(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`I IIIII IIIIIIII II IIIIII IIIII IIIII IIIII IIII I II Ill lllll lllll lllll lllll lllll llll 1111111111111111111
`
`( 43) International Publication Date
`28 July 2005 (28.07.2005)
`
`PCT
`
`(10) International Publication Number
`WO 2005/069267 Al
`
`(51) International Patent Classification 7:
`
`G09G3/32
`
`(21) International Application Number:
`PCT/IB2005/050029
`
`(22) International Filing Date: 4 January 2005 (04.01.2005)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`0400216.8
`
`7 January 2004 (07.01.2004) GB
`
`(71) Applicant (for all designated States except US): KONIN(cid:173)
`KLUKE PHILIPS ELECTRONICS N.V. [NL/NL];
`Groenewoudseweg 1, NL-5621 BA Eindhoven (NL).
`
`(72) Inventor; and
`(75) Inventor/Applicant (for US only): CHILDS, Mark, J.
`[GB/GB]; c/o Philips Intellectual Property & Standards,
`Cross Oak Lane, Redhill, Surrey RHl 5HA (GB).
`
`iiiiiiiiiiii
`
`(74) Agents: WILLIAMSON, Paul, L. et al.; c/o Philips In(cid:173)
`tellectual Property & Standards, Cross Oak Lane, Redhill,
`Surrey RHl 5HA (GB).
`
`(81) Designated States ( unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ, CA, CH, CN,
`CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE, EG, ES, Fl,
`GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE,
`KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD,
`
`MG, MK, MN, MW, MX, MZ, NA, NI, NO, NZ, OM, PG,
`PH, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL, SY, TJ, TM,
`TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, YU, ZA, ZM,
`zw.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl,
`FR, GB, GR, HU, IE, IS, IT, LT, LU, MC, NL, PL, PT, RO,
`SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN,
`GQ, GW, ML, MR, NE, SN, TD, TG).
`
`Declaration under Rule 4.17:
`as to applicant's entitlement to apply for and be granted
`a patent (Rule 4.17(ii)) for the following designations AE,
`AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ,
`CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE,
`EG, ES, Fl, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS,
`JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA,
`MD, MG, MK, MN, MW, MX, MZ, NA, NI, NO, NZ, OM,
`PG, PH, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL, SM, SY,
`Tl, TM, TN, TR, TT, IZ, VA, VG, UZ, VC, VN, YU, ZA,
`ZM, ZW, AR/PO patent (BW, GH, GM, KE, LS, MW, MZ,
`NA, SD, SL, SZ, TZ, VG, ZM, ZW), Eurasian patent (AM,
`AZ, BY, KG, KZ, MD, RU, Tl, TM), European patent (AT,
`BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl, FR, GB, GR,
`HU, IE, IS, IT, LT, LU, MC, NL, PL, PT, RO, SE, SI, SK,
`TR), OAP/ patent (BF, BJ, CF, CG, CI, CM, GA, GN, GQ,
`GW, ML, MR, NE, SN, TD, TG)
`
`[Continued on next page}
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`iiiiiiiiiiii ---iiiiiiiiiiii
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`iiiiiiiiiiii ----
`
`(54) Title: THRESHOLD VOLTAGE COMPENSATION METHOD FOR ELECTROLUMINESCENT DISPLAY DEVICES
`
`6
`
`(57) Abstract: An active matrix electroluminescent
`display device has a shorting transistor (30) connected
`between the gate and drain of the drive transistor (22).
`Means (42) is provided for measuring a voltage on the
`data line (6). The shorting transistor (30) can be used to
`discharge the voltage on the gate of the drive transistor
`(22) until it switches off. By storing the resultant voltage
`on the data line (6) through an address transistor (16), the
`data line is used as one of the control/measurement lines
`for the threshold measurement.
`
`34
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 001
`
`

`

`WO 2005/06 926 7 A 1
`
`I IIIII IIIIIIII II IIIIII IIIII IIIII IIIII IIII I II Ill lllll lllll lllll lllll lllll llll lllllll 111111111111
`
`Published:
`-
`with international search report
`
`For two-letter codes and other abbreviations, refer to the "Guid(cid:173)
`ance Notes on Codes and Abbreviations" appearing at the begin(cid:173)
`ning of each regular issue of the PCT Gazette.
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 002
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`THRESHOLD VOLTAGE COMPENSATION METHOD FOR ELECTROLUMINESCENT DISPLAY DEVICES
`
`s
`
`This invention relates to electroluminescent display devices, particularly
`
`active matrix display devices having thin film switching transistors associated
`with each pixel.
`
`Matrix display devices employing electroluminescent, light-emitting,
`display elements are well known. The display elements may comprise organic
`
`10
`
`thin film electroluminescent elements, for example using polymer materials, or
`traditional 111-V semiconductor
`else
`light emitting diodes (LEDs) using
`
`compounds. Recent developments in organic electroluminescent materials, :
`particularly polymer materials, have demonstrated their ability to be used
`practically for video display devices. These materials typically comprise one or
`more layers of a semiconducti,ng conjugated polymer sandwiched between a ,
`
`1s
`
`pair of electrodes, one of which is transparent and the other of which is of a
`
`material suitable for injecting holes or electrons into the polymer layer.
`The polymer material can be fabricated using a CVD process, or simply
`
`20
`
`by a spin coating technique using a solution of a soluble conjugated polymer. ,
`Ink-jet printing may also be used. Organic electroluminescent materials exhibit
`
`diode-like 1-V properties, so that they are capable of providing both a display
`function and a switching function, and can therefore be used in passive type
`
`displays. Alternatively, these materials may be used for active matrix display
`
`25
`
`devices, with each pixel comprising a display element and a switching device
`for controlling the current through the display element.
`
`Display devices of this type have current-driven display elements, so
`that a conventional, analogue drive scheme involves supplying a controllable
`
`current to the display element.
`
`It is known to provide a current source
`
`30
`
`transistor as part of the pixel configuration, with the gate voltage supplied to
`
`the current source transistor determining the current through the display
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 003
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`2
`
`element. A storage capacitor holds the gate voltage after the addressing
`
`phase.
`Figure 1 shows a known pixel circuit for an active matrix addressed
`
`electroluminescent display device. The display device comprises a panel
`
`5
`
`having a row and column matrix array of regularly-spaced pixels, denoted by
`
`the blocks 1 and comprising electroluminescent display elements 2 together
`with associated switching means,
`located at the
`intersections between
`
`crossing sets of row (selection) and column (data) address conductors 4 and
`6. Only a few pixels are shown in the Figure for simplicity.
`In practice there
`
`10 may be several hundred rows and columns of pixels. The pixels 1 are
`addressed via the sets of row and column address conductors by a peripheral
`
`drive circuit comprising a row, scanning, driver circuit 8 and a column, data,
`driver circuit 9 connected to the ends of the respective sets of conductors.
`The electroluminescent display element 2 comprises an organic light
`emitting diode, represented here as a diode element (LED) and comprising a
`
`15
`
`pair of electrodes· between which one or more active layers of organic
`electroluminescent material is sandwiched. The display elements of the array
`
`are carried together with· the associated active matrix circuitry on one side ·of
`an insulating ·support. Either the cathodes or the anodes of the display
`
`20
`
`elements are formed of transparent conductive material. The support is of
`transparent material such as glass and the electrodes of the display elements
`
`2 closest to the substrate may consist of a transparent conductive material
`such as ITO so that light generated by the electroluminescent layer is
`
`transmitted through these electrodes and the support so as to be visible to a
`
`25
`
`viewer at the other side of the support. Typically, the thickness of the organic
`
`electroluminescent material layer is between 100 nm and 200nm. Typical
`
`examples of suitable organic electroluminescent materials which can be used
`
`for the elements 2 are known and described in EP-A-0 717446. Conjugated
`
`polymer materials as described in W096/36959 can also be used.
`
`30
`
`Figure 2 shows in simplified schematic form a known pixel and drive
`
`circuitry arrangement for providing voltage-programmed operation. Each pixel
`
`1 comprises the EL display element 2 and associated driver circuitry. The
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 004
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`3
`
`driver circuitry has an address transistor 16 which is turned on by a row
`
`address pulse on the row conductor 4. When the address transistor 16 is
`turned on, a voltage on the column conductor 6 can pass to the remainder of
`
`the pixel.
`
`In particular, the address transistor 16 supplies the column
`
`5
`
`conductor voltage to a current source 20, which comprises a drive transistor 22
`
`and a storage capacitor 24. The column voltage is provided to the gate of the
`drive transistor 22, and the gate is held at this voltage by the storage capacitor
`
`24 even after the row address pulse has ended. The drive transistor 22 draws
`a current from the power supply line 26.
`
`10
`
`The drive transistor 22 in this circuit is implemented as a PMOS TFT, so
`that the storage capacitor 24 holds the gate-source voltage fixed. This results
`in a fixed source-drain current through the transistor, which therefore provides
`the desired current source operation of the pixel.
`
`One problem with voltage-programmed pixels, particularly using
`polysilicon thin film transistors, is that different transistor characteristics across
`
`15
`
`to different
`threshold voltage) give rise
`the substrate (particularly the
`relationships between the gate voltage and the source-drain current, and
`artefacts in the displayed image result.
`Various techniques have been proposed for compensating for these
`
`20
`
`threshold voltage variations. Some techniques perform in-pixel measurement
`of the drive transistor threshold voltage, and add this threshold voltage to the
`
`pixel drive signal, so that the combined drive voltage takes account of the
`threshold voltage. A pixel circuit to perform this requires two storage
`
`capacitors, one for the threshold voltage and one for the pixel drive voltage.
`25 Additional switching transistors are also required to enable the threshold
`
`voltage to be measured, for example by discharging a capacitance across the
`gate-source of the drive transistor until it turns off.
`
`Other proposed techniques perform measurement of the threshold
`
`voltage externally of the pixel array, and then compensate for the threshold
`
`30
`
`voltage by adjusting the pixel drive signals. These pixel circuits again require
`
`additional elements in order to enable signals to be provided to the external
`
`circuitry to enable the threshold voltage to be determined. For example, it has
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 005
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`4
`
`been proposed to measure the pixel current at two drive voltages (both within
`the saturated region of the drive transistor) and to extrapolate the threshold
`
`voltage (and mobility) from them. This provides a more complicated pixel drive
`scheme as well as more complicated pixel circuit.
`
`5
`
`Although this avoids the need for circuit elements for providing in-pixel
`compensation, there still remains a need for a simple pixel circuit which
`
`enables threshold voltage information to be provided to external measuring
`circuitry with a simple drive scheme. Any simplification of the pixel circuitry
`
`makes manufacturing of large size displays less problematic and improves
`yield.
`In addition, a reduction in the number of pixel circuit elements can
`
`10
`
`enable the pixel aperture to be increased (depending on the configuration of
`the pixel circuits), and a reduction in space needed for the pixel circuitry
`enables resolution to be increased.
`
`15
`
`20
`
`25
`
`30
`
`is provided an active matrix
`there
`invention,
`the
`to
`According
`electroluminescent display device comprising an array of display pixels, each
`· pixel comprising:
`an electroluminescent (EL) display element;
`a drive transistor for driving a current through the display element;
`an address transistor for providing a pixel drive signal from a data line to
`the gate of the drive transistor; and
`
`a shorting transistor connected between the gate and drain of the drive
`transistor,
`wherein the display device further comprises means for measuring a
`voltage on the data line.
`
`This pixel arrangement enables one additional transistor (the shorting
`transistor) to be used to discharge the voltage on the gate of the drive
`
`transistor until it switches off. By storing the resultant voltage on the data line
`(through the address transistor), the data line is used as one of the
`control/measurement lines for the threshold measurement. This reduces the
`pixel complexity.
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 006
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`5
`
`The EL display element and
`
`the drive transistor are preferably
`
`connected in series between first and second power lines, and the voltage on
`
`the second power line can be switchable between two values, one of which
`
`causes the EL display element to be turned off. Again, this enables the
`
`5
`
`common cathode line (in particular) to be used as one of the control lines for
`
`the threshold measurement operation, again limiting any additional complexity
`
`of the pixel circuit.
`The data input line is preferably switchable between a voltage driving
`mode in which it provides voltages to the pixels connected to the line (the
`
`10
`
`normal pixel drive mode) and a floating mode. In the floating mode, the data
`line can float to the voltage of the gate of the drive transistor of an addressed
`
`pixel. Thus, the resultant gate voltage is stored· on the data line, in particular
`on the existing column capacitance.
`
`Thus, each pixel is operable in two modes. In a first, threshold voltage
`15 measuring mode, the display element is disabled, the address transistor is
`
`turned on and the shorting transistor is turned on. The drive transistor current
`is shorted to the gate, and the gate voltage thus rises until the transistor
`
`switches off (if it is a p-type device). In a second, pixel drive mode, the display
`element is enabled, the address transistor is turned on and the shorting
`
`20
`
`transistor is turned off. This is the normal drive mode.
`During the first, threshold voltage measuring mode, during a first period
`
`a predetermined voltage is applied to the data line so that a current is driven
`through the drive transistor and during a second period the data line is allowed
`
`to float so that the voltage on the data line substantially follows the gate
`
`25
`
`voltage of the drive transistor.
`
`In this way, the first period makes sure a
`
`current is sourced through the drive transistor. The second period allows the
`
`drive transistor to be turned off as described above, with the resultant gate
`
`voltage stored on the data line.
`The drive transistor is preferably a polysilicon TFT, for example a p-type
`
`30
`
`low temperature polysilicon TFT.
`A storage capacitor is preferably between the gate and source of the
`
`drive transistor.
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 007
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`6
`
`The invention also provides a method of addressing the pixels of an
`
`an
`comprising
`device,
`display
`electroluminescent
`active matrix
`electroluminescent {EL) display element and a drive transistor for driving a
`current through the display element, the method comprising:
`
`5
`
`disabling the display element;
`applying a first voltage to a data line;
`
`driving a current through the drive transistor, through a shorting
`transistor connected between the gate and drain of the drive transistor and
`
`through an address transistor connected between the gate of the drive
`transistor and the data line;
`
`10
`
`allowing the data line electrically to float;
`measuring a voltage on the data line; and
`modifying a data voltage to be applied to the drive transistor using the
`voltage measured on the data line.
`
`This method provides the operation of the device of the invention.
`Disabling the display element preferably comprises applying a disable
`
`voltage to a terminal of the display element, for example a common cathode
`terminal.
`The.method preferably further comprises enabling the display element,
`
`and addressing the pixel with the modified data voltage on the data line, with
`the shorting transistor turned off.
`
`15
`
`1
`
`•
`
`20
`
`The invention will now be described by way of example with reference
`
`to the accompanying drawings, in which:
`
`25
`
`Figure 1 shows a known EL display device;
`
`Figure 2 is a schematic diagram of a known pixel circuit for current(cid:173)
`addressing the EL display pixel using an input drive voltage;
`Figure 3 shows a schematic diagram of pixel layout for a display device
`
`of the invention;
`
`30
`
`Figure 4 shows the timing diagrams for the operation of the circuit of
`
`Figure 3; and
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 008
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`7
`
`Figure 5 shows one possible design of column driver circuit for use
`within the display device of the invention.
`
`The same reference numerals are used in different figures for the same
`
`s
`
`components, and description of these components will not be repeated.
`
`The invention provides a display pixel circuit in which one additional
`transistor is connected between the gate and drain of the drive transistor in
`
`order to provide a threshold voltage measurement function, externally of the
`pixel array.
`Figure 3 shows a pixel arrangement in accordance with the invention.
`As in the conventional pixel of Figure 2, the pixel is voltage-addressed, and a
`storage capacitor 24 holds the voltage on the gate of the drive transistor 22
`after the pixel addressing phase.
`Compared to the standard pixel layout of Figure 2, the invention
`provides one additional shorting transistor 30 connected between the gate and
`drain of the drive transistor 22. This is controlled by an additional control line
`32. The invention also requires the common cathode terminal 34
`to be
`switchable between two voltages, as will be apparent from the description of
`the operation of the circuit below.
`The shorting transistor 30 is used to discharge the voltage on the gate
`of the drive transistor 22 until it switches off. This discharge operation involves
`the removal of charge from the storage capacitor 24 until the voltage across
`the capacitor reaches the threshold voltage. The resulting voltage on the data
`line, through the address transistor which is turned on, is measured.
`The operation of the circuit of Figure 3 will now be explained with
`reference to the timing diagram of Figure 4. Figure 4 shows only the part of
`the address cycle during which the threshold voltage of the drive transistor is
`
`measured.
`Plot 4 shows the operation of the address transistor 16. Before (or at
`the same time as) the address pulse, the cathode line 34 is brought high
`disabling the display element, by ensuring it is reverse biased.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 009
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`8
`
`A first voltage is applied to the data line 6 during period 40, and this
`voltage ensures that a current can be driven through the drive transistor 22,
`
`once the shorting transistor 30 has been turned on. When the shorting
`transistor is turned on, as shown in plot 32, it provides a path from the power
`supply line 26, through the drive transistor 22, through the address transistor
`16 to the data line 6. As shown, the first voltage on the data line 6 can be
`
`ground.
`Once a current flow has been established through the drive transistor
`22, the data line is made to float, by placing the data line in a high impedance
`state. The data line is a column conductor for a column of pixels, and is
`associated with a column capacitance.
`As the gate voltage for the drive transistor 22 is held by the capacitor
`24, it remains conducting, and the path for the drain-source current is through
`the shorting transistor 30 and the capacitor 24. This has the effect of reducing
`the voltage drop across the capacitor (which was previously the difference
`between the "first voltage" e.g. ground and the power supply line voltage).
`When the voltage across the capacitor has "discharged" to the threshold
`voltage (although the voltage on the gate is rising), the drive transistor 22
`switches off, and no further current flows. Thus, the capacitor 24 stores the
`threshold voltage, and this voltage is transferred to the column capacitance.
`In practice, the column capacitance charges relatively slowly, and
`continues to charge until it reaches the power supply line voltage, as the drive
`transistor 22 will have significant sub-threshold currents.
`The voltage on the data line is measured to enable the threshold
`voltage to be determined.
`In view of the sub-threshold currents mentioned
`above, the data line voltage is measured as soon as the voltage has had time
`to stabilise at the gate voltage corresponding to switch-off of the drive
`transistor. This time may be around 1 ms after the data line is allowed to float,
`and is within the period shown as 42.
`Once the threshold voltage has been determined, the pixel data
`voltages to be applied to the pixels are modified. This can be carried out in the
`column driver circuits, and can be carried out in the digital or analogue domain.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 010
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`9
`
`It will be immediately apparent to those skilled in the art how pixel data signals
`can be modified before application to the display. In some cases, a field store
`
`may be required so that all threshold values can be obtained before
`compensation, or else it may be possible to correct the data voltage to be
`
`5
`
`applied immediately after the measurement.
`As will now be apparent, the invention requires only minor modifications
`
`In addition to the one extra shorting
`to the standard pixel circuit of Figure 2.
`transistor, a switchable common cathode terminal is required.
`
`The high impedance state for the data input line as well as the voltage
`10 measurement circuitry are implemented outside the pixel array, in particular in
`
`the column driver circuit. This may be on a separate substrate, and in
`crystalline silicon, although some or all of the column driver functions can also
`be implemented on the same substrate as the pixel array, using L TPS
`processing.
`
`15
`
`The invention enables compensation for the threshold voltage variations
`in polysilicon drive transistors (for example a low temperature polysilicon
`TFTs} .
`.The circuit above uses a p-type drive transistors. There is of course an
`equivalent n.,-type implementation.
`
`20
`
`, The processing of the threshold voltage measurement from the pixel
`
`circuit of the invention can be carried out in a variety of ways. The measured
`
`threshold voltage can be combined digitally with the pixel data signal before
`DIA conversion) or in the analogue domain. This combination can take place
`
`immediately after the threshold voltage measurement, so that the delay in
`providing image data to the display is kept to a minimum.
`
`25
`
`Figure 5 shows one example of possible architecture for the column
`
`driver circuit. The circuit is operable in two modes, defined by an output switch
`
`40 for each column.
`
`During a sense mode, the switch 40 connects the column 6 to sense
`
`30
`
`circuitry, comprising a voltage sense circuit 42. The sense circuit 42 measures
`
`the voltage on the column at the end of the sense period. It then passes this
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 011
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`10
`
`data to a frame store 44. The frame store stores the threshold voltages of all
`
`the drive TFTs in the display.
`
`During a pixel driving mode, the switch 40 connects the column 6 to a
`column drive circuit 46. The data for a pixel is then supplied to the column
`
`5
`
`driver 46 and the frame store 44 supplies the corresponding threshold voltage.
`These are added together by adder 48 to give the data plus the threshold
`
`voltage offset, which combination signal is passed to the column driver 46.
`This is an analogue implementation, but the measured threshold voltages
`
`could equally be digitised for processing with the pixel data in the digital
`domain.
`
`10
`
`The threshold measurement can be carried out once per frame of image
`data, so that the threshold measurement cycle is part of every addressing
`
`phase. In this case, the threshold measurement operations precede the pixel
`drive operation.
`
`15
`
`However, the threshold measurement does not need to performed this
`frequently, as the compensation required derives more from variations across
`
`the substrate than differential ageing. Thus, the threshold measurement can
`be carried out at the beginning of a display cycle, for example each time the
`display is turned on.
`
`20 ·
`
`The specific voltages applied to the pixel circuit of the invention have
`not been described in detail, nor the detailed timing requirements, as these are
`
`all routine design parameters to those skilled in the art.
`
`The example of column driver shows as a "means for measuring
`
`column voltage" a column voltage sense circuit. This circuit can take various
`forms, and numerous specific circuits for this purpose will be apparent to those
`
`25
`
`skilled in the art.
`
`Various other modifications will be apparent to those skilled in the art.
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 012
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`11
`
`CLAIMS
`
`1.
`
`An active matrix electroluminescent display device comprising an array
`
`of display pixels, each pixel comprising:
`
`an electroluminescent (EL) display element (2);
`a drive transistor (22) for driving a current through the display element
`
`5
`
`(2);
`
`an address transistor (16) for providing a pixel drive signal from a data
`
`line to the gate of the drive transistor (22); and
`a shorting transistor (30) connected between the gate and drain of the
`
`. 10
`
`drive transistor,
`wherein the display device further comprises means (42) for measuring
`
`a voltage on the data line.
`
`15
`
`A device as claimed in claim 1, wherein the EL display element (2) and
`2.
`the drive transistor (22) are connected in series between first (26) and second
`
`(34) power lines.
`
`20
`
`A device as claimed in claim 2, wherein the voltage on the second
`3.
`power line (34) is switchable between two values, one of which causes the EL
`display element (2) to be turned off.
`
`4.
`
`A device as claimed in any preceding claim, wherein the data input line
`
`(6) is switchable between a voltage driving mode in which it provides voltages
`to the pixels connected to the line and a floating mode in which it can float to
`
`25
`
`the voltage of the gate of the drive transistor of an addressed pixel.
`
`5.
`
`A device as claimed. in any preceding claim, wherein each pixel is
`
`operable in two modes:
`
`30
`
`a first, threshold voltage measuring mode, in which the display element
`
`is disabled, the address transistor is turned on and the shorting transistor is
`
`turned on; and
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 013
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`12
`
`a second, pixel drive mode, in which the display element is enabled, the
`address transistor is turned on and the shorting transistor is turned off.
`
`6.
`
`A device as claimed in claim 5, wherein during the first, threshold
`
`5
`
`voltage measuring mode, during a first period (40) a predetermined voltage is
`applied to the data line so that a current is driven through the drive transistor
`
`(22) and during a second period (42) the data line is allowed to float so that the
`voltage on the data line (6) substantially follows the gate voltage of the drive
`
`transistor (22).
`
`10
`
`A device as claimed in any preceding claim, wherein the drive transistor
`7.
`(22) is a polysilicon TFT.
`
`A device as claimed in claim 7, wherein the drive transistor (22) is a low
`8.
`temperature polysilicon TFT.
`
`15
`
`A device as claimed in any preceding claim, further compnsrng a
`9.
`storage capacitor (24) between the gate and source of the drive transistor {22).
`
`20
`
`10.
`
`A method of addressing
`
`the pixels of an active matrix
`
`electroluminescent display device, comprising an electroluminescent (EL)
`
`display element (2) and a drive transistor (22) for driving a current through the
`display element (2), the method comprising:
`
`disabling the display element (2);
`
`25
`
`applying a first voltage to a data line (6);
`
`driving a current through the drive transistor (22), through a shorting
`
`transistor (30) connected between the gate and drain of the drive transistor
`
`and through an address transistor (16) connected between the gate of the
`
`drive transistor and the data line (6);
`
`30
`
`allowing the data line (6) electrically to float;
`
`measuring a voltage on the data line (6); and
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 014
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`13
`
`modifying a data voltage to be applied to the drive transistor (22) using
`
`the voltage measured on the data line.
`
`11.
`
`A method as claimed in claim 10, wherein disabling the display element
`
`5
`
`comprising applying a disable voltage to a terminal of the display element.
`
`12.
`
`A method as claimed in claim 11, wherein disabling the display element
`
`comprising applying a disable voltage to terminal (34) of the display element
`(2) which is common to all display elements.
`
`10
`
`13.
`
`A method as claimed in any one of claims 1 O to 12, further comprising
`
`enabling the display element (2), and addressing the pixel with the modified
`data voltage on the data line, with the shorting transistor turned off.
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 015
`
`

`

`WO 2005/069267
`
`PCT/IB2005/050029
`
`1/3
`
`i-.,--- 6 ----
`
`g---._
`
`8
`
`\
`
`1
`f
`J
`\... T (
`,,_ ~
`
`,..--
`
`T
`
`,,--
`
`,..--
`
`T
`
`l
`
`T
`
`T
`
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`
`,,--
`
`-
`
`1
`)
`I (
`
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`- )
`I /
`
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`
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`
`~
`
`T
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`
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`
`I
`
`l
`
`,_
`
`·~
`
`-
`-
`
`I
`
`T
`
`T
`
`FIG. 1 PRIOR ART
`
`J4
`
`,u
`
`4
`
`r
`
`6
`
`24
`
`r ------------,
`I
`I
`I 26
`I
`I
`~ 1
`I
`I
`I
`I
`I
`
`1
`I
`I
`
`16
`
`I
`I
`2 :
`:
`I
`I
`L ------- ___ _J
`
`FIG. 2 PRIOR ART
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 016
`
`

`

`WO 2005/069267
`
`PCT/IB2005/050029
`
`2/3
`
`6
`
`26
`
`FIG. 3
`
`34
`
`42
`
`I
`
`llol
`
`I~
`I
`
`I
`I
`I
`I
`I
`I
`
`I
`
`I
`I
`I
`I
`I
`I
`
`I
`
`I
`I
`
`I
`I
`I
`I
`I
`I
`
`-~
`
`32
`(shorting)
`
`J~
`
`4
`(address)
`
`I
`I
`I
`I
`I
`I
`I
`
`I
`I
`
`I
`I
`I
`I
`I
`I
`I
`
`I
`I
`I
`I
`I
`I
`
`I
`
`34
`(cathode)
`
`6
`(data line)
`
`I
`I
`I
`I
`I
`I
`'--y---1
`40
`
`FIG. 4
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 017
`
`

`

`WO 2005/069267
`
`PCT /IB2005/050029
`
`3/3
`
`Column
`data
`
`44
`
`42
`
`Threshold
`voltage
`frame store
`
`48
`
`Column
`voltage
`sense circuit
`
`Column
`data drive
`circuit
`
`46
`
`40-
`
`6
`
`FIG. 5
`
`LG Display Co., Ltd.
`Exhibit 1006
`Page 018
`
`

`

`INTERNATIONAL SEARCH REPORT
`
`1al Application No
`Inter,
`PCT/IB2005/050029
`
`A. CLASSIFICATION oiuBJECT MATTER
`IPC 7 G09G3 32
`
`According to International Patent Classification (IPC) or to both national classification and IPC
`
`B. FIELDS SEARCHED
`Minimum documentation searched (classification system followed by classification symbols)
`IPC 7 G09G
`
`Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched
`
`Electronic data base consulted during the international search (name of data base and, where practical, search terms used)
`EPO-Internal, WPI Data, PAJ
`
`C. DOCUMENTS CONSIDERED TO BE RELEVANT
`
`Category 0 Citation of document, with indication, where appropriate, of the relevant passages
`
`Relevant to claim No.
`
`P,X
`
`X
`
`A
`
`us 2004/017161 Al (CHOI JEUNG-HIE)
`29 January 2004 (2004-01-29)
`the whole document
`-----
`WO 98/48403 A (SARNOFF CORPORATION)
`29 October 1998 (1998-10-29)
`page 3, 1 i nes 19-34
`page 6, 1 i ne 20 - page 8,