Po Chun Lai

Driving Scheme Using Bootstrapping Method for Blue-Phase LCDs

We present a new pixel circuit on glass using hydrogenated amorphous silicon (a-Si:H) for driving polymer-stabilized blue-phase liquid crystal displays (BPLCDs). Different from conventional nematics, BPLC demands a large dielectric anisotropy in order to lower the operation voltage. As a result, the pixels capacitance is increased by ~ 10×, which seriously limits the charging capability and optical efficiency. Simulation results show that the average error rate of storage voltage in pixel circuit is below 5.14% for 180 Hz operating frequency.

A Charge-Pump-Based Current Feedback Method for AMOLED Displays

This work presents a new external driving scheme that uses the current feedback method with a 3T1C pixel circuit. The proposed circuit provides a stable OLED driving current by compensating for the threshold voltage shift of amorphous-silicon thin-film transistors (a-Si TFTs). For fabricated a-Si TFTs and the 0.35 μm CMOS process associated with the proposed driving scheme, measurements reveal that the normalized OLED current degradation is less than 5% after 60 hours of operation at 60°C. Moreover, for a data line load of 1.69 K Ω/110 pF, the relative error rates between data currents and OLED currents are less than 4% within a settling time of 19 μs.

Design of Pixel Circuits for Blue-Phase Liquid Crystal Displays

This work reviews pixel circuits for blue-phase liquid crystal displays (BPLCDs) and presents two novel pixel circuits for the BPLC. With respect to the high-operating-voltage BPLC, the first developed pixel circuit comprises practical source driver integrated circuits (ICs) and an additional signal with three voltage levels to widen the voltage range from a data line in order to enable the BPLC to achieve high transmittance. For the low-operating-voltage BPLC with a large dielectric anisotropy, the second pixel circuit boosts the gate voltage of the switch thin-film transistor (TFT) to enhance its driving capability to deal with the large equivalent capacitance of the BPLC. Simulation results verify the functions of both new pixel circuits with Full High Definition (FHD, 1920 ×1080) resolution and a frame rate of 120 Hz.

New 2-D/3-D Switchable Pixel Circuit to Achieve Uniform OLED Luminance for High-Speed AMOLED Displays

This paper presents a new 2-D/3-D switchable pixel circuit based on low-temperature polycrystalline-silicon thin-film transistors (TFTs) at a frame rate of 240 Hz for active-matrix organic light-emitting diode (OLED) displays. The proposed circuit compensates for threshold voltage (VTH) variations of TFTs, VDD IR drops, and degradation of OLED luminance. To achieve highly uniform displays during high-speed operation, the circuit uses simultaneous emission in 3-D mode and parallel addressing in 2-D mode to ensure that the period of compensation is sufficiently long to detect each variation of normalized luminance. Simulation results verify that variations in the normalized luminance of the proposed circuit are all less than 4% when the VTH of the driving TFT varies by ±0.5 V, VDD drops by 1 V, and the VTH shift of the OLED increases from 0 to 0.9 V, simultaneously.