IHS Electronics & Media Key Patent Report AMOLED compensation circuit patent analysis AMOLED pixel driving circuit with threshold voltage and IR-drop compensation July 2013 ihs.com Ian Lim, Senior Analyst, + 82 (0)31 704 7188, Ian.Lim@ihs.com
Contents. I Patent analysis overview 4 1. Analysis background 5 2. Scope and method of patent analysis 6 3. Use of patent information 7. II Technology overview 8 1. AMOLED technology overview 9 2. Vth and IR-Drop of AMOLED 10. III Analysis of patent application trend 11 1. Patent application trend by year 12 2. Patent application trend by technology 13 3. Status of assignees 14 Patents) 15. IV Key patent analysis (50 1. Key patent selection 16 2. Key patent status 17 3. Technology development trends 22 4. Key patent abstracts 26 5. Key patent embodiments 76 V. Analysis of new technology patents (39 patents) 82 1. Selection of new technology patents 83 2. Status of new technology patents 84 3. Technology development trends 88 4. Abstracts of new technology patents 92 5. Embodiments of new technology patents 131. VI Conclusion 137 1. AMOLED market outlook 138 2. Summary of patent application trend 139 3. Patent competitiveness by major company 140 4. Conclusion and implications 141. VII Appendix 142 1. Patent list by company (244 Patents) 143 2
Executive summary This key patent analysis on AMOLED pixel driving circuit for threshold voltage (Vth) and IR-drop compensation deals with US patents published and issued until 4 June 2013 and has extracted a total of 244 related patents. This analysis has conducted a quantitative analysis on the patent application trend with the 244 related patents, and has selected 50 key patents and 39 new technology patents from among them for an in-depth analysis. Analysis of Patent Applications The number of patents for the AMOLED pixel driving circuit (Vth and IR-Drop compensation) technology applied in the United States has been growing, with the threshold voltage (Vth) compensation technology making up the largest portion. Major companies with numerous applications include Samsung Display Co. Ltd., Global OLED Technology LLC, LG Display Co. Ltd, Chimei Innolux Corporation, and Sharp Corporation. Key Patent Analysis Of the 244 US patents, the top 50 issued patents with the greatest number of forward citation have been selected as the key patents for an in-depth analysis on technology development trends, key patent abstracts and embodiments. Analysis of New Technology Patents Of the 244 US patents, 39 patents which had been applied in more than three countries over the past five years (29 published patents, 10 issued patents) have been selected as the new technology patents for an in-depth analysis on technology development trends, key patent abstracts and embodiments. Others Patent list by company (244 patents) 3
I. Patent analysis overview Key Patent Report - Compensation Circuit for AMOLED - 2013 ihs.com
1. Analysis background wide-, OLED a self-light-emitting device, is emerging as a next-generation display because it does not require a back light and has a viewing angle, fast response, and low power consumption. In particular, LG released a 55-inch curved OLED TV in April following the launch of the world s first 55-inch flat panel OLED TV early this year. Samsung has joined LG in releasing a 55-inch curved OLED TV recently, heralding a fierce competition in the OLED TV market. Against this backdrop, OLED TVs look set to flourish in full swing from next year. The OLED mass-production technology is expected to emerge as a major issue, now that OLED TVs can encroach on the area of LCD in the future. When it comes to OLED manufacturing process, technologies on TFT backplane, color patterning, encapsulation, and driving circuit are being actively studied. Among them, a number of studies are under way on the development of compensation circuits to resolve the brightness deterioration caused by the threshold voltage (Vth) and IR-drop in the driving TFT of AMOLED display. That is, brightness of the OLED, a current driving device, changes very sensitively to the changes of electric currents. The driving TFT of each pixel circuit of AMOLED display can have different Vth from each other, which causes deterioration in the uniformity of brightness of display panels. In addition, the IR-drop occurs with the VDD passing through each pixel circuit, so the brightness of pixel gets poorer in the lower part of the panel, which requires compensation. Hereupon, IHS Displaybank publishes a key patent analysis report on AMOLED pixel driving circuit for compensation of Vth and IRdrop. This report extracts related patents especially from the US patents to analyze the patent application trend and patents of major companies. Key patents and new technology patents are picked to provide a range of in-depth analysis. This report will be of a great help to examine the technology development trends and key patented technologies on the AMOLED pixel driving circuit (Vth and IRdrop compensation). 5
2. Scope and method of patent analysis This report examines and analyzes the AMOLED pixel driving circuit technology for Vth and IR-drop compensation. The patent examination deals with US patents published and issued until 4 June 2013, and a total of 244 patents related to the AMOLED pixel driving circuit (Vth and IR-drop compensation) are extracted. In general, US patents are frequently used as an indicator to judge the technological capability of companies. A quantitative analysis on the patent application trend has been conducted on the 244 related patents, and of these, 50 key patents and 39 new technology patents are selected for an in-depth analysis. For reference, the key patents are picked from among the top 50 issued patents with the greatest number of forward citation. The new technology patents are selected from among the patents applied in three or more countries over the past five years. Analysis scope and method 1 Patent Research Scope Research Period: Until 4 June 2013 Subject Countries: US (published/issued patents) Search Scope: Name, abstract, claims Patent Search DB: Focust, USPTO 2 Analysis of Patent Application Trend Patent Research and Removal of Noise Technology Classification and Related Patent Selection Quantitative Analysis by Year, Technology and Assignee 3 Key Patent Analysis (50 Patents) Key Patent Selection Analysis of Technology Development Trends Analysis of Key Patent Abstract and Embodiments 4 Analysis of New Technology Patents (39 Patents) Selection of New Technology Patents Analysis of Technology Development Trends Analysis of New Technology Patent Abstract and Embodiments 5 Conclusion Summary of Patent Application Trend Patent Competitiveness by Major Company Conclusion and Implications Major search keywords: Vth(threshold voltage), IR drop, compensation circuit, AMOLED Notes: Although this analysis report focuses on US patents, the overseas patent applications of companies can be found through the status of patent families. Source: IHS 6
3. Use of patent information Use and benefit of patent information Patent information is objective documents, including technology and corporate information. When well used, the information is expected to provide trends of related technologies and prior arts; to inspire new ideas; and to prevent patent disputes by identifying third parties claim Use of Patent Information (Prior Art Search) Technical information with up-to-date technology trends Legal information with examination history and registration information Company information with corporate strategies including R&D and market entry Scope Legal Information Use Infringement Detection Prior Art Search Benefit Avoidance of Overlapping Investment Patent Information R&D Trend Analysis Determination of R&D Direction Speed-up of R&D Acquisition of Valid Patent Technical Information Company Information Prevention of R&D Repetition Commercialization Review, etc. Invalidation of Competitor s Rights Others Source: IHS 7
II. Technology overview Key Patent Report - Compensation Circuit for AMOLED - 2013 ihs.com
1. AMOLED technology overview Organic light emitting diode (OLED) is divided into passive matrix OLED (PMOLED) and active matrix OLED (AMOLED) by the driving method. PMOLED has a simple structure where organic matter is inserted in between anode wiring and cathode wiring, while AMOLED has TFT, which drives pixels, in each pixel so that it consumes less power and provides superior resolution. In the AMOLED, organic matter is formed in the shape of several thin films between two electrodes. When voltage is applied to both electrodes, the positive charge (positive hole) injected from the anode and the negative charge (positive hole) injected from the cathode meet with each other at the light emitting layer and form exciton to translate into energy such as light or heat. In the AMOLED, organic matter plays the biggest role in transforming electric energy into light energy to use it as display. Because the light is generated in the organic matter layer, AMOLED does not require any light source like back light in the LCD, so that it can be thinner and provide superior color reproduction. This characteristic does not change even if organic matter gets formed in a variety of shape, and thus AMOLED can also be applied as a flexible display. Structure of AMOLED Encapsulation Electrode Organic Multi-Layers Electrode Encapsulation OLED TFT Array Glass Active Matrix TFT Substrate Light emitting Source: IHS 9
2. Vth and IR-drop of AMOLED AMOLED displays control the brightness of each pixel and show an image by controlling the amount of electric current flowing in the OLED of each pixel. That is, there is the driving TFT inside pixels to control OLED electric currents, and the Vth of driving TFT of each pixel can differ because of errors in the manufacturing process of the display panel. In this case, as the electric current between the drain and the source of the driving TFT depends on the Vth of the driving TFT, the electric current supplied to the OLED differs by pixel even though the same data voltage is provided to each of the pixels. Therefore, there arises the issue of different brightness of light emitted by the organic light emitting diode of each pixel, even though the same data voltage gets supplied to each of the pixels. In addition,. Pixel circuit to compensate for Vth and IR-drop of AMOLED driving TFT Source: US 10
III. Analysis of patent application trend Key Patent Report - Compensation Circuit for AMOLED - 2013 ihs.com
Number of application 1. Patent application trend by year The number of patents on the AMOLED pixel driving circuit (Vth and IR-drop compensation) technology applied in the United States have been growing, with many of them applied in 2006 and 2010. For reference, patent information is disclosed to the public in one and a half years after their application date. Thus, there remain unpublished patents yet from 2011, resulting in a smaller number of patent applications than the previous years as shown in the graph as below. Patent applications by year 40 Invalid Period 35 30 25 20 15 10 5 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Year of application US Patent Application Source: IHS 12
Number of application 2. Patent application trend by technology The examination of patent applications by technology shows the Vth compensation technology accounts for. Patent application trend by technology Invalid Period 35 30 Vth + IR drop IR drop 6% 11% 25 20 Vth 83% 15 10 5 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Year of application Vth Compensation IR-Drop Compensation Vth + IR-Drop Compensation Source: IHS 13
Number of application 3. Status of assignees The examination of assignees of the patents on the AMOLED pixel driving circuit (Vth and IR-drop compensation) technology applied in the United States shows Samsung Display Co. Ltd. applied for the greatest number... Status of assignees 100 90 98 80 70 60 50 40 41 30 20 10 0 Samsung Display 15 Global OLED Technology 13 10 10 9 9 9 7 7 LG Display Chimei Innolux Sharp Royal Philips Seiko Epson Sony AU Optronics Wintek Semiconductor Energy Laboratory 6 5 5 BOE Technology Canon Others (.. )patents.. Others: * (. )patents.... patents (..).. patent ( ) Source: IHS 14
IV. Key patent analysis (50 patents) Key Patent Report - Compensation Circuit for AMOLED - 2013 ihs.com
1. Key patent selection The key US patents on the AMOLED pixel driving circuit (Vth and IR-drop compensation) technology have been looked at. In particular, the patents cited during the examination of US patents were referred to for the selection of key patents. Of the 244 US patents, the top 50 issued patents with the greatest number of forward citation were selected for an in-depth analysis. The in-depth analysis has been conducted on the technology development trends and key patent abstracts and embodiments. Key patent selection 244 US Patents 116 Published Patents 128 Issued Patents Top 50 Issued Patents with Greatest Number of Forward Citation Analysis of 50 Key Patents Source: IHS Citation Analysis The citation reference include the prior arts documents described by the inventor and the technological document information that the examiner judges is highly related to the pertinent patent during the examination process. When there is much cited information, it helps grasp the technological trends, trace the original patents, and discover prior arts, new markets, and cooperators. In general, the more important patents are, the greater number of forward citation they have. Forward citation: It means the patents that cited Patent A. A patent with a great number of forward citation is highly likely to be an original technology that must have been developed faster than competitors. 16
2. Key patent status The 50 key patents on the AMOLED pixel driving circuit (Vth and IR-drop compensation) technology are as follows. Key patent status No. Patent No. Title Application No. (Date) Assignee Forward Citation Backward Citation Family Patent 1 Active-matrix display device and method of driving the same 2 Organic electroluminescent display, driving method and pixel circuit thereof 3 Luminescent display, and driving method and pixel circuit thereof, and display device Sony 54 2 7 Samsung Display 50 4 15 Samsung Display 46 13 14 4 5 6 7 8 9 10 17
3. Technology development trends Key patent technology development chart (2001-2003) 2001 2002 2003 Sony Presents a circuit in which the Vth compensation circuit block is arranged between the data line and the pixel Samsung Display Mitsubishi Denki Suppresses the noise current by providing the switching device that can short-circuit the electrode of the selflight emitting device Provides the voltage sustaining circuit that maintains the voltage set on the basis of the Vth of the driving transistor Simplifies the circuit and driving method and prevents the increase in unnecessary electric current Simplifies the control by detecting the Vth and recording the data simultaneously Canon Canon Notes: PTRI(Pendragon and Telecommunications Research Institute) Source: IHS Vth Compensation IR-Drop Compensation Vth + IR-Drop Compensation Same Assignees 18
4. Key patent abstracts The following is the abstracts of the analysis of 50 key patents. Patent 1 Publication No. (Date) Legal status Alive Title Active-matrix display device and method of driving the same Application No. (Date) Assignee Sony Technology Classification Vth Compensation Abstract Rep. claim Family members In an active-matrix display device and a method for driving the active-matrix display device, a fifth transistor is connected between a power line and a drain terminal of a first transistor so that a power-supply voltage, namely the fixed voltage required for the compensation of the threshold voltage, is supplied by the power line via a fifth transistor and not by a signal line. Thus, a sufficient length of time for the threshold voltage compensation period can be maintained, and a second transistor of each pixel can accurately be compensated for threshold voltage irregularities. 1. An active-matrix display device comprising: pixel circuits arrayed in a matrix; signal lines each of which is interconnected with a corresponding column of the matrix-arrayed pixel circuits; and a first scanning line, a second scanning line, a third scanning line, and a fourth scanning line that are interconnected with a corresponding row of the matrix-arrayed pixel circuits; each of the pixel circuits comprising: a first transistor of which a gate terminal is connected with the first scanning line and of which a first electrode terminal is connected with one of the signal lines; a first capacitor of which a first end is connected with a second electrode terminal of the first transistor; a second capacitor of which a first terminal is connected with the first end or a second end of the first capacitor; a second transistor of which a gate terminal is connected with the second end of the first capacitor and of which a first electrode terminal is connected with a first power line; a third transistor of which a gate terminal is connected with the second scanning line, a first electrode terminal of the third transistor is connected with the gate terminal of the second transistor, and a second electrode terminal of the third transistor is connected with a second electrode terminal of the second transistor; a fourth transistor of which a gate terminal is connected with the third scanning line and of which a first electrode terminal is connected with the second electrode terminal of the second transistor; a fifth transistor of which a gate terminal is connected with the fourth scanning line, a first electrode terminal of the fifth transistor is connected with a third power line, and a second electrode terminal of the fifth transistor is connected with the second electrode terminal of the first transistor; and a display element connected with both a second electrode terminal of the fourth transistor and a second power line. Source: US7057588 19
5. Key patent embodiments Key patent embodiment (1) US / The patent of US.. is on an OLED pixel circuit that effectively compensates for the TFT Vth when driving the OLED by using the TFT. Its pixel circuits include: a first transistor to apply data signals following the selected signals; a second transistor to compensate for the Vth to the data signals applied through the first transistor; a fourth transistor to provide electric currents to light-emitting cells following the data signals applied through the second transistor; and a third transistor to initialize the data signals applied to the condenser and the fourth transistor to maintain the data signals for a certain period of time. US. Organic electroluminescent display, driving method and pixel circuit thereof An organic electroluminescent display (OELD), comprising: a plurality of data lines for transmitting data voltages for representing image signals; a plurality of scan lines for transmitting select signals; and a plurality of pixel circuits respectively formed on a plurality of pixels defined by the data lines and the scan lines, wherein each of the pixel circuit comprises: an organic electroluminescent (EL) element for emitting light corresponding from a supplied current; a first switch for switching data voltage supplied to a data line in response to a select signal supplied to a scan line; a first thin film transistor (TFT) for supplying the current to the organic EL element in response to the data voltage supplied to a gate of the first TFT via the first switch; a second TFT having a gate coupled to the gate of the first TFT and compensating for a threshold voltage deviation of the first TFT; a capacitor for maintaining the data voltage supplied to the gate of the first TFT during a predetermined time; and a second switch for initializing the data voltage supplied to the gate of the first TFT in response to a control signal. Drawings Source: US. 20
The following is an analysis on the major drawings of US. through embodiments. US7015884 Embodiment analysis Source: US. 21
V. Analysis of new technology patents Key Patent Report - Compensation Circuit for AMOLED - 2013 ihs.com
1. Selection of new technology patents The new technology patents on the AMOLED pixel driving circuit (Vth and IR-drop compensation) technology have been examined from among the US patents applied over the past five years (2008-2013). For the selection of new technology patents, patent families, which mean overseas applications, were referred to and especially those patents applied in three or more countries were picked as new technology patents. Of the 244 US patents, 39 patents applied in three or more countries over the past five years were selected as the new technology patents for an in-depth analysis. The in-depth analysis deals with the technology development trends and key patent abstracts and embodiments. (29 published patents, 10 issued patents) Selection of new technology patents 244 Patents Applied in the United States 116 Published Patents 128 Issued Patents Patents Applied over the Past Five Years (2008-2013) Patents Applied in Three or More Countries (Patent Family) Analysis of 39 New Technology Patents - 29 Published Patents - 10 Issued Patents Source: IHS Patent Family Analysis The analysis on which country an assignee has applied for a patent in helps to understand the target market which the assignee plans to enter and to judge the importance of the pertinent technology. Patent family is a set of patents taken in various countries to protect a single invention, by a common inventor(source: USPTO). The issued patents of the aforementioned new technology patents are recently applied and registered. Therefore, they do not overlap with the key patents described in the previous pages. 23
2. Status of new technology patents The 39 new technology patents on the AMOLED pixel driving circuit (Vth and IR-drop compensation) technology are as follows. Status of new technology patents No. Patent No. Title Application No. (Date) Assignee Family Country Family Patent 1 Electroluminescent subpixel compensated drive signal Global OLED Technology 7 CN, EP, JP, KR, TW, US, WO 9 2 Pixel circuit, display device, and inspection method Global OLED Technology 3 4 7 CN, EP, JP, KR, TW, US, WO 8 5 6 7 8 9 10 24
3. Technology development trends Technology development chart of new technology patents (2008 2009) 2008 2009 Sharp Suppresses the errors of driving current on a plurality of gradation values Global OLED Technology Provides the drive transistor control signal Global OLED Technology Samsung Display Canon Displays a uniform image by compensating for the Vth of the driving transistor Compensates for the IR-drop in the connecting wiring on a flexible substrate with a high degree of precision Samsung Display Displays an image with a uniform brightness by compensating for the Vth and IR-drop of the driving transistor Source: IHS Vth Compensation IR-Drop Compensation Vth + IR-Drop Compensation Same Assignees 25
4. Abstracts of new technology patents Below is the abstracts of the analysis of 39 new technology patents. Patent 1 Publication No. (Date) Legal status Alive Title Electroluminescent subpixel compensated drive signal Application No. (Date) Assignee Global OLED Technology Technology Classification Vth Compensation Abstract Rep. claim An electroluminescent (EL) subpixel, such as an organic light-emitting diode (OLED) subpixel, is compensated for aging effects such as threshold voltage Vth shift, EL voltage VOLED shift, and OLED efficiency loss. The drive current of the subpixel is measured at one or more measurement reference gate voltages to form a status signal representing the characteristics of the drive transistor and EL emitter of the subpixel. Current measurements are taken in the linear region of drive transistor operation to improve signal-to-noise ratio in systems such as modern LTPS PMOS OLED displays, which have relatively small VOLED shift over their lifetimes and thus relatively small current change due to channel-length modulation. Various sources of noise are also suppressed to further increase signal-to-noise ratio. 1. An apparatus for providing a drive transistor control signal to a gate electrode of a drive transistor in an electroluminescent (EL) subpixel, comprising: the electroluminescent (EL) subpixel having an EL emitter with a first and second electrode, and comprising the drive transistor with a first supply electrode, a second supply electrode, and the gate electrode, the second supply electrode of the drive transistor being electrically connected to the first electrode of the EL emitter for applying current to the EL emitter; a first voltage supply electrically connected to the first supply electrode of the drive transistor; a second voltage supply electrically connected to the second electrode of the EL emitter; a test voltage source electrically connected to the gate electrode of the drive transistor; a voltage controller for controlling voltages of the first voltage supply, second voltage supply, and test voltage source to operate the drive transistor in a linear region; a measuring circuit for measuring the current passing through the first and second supply electrodes of the drive transistor at different times to provide a status signal representing variations in the characteristics of the drive transistor and EL emitter caused by operation of the drive transistor and EL emitter over time, the current being measured while the drive transistor is operated in the linear region; means for providing a linear code value; a compensator for changing the linear code value in response to the status signal to compensate for the variations in the characteristics of the drive transistor and EL emitter; and a source driver for producing the drive transistor control signal in response to the changed linear code value for driving the gate electrode of the drive transistor, wherein the measuring circuit comprises: a first current mirror for producing a mirrored current which is a function of the drive current passing through the first and second supply electrodes, and a second current mirror for applying a bias current to the first current mirror to reduce impedance of the first current mirror. Family members Source: US. 26
5. Embodiments of new technology patents New technology patent embodiment (1) US. / The patent of US. is on an OLED device that can compensate for the Vth of the driving transistor and the IR-drop of the high voltage source. It includes a transistor that senses the Vth of the driving transistor; compensates the Vth of the driving transistor by reflecting the Vth of the driving transistor sensed by using a first capacitor to a first node to which a gate electrode of the driving transistor is connected; and controls the supply of high voltage to a second node to which a source electrode of the driving transistor is connected. Thus, it compensates for the IR-drop of the high voltage by reflecting it to the first node via the first capacitor. US. Organic light emitting diode display device A display pixel, comprising: a first capacitor coupled between a first and second nodes; a data transistor coupled to the first node and configured to set the first node to a data voltage responsive to turning on of the data transistor; a control transistor coupled to the second node and configured to set the second node to a supply voltage responsive to turning on of the control transistor, wherein setting the second node to the supply voltage causes, via the first capacitor, an adjustment in the data voltage at the first node to generate an adjusted data voltage at the first node; and a driving transistor, a gate of the driving transistor coupled to the first node and a source of the driving transistor coupled to the second node, wherein the adjusted data voltage at the first node is applied to the gate of the driving transistor to control current in a light emitting diode (LED). Drawings Source: US. 27
VI. Conclusion Key Patent Report - Compensation Circuit for AMOLED - 2013 ihs.com
VII. Appendix Key Patent Report - Compensation Circuit for AMOLED - 2013 ihs.com
1. Patent list by company (244 patents) No. Patent / Publication No. Title Assignee 1 Method and device for brightness stabilization in AMOLED display 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 30
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