Bo-Yong Chung

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%.

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.

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.

27.1: Integrated pMOS Gate Driver for a 3D AMOLED Display

Simultaneous Emission with Active Voltage control (SEAV) is a strong candidate for crosstalk-free driving of 3D Active Matrix Organic Light Emitting Diode (AMOLED) displays. A gate driver for a SEAV 3D AMOLED panel needs two operating modes: the simultaneous switching mode and the progressive scanning mode. However, conventional gate drivers can operate in only progressive scanning mode. In this paper, a new integrated gate driver to support both of these modes is proposed and applied to a prototype 3D AMOLED display panel.

53.4: Off-Current Control Method to Improve Random Mura of SGS AMOLED Panel

A new method to reduce leakage current and a new pixel circuit based on super grain silicon (SGS) backplane are proposed. This method has three strong points. First, it is possible to reduce random mura caused by leakage current. Second, the number of gates to reduce leakage current can be minimized. Finally, it is also possible to decrease the storage capacitor size.