111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US007612843B2
`
`c12) United States Patent
`Chou
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,612,843 B2
`Nov. 3, 2009
`
`(54) STRUCTURE AND DRIVE SCHEME FOR
`LIGHT EMITTING DEVICE MATRIX AS
`DISPLAY LIGHT SOURCE
`
`(76)
`
`Inventor: Chen-Jean Chou, 21 Ridgefield Rd.,
`New City, NY (US) 10956
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 264 days.
`
`(21) Appl. No.: 11/754,268
`
`(22) Filed:
`
`May25, 2007
`
`(65)
`
`Prior Publication Data
`
`US 2008/0170054 AI
`
`Jul. 17, 2008
`
`Related U.S. Application Data
`
`(60) Provisional application No. 60/767,534, filed on May
`25,2006.
`
`(51)
`
`Int. Cl.
`G02F 111335
`G06F 31038
`
`(2006.01)
`(2006.01)
`
`(52) U.S. Cl. ......................................... 349/61; 345/205
`(58) Field of Classification Search ................... 349/61;
`345/205
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`7,187,391 B2 * 3/2007 Itoh eta!.
`................... 345/629
`7,202,613 B2 * 4/2007 Morgan eta!. .............. 315/312
`2007/0296886 A1 * 12/2007 Inada eta!. ................... 349/61
`* cited by examiner
`Primary Examiner-Mike Qi
`
`(57)
`
`ABSTRACT
`
`A system and driving method are provided to accurately
`reproduce an input image using calibrated intensity profile.
`Extended dynamic range can be obtained according to the
`computation method. Improved structures for solid-state
`backlighting system suitable for such application are pro(cid:173)
`vided.
`
`51 Claims, 13 Drawing Sheets
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`Nov. 3, 2009
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`Nov. 3, 2009
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`Nov. 3, 2009
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`U.S. Patent
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`Nov. 3, 2009
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`Nov. 3, 2009
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`U.S. Patent
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`Nov. 3, 2009
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`Nov. 3, 2009
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`U.S. Patent
`
`Nov. 3, 2009
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`US 7,612,843 B2
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`Page 11
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`

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`U.S. Patent
`
`Nov. 3, 2009
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`Sheet 11 of 13
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`US 7,612,843 B2
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`Page 12
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`

`U.S. Patent
`
`Nov. 3, 2009
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`Sheet 12 of 13
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`US 7,612,843 B2
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`

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`U.S. Patent
`
`Nov. 3, 2009
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`Sheet 13 of 13
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`Page 14
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`

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`US 7,612,843 B2
`
`1
`STRUCTURE AND DRIVE SCHEME FOR
`LIGHT EMITTING DEVICE MATRIX AS
`DISPLAY LIGHT SOURCE
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`The present application claims priority ofU.S. Provisional
`Patent Application No. 60/767,534, filed on May 25, 2006,
`which is hereby incorporated by reference.
`
`BACKGROUND OF THE INVENTION
`
`2
`menting sensor, while practical for a small number of LED
`elements, increases system complexity and cost substantially
`for a large LED system.
`The present invention addresses these issues by providing
`a system solution which includes a structural aspect, a drive
`scheme aspect, and a system design aspect.
`Examples ofliquid crystal display (LCD) as light modula(cid:173)
`tors and backlight construction are provided in U.S. Pat. No.
`3,881,809, U.S. Pat. No. 4,540,243, U.S. Pat. No. 4,772,099,
`10 and U.S. Pat. No. 6,489,952, all of which are hereby incor(cid:173)
`porated by reference.
`
`1. Field of the Invention
`The present invention relates to a display comprising a 15
`light-emitting device 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 20
`front panel.
`2. Description of the Prior Art
`Conventional liquid crystal displays (LCD), or similar
`light modulating displays, typically operate with an array of
`liquid crystal light valves modulating the light from a static 25
`light source. Dynamically controlled light sources have been
`proposed to operate in conjunction with the light modulators
`to deliver enhanced image quality where the light source
`intensity is controlled in accordance with the image data. It is
`perceivable that a better image enhancement is achieved with 30
`a higher degree of partition of dynamically varied light
`sources. For example, a greater benefit of image enhancement
`can be obtained in a multiple partition of controlled light
`sources than a single controlled source illuminating the entire
`screen. Similarly, a greater power efficiency is achievable in 35
`systems that comprises higher degree of partitioned light
`sources.
`Dynamic control of light source in the real time requires
`light sources responding fast enough to varying drive current
`as to synchronize with the refreshing image data. In this 40
`regard, a light source based on light emitting diode (LED)
`offers a greater advantage than a cold cathode fluorescent
`lamp (CCFL), as the response time of LEDs is orders of
`magnitude faster than CCFL.
`Light emitting diodes have been used in display applica- 45
`tions as lighting elements, either as direct light emitting
`image pixels or as light sources from which the light is modu(cid:173)
`lated by light modulators such as LCD light valves. Examples
`of the first application includes organic light emitting diode
`display (OLED) and discrete LED billboard. An example of 50
`second application is LED backlight. In all such display sys(cid:173)
`tems, a common challenge is the uniformity and stability of
`LED components. More specifically, the issue involves the
`requirement of a narrow distribution of initial spectra of the
`LEDs, as well as the controllability of subsequent time depen- 55
`dent decay. These issues have received substantial attention,
`but the current solutions are costly, or involves substantial
`technically complexity. This is especially so for a system
`comprising a large number of LED elements. For example,
`one current solution for the initial spectra control is sorting 60
`(binning) the LED elements and select specific spectral dis(cid:173)
`tribution for a certain product application. A solution for the
`time dependent decay, which varies from one LED element to
`another, and between different colors, is to construct build-in
`light sensors to detect the light output of selected LED ele- 65
`ments. It is conceivable that a sorting procedure causes yield
`to drop and cost to increase. It is also conceivable that imple-
`
`SUMMARY OF THE INVENTION
`
`The present invention comprises architectures that provide
`a structure combining a matrix of LED and a matrix oflight
`valves, such as LCD, to form a composite image display
`system. The matrix of LED may be an active matrix compris(cid:173)
`ing individual current control circuit within each lighting
`unit, or connected to a peripheral driver circuit. More specifi(cid:173)
`cally, 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 refer(cid:173)
`ence information. The structure and operating method allow
`the image to be produced in high precision, both in intensity
`and color.
`The present invention further comprises an image scanning
`scheme that provides a preferred method to address the com(cid:173)
`bined system.
`The present invention further provides a preferred structure
`for constructing high degree partitioned and controlled light(cid:173)
`ing elements for individual source control.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG.1 is the schematic diagram of a preferred embodiment
`of the present invention.
`FIG. 2 is the schematic diagram of a preferred embodiment
`of the present invention.
`FIG. 2A is the schematic diagram of a preferred embodi(cid:173)
`ment of the present invention.
`FIG. 3 is a preferred embodiment of the present invention.
`FIG. 4 is an example of a preferred embodiment of a light
`emitting device unit in an active matrix in the present inven(cid:173)
`tion.
`FIG. 5 is an illustration of a display structure of the present
`invention.
`FIG. 6 is an illustration of a display structure of the present
`invention.
`FIG. 7 is an illustration of the present invention.
`FIG. 8 is an illustration of the present invention.
`FIG. 9 is a preferred embodiment of the present invention.
`FIG. 10 is a preferred embodiment of the present invention.
`FIG. 11 is a preferred embodiment of the present invention.
`FIG.12 is a preferred embodiment of the present invention.
`FIG. 13 is a schematics of a preferred embodiment of a
`method of the present invention.
`FIG. 14 is a schematics of a preferred embodiment of a
`method of the present invention.
`FIG. 15 is a schematic drawing of a preferred embodiment
`of the present invention.
`FIG. 16 is a schematic drawing of a preferred embodiment
`of the present invention.
`
`Page 15
`
`

`

`US 7,612,843 B2
`
`3
`DETAILED DESCRIPTION OF THE INVENTION
`
`The present invention is directed to the structure of a sys(cid:173)
`tem comprising an array oflight emitting device and an array
`of light modulators, and the operation methods of such dis(cid:173)
`play system. Preferred embodiments are explained in appli(cid:173)
`cations for display apparatus. The light emitting diode is used
`as the preferred embodiment for the light emitting device. The
`liquid crystal display (LCD) is used as the preferred embodi(cid:173)
`ment of light modulator. For those skilled in the art, it is
`readily conceivable that any light emitting devices with suf(cid:173)
`ficiently fast response time will work equally well in all For
`example, a bi-directional light emitting device or a fast
`response lamp may also be used as the light sources. In
`addition, the light valve is used as preferred embodiment for
`light modulator.
`The present invention will hereinafter be described in
`detail with reference to the drawings.
`FIG. 1 provides a schematic diagram of a preferred
`embodiment of a light emitting device display 100 of the 20
`present invention, wherein the display comprising an array of
`LED. The display 100 further comprises a current control
`circuit wherein each output channel1 02 of said control circuit
`delivers a drive current to an LED 101, an EEPROM 103 as
`the data storage device to store the first reference information, 25
`a data processor to generate current control signal according
`to an input data signal. An LED 101 produces light output
`according to the drive current set by the control circuit. A
`preferred embodiment of the current control circuit com(cid:173)
`prises a commercially available current driver delivering out- 30
`put current modulated in amplitude or pulse width according
`to a 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 35
`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 proportion(cid:173)
`ally representing the input data signal. Such deviation oflight
`output may arise from both the variation of LED character- 40
`istics in electrical current at a given voltage and in light output
`at a given electrical current. One feature of the present inven(cid:173)
`tion provides a first reference information stored in the
`EEPROM 103 as part of a display system to adjust the drive
`current accordingly. This reference information is the mea- 45
`sured output light intensity at a given current set by a given
`input data signal. A preferred input data signal for such setting
`is the highest gray level corresponding to the full bright level.
`In FIG. 1, a detachable sensor device 109 comprising an array
`of light sensing elements is illustrated. Sensor 109 is an 50
`external measuring device detachable from the system. A
`CCD camera may be used as a preferred measurement device.
`The measured intensity in the CCD array corresponding to a
`specific LED 101 at specific time during a drive period is sent
`via a data signal link 105, such as a data cable, to the data 55
`storage EEPROM 103. The timing of sending/receiving such
`data is synchronize with the timing of drive current by the
`control circuit. The data processor uses this stored reference
`information to re-process the input data signal with a scaling
`operation. A preferred embodiment of the function of the data 60
`processor is to perform a scaling of the input data signal
`according to the stored reference information.
`As a preferred scaling operation of the data processor,
`given an array of input data signal (S1, S2, ... , Sn) and an
`array of data value (R1, R2, ... , Rn) as part of the reference 65
`information representing the maximum light output mea(cid:173)
`sured by sensor 109 when a respective LED is driven at a full
`
`4
`scale (highest gray scale), the processor operates to produce a
`current driving signal (S1xR1, S2xR2, ... , SnxRn)/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.
`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 a storage capacitor. An
`example of a unit circuit of such LED matrix is provided in
`10 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 writ(cid:173)
`ten into the storage capacitor 404 from a data electrode when
`a data control transistor 403 is selected by the scan electrode
`15 410.
`FIG. 1b provide another preferred embodiment of LED
`array where each array is driven by a current source, wherein
`the current source is embedded in an integrated circuit and
`said integrated circuit further comprising control circuit for
`setting multiple levels of brightness according to an input
`signal.
`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 progrannning
`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 synchro(cid:173)
`nously to the programming circuit to synchronize the data
`writing with the drive current so that the data measured from
`the sensor 209 is correctly registered to a proper LED at a
`specific time when such LED is driven at a given current level.
`Progrannning or data recording operation of the data stor(cid:173)
`age device may be performed before or after the assembly of
`the LED array with the light valve matrix of the display nnit.
`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 with one of the computer's
`port connected to said communication port of the display with
`a cable. Method of programming an EEPROM is commer(cid:173)
`cially available.
`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 gen(cid:173)
`erate 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 pre(cid:173)
`ferred embodiment enables re-progrannning of the data stor(cid:173)
`age device to update the stored reference information at a later
`time, and periodically to re-adjust the display as the charac(cid:173)
`teristics of the light emitting devices in the display drifted
`away from its initial conditions.
`In another preferred embodiment where an array of light
`emitting 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
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`5
`the sensor position is referenced to the location of the pattern
`and synchronized with the drive current control circuit via a
`timing circuit.
`FIG. 3 is a preferred embodiment of the present invention
`wherein the display further comprises a first active matrix 310
`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 310. A
`preferred embodiment of light valve array 320 is a LCD
`panel, and a preferred embodiment of light emitting device
`array 310 is an active matrix of LEDs. A preferred embodi(cid:173)
`ment of an LED matrix has a current control circuit associated
`with each light emitting element, either placed in close prox(cid:173)
`imity with the LED element, or in the peripheral of the LED
`matrix connected thereto via conductive lines such as pat(cid:173)
`terned 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.
`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 connec(cid:173)
`tions from the OLEDs to the data driver and scan driver
`respectively.
`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 embodi(cid:173)
`ment, 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 connec(cid:173)
`tion from each LED to the circuit elements, and to the drivers
`mounted at the peripheral of the circuit board.
`As a further preferred embodiment of the LED array in the
`present invention, each nnit circuit (pixel) associated with an
`LED in the LED array comprises a drive transistor to modu(cid:173)
`late the drive current according to a data signal, a select
`transistor selecting said pixel to receive such data signal, and 40
`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 410. Such
`active circuit may be placed in the close proximity of the LED 50
`elements, or at a distant location such as the peripheral of the
`array connected thereto by conductive lines.
`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.
`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) over(cid:173)
`lap 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.
`For a preferred embodiment of a display comprising a first
`array of light emitting devices and a second array of liquid
`
`6
`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 emit(cid:173)
`ting devices. Such preferred embodiment may further com(cid:173)
`prise a second data storage device storing a second reference
`information corresponding to light intensity exiting the sec(cid:173)
`ond matrix of LCD light valves. Such second reference infor(cid:173)
`mation comprises data points corresponding to the pixels in
`the second matrix. In a preferred embodiment, said data
`10 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 ref(cid:173)
`erence information stored in said second data storage device
`further comprises a plurality of groups of data, each group of
`15 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
`20 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
`25 group of data corresponding to an 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
`30 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 ofFIG. 7 where intensity oflight exiting the light
`valve is plotted along on direction, area A corresponds to an
`35 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.
`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
`45 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 toN+ 1-W toN+ 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 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 pre-
`55 ferred embodiment, said first reference information com(cid:173)
`prises 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
`60 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
`65 device. In 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
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`7
`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.
`An example of the measured reference information is illus(cid:173)
`trated 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 obtain(cid:173)
`ing the 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 mea(cid:173)
`sured.
`FIG. 9 provides an illustration of a preferred embodiment
`of the recording method and apparatus wherein a display
`comprises an array oflight 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 infor(cid:173)
`mation, 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 infor(cid:173)
`mation.
`Another preferred embodiment of the measuring method
`and apparatus is provided in FIG. 10, wherein a display com(cid:173)
`prises an array of light emitting devices 1010, and an LCD
`panel comprising an array of light valves 1020. The optical
`sensing device 1030 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 correspond(cid:173)
`ing light valve which is turned on by a timing controller, and
`only one light emitting device 1002 is turned on while all
`other light emitting device, such as 1001, 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 refer(cid:173)
`ence 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 refer(cid:173)
`ence information.
`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.
`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
`
`8
`on one at a time se