of from zero volts 
to about 25 DC volts. In the case of larger formats where voltage 
restrictions might become a problem, more than one interdigital surface 
electrode may be used per PIXEL. 
This display may be simplified for monochrome operation. Instead of having 
separate voltages applied to every third of electrodes 40 and 41 for color 
operation, all three electrodes may be switched simultaneously. 
Among the advantages of this device is the capability of the monochrome 
version to operate directly from the output of a modular forward looking 
infrared device (FLIR) with no additional multiplexing required, and 
therefore the serial-to-parallel electronic means 80 eliminated. For this 
operation, the plane of polarization of the device should be rotated 
90.degree. from the three color version described herein above wherein the 
opaque stripe electrodes are now vertical and the interdigital electrodes 
are horizontal. One opaque stripe electrode of the active display is on at 
any instant as in the color display, but the activated scan line 
corresponds to the horizontal position of the infrared detector column in 
the field of view of the FLIR. The output signal from each of the infrared 
detectors in the column is connected directly to a corresponding 
horizontal interdigital surface electrode for controlling the transmission 
of the image from the FLIR. The serial-to-parallel electronic means 80 is 
not needed at all in this monochrome version of operation. Also, by using 
the PLZT plates with the two dischroic polarizers the display may be 
enlarged from the previous displays that have used microchannel plates. 
The enlargement can easily be up to a 12 to 15 inch diameter display from 
the limit of about 3 inches diameter of the microchannel plate display. 
Even though only one preferred color embodiment and a monochromatic 
embodiment are disclosed, obviously other modifications and variations are 
possible in the light of the above teaching. It is the intention, 
therefore, to be limited only as indicated by the scope of the following 
claims.