Structure and drive scheme for active matrix light emitting devices
`
`DESCRIPTION
`
`BACKGROUND OF THE INVENTION
`
`[Para 1]
`
`1. Field of the Invention
`
`[Para 2] The present invention relates to a display comprising a light-
`emitting device (LED) array and a drive scheme to operate such. More
`specifically, the present invention provides a method to operate the light
`emitting device array in response to a stream of input image data to provide
`dynamic control of light emitting device array to deliver a composite image on
`a front panel.
`
`[Para 3]
`
`2. Description of the Prior Art
`
`Light emitting diodes are attracting wide interests in display
`[Para 4]
`application in recent years. The applications include direct view screen
`constructed from organic or inorganic light emitting diodes and backlight for
`LCD. Its excellent form factor, fast response time, lighter weight, low operating
`voltage, make it the ideal device for a wide range of applications. These
`emerging applications typically involve an array of LED or OLED with active
`control element for each light emitting element. Despite superior performance
`in displaying images, these new applications still face various technical
`challenges associated with its commercialization. For example, the OLED
`displays need a longer operation lifetime. Furthermore, the processing
`techniques for generating small geometry OLED pixels in large number, and
`the complexity of pixel circuit needed for a uniform large size display panel
`remain to be the gating factors for a full commercialization of OLED display.
`On the other hand, the LED or OLED may be structured as a light source for
`light valve-controlled display device such as LCD. This invention provides a
`structure that uses LED or OLED array to generate a structured coarse light
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`condition, and combines a second active matrix of light valves, such as LCD, to
`produce a final fine grained image.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides architectures that provide a
`[Para 5]
`structure that combines a matrix of LED and a matrix of light valve, such as
`LCD, to form a composite image display system. The matrix of LED may be an
`active matrix comprising individual current control circuit within each lighting
`unit, or connected to a peripheral driver circuit. More specifically, the system
`comprises a data storage device storing reference information corresponding
`to exiting light from the light valve matrix. Both the LED control signal and the
`light valve (or LCD) control signal are modulated by such reference
`information. The structure and operating method allow the image to be
`produced in high precision, both in intensity and color.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is the schematic diagram of a preferred embodiment of the
`[Para 6]
`present invention.
`
`[Para 7]
`FIG. 2 is the schematic diagram of a preferred embodiment of the
`present invention.
`
`FIG. 2A is the schematic diagram of a preferred embodiment of the
`[Para 8]
`present invention.
`
`[Para 9]
`
`FIG. 3 is a preferred embodiment of the present invention.
`
`[Para 1 0] FIG. 4 is an example of a preferred embodiment of a light emitting
`device unit in an active matrix in the present invention.
`
`[Para 11] FIG. 5 is an illustration of a display structure of the present
`invention.
`
`[Para 12] FIG. 6 is an illustration of a display structure of the present
`invention.
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`[Para 1 3] FIG. 7 is an illustration of the present invention.
`
`[Para 14] FIG. 8 is an illustration of the present invention.
`
`[Para 1 5] FIG. 9 is a preferred embodiment of the present invention.
`
`[Para 16] FIG. 1 0 is a preferred embodiment of the present invention.
`
`[Para 1 7] FIG. 11 is a preferred embodiment of the present invention.
`
`[Para 18] FIG. 12 is a preferred embodiment of the present invention.
`
`[Para 19] FIG. 1 3 is a schematics of a preferred embodiment of a method of
`the present invention.
`
`[Para 20] FIG. 14 is a schematics of a preferred embodiment of a method of
`the present invention.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`[Para 21] The present invention is directed to the structure of a system
`comprising a light emitting device array and light valve array such as LCD, and
`the operation methods of such display system. Preferred embodiments are
`explained in applications for display apparatus. In this description, light
`emitting diode is used as preferred embodiment. For those skilled in the art, it
`is readily conceivable that any light emitting devices with sufficiently fast
`response time will work equally well in all embodiments presented herein.
`
`In this description, transmissive liquid crystal light valve array is
`[Para 22]
`used as preferred illustration as a second active matrix for displaying the final
`image. An LCD array in this system may comprise a typical structure of a
`commercially available LCD array, however, the drive electronic, light source,
`and operating method allow an image to be displayed in a higher quality.
`
`[Para 23] Light emitting diodes are used as the preferred embodiment in this
`description. It is readily conceivable that a light emitting device of similar or
`faster response time works equally well. For example, a bi-directional light
`emitting device or a fast response lamp may also be used as the light sources.
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`[Para 24] The present invention will hereinafter be described in detail with
`reference to the drawings.
`
`[Para 25] Fig. 1 provides a schematic diagram of a preferred embodiment of a
`light emitting device display 1 00 of the present invention, wherein the display
`comprising an array of light emitting devices. The display 1 00 further
`comprises a current control circuit wherein each output channel of said control
`circuit delivers a drive current to an LED 1 01, an EEPROM 1 03 as the data
`storage device to store reference information, a data processor to generate
`current control signal according to an input data signal. An LED 1 01 produces
`light output according to the drive current. A commercially available current
`driver may be used as a preferred embodiment for generating an output
`current according to an input data signal. The input data signal represents a
`set of data values corresponding to the desired brightness levels (gray scales)
`that the LEDs to be operated to display to a viewer. As the characteristics of
`LEDs may vary, the drive current directly converted from an input data signal
`by a current control circuit will typically result in a light output distorted by
`such variation, i.e. an output light intensity not in proportionally representing
`the input data signal. Such deviation of light output may arise from both the
`variation of LED characteristics in electrical current at a given voltage and in
`light output at a given electrical current. One feature of the present invention
`provides reference information stored in the EEPROM 1 03 as part of a display
`system to adjust the drive current accordingly. This reference information is
`the measured output light intensity at a given current set by a given input data
`signal. In Fig 1, a sensor device 1 09 comprising an array of light sensing
`elements is illustrated. A CCD camera may be used as a preferred
`measurement device. The measured intensity in the CCD array corresponding
`to a specific LED 1 01 at specific time during a drive period is sent via a data
`signal link, such as a data cable, to the data storage EEPROM 1 03. The data
`processor use this stored reference information to re-process the input data
`signal. A preferred embodiment of the function of the data processor is to
`perform a scaling of the input data signal according to the stored reference
`information.
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`[Para 26] As a preferred scaling operation of the data processor, given an
`array of input data signal (51, 52, ... , Sn) and an array of data value (R1, R2, ... ,
`Rn) as part of the reference information representing the maximum light
`output measured by sensor 1 09 when a respective LED is driven at a full scale
`(highest gray scale), the processor operates to produce a current driving signal
`(51 x R1, 52 x R2, ... ,Sn x Rn)/M, where M is the maximum value of (R1 R2 ...
`Rn). Such scaled current drive signal is then sent to current control circuit for
`generating drive current.
`
`[Para 27] As a preferred embodiment for Fig. 1, the LED array forms an active
`matrix wherein each unit cell comprises an LED element, a drive transistor, and
`
`[Para 28] Fig 2. provides a schematic diagram of further detail of a preferred
`embodiment of a display system of the present invention. The system 200
`further comprises a programming circuit 204 as an input-output interface for
`writing data into and reading data from the data storage EEPROM. A timing
`control circuit is provided as a circuit separated from current control circuit to
`provide timing control to the current control circuit. The same timing control
`signal is provided synchronously to the programming circuit to synchronize
`the data writing with the drive current so that the data measured from the
`sensor 209 is correctly register to a proper LED at a specific time when such
`LED is driven at a given current level.
`
`[Para 29] Programming or data recording operation of the data storage device
`may be performed before or after the assembly of the LED array with the light
`valve matrix of the display unit. In a preferred embodiment, a communication
`port is provided for accessing the storage device to program or re-program
`the reference information. One preferred embodiment of such data storage
`device is an EEPEOM that may be programmed with software from a computer
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`with one of the computer's port connected to said communication port of the
`display with a cable. Method of programming an EEPROM is commercially
`available.
`
`[Para 30] A preferred embodiment for structuring the display and recording
`the reference information into the data storage device is to provide a
`communication port to receive data of the reference information. A preferred
`location for such a communication port is on a side, left side or right side, on
`the case enclosing the LED array assemble. With this preferred embodiment,
`an external sensor device may be used to generate intensity data of light
`output by reading the brightness for each and every light emitting device when
`it is turned on. The sensor device comprises multiple light sensing elements
`each generating an intensity reading for its corresponding location. A
`preferred embodiment for such sensor device is a CCD camera for line or 2-
`dimensional imaging. This preferred embodiment enables re-programming of
`the data storage device to update the stored reference information at a later
`time, and periodically to re-adjust the display as the characteristics of the light
`emitting devices in the display drifted away from its initial conditions.
`
`In another preferred embodiment where an array of light emitting
`[Para 31]
`diode is implemented, a pre-determined pattern is generated for lighting up
`the LED array. Such pattern may be moved to different location in the array at
`different time, and the sensor position is referenced to the location of the
`pattern and synchronized with the drive current control circuit via a timing
`circuit.
`
`[Para 32] Fig. 3 is a preferred embodiment of the present invention wherein
`the display further comprises a first active matrix 31 0 comprising an array of
`light emitting devices and a second active matrix 320 comprising an array of
`light valves placed in alignment with the light emitting device array 31 0. A
`preferred embodiment of light valve array 320 is a LCD panel, and a preferred
`embodiment of light emitting device array 31 0 is an active matrix of LEDs. A
`preferred embodiment of an LED matrix has a current control circuit
`associated with each light emitting element, either placed in close proximity
`with the LED element, or in the peripheral of the LED matrix connected thereto
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`via conductive lines such as patterned copper foil on a printed circuit board.
`The LCD matrix comprises a greater number of elements (pixels) than the LED
`matrix. A preferred embodiment of the LCD matrix is an active matrix LCD
`wherein each pixel has a transistor and a storage capacitor.
`
`[Para 33] A preferred embodiment of the light emitting device array
`comprising organic light emitting diodes formed with a stack of thin films of
`organic and inorganic materials on a substrate, and wherein the data
`electrodes and scanning electrodes are fabricated on the same substrate
`surface providing connections from the OLEOs to the data driver and scan
`driver respectively.
`
`[Para 34] Another preferred embodiment of the light emitting device array is
`an array of LEDs in discrete packages, each package comprising single or
`multiple LEDs. As a preferred embodiment, the LED array is assembled on a
`connection base board such as a printed circuit board wherein conductive foils
`are patterned in multiple layers to provide desired circuit connection from each
`LED to the circuit elements, and to the drivers mounted at the peripheral of the
`circuit board.
`
`[Para 35] As a further preferred embodiment of the LED array in the present
`invention, each unit circuit (pixel) associated with an LED in the LED array
`comprises a drive transistor to modulate the drive current according to a data
`signal, a select transistor selecting said pixel to receive such data signal, and a
`storage element holding said data signal for an extended period of time when
`the input signal is isolated from the pixel by turning off the select transistor.
`An example of a preferred embodiment of such a pixel circuit is provide in Fig.
`4, wherein a transistor 402 modulates the current directed to the LED 405
`according to a data information stored in storage capacitor 404. The data
`information is written into the storage capacitor 404 from a data electrode
`when a data control transistor 403 is selected by the scan electrode 41 0. Such
`active circuit may be placed in the close proximity of the LED elements, or at a
`distant location such as the peripheral of the array connected thereto by
`conductive lines.
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`[Para 36] As a further example of a preferred embodiment, the LEDs may be
`assembled in packages before placed into circuit. Each LED package may
`comprise single or multiple LED elements. A package may also comprise LED
`elements of different colors.
`
`[Para 37] Fig. 5 provides an illustration of a preferred arrangement of the LED
`array wherein the areas on the second matrix of LCD illuminated by two
`adjacent light sources (LEDs) overlap each other. In Fig. 5, area A is an area of
`LCD panel (second matrix) illuminated by the light emitting device 501, and
`area B is an area on LCD illuminated by light emitting device 502. The two
`areas may overlap as shown in Fig. 5, or closely join with a narrow seaming
`region as shown in Fig. 6.
`
`[Para 38] For a preferred embodiment of a display comprising a first array of
`light emitting devices and a second array of liquid crystal light valves, such
`preferred embodiment may further comprise a first data storage device storing
`first reference information corresponding to the intensity of the light emitting
`devices. Such preferred embodiment may further comprise a second data
`storage device storing a second reference information corresponding to light
`intensity exiting the second matrix of LCD light valves. Such second reference
`information comprises data points corresponding to the pixels in the second
`matrix. In a preferred embodiment, said data points comprise data
`corresponding to light intensity exiting each and every pixel in an area
`illuminated by one light emitting device. In a preferred embodiment, said
`second reference information stored in said second data storage device further
`comprises a plurality of groups of data, each group of data comprises data
`points corresponding to light intensity exiting each and every pixel in an area
`illuminated by one light emitting device. The density of data points may be
`varied. For example, in another preferred embodiment, one said group of data
`may comprise data points corresponding to the light intensity exiting every
`other pixels of the second matrix of liquid crystal light valve in an area
`illuminated by one light emitting device. The density of data points may also
`vary from location to location or according to the sensitivity. For example, in
`another preferred embodiment, in one said group of data corresponding to an
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`area illuminated by a light emitting device, the density of data points in the
`center region of the illumination where the intensity is more uniform is set to
`be lower than the density of data points near the edges where the intensity
`varies rapidly. For example, the reference information of a group of data
`comprises data points every corresponding to every 9 pixels in the center
`region, and every pixels near the edge of the illuminated area. As illustrated in
`an example of Fig. 7 where intensity of light exiting the light valve is plotted
`along on direction, area A corresponds to an area illuminated by one light
`emitting device. The intensity profile is high and slow-varying in the center
`region, and rapidly drops to the negligible background at the edge. The low
`density reference data may be stored for the plateau and a high density, such
`as every pixel, intensity profile is stored.
`
`[Para 39]
`In a preferred embodiment of the data storage device and data
`structure for reference information, the data comprises a plurality of groups,
`wherein each group comprises data points corresponding to an area
`illuminated by a light emitting device. For example, the group N of data
`comprises data points corresponding to pixels from N-W to N+W in area A as
`illustrated in Fig. 7, and group N+ 1 comprises data points corresponding to
`N+ 1-W to N+ 1 +Win area B, where areas A and Bare two adjacent area
`illuminated by two adjacent light emitting devices.
`
`In a preferred embodiment of the present invention, the reference
`[Para 40]
`data for a display comprising a first array of light emitting devices and a
`second matrix of light valves such as LCD is obtained by placing an optical
`sensing device to measure the light intensity exiting the light valves. In a
`preferred embodiment, said first reference information comprises a data value
`for a light emitting device corresponding to the maximum measured intensity
`of light exiting the light valves in the area illuminated by said light emitting
`device. In another preferred embodiment of the present invention, the first
`reference information comprises a data value for a light emitting device
`corresponding to the measured intensity of light exiting the light valves in the
`area illuminated by said light emitting device set at a specified state, wherein
`said state corresponds to a scale of light output of the light emitting device. In
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`a preferred embodiment, the measurement of light exiting the light valve is
`performed while setting all light valves at the highest transmission level. In
`another preferred embodiment, the reference information further comprises
`data value corresponding to a measurement while setting the light valves in an
`area to the lowest transmission level. In a preferred embodiment, the
`measurement of light exiting the light valves in one area illuminated by a light
`emitting device is performed while setting all other light emitting device to off
`or the lowest lighting state.
`
`[Para 41] An example of the measured reference information is illustrated in
`Fig 8, wherein only the light emitting device whose profile is being record is
`turned on, and the rest of the devices are turned off. The profile shown
`represents the light intensity at various locations along the spatial coordinate
`along one direction of the matrix.
`
`In the present invention, a preferred embodiment of obtaining the
`[Para 42]
`second reference information for the light valve matrix is placing an optical
`sensing device to measure the light intensity exiting the light valves while
`turning on only one light emitting device whose illumination area is measured.
`
`[Para 43] Fig. 9 provides an illustration of a preferred embodiment of the
`recording method and apparatus wherein a display comprises an array of light
`emitting devices 910, and an LCD panel comprising an array of light valves
`920. The optical sensing device 930 is placed after LCD to record the light
`intensity passing through the LCD array where all the light valves are turned
`on, and only one light emitting device 902 is turned on while all other light
`emitting device, such as 901, are turned off. The optical data measured by the
`array of optical sensing device 930 is processed to provide both the area
`intensity information as used for the first reference information, and pixilated
`data representing each and every pixel of the light valves in the area
`illuminated by each and every light emitting device, to be used as second
`reference information.
`
`[Para 44] Another preferred embodiment of the measuring method and
`apparatus is provided in Fig. 1 0, wherein a display comprises an array of light
`emitting devices 1010, and an LCD panel comprising an array of light valves
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`1 020. The optical sensing device 1 030 is placed after LCD to record the light
`intensity passing through the LCD array where the light valves are turned on
`one at a time to allow a sequential recording of light intensity passing through
`the corresponding light valve which is turned on by a timing controller, and
`only one light emitting device 1 002 is turned on while all other light emitting
`device, such as 1 001, are turned off. This recording process repeats one light
`emitting device at a time, for all light emitting devices. The optical data
`measured by the array of optical sensing device 930 is processed to provide
`both an area intensity information as used for the first reference information,
`and pixilated data representing each and every pixel of the light valves in the
`area illuminated by each and every light emitting device, to be used as second
`reference information.
`
`[Para 45] One preferred embodiment for the optical sensing device is a CCD
`camera that has array of pixels covering at least an area illuminated by a light
`emitting device. Another embodiment of the present invention of the optical
`sensing device is a CCD camera comprising an array of pixels covering the
`entire array of the light valves. Another preferred embodiment of the optical
`sensing device is a device comprising a lens and an optical sensor, such as a
`photo detector. An example of the photo detector is a photo diode.
`
`[Para 46] Another preferred embodiment for the reference recording device is
`provided in Fig. 11, where and optical device 1140, such as a lens, is used to
`project the light output to an optical sensor 1140. In this preferred
`embodiment, the pixel is turned on one at a time sequentially. The recording
`is performed one light emitting device at time, and repeat for all light emitting
`devices.
`
`[Para 47]
`In a further preferred embodiment of the present invention, the
`optical sensing device used for record the reference information comprises a
`timing controller as illustrated in Fig. 12, wherein said timing controller
`receives timing signal from or sets timing signal for the display device being
`measured. In a preferred embodiment, the display device comprises an array
`of light emitting devices 121 0 and an array of LCD light valves 1220. The
`timing controller synchronizes the measured optical signal with the display
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`data signal, wherein the synchronization enables the measuring device to
`record and register the optical signal for each location of the pixels of the light
`valve. In a preferred embodiment of the synchronization, the address of data
`signal that sets the state of a light valve is sent to the timing controller, and
`the timing controller use such address information to place the measured
`optical data measured by an optical sensor 1230 into the corresponding
`location of a data storage device (Memory device). In a further preferred
`embodiment, said timing controller is integrated with the optical sensing
`device. In another preferred embodiment, the timing controller is integrated
`and assembled with the display device being measured comprising a first array
`of light emitting device and a second array of light valves. In a further
`preferred embodiment, the data storage device is integrated with said display
`device.
`
`[Para 48] Fig. 1 3 provides a preferred embodiment of the drive scheme for
`the display of the present invention. The input image data signals to be
`displayed by the display device is first stored in a buffer memory and
`processed to extract the highest brightness level for the area illuminated by
`each and every light emitting device. For example, for an area A illuminated
`by a light emitting device as illustrated in Fig. 5 and Fig. 7, the first reference
`information recorded for this area is read from the data storage device (such
`as an EEPROM) to scale the input data corresponding to the this area. The
`result of the scaling provides the actual intensity information for the area A,
`and is sent to the current control driver in the lighting control circuit to
`generate corresponding drive current to drive the light emitting device
`illuminating area A.
`
`[Para 49] Fig. 14 provides a preferred embodiment with further detail of the
`drive scheme for present invention. In parallel with the processing of the
`lighting control signal, the scaled light control signals resulting from scaling of
`the highest brightness level with the first reference information for areas A, B,
`... illuminated by each and every light emitting device are directed to scale
`each and every corresponding group of data in the second reference
`information. The resulting groups of scaled data corresponding to areas A, B,
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`... , are composed to form a composite reference information. A preferred
`embodiment of the composition is a addition of all groups of data, A+B+C+ ....
`In a typical situation, theer are overlaps between each and every two adjacent
`groups as illustrated in Fig. 5 and Fig. 7. The composite scaled reference
`information is directed to scale the input image data signal for each and every
`pixel of the light valves (for example, LCD array). The resulting scaled image
`data signals represent the signal used for drive the LCD array for displaying
`the image while the light emitting device delivers a scaled light intensity for
`each and every area of illumination.
`
`[Para 50] Another preferred embodiment of the present invention comprises a
`display device comprising:
`
`[Para 51] a plurality of light emitting devices;
`
`[Para 52] a second addressing means to delivery data information to said
`plurality of light emitting devices;
`
`[Para 53] a scanning means along a first direction, wherein said scanning
`means along said first direction comprises a first control means for selecting a
`group of said light emitting devices distributed along a second direction for
`receiving said data information;
`
`[Para 54] wherein said scanning means along said first direction further
`comprises a second control means for setting a group of light emitting devices
`distributed along said second direction to the lowest brightness state;
`
`[Para 55] wherein said setting a group of light emitting devices distributed
`along said second direction to the lowest brightness state precedes said
`selecting said group of said light emitting devices distributed along said
`second direction for receiving said data information.
`
`[Para 56] As a further preferred embodiment, said setting a group of light
`emitting devices distributed along said second direction to the lowest
`brightness state is followed by selecting said group of said light emitting
`devices distributed along said second direction for receiving said data
`information.
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`[Para 57] Another preferred embodiment of the present invention comprises a
`display comprising:
`
`[Para 58] a plurality of pixels of light valves such as liquid crystal light valves;
`
`[Para 59] a first addressing means to deliver a first data information to said
`pixels;
`
`[Para 60] a scanning means along a first direction, wherein said scanning
`means along a first direction comprises a first control means for selecting a
`first group of pixels distributed along a second direction for receiving said first
`data;
`
`[Para 61] wherein said scanning means along said first direction further
`comprises a second control means for setting a second group of pixels
`distributed along said second direction to the lowest brightness state;
`
`[Para 62] wherein said second group comprises said first group; wherein said
`second group comprises a plurality of said first groups;
`
`[Para 63] wherein said setting a second group of pixels distributed along said
`second direction to the lowest brightness state precedes said selecting any
`first group of pixels distributed along a second direction for receiving said first
`data in said second group of pixels;
`
`[Para 64] wherein said selecting said first group of pixels select sequentially
`said plurality of said first groups in said second group.
`
`[Para 65] As a further preferred embodiment, such display device further
`comprises:
`
`[Para 66] a plurality of light emitting devices;
`
`[Para 67] a second addressing means to delivery second data information to
`said plurality of light emitting devices;
`
`[Para 68] a second scanning means along said first direction, wherein said
`second scanning means along said first direction comprises a third control
`means for selecting a group of said light emitting devices distributed along
`said second direction for receiving said second data information;
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`[Para 69] wherein said second scanning means along said first direction
`further comprises a fourth control means for setting a group of light emitting
`devices distributed along said second direction to the lowest brightness state;
`
`[Para 70] wherein said setting a group of light emitting devices distributed
`along said second direction to the lowest brightness state precedes said
`selecting said group of said light emitting devices distributed along said
`second direction for receiving said second data information.
`
`[Para 71] As a further preferred embodiment, a group of light emitting
`devices distributed along said second direction illuminates a said second
`group of pixels,
`
`[Para 72] and wherein said setting said group of light emitting devices
`distributed along said second direction to the lowest brightness state precedes
`said selecting of any said first group of pixels in said second group of pixels.
`
`[Para 73] As a further preferred embodiment, the selecting of said group of
`said light emitting devices distributed along said second direction for receiving
`said second data information is performed at the completion of all said
`selecting said first groups of pixels in said second group of pixels for receiving
`said first data information.
`
`[Para 74] Various light emitting devices may be incorporated to form an array
`of display elements or light source. Such light emitting device include organic
`light emitting devices such as small molecule OLED and polymer OLED. These
`light emitting devices my also include such structures and materials as silicon
`and GaN LEDs, or white LEDs. Such light emitting devices and systems may
`readily adopt the principles and methods of the present invention, or to
`include the circuit and drive method directly derived from this invention. Such
`combinations are conceivably within the scope of the present invention, and
`the present invention embraces all such applications. It is also conceivable
`that various types of materials may be used to construct elements for the
`circuit, and all such variations are embraced by the present invention.
`
`[Para 75] For example, a system comprising a first reference information for
`scaling the light source and a second reference information for scaling the
`
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