United States Patent (19)
`Bell et al.
`
`[54] ELECTROLUMINESCENT STORAGE
`DISPLAY WITH IMPROVED INTENSTY
`DRIVER CIRCUITS
`
`75) Inventors: Cynthia S. Bell, Webster; Michael J.
`Gaboury, Spencerport, both of N.Y.
`
`(73) Assignee: Eastman Kodak Company,
`Rochester, N.Y.
`
`21 Appl. No.: 260,103
`
`(22
`
`Filed:
`
`Oct. 20, 1988
`
`51) Int. Cl. ............................................... G09G 3/30
`52 U.S. Cl. .................................... 340/781; 340/782;
`340/767; 340/793
`58 Field of Search ............... 340/781, 782, 762, 767,
`340/793
`
`56
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,696,393 10/1972 McDonald .......................... 340/782
`3,740,570 6/1973 Kaelin et al...
`... 340/793
`4,688,030 8/1987 Uemura et al. ..................... 340/781
`
`Patent Number:
`11
`(45) Date of Patent:
`
`4,996,523
`Feb. 26, 1991
`
`OTHER PUBLICATIONS
`Tannas, "Flat-Panel Displays and CRTs', Van Nos
`trand Reinhold Company, New York, 1985, pp. 16-17.
`Primary Examiner-Alvin E. Oberley
`Attorney, Agent, or Firm-Edward Dugas
`(57)
`ABSTRACT
`In the present invention a matrix array of organic elec
`troluminescent storage display elements along with row
`and column selection circuitry are used to select the
`particular display elements within the matrix to be illu
`minated. Interposed between the column and row selec
`tion electronics are a plurality of memory cells receiv
`ing as inputs bit values that correspond to the desired
`intensity requested from a display element. The mem
`ory cells output activation signals which drive corre
`sponding MOS switches each of which in turn is paral
`lel connected as part of a current driver source feeding
`a single display element. Activation of one or more of
`the MOS switches provides a controlled amount of
`current to be applied to the display element to in turn
`provide a related amount of light from the display ele
`net.
`
`7 Claims, 2 Drawing Sheets
`
`
`
`ROW
`
`
`
`n BIT
`COLUMN
`INPUT
`
`
`
`M
`
`m
`
`22n-3
`
`HTC, Exhibit 1015
`
`

`

`U.S. Patent
`
`Feb. 26, 1991
`
`Sheet 1 of 2
`
`4,996,523.
`
`BRIGHTNESS CONTROL
`
`A/G. /
`
`CONTROL
`LOGIC
`
`/O
`
`7
`
`as
`
`a
`
`/2
`- - - -
`COLUMN DATA REGISTER
`---
`--
`DISPLAY INPUT/READOUT LOGIC
`
`SERAL
`OUT
`
`ano
`
`/7
`
`/3
`
`
`
`
`
`MEMORY
`CELL
`
`SYSTEM CLK
`PXEL CLK
`LINE CLK
`FRAMERs
`DATA IN
`N/OUT
`it PXEL
`
`TO AVG.
`
`ROW
`STROBE
`REGISTER
`
`/6
`
`
`
`ROW
`
`in BIT
`COLUMN
`INPUT
`
`HTC, Exhibit 1015
`
`

`

`U.S. Patent
`
`Feb. 26, 1991
`
`Sheet 2 of 2
`
`4,996,523
`
`"
`
`22n
`146
`
`TO MOS
`DRIVER
`24
`
`
`
`TO MOS
`DRVER
`24
`
`HTC, Exhibit 1015
`
`

`

`10
`
`15
`
`30
`
`1.
`
`ELECTROLUMNESCENT STORAGE DISPLAY
`WITH IMPROVED INTENSTY DRIVER
`CIRCUITS
`
`4,996,523
`2
`trols the current flowing to the pixel element and in turn
`the intensity of the light generated by the pixel element.
`The memory driver circuit for each pixel element thus
`acts as a memory cell, a D/A converter, and as an elec
`tronic switch for controlling the current supplied to the
`pixel element. This particular driver configuration al
`lows for a continuous, static current to be driven
`through the pixel element for each brightness level in
`response to a binary number. In turn, this reduces the
`peak drive current required to ligh the pixel elements
`and indirectly reduces the voltage and the power con
`sumption levels for a matrix display incorporating the
`improved intensity drivers.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram illustrating the arrangement
`of an addressable matrix display incorporating the im
`proved driver circuits.
`FIG. 2 is a block circuit diagram of an improved
`driver circuit of the type used in FIG. 1.
`FIG. 3 is a transistor level schematic of a memory cell
`that may be used as a memory cell of a FIG. 2.
`FIG. 4 is a transistor level schematic of a memory cell
`which also may be used as a memory cell of FIG. 2.
`FIG. 5 is a drawing of the layers of one type of elec
`troluminescent device that can be used as the pixel
`element in a matrix of such elements.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`In FIG. 1, a control logic circuit 10 receives incom
`ing data (DATA IN) and other interface timing signals.
`The control logic synchronizes the incoming data with
`the signals PIXEL CLK, LINE CLK, and FRAME
`RST as is standard procedure. A SYSTEM CLK signal
`provides a high speed clock for controller internal tim
`ing. An IN/OUT line allows data to be read in and out
`of the memory storage. This mode is also useful in auto
`mating the testing of the display circuitry. The
`#PIXEL TO AVG. signal allows data from sources of
`varying resolution to be displayed. Normally, the data
`would be subsampled or otherwise pre-processed exter
`nal to the display system. This feature allows the data to
`be averaged while it is incoming direct from the data
`source. A BRIGHTNESS CONTROL allows for an
`adjustment of the display brightness level for various
`applications. The level of this input may be controlled,
`for example, by a user through a potentiometer, by a
`light meter circuit, or by other means.
`Outputs from the control logic circuitry are directed
`to a column data register 12, a display input/readout
`logic circuit, and a row strobe register 16 over lines 6, 7,
`and 8, respectively. The parallel outputs 9 from the
`column data register 12 are connected to the display
`input/readout logic 14 to provide bidirectional data
`paths there between. The display input/readout logic 14
`has a corresponding number of bidirectional lines out
`put 15.
`The row strobe register 16 has a number of output
`lines 17 corresponding in number to the number of rows
`in a driven display matrix.
`A memory driver circuit 20 is connected to a column
`line 15 by means of a MOS switch 18 when the row line
`17 associated with a memory driver circuit is selected
`(energized). The output of the memory driver circuit 20
`is connected to an electroluminescent cell 40 (pixel
`element).
`
`I. TECHNICAL FIELD OF THE INVENTION
`The present invention relates to the field of thin film
`electroluminescent display devices and, more particu
`larly, to organic electroluminescent display devices
`with driver circuitry.
`II. BACKGROUND OF THE INVENTION
`Electroluminescence is the emission of a light from a
`luminescent material when an electrical field of proper
`value is applied to the material. This property has been
`utilized in the prior art to construct display panels. The
`first wave of devices were of the AC type which used
`the luminescent material as the dielectric in a parallel
`plate capacitor where one of the parallel plates was
`transparent. When an alternating voltage was applied to
`20
`the parallel plates the luminescent material emitted
`light. By depositing rows of conductive material on one
`surface of the luminescent material and columns of
`conductive material on the opposite surface, an X-Y
`matrix is formed. At each crossover point of a column
`25
`and a row a pixel for a video display is formed. With the
`proper excitation at the crossover points the pixel posi
`tioned at that point will emit light. Drive circuits are
`then coupled to the rows and the columns to vary the
`level of current or voltage that is applied as a function
`of the amount of light that is to be generated by each
`pixel.
`Advances in the electroluminescent material art have
`led to organic materials being used in such type displays
`which materials provide high brightness levels, and low
`35
`DC voltage requirements along with multicolors. In
`addition, recent developments have resulted in display
`panels with a high density of addressable pixels. With
`such displays, it is desirable to be able to store imaging
`data so that the display can be operated without exter
`nal memory and without continual refreshing. In addi
`tion, it would be advantageous to be able to control the
`brightness of the display with binary signals rather than
`analog signals thereby permitting the display to be
`driven by a computer.
`45
`SUMMARY OF THE INVENTION
`It is an object of the present invention to provide an
`electroluminescent matrix addressable display with in
`proved driver circuits.
`50
`It is another object of the present invention to pro
`vide driver circuits with memory for an improved elec
`troluminescent matrix display.
`It is a further object of the present invention to pro
`vide an electroluminescent matrix display incorporating
`55
`driver circuitry for selecting multiple levels of drive
`CurrentS.
`According to one aspect of the present invention,
`each organic electroluminescent pixel element in a ma
`trix of organic electroluminescent pixel elements is pro
`vided with a plurality of memory cells for receiving a
`corresponding plurality of binary input bits. The output
`of each memory cell is connected to a current driver
`such that each memory cell controls a portion of the
`total current applied to the pixel element. Each memory
`65
`cell activates a MOS transistor to place it into parallel
`circuit with other activated MOS transistors such that
`the combination of parallel activated transistors con
`
`HTC, Exhibit 1015
`
`

`

`15
`
`4,996,523
`3.
`4
`An image display is formed by physically positioning
`FIG. 3 illustrates a first circuit implementation for a
`a plurality of these pixel elements 40 closely together,
`memory cell 22. A column input, signal Bn, is gated to
`generally in a matrix configuration of rows and columns
`the input of a CMOS inverter gate 36 and to one elec
`or by forming the pixel elements 40 in a VLSI multi
`trode of a MOS transmission gate 34 via a MOS trans
`layer type structure.
`mission gate 30. A ROW input is connected to the input
`Each pixel element is provided with its own memory
`of a CMOS inverter 32, to the gate electrode of the
`driver circuit 20. Within each memory driver circuit
`MOS transistor 34, and to the gate electrode of the
`there is a memory cell 22 that is connected on its input
`MOS transistor 30. One electrode of the MOS transistor
`34 is connected to the input to a CMOS inverter 38. The
`via the switch 18 to the line 15. The output of the mem
`output of the memory cell 22n is directed to the gate
`ory cell is connected to a current drive source 28. The
`10
`current driver source is powered by a voltage supply
`electrode of an associated MOS transistor 24.
`FIG. 4 illustrates a second circuit implementation for
`+V to provide a driving current to the pixel element
`a memory cell 22n. A MOS transistor 31 has its drain
`40. The magnitude of the driving current is controlled
`electrode connected to receive the signal Bn, its gate
`by the output signal from the memory cell 22 which
`electrode is connected to receive the ROW signal and
`magnitude in turn determines the brightness level of the
`its source electrode is connected to the inputs of CMOS
`light emitted by the pixel element 40.
`inverters 33 and 35. The outputs from inverter 33 and
`The combination of an active IN signal and FRAME
`inverter 35 are connected to the gate electrode of an
`RST signal causes the controller 10 to load in new data
`associated MOS transistor 24.
`for display. This is accomplished by setting the display
`Referring to FIG. 5, the pixel element 40 is formed on
`20
`input/readout 14 to its read-in state with an enable sig
`a glass base 41 having an indium-tin-oxide (ITO) layer
`nal on line 7. The incoming data is averaged as directed
`42 vacuum deposited thereon. A positive electrode is
`by the #PIXEL TO AVG. signal, and then passed on to
`affixed to layer 42. A first organic layer 43 of an aro
`the memory driver circuitry 20. This is done by convey
`matic diamine is vacuum deposited on layer 42.
`ing the data serially to the column data register 12 over
`A second organic layer 44 is a luminescent ALa3 film
`25
`line 6 in a line-by-line fashion. When an entire line has
`which is vacuum deposited onto layer 43. An electrode
`been conveyed, the control logic sends out a pulse to
`45, which is an alloy or mixture of magnesium and silver
`the row strobe register 16 over line 8, which closes the
`(MgAg), is vacuum deposited onto layer 44. A conduc
`transistor switch(s) 18 associated with that row, thereby
`tor is connected to layer 45 and to a source of negative
`enabling the transfer of column data to the memory
`potential, with respect to the positive potential of layer
`30
`cell(s) 22. Following the loading of the data, the row
`42. The device thus formed is an organic electrolumi
`switch(s) 18 are re-opened and the next line is loaded.
`nescent diode which is responsive to d.c. to provide a
`The combination of an active OUT signal and
`light output. Such a device is described in detail in an
`FRAME RST signal cause the control logic to set the
`article entitled "Organic Electroluminescent Diodes'
`display input/readout 14 to its read-out state. As each
`by C. W. Tang, Appl. Phys. Lett. 51(12), Sept. 21, 1987,
`35
`row strobe line 17 is enabled, and the logical state of
`pps 913 and 914.
`each memory cell 22 is sensed on each column line 15,
`To form a large scale display a plurality of these
`the data in each memory cell is transferred in parallel to
`elements can be positioned together in a frame type
`the column data register 12 which serially conveys the
`structure or they may be fabricated as either a single or
`data out, line-by-line on the serial out line.
`as separate VLSI chips which are interconnected to
`In FIG. 2 a group of memory cells, 22n through
`form the display.
`22n-3, responding to binary bit signals, Bn through B-3
`While there has been shown what is considered to be
`activate one or more MOS transistors 24. The MOS
`the preferred embodiment of the invention, it will be
`transistors 24, 26, and 27 form the current driver 28 for
`manifest that many changes and modifications may be
`driving the pixel element 40. The MOS transistors 26
`made therein without departing from the essential spirit
`45
`and 27 are connected and sized to function as current
`of the invention. It is intended, therefore in the annexed
`mirrors, that is, the current through MOS transistor 27,
`claims to cover all such changes and modifications as
`which can be called Ipixel, is equal to the current flowing
`fall within the true scope of the invention.
`through MOS transistor 26, which current can be called
`We claim:
`I2. The current I2 is a function of the number of MOS
`1. An electroluminescent storage display with in
`50
`transistor 24 that are turned ON or OFF (actively con
`proved intensity driver circuits comprising:
`nected in parallel). With all MOS transistors 24 turned
`an electroluminescent element;
`ON the highest level of current flows through the pixel
`a plurality of memory elements;
`element 40. With all of the MOS transistors 24 in an
`a current source connected in circuit to said electro
`OFF state the pixel element 40 is not illuminated.
`luminescent element;
`Generally speaking, when devices 26 and 27 are the
`a plurality of elements, corresponding in number to
`same size the following relationship holds true: Ipixel.
`said plurality of memory elements, each connected
`= 12-i-In--In--1-- . . . .
`to a respective memory element and responsive to
`If each MOS transistor is fabricated to have a differ
`the signals stored therein for causing an incremen
`ent current flow when it is ON then a selection can be
`tal current to flow from said current source to said
`made as to which transistors are turned ON, in combi
`electroluminescent element; and
`nation, to achieve the desired intensity level.
`means for applying signals to said memory elements
`Selection of the MOS transistors 24 is accomplished
`indicative of the intensity desired from said electro
`by applying an enable signal to the ROW inputs of the
`luminescent element.
`memory cells 22n through 22n-3. The column bits are
`2. The electroluminescent storage display of claim 1
`65
`applied to the Bn inputs prior to the ROW enable signal
`wherein said plurality of elements are MOS transistors
`and are latched into the memory cells upon receipt of
`each having a gate electrode connected to a respective
`the ROW enable signal.
`memory element.
`
`55
`
`HTC, Exhibit 1015
`
`

`

`5
`
`10
`
`4,996,523
`5
`3. The electroluminescent storage display of claim 1
`wherein said means for applying signals to said memory
`elements is comprised of: a plurality of binary bits corre
`sponding in number to said plurality of memory ele
`ments and an enabling signal source for providing an
`enabling signal for loading said binary bits into said
`memory elements.
`4. An electroluminescent storage display with im
`proved intensity driver circuits comprising:
`a column data register means having an input for
`serially receiving image signals, and having a plu
`rality of parallel outputs for providing said image
`signals thereon;
`an input/output logic means responsive to an enable
`signal, and coupled to the plurality of parallel out
`15
`puts of said column data register means for gating
`said image signals to respective column outputs;
`a row strobe register means responsive to an input
`signal for sequentially providing an enabling strobe
`signal on each of a plurality of row outputs;
`20
`a plurality of switch means, each connected to a re
`spective one of a plurality of row outputs of said
`row strobe register means for connecting a respec
`tive one of said column outputs of said input/out
`put logic means to a switch output;
`25
`a plurality of memory driver circuit means having an
`input connected to the switch output of a respec
`tive switch means and having an output for provid
`ing a current as a function of the image signal re
`ceived on its input;
`30
`a plurality of electroluminescent display means each
`connected to an output of a respective memory
`driver circuit means for illumination by the pro
`vided current therefrom wherein each of said plu
`rality of memory driver circuit means is comprised
`35
`of:
`a plurality of memory elements;
`a current source connected in circuit to an electro
`luminescent display means;
`a plurality of elements corresponding in number to
`said plurality of memory elements, each con
`nected to a respective memory element and re
`sponsive to the signals stored therein for causing
`an incremental current to flow from said current
`
`6
`source to said electroluminescent display means;
`and
`means for applying signals to said memory ele
`ments indicative of the intensity desired from
`said electroluminescent display means.
`5. The electroluminescent storage display of claim 4
`wherein said plurality of elements are MOS transistors
`each having a gate electrode connected to a respective
`memory element.
`6. The electroluminescent storage display of claim 4
`wherein said means for applying signals to said memory
`elements is comprised of:
`a plurality of binary bits corresponding in number to
`said plurality of memory elements and an enabling
`signal source for providing an enabling signal for
`loading said binary bits into said memory elements.
`7. An electroluminescent display matrix comprising:
`a plurality of electroluminescent elements arranged in
`a display;
`a plurality of storage means for each of said plurality
`of electroluminescent elements for receiving binary
`number signals corresponding to the intensity level
`desired from an associated electroluminescent ele
`ment;
`a plurality of current sources each coupled to a re
`spective plurality of said storage means and an
`associated electroluminescent element for provid
`ing a current as a function of the binary number
`signals stored in said storage means, and wherein
`each of said plurality of current sources is con
`prised of:
`a two MOS device current mirror, with the first of
`said MOS devices connecting said electrolumi
`nescent element to a source of power and with
`the second of said MOS devices connecting said
`source of power to a selectable current means;
`and
`a selectable current means connected to said plural
`ity of storage means and responsive to the signals
`stored therein for causing the current in said
`second MOS device to be a function of the sig
`nals stored in said plurality of storage means.
`
`t
`
`k
`
`k
`
`45
`
`50
`
`55
`
`65
`
`HTC, Exhibit 1015
`
`