Li-Rong Zhang

An AC Driving Pixel Circuit Compensating for TFTs Threshold-Voltage Shift and OLED Degradation for AMOLED

This paper presents an ac driving pixel circuit for active-matrix organic light-emitting diode (AMOLED) displays, which is composed of one driving thin-film transistor (TFT), three switching TFTs and one capacitor. The proposed pixel circuit can not only make OLED work at the ac driving mode, but also effectively compensate for the threshold-voltage shift of the driving TFT and the degradation of OLED. Simulation results show that the nonuniformity of the proposed pixel circuit is significantly reduced (<; 10%) with an average value of 4.2% compared with that of the conventional 2T1C pixel circuit, and thus, the brightness uniformity of AMOLED displays can be enhanced. Moreover, a high contrast ratio can be achieved by the proposed pixel circuit due to no light emitting except for the emission period, as well as a relatively high aperture ratio due to a small number of components.

A Highly Stable Biside Gate Driver Integrated by IZO TFTs

This brief presents a new gate driver integrated by In-Zn-O thin-film transistors (IZO TFTs), including a clock-controlled inverter and an additional stabilized module. The biside driving method is used in the proposed gate driver, which will be allocated on both sides of the panel to drive the odd and even lines of pixel array, respectively. Thus, the space symmetry of the panel can be fully utilized for high resolution displays. The output signal of the biside gate driver can be generated stably up to 480th stage with a good noise-suppressed characteristic. The measured power consumption for one stage of the proposed gate driver is 0.5 mW with the clock frequency as 50 kHz. It is shown that the proposed gate driver can output a 3-\(\mu \) s pulsewidth with a good stability under 120-h test. Furthermore, a 3-in demonstration panel of 320*480 AMOLED display by the IZO TFTs process is fabricated to verify the function of the proposed biside gate driver.

A Low-Power High-Stability Flexible Scan Driver Integrated by IZO TFTs

This brief presents a low-power high-stability scan driver integrated by In-Zn-O (IZO) TFTs on polyimide substrate. Observed from the experimental results of the scan driver with 48 stages, there is no distortion and good noise-suppressed characteristics for the output waveforms. In one stage of the proposed scan driver, there only needs a small TFT connected to clock signals by using a feedback inverter and a dc output module to minimize the dynamic power consumption. It is measured that the power consumption for one stage of the proposed gate driver is 18.3 μW at the output swing of 15.3 V and the clock frequency of 50 kHz. There is a good noise-suppressed characteristic and high stability for the proposed scan driver as shown from a 300-h test.

A new compensation pixel circuit with all-p-type TFTs for AMOLED displays

Abstract This paper presents a new pixel circuit with all-p-type TFTs for AMOLED displays. The proposed pixel circuit can effectively compensate for the threshold-voltage shift of the driving TFT, the degradation of OLED and the parasitic resistance of the power supply line. And thus, the brightness uniformity of AMOLED displays can be enhanced. It is shown that the nonuniformity of the OLED current with an average value of 7.3% can be achieved by the proposed pixel circuit, while that of the conventional 2T1C pixel circuit is 73%. Moreover, a high contrast ratio can be also obtained by the proposed pixel circuit since there is no light emitting except for the emission period.

Low-Power Bi-Side Scan Driver Integrated by IZO TFTs Including a Clock-Controlled Inverter

This letter presents a low power In-Zn-O thin-film transistors (IZO TFTs) scan driver including a clock-controlled inverter to avoid the direct current path compared with the conventional diode-connected inverter. The so-called bi-side scan driver is divided into two parts, laying on the two sides of panel to drive the odd lines and the even lines of pixel arrays, respectively. Due to a smaller duty ratio of the clock in the output section than that of clocks in the inner section, only one large size transistor is required for both charging and discharging the scan line, and the discharging speed is faster than that of other merging TFT methods because it is at the bootstrapped state for the whole driving phase. Experimental results show that the output signal of each stage for the proposed scan driver has no distortion and exhibits good noise-suppressed characteristics. It is also verified that the power consumption of the clock-controlled inverter can be significantly reduced compared with the conventional diode-connected inverter.

High-Speed Voltage-Programmed Pixel Circuit for AMOLED Displays Employing Threshold Voltage One-Time Detection Method

This letter presents a high-speed, voltage-programmed pixel circuit for active-matrix organic light-emitting diode displays employing threshold voltage one-time detection method. The proposed pixel circuit that consists of one driving thin-film transistor (TFT), four switching TFTs, two capacitors, and four control signal lines can effectively compensate for the threshold voltage shift of the driving TFT and the OLED degradation. The threshold voltage of one-time detection method is realized by an ingenious application of capacitor coupling effect, and it is well-verified by comparing it with the conventional driving scheme. In this method, data is directly renewed without the periods of initialization and threshold voltage detection from the second-frame beginning. Moreover, this method can also be applied to other compensation pixel circuits.

Power Consumption Model for AMOLED Display Panel Based on 2T-1C Pixel Circuit

The display device has a significant contribution to the total power, which is critical for mobile consumer-electronic devices due to a limited battery capacity. We develop a power model of the active-matrix organic light-emitting diode (AMOLED) display and analyze the power contribution of thin-film transistor (TFT), OLED, and VDD line drop. Both theoretical analysis and calculation are derived from TFT mobility, OLED luminous efficiency, pixel aperture ratio, and VDD line drop. The TFT mobility from 0.1 to 10 cm2/(V · s) is a bottleneck of display power. Metal oxide TFT may be more suitable for AMOLED display since relatively high mobility and low fabrication temperature. High luminous efficiency of OLED and top emission structure can decrease power consumption abundantly. The impact of copper wire technology is also discussed in large-size panels.

A High-Reliability Gate Driver Integrated in Flexible AMOLED Display by IZO TFTs

This paper presents a new gate driver integrated by IZO thin-film transistors (TFTs) with the etch stop layer structure on the polyimide substrate, which consists of nine TFTs and two capacitors. There are several advantages for the proposed gate driver, such as simple circuitry, full-swing output, low power, and good reliability. The proposed gate driver has been successfully integrated in a flexible active matrix organic light emitting display with the resolution of 200 (RGB)

High-speed low-power voltage-programmed driving scheme for AMOLED displays

\times 600

Alternating-current pixel driving circuit and method for active organic light-emitting diode (OLED) display

, in which the conventional 2T1C pixel circuit with bottom-emission structure is used. It is shown that there are no distortion and good noise-suppressed characteristics for the output signals even up to 600 stages. In addition, the proposed gate driver has a good stability, since no voltage fluctuation occurs under 720-h test. Moreover, the flexible panel works well after a 10000 times repetitive bending performed on a test bench, which is mainly composed of a programmed logic controller and dc motor. During the bending test, the minimum curvature radius of flexible panel can reach to be about 5 mm.