Mao Hsun Cheng

Highly Reliable Integrated Gate Driver Circuit for Large TFT-LCD Applications

This letter presents a novel integrated hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) gate driver circuit using ac driving (33% duty) to prevent the floating of row lines and reduce the bias voltage of pull-down TFTs to suppress the threshold voltage (VTH) shift of a-Si:H TFTs. The VTH shift of the TFTs in this design is reduced by 49.93% from that achieved using the 25%-duty ac-driving structure. In a reliability test, the new circuit operates stably at a high temperature (T = 60°C) for more than 240 h.

2-D–3-D Switchable Gate Driver Circuit for TFT-LCD Applications

This paper presents a novel 2-D-3-D switchable gate driver circuit for active-matrix liquid crystal displays (AMLCDs) applications using the hydrogenated amorphous silicon (a-Si:H) technology. While consisting of 12 thin-film transistors (TFTs), the proposed gate driver circuit includes a pull-up circuit, two alternative circuits, and a key pull-down circuit. To provide a stable output waveform for switching between the 2-D and 3-D modes in AMLCD panel, the proposed circuit can improve the threshold voltage shift of a-Si:H TFT using reversed bias stress. Based on a real circuit integrated on glass with a standard five-mask process applied to a large-sized FHD TFT-LCD panel, the layout area of each gate driver circuit is 359.25 μm × 2296.25 μm. In addition, the power consumption of a 12-stage gate driver circuit is 3.25 and 7.21 mW, while operating at 2-D and 3-D modes, respectively. Measurement results indicate that the output waveform, including output voltage, rising time, and falling time can be stabilized and made almost equal to the initial state after the reliability test at 100 °C over 240 h.

Voltage Driving Scheme Using Three TFTs and One Capacitor for Active-Matrix Organic Light-Emitting Diode Pixel Circuits

This work presents a new active-matrix organic light-emitting diode (AMOLED) pixel circuit with a novel driving scheme that is based on low-temperature polycrystalline-silicon thin film transistors (LTPS TFTs). The proposed circuit that consists of one driving TFT and two switching TFTs, which are all p-type, can successfully compensate for not only variations in the TFT threshold voltage but also the current-resistance (IR) voltage drop in the power line. The functionality of the pixel circuit for the array structure and the uniformity of organic light-emitting diode (OLED) current are verified using H-Simulation Program with Integrated Circuit Emphasis (HSPICE). According to the results of a simulation, over the entire range of tested data voltages (-4.5 to -2.5 V), the relative errors of the OLED current of the proposed circuit are below 1.2% when the driving TFT threshold voltage varies from -0.5 to +0.5 V.

Low-Power a-Si:H Gate Driver Circuit With Threshold-Voltage-Shift Recovery and Synchronously Controlled Pull-Down Scheme

This paper presents a new low-power gate driver circuit designed by hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs). An attempt is also made to reduce the power consumption resulting from the high-frequency pulldown structure, in which a pair of 0.25-Hz clock signals is used to implement a low-frequency and synchronously controlled pull-down scheme for recovering the threshold voltage shifts of a-Si:H TFTs under the negative gate-to-source voltage and decreasing the used TFTs. Measurement results indicate that the proposed gate driver circuit consumes 98.7 μW/stage, and the output waveforms are very stable without distortion when the proposed circuit is operated at 100 °C for 840 h. Furthermore, the feasibility of the proposed gate driver circuit is demonstrated for the quad-extended-video-graphics-array resolution.

Novel Dual-Coupling Pixel Circuit to Achieve High Transmittance of Blue-Phase Liquid Crystal

A new pixel circuit for in-plane switching blue-phase liquid crystal displays (IPS BPLCDs) is developed. The dual-coupling method enables the proposed circuit to generate twice the maximum output voltage of source driver integrated circuits (ICs) for the BPLC with a simple structure, so the achievable transmittance is about four times that of the BPLC that is simply driven using practical source driver ICs. A 10.1-in prototype IPS BPLC panel (720 × 360) and simulation results demonstrate the feasibility of the proposed circuit for practical BPLCD applications, and the tone rendering distortion index is as low as 0.11.

A Three-Transistor Pixel Circuit to Compensate for Threshold Voltage Variations of LTPS TFTs for AMOLED Displays

This work presents a new pixel circuit adopting low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) for active-matrix organic light-emitting diode (AMOLED) displays. The proposed pixel circuit can compensate for the threshold voltage variations of the LTPS TFTs with a simple structure. Simulated results demonstrate that the OLED currents over the entire data voltage range are uniform for ±0.5 V variations in the threshold voltage of the driving TFT, unlike in a conventional circuit. Furthermore, the relative current error rates for parasitic loads in the 1280 ×720 resolution AMOLED display are less than 6%.

Highly Reliable Bidirectional a-InGaZnO Thin-Film Transistor Gate Driver Circuit for High-Resolution Displays

This paper presents a new bidirectional gate driver circuit that utilizes amorphous indium-gallium-zinc oxide thin-film transistors (TFTs). To ensure the compactness of the display system, bidirectional transmission function is implemented by adjusting the sequence of clock signals without extra controlling signal. The lifetime of the proposed gate driver circuit is increased by reducing the drain bias stress of the input TFTs. The measurement results indicate that the proposed gate driver circuit can remain stable for more than 812 h at 70 °C, demonstrating its feasibility and long-term reliability for full high-definition resolution.

Amorphous InSnZnO Thin-Film Transistor Voltage-Mode Active Pixel Sensor Circuits for Indirect X-Ray Imagers

An amorphous indium-tin-zinc-oxide thin-film transistor (a-ITZO TFT)-based voltage-mode active pixel sensor (V-APS) is discussed, for the first time, in this paper. The a-ITZO TFT shows superior electrical characteristics, including a high field-effect mobility (μEFF > 30 cm2/V · s), a steep subthreshold slope (SS <; 200 mV/decade), and a low OFF-current (IOFF <; 10-14 A), that are suitable for applications such as X-ray imagers. The proposed V-APS is based on the topilluminated organic photodiode (OPD) or amorphous silicon p+-i-n+ photodiode (a-Si +-i-n+ PD). Simulation results indicate that, in contrast with common source V-APS, source follower (SF) V-APS is more desirable for X-ray imagers due to its better linearity property. The OPD or the a-Si p+-i-n+ PD does not affect the voltage gain of SF V-APS. But the PDs have different influences on charge-to-voltage conversion gain. The impact of PD capacitances and dark saturation currents on detectable quantities of electrons is also investigated. The influence of the TFT threshold voltage shift on circuit performance, sensitivity, and noise analysis of SF V-APS is discussed.

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.