(12) United States Patent
`Nathan et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,115,707 B2
`Feb. 14, 2012
`
`US008115707B2
`
`(54) VOLTAGE-PROGRAMMING SCHEME FOR
`CURRENT DRIVEN AMOLED DISPLAYS
`
`(75) Inventors: Arokia Nathan, Waterloo (CA); Rick
`Huang, Waterloo (CA); Stefan
`Alexander, Waterloo (CA)
`(73) Assignee: Ignis Innovation Inc., Kitchener,
`Ontario (CA)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 937 days.
`111571,480
`
`(21) Appl. No.:
`
`(*) Notice:
`
`Jun. 28, 2005
`
`(22) PCT Filed:
`(86). PCT No.:
`S371 (c)(1),
`(2), (4) Date:
`(87) PCT Pub. No.: WO2006/000101
`PCT Pub. Date: Jan. 5, 2006
`
`Apr. 22, 2008
`
`(65)
`
`(30)
`
`Prior Publication Data
`US 2008/O191976 A1
`Aug. 14, 2008
`
`Foreign Application Priority Data
`
`Jun. 29, 2004 (CA) ...................................... 2472671
`(51) Int. Cl.
`(2006.01)
`G09G 3/30
`(52) U.S. Cl. ............ 345/78:345/76; 34.5/214; 34.5/600;
`315/169.3
`(58) Field of Classification Search .............. 345/76-81,
`345/82, 83, 204-214, 600-605, 690-699;
`315/169.3
`See application file for complete search history.
`
`(56)
`
`References Cited
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`Primary Examiner — Amare Mengistu
`Assistant Examiner — Dmitriy Bolotin
`(74) Attorney, Agent, or Firm — Nixon Peabody LLP
`
`ABSTRACT
`(57)
`A system and method for driving an AMOLED display is
`provided. The AMOLED display includes a plurality of pixel
`circuits. A Voltage-programming scheme, a current-program
`ming scheme or a combination thereof is applied to drive the
`display. Threshold shift information, and/or Voltage neces
`sary to obtain hybrid driving circuit may be acquired. A data
`sampling may be implemented to acquire a current/voltage
`relationship. A feedback operation may be implemented to
`correct the brightness of the pixel.
`
`37 Claims, 23 Drawing Sheets
`
`- 2
`
`- 18A
`
`
`
`Wise
`Gate driver
`
`/ 18B
`
`- 10
`
`Pixel Circuit
`
`5
`
`Pixel Circuit
`
`Pixel Circuit
`
`Hybrid signal
`
`
`
`
`
`Hybrid
`Driving
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 001
`
`

`

`US 8,115,707 B2
`Page 2
`
`s's
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`
`»s.
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 002
`
`

`

`US 8,115,707 B2
`Page 3
`
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`* cited by examiner
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 003
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 1 of 23
`
`US 8,115,707 B2
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 004
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 2 of 23
`
`US 8,115,707 B2
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`g N
`
`
`
`g
`
`2
`-
`55
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 005
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 3 of 23
`
`US 8,115,707 B2
`
`
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`s
`N s
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`
`g
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`s
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`
`
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 006
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 4 of 23
`
`US 8,115,707 B2
`
`Enabling pre-charge mode
`
`Selecting a pixel circuit, and
`Pre-charging (Vp)
`
`Enabling Vt acquisition mode
`
`Discharging (Vp)
`
`Enabling writing mode
`
`SO
`
`S12
`
`S14
`
`S16
`
`S18
`
`FIG. 4
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 007
`
`

`

`U.S. Patent
`
`US 8,115,707 B2
`
`Ç’OIH
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 008
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 6 of 23
`
`US 8,115,707 B2
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 009
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 7 of 23
`
`US 8,115,707 B2
`
`S10
`
`S12
`
`S14
`
`S16
`
`S20
`
`S22
`
`Sl. 8
`
`S24
`
`Enabling pre-charge mode
`
`Selecting a pixel circuit, and
`Pre-charging (Vp)
`
`Enabling Vt acquisition mode
`
`w
`Discharging (Vp)
`
`Sampling Vit (42)
`
`
`
`Producing new data (i.e. the
`sum of Vt and Vdata) (40)
`
`Enabling writing mode
`
`programming
`a
`Enabling
`control signal (46)
`
`FIG. 7
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 010
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 8 of 23
`
`US 8,115,707 B2
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`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 011
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 9 of 23
`
`US 8,115,707 B2
`
`h
`
`Enabling pre-charge mode
`
`S10
`
`Selecting a pixel circuit, and
`Pre-charging
`
`Enabling Vt acquisition mode
`
`Discharging
`
`h
`
`S12
`
`S14
`
`S16
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`-
`
`Vit
`Sampling
`Recording Vit (50)
`
`(56)
`
`
`
`and
`
`S30
`
`Enabling writing mode
`
`Providing new data (i.e. sum of
`Vt and Vdata)
`
`S18
`
`S32
`
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`
`
`
`
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`
`FIG. 9
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 012
`
`

`

`U.S. Patent
`
`US 8,115,707 B2
`
`() I "OIH
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 013
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 11 of 23
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`Feb. 14, 2012
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`Page 015
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 015
`
`
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`
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`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 13 of 23
`
`US 8,115,707 B2
`
`Enabling a calibration mode
`
`Selecting a pixel circuit and
`Current-programming (94) to
`the pixel circuit
`
`
`
`Enabling switch matrix enable
`signal
`
`Sampling Vit (96)
`
`Creating (correcting) correction
`table (80)
`
`S40
`
`S42
`
`S44
`
`S46
`
`S48
`
`FIG. 13
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 016
`
`

`

`U.S. Patent
`
`Feb. 14, 2012
`
`Sheet 14 of 23
`
`US 8,115,707 B2
`
`Correcting Video data based on
`the correction table (92)
`
`
`
`
`
`Producing Vdata based on the
`corrected data (14)
`
`S50
`
`S52
`
`FIG. 14
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 017
`
`

`

`US. Patent
`
`Feb. 14, 2012
`
`Sheet 15 of 23
`
`US 8,115,707 B2
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 018
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 018
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`U.S. Patent
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`Feb. 14, 2012
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`Sheet 16 of 23
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`US 8,115,707 B2
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`Producing a current/voltage
`correction curve
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`Measuring a point along the curve
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`correction curve.
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 019
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`U.S. Patent
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`Feb. 14, 2012
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`Sheet 17 of 23
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`US 8,115,707 B2
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 020
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`U.S. Patent
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`Feb. 14, 2012
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`Sheet 18 of 23
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`U.S. Patent
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`Feb. 14, 2012
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`Sheet 19 Of 23
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`US 8,115,707 B2
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 022
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`U.S. Patent
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`Feb. 14, 2012
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`U.S. Patent
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`Feb. 14, 2012
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`U.S. Patent
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`Feb. 14, 2012
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`Sheet 22 of 23
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`US 8,115,707 B2
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`U.S. Patent
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`US 8,115,707 B2
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`£Z "OIH
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`LG Display Co., Ltd.
`Exhibit 1016
`Page 026
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`

`

`1.
`VOLTAGE-PROGRAMMING SCHEME FOR
`CURRENT DRIVEN AMOLED DISPLAYS
`
`FIELD OF INVENTION
`
`The present invention relates to a display technique, and
`more specifically to technology for driving pixel circuits.
`
`BACKGROUND OF THE INVENTION
`
`Active matrix organic light emitting diode (AMOLED)
`displays are well known in the art. The AMOLED displays
`have been increasingly used as a flat panel in a wide variety of
`tools.
`The AMOLED displays are classified as either a voltage
`programmed display or a current-programmed display. The
`Voltage-programmed display is driven by a Voltage-pro
`grammed Scheme where data is applied to the display as a
`Voltage. The current-programmed display is driven by a cur
`rent-programmed scheme where data is applied to the display
`as a Current.
`The advantage of the current-programming scheme is that
`it can facilitate pixel designs where the brightness of the pixel
`remains more constant over time than with Voltage program
`ming. However, the current-programming requires longer
`time of charging capacitors associated with the column.
`Therefore, there is a need to provide a new scheme for
`driving a current-driven AMOLED display, which ensures
`high speed and high quality.
`
`10
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`15
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`SUMMARY OF THE INVENTION
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`30
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`40
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`45
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`The present invention relates to a system and method of
`driving a pixel circuit in an AMOLED display.
`The system and method of the present invention uses Volt
`35
`age-Programming Scheme For Current-Driven AMOLED
`DisplayS.
`In accordance with an aspect of the present invention there
`is provided a system for driving a display which includes a
`plurality of pixel circuits, each having a plurality of thin film
`transistors (TFTs) and an organic light emitting diode
`(OLED), which includes: a voltage driver for generating a
`Voltage to program the pixel circuit; a programmable current
`Source for generating a current to program the pixel circuit;
`and a Switching network for selectively connecting the data
`driver or the current source to one or more pixel circuits.
`In accordance with a further aspect of the present invention
`there is provided a system for driving a pixel circuit having a
`plurality of thin film transistors (TFTs) and an organic light
`emitting diode (OLED), which includes: a pre-charge con
`troller for pre-charging and discharging a data node of the
`pixel circuit to acquire threshold Voltage information of the
`TFT from the data node; and a hybrid driving circuit for
`programming the pixel circuit based on the acquired thresh
`old Voltage information and video data information displayed
`on the pixel circuit.
`In accordance with a further aspect of the present invention
`there is provided a system for driving a pixel circuit having a
`plurality of thin film transistors (TFTs) and an organic light
`emitting diode (OLED), which includes: a sampler for sam
`60
`pling, from a data node of the pixel circuit, a Voltage required
`to program the pixel circuit; and a programming circuit for
`programming the pixel circuit based on the sampled Voltage
`and video data information displayed on the pixel circuit.
`In accordance with a further aspect of the present invention
`there is provided a method of driving a pixel circuit having a
`plurality of thin film transistors (TFTs) and an organic light
`
`50
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`US 8,115,707 B2
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`2
`emitting diode (OLED), which includes the steps of selecting
`a pixel circuit and pre-charging a data node of the pixel
`circuit; allowing the pre-charged data node to be discharged;
`extracting a threshold voltage of the TFT through the dis
`charging step; and programming the pixel circuit, including
`compensating a programming data based on the extracted
`threshold voltage.
`This Summary of the invention does not necessarily
`describe all features of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`These and other features of the invention will become more
`apparent from the following description in which reference is
`made to the appended drawings wherein:
`FIG. 1 is a block diagram showing a system for driving an
`AMOLED display in accordance with an embodiment of the
`present invention;
`FIG. 2 is a schematic diagram showing one example of a
`pixel circuit of FIG. 1;
`FIG. 3 is a schematic diagram showing an example of a
`hybrid driving circuit, which is applicable to FIG. 1;
`FIG. 4 is an exemplary flow chart for showing the operation
`of the hybrid driving circuit of FIG. 3;
`FIG. 5 is an exemplary timing chart for showing the opera
`tion of the hybrid driving circuit of FIG. 3;
`FIG. 6 is a schematic diagram showing a further example of
`a hybrid driving circuit, which is applicable to FIG. 1;
`FIG. 7 is an exemplary flow chart for showing the operation
`of the hybrid driving circuit of FIG. 6;
`FIG. 8 is a schematic diagram showing a further example of
`a hybrid driving circuit, which is applicable to FIG. 1;
`FIG.9 is an exemplary flow chart for showing the operation
`of the hybrid driving circuit of FIG. 8:
`FIG. 10 is an exemplary timing chart for showing the
`operation of the hybrid driving circuit of FIG. 8:
`FIG. 11 is a schematic diagram showing a further example
`of the pixel circuit of FIG. 1;
`FIG. 12 is a block diagram showing a system for driving an
`AMOLED display in accordance with a further embodiment
`of the present invention;
`FIG. 13 is an exemplary flow chart for showing the opera
`tion of the system of FIG. 12;
`FIG. 14 is an exemplary flow chart for showing the opera
`tion of the system of FIG. 12;
`FIG. 15 is an exemplary timing chart for showing the
`operation of the system of FIG. 12;
`FIG. 16 is an exemplary flow chart for a hidden refresh
`operation of the system of FIG. 12;
`FIG.17 is a diagram showing an example of a sample of the
`current/voltage correction curve;
`FIG. 18 is a diagram showing the current/voltage correc
`tion curve of FIG. 17 and an example of a newly measured
`data point:
`FIG. 19 is a diagram showing an example of a new current/
`voltage correction curve based on the measured point of FIG.
`18:
`FIG. 20 is a block diagram showing a further example of a
`programming circuit for implementing a combined current
`and Voltage-programming technique;
`FIG. 21 is a block diagram showing a system for driving an
`AMOLED display in accordance with a further embodiment
`of the invention;
`FIG. 22 is a schematic diagram showing an example of a
`switch network of FIG. 21; and
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 027
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`US 8,115,707 B2
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`3
`FIG. 23 is a schematic diagram showing a system for
`correcting the current/voltage information of the pixel circuit.
`
`DETAILED DESCRIPTION
`
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`Embodiments of the present invention are described using
`an AMOLED display. Drive scheme described below is appli
`cable to a current programmed (driven) pixel circuit and a
`Voltage programmed (driven) pixel circuit.
`In addition, hybrid technique described below can be
`applied to any existing driving scheme, includinga) any drive
`schemes that use Sophisticated timing of the data, select, or
`power inputs to the pixels to achieve increased brightness
`uniformity, b) any drive schemes that use current or Voltage
`feedback, c) any drive schemes that use optical feedback.
`The light emitting material of the pixel circuit can be any
`technology, specifically organic light emitting diode (OLED)
`technology, and in particular, but not limited to, fluorescent,
`phosphorescent, polymer, and dendrimer materials.
`Referring to FIG. 1, there is illustrated a system 2 for
`driving an AMOLED display 5 in accordance with an
`embodiment of the present invention. The AMOLED display
`5 includes a plurality of pixel circuits. In FIG. 1, four pixel
`circuits 10 are shown as an example.
`The system 2 includes a hybrid driving circuit 12, a voltage
`Source driver 14, a hybrid programming controller 16, a gate
`driver 18A and a power-supply 18B. The pixel circuit 10 is
`selected by the gate driver 18A (Vsel), and is programmed by
`either Voltage mode using a node Vdata or current mode using
`a node Idata. The hybrid driving circuit 12 selects the mode of
`programming, and connects it to the pixel circuit 10 through
`a hybrid signal. A pre-charge signal (Vp) is applied to the
`pixel circuit 10 to acquire threshold Vt information (or Vt
`shift information) from the pixel circuit 10. The hybrid driv
`ing circuit 12 controls the pre-charging, if pre-charging tech
`nique is used. The pre-charge signal (Vp) may be generated
`within the hybrid driving circuit 12, which depends on the
`operation condition. The power-supply 18B (Vdd) supplies
`the current required to energize the display 5 and to monitor
`the power consumption of the display 5.
`40
`The hybrid controller 16 controls the individual compo
`nents that make up the entire hybrid programming circuit.
`The hybrid controller 16 handles timing and controls the
`order in which the required functions occur. The hybrid con
`troller 16 may generate data Idata and supplied to the hybrid
`driving circuit 12. The system 2 may have a reference current
`source, and the Idata may be supplied under the control of the
`hybrid controller 16.
`The hybrid driver 12 may be implemented either as a
`switching matrix, or as the hybrid driving circuit(s) of FIG.3,
`6, 8 or 20 or combination thereof.
`In the description, Vdata refers to data, a data signal, a data
`line or a node for Supplying the data or data signal Vdata, or
`a voltage on the data line or the node. Similarly, Idata refers to
`data, a data signal, a data line or a node for Supplying the data
`or data signal Idata, or a current on the data line or the node.
`Vp refers to a pre-charge signal, a pre-charge pulse, a pre
`charge Voltage for pre-charging/discharging, a line or a node
`for Supplying the pre-charge signal, pre-charge pulse or pre
`charge Voltage Vp. Vsel refers to a pulse or a signal for
`selecting a pixel circuit or a line or a node for Supplying the
`pulse or signal Vs. The terms “hybrid signal”, “hybrid signal
`node', and “hybrid signal line' may be used interchangeably.
`The pixel circuit 10 includes a plurality of TFTs, and an
`organic light emitting diode (OLED). The TFT may be an
`n-type TFT or a p-type TFT. The TFT is, for example, but not
`limited to, an amorphous silicon (a-Si:H) based TFT, a poly
`
`50
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`crystalline silicon based TFT, a crystalline silicon based TFT,
`or an organic semiconductor based TFT. The OLED may be
`regular (P-I-N) stack or inverted (N-I-P) stack. The OLED
`can be located in the source or the drain of one or more driving
`TFTS.
`FIG. 2 illustrates an example of the pixel circuit 10 of FIG.
`1. The pixel circuit of FIG.2 includes fourthin film transistors
`(TFTs) 20-26, a capacitor Cs 28 and an organic light emitter
`diode (OLED)30. The TFT (Tdrive) 26 is a drive TFT that is
`connected to the OLED30 and the capacitor Cs28. The pixel
`circuit of FIG. 2 is selected by the select line Vsel, and is
`programmed by a data line DL. The data line DL is controlled
`by the hybrid signal output from the hybrid driving circuit 12
`of FIG. 1.
`In FIG. 2, four TFTs are illustrated. However, the pixel
`circuit 10 of FIG.1 may include less than four TFTs or more
`than four TFTs.
`In the description, the terms “data line DL and “data node
`DL may be used interchangeably.
`Referring to FIGS. 1-2, the data node DL is pre-charged
`and discharged to acquire the threshold Vt of a drive TFT
`(e.g., Tdrive 26 of FIG. 2) or the threshold Vit shift. In the
`description, Vt shift, Vt shift information, Vt, and Vt infor
`mation may be used interchangeably. The pixel circuit 10 is
`then consecutively programmed by the Source driver 14 using
`Voltage-programming. The acquired Vit shift information is
`utilized to compensate for degradation of the pixel circuit 10,
`thus maintaining uniform brightness of the display 5.
`The process of acquiring Vit starts by applying Vsel to T1
`20 and T2 22 to the pixel circuit illustrated in FIG. 2. Such
`action causes the drain and gate of T3 24 to be at the same
`voltage. This allows the Vt of T3 24 to be extracted by first
`applying the pre-charge Voltage Vp to the data line DL, which
`is than allowed to be discharged. The rate of discharge is a
`function of Vt. Thus, by measure of the rate of discharge, Vt
`can be obtained.
`FIG. 3 illustrates an example of a hybrid driving circuit,
`which is applicable to the hybrid driving circuit 12 of FIG.1.
`The hybrid driving circuit 12A of FIG.3 implements voltage
`programming technique.
`The hybrid driving circuit 12A of FIG. 3 includes a charge
`programming capacitor Ce 32. The charge programming
`capacitor CC 32 is provided between the data line Vdata and
`the data node DL. The pre-charge line Vp is also connected to
`the data node DL.
`The hybrid driving circuit 12A is provided to a pixel circuit
`10A having four TFTs (such as the pixel circuit of FIG. 2).
`However, the pixel circuit 10A may include more than four
`TFTs or less than four TFTs.
`The charge programming capacitor CC 32 is provided to
`program the pixel circuit 10A with a Voltage that is equal to
`the sum of threshold Vt of the TFT and Vdata, scaled by a
`constant K. The constant is determined by the voltage divi
`sion network formed by the charge storage capacitor (e.g. Cs
`28 of FIG. 2) and the charge programming capacitor Ce 32.
`FIG. 4 illustrates an exemplary flow chart for showing the
`operation of the hybrid driving circuit 12A of FIG. 3. At step
`S10, pre-charge mode is enabled. At step S12, a pixel circuit
`is selected and pre-charging (Vp) is started. At step S14, Vt
`acquisition mode is enabled, and at step S16, discharging
`(Vp) starts. The Vt information is acquired through CC 32.
`Then at step S18, writing mode is enabled.
`FIG. 5 illustrates an exemplary timing chart for showing
`the operation of the hybrid driving circuit 12A of FIG. 3. In
`the drawings, Vdata0 represents Voltage at the data node (e.g.
`DL of FIG. 2) of the pixel circuit; Idata0 represents-current at
`the data node (e.g. DL of FIG. 2) of the pixel circuit.
`
`LG Display Co., Ltd.
`Exhibit 1016
`Page 028
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`US 8,115,707 B2
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`5
`The programming procedure starts by selecting the pixel to
`be programmed with the pulse Vsel. At the same time, the
`pre-charge pulse Vp is applied to the pixel circuits data input
`(e.g. DL of FIG. 2).
`During the Vt acquisition phase, Voltage on the data line
`(DL) is allowed to be discharged through the pixel circuit,
`which is in a current mirror connection with the Vsel line held
`high. The data line (DL) is discharged to a certain Voltage, and
`the Vt of a drive TFT is extracted from that voltage. The
`Voltage at Vdata is at ground.
`During the programming (writing) phase, the calculated
`compensated Voltage is applied to the data input line (DL) of
`the pixel circuit. The programming routine finishes with the
`lowering of the Vsel signal.
`The calculated compensated Voltage is obtained through
`analog means of a charge programming capacitor Ce32.
`However, any other analog means for obtaining compensated
`Voltage may be used. Further, any (external) digital circuit
`(e.g. 50 of FIG. 7) may be used to obtain the calculated
`compensated Voltage.
`The source driver (14 of FIG. 1) supplies Vdata to the
`capacitor CC 32. When Vdata is increased from ground to the
`desired Voltage level, th