Chul-Kyu Kang

4.2: Integrated Scan Driver with Oxide TFTs Using Floating Gate Method

An on-glass integrated scan driver is proposed for oxide thin film transistors TFTs with negative threshold voltage. A coupling capacitor and a TFT for setting the initial voltage to the gate of a TFT were added to minimize the off-state current. Simulated and measured results indicate that the proposed scan driver shows no ripple and fast rise time/fall time of scan outputs. Circuit operation was verified with a 14-inch AMOLED panel.

49.3: Oxide TFT Scan Driver with Dynamic Threshold Voltage Control

Oxide TFTs have a negative threshold voltage (Vth), which can become even more negative in response to DC or AC stress. Therefore, these voltage stresses can cause severe leakage current in a scan driver. In this paper, a scan driver with dynamic threshold voltage control (DTVC) is proposed to minimize the leakage current and enlarge operating margin. Effectiveness of DTVC was verified with a 14-inch AMOLED.

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%.

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

53.5: High-Speed AMOLED Pixel Circuit and Driving Scheme

An active matrix organic light emitting diode pixel circuit and its driving scheme for high frame frequency are proposed for implementation of a 3D display. The proposed pixel circuit can compensate the threshold voltage distribution of low temperature poly silicon-thin film transistors at high-speed operation of 240Hz or more. According to the simulation, current deviation of 1.73% and 3.94% are obtained at frame rates of 240Hz and 480Hz when Vth distribution is ±0.5 V.

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.