Keum-Nam Kim

An Advanced External Compensation System for Active Matrix Organic Light-Emitting Diode Displays With Poly-Si Thin-Film Transistor Backplane

An advanced method for externally compensating the nonuniform electrical characteristics of polycrystalline silicon thin-film transistors (TFTs) and the degradation of organic light-emitting diode (OLED) devices is proposed, and the method is verified using a 14.1-in active matrix OLED (AMOLED) panel. The proposed method provides an effective solution for high-image-quality AMOLED displays by removing IR-drop and temperature effects during the sensing and displaying operations of the external compensation method. Experimental results show that the electrical characteristics of TFTs and OLEDs are successfully sensed, and that the stained image pattern due to the nonuniform luminance error and the differential aging of the OLED is removed. The luminance error range without compensation is from -6.1% to 9.0%, but it is from -1.1% to 1.2% using the external compensation at the luminance level of 120 cd/m2 in a 14.1-inch AMOLED panel.

High-speed pixel circuits for large-sized 3-D AMOLED displays

— Large-sized active-matrix organic light-emitting diode (AMOLED) displays require high-frame-rate driving technology to achieve high-quality 3-D images. However, higher-frame-rate driving decreases the time available for compensating Vth in the pixel circuit. Therefore, a new method needs to be developed to compensate the pixel circuit in a shorter time interval. In this work, image quality of a 14-in. quarter full-high-definition (qFHD) AMOLED driven at a frame rate of over 240 Hz was investigated. It was found that image degradation is related to the time available for compensation of the driving TFT threshold voltage. To solve this problem, novel AMOLED pixel circuits for high-speed operation are proposed to compensate threshold-voltage variation at frame rates above 240 Hz. When Vth is varied over ±1.0 V, conventional pixel circuits showed current deviations of 22.8 and 39.8% at 240 and 480 Hz, respectively, while the new pixel circuits showed deviations of only 2.6 and 5.4%.

21.2: Driving Method for a 2D-3D Switchable AMOLED Display Using Progressive or Simultaneous Emission

A driving method has been developed for a 2D-3D switchable AMOLED using progressive emission PE or simultaneous emission SE. The proposed method is implemented by selecting PE mode for 2D to improve light emission ratio and SE mode for 3D to reduce left-right crosstalk without sacrificing luminance. This method also improves the contrast ratio by removing unnecessary light emission and can offer better uniformity by increasing the threshold voltage compensation time. A 240Hz-driven 30″ 3D AMOLED display was built and it was confirmed that there is no ELVDD surge current in the SE mode.

An 8b Source Driver for 2.0 inch Full-Color Active-Matrix OLEDs Made with LTPS TFTs

An 8b source driver for 2.0 inch QVGA active-matrix OLEDs is fabricated using LTPS TFTs. This driver uses an 8b DAC that is separated into two parts, a 1-to-3 DEMUX, and a pre-charge method. This scheme reduces the source driver size by 40%. The maximum DNL is under 1LSB. The output voltage variation of the source driver is less than 1 LSB even though the variation of the threshold voltage is plusmn0.5V

P-8: A New Hybrid Analog-Digital Driving Method to Improve AMOLED Lifetime

We propose a new hybrid pixel driving method that combines conventional digital driving with analog compensation for the declining electrical performance that occurs as OLEDs age. Image uniformity, and thus display lifetime, is improved by directly measuring the variation in OLED voltage at each pixel for a given OLED current level and then controlling the voltage drop across its driving TFT of an individual pixel.

38.4: 6-bit AMOLED with RGB Adjustable Gamma Compensation LTPS TFT Circuit

RGB adjustable gamma compensation circuit to choose one of the three different gamma characteristics for each color has been integrated by LTPS TFT for AMOLED. A timing controller to generate all timing signals for a 6-bit data driver and a scanning driver has also been integrated by the TFT on the AMOLED panel.

53.3: Redundant Pixel Line Insertion for Laser Crystallization Based Large Size LTPS AMOLED Displays

With an excimer laser annealing (ELA) process, maximum display size is limited by the laser beam length because performance variations of the transistors in the overlapped regions cannot be sufficiently compensated to remove the brightness non-uniformity. In this paper, a redundant pixel line design is proposed to remove overlap mura. A 4.82″ AMOLED was successfully fabricated in order to verify the panel design method.

Voltage Drop Compensation Method for Active Matrix Organic Light Emitting Diode Displays

In this paper, the conventional voltage drop compensation methods are reviewed and the novel design and driving scheme, the advanced power de-coupled (aPDC) driving method, is proposed to effectively compensate the voltage IR drop of active matrix light emitting diode (AMOLED) displays. The advanced PDC driving scheme can be applied to general AMOLED pixel circuits that have been developed with only minor modification or without requiring modification in pixel circuit. A 14-in. AMOLED panel with the aPDC driving scheme was fabricated. Long range uniformity (LRU) of the 14-in. AMOLED panel was improved from 43% without the aPDC driving scheme, to over 87% at the same brightness by using the scheme and the layout complexity of the panel with new design scheme is less than that of the panel with the conventional design scheme.

P-188L: Late-News Poster: Quantification of Image Sticking for Images with Different Long-Range Non-Uniformity

A new estimation method for image sticking has been developed that can effectively eliminate the influence by the difference in long-range non-uniformity pattern. An 8×8 chessboard pattern was used for selective degradation, and normalization based on extracted reference and coefficient of variation were adopted for better results.

21.3: Low Frequency Driving Methods for 3D Displays

Stereoscopic 3D displays are generally operated at 240Hz in order to fully separate left eye and right eye images. New low frequency driving methods are proposed for 3D displays. In addition to reducing driving frequency, the new driving methods can increase luminance and reduce cross-talk and power consumption.