Hai-Jung In

External Compensation of Nonuniform Electrical Characteristics of Thin-Film Transistors and Degradation of OLED Devices in AMOLED Displays

The variation of electrical characteristics of polycrystalline-silicon thin-film transistor (TFT) and degradation of organic light-emitting-diode (OLED) device cause nonuniform intensity of luminance and image sticking in active-matrix OLED (AMOLED) displays. An external compensation method that senses and compensates variations of threshold voltage and mobility of TFTs and degradation of OLED device is proposed. The effect of the external compensation method on AMOLED pixel is experimentally verified by measuring the luminance of OLEDs and the electrical characteristics of TFTs in AMOLED pixels.

An Advanced External Compensation System for Active Matrix Organic Light-Emitting Diode Displays With Poly-Si Thin-Film Transistor Backplane

An advanced method for externally compensating the nonuniform electrical characteristics of polycrystalline silicon thin-film transistors (TFTs) and the degradation of organic light-emitting diode (OLED) devices is proposed, and the method is verified using a 14.1-in active matrix OLED (AMOLED) panel. The proposed method provides an effective solution for high-image-quality AMOLED displays by removing IR-drop and temperature effects during the sensing and displaying operations of the external compensation method. Experimental results show that the electrical characteristics of TFTs and OLEDs are successfully sensed, and that the stained image pattern due to the nonuniform luminance error and the differential aging of the OLED is removed. The luminance error range without compensation is from -6.1% to 9.0%, but it is from -1.1% to 1.2% using the external compensation at the luminance level of 120 cd/m2 in a 14.1-inch AMOLED panel.

A Low-Power Single-Clock-Driven Scan Driver Using Depletion-Mode a-IGZO TFTs

A new low-power scan driver using amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) is proposed. The proposed scan driver employs only one-clock signal and connects power supply voltage to the drain node of pull-up TFTs in the output stage to reduce the power consumption. The measured power consumption of the proposed scan driver of ten stages is 265 μW at an output voltage of 20 V and a clock frequency of 46.1 kHz, which is the driving condition of the extended graphics array (1024 × 768) panel. The power consumption is less than 11.9% of the previously reported results.

Current-Sensing and Voltage-Feedback Driving Method for Large-Area High-Resolution Active Matrix Organic Light Emitting Diodes

There is the problem of picture quality nonuniformity due to thin film transistor (TFT) characteristic variations throughout a panel of large-area high-resolution active matrix organic light emitting diodes. The current programming method could solve this issue, but it also requires very long charging time of a data line at low gray shades. Therefore, we propose a new driving method and a pixel circuit with emission-current sensing and feedback operation in order to resolve these problems. The proposed driving method and pixel circuit successfully compensate threshold voltage and mobility variations of TFTs and overcome the data line charging problem. Simulation results show that emission current deviations of the proposed driving method are less than 1.7% with ±10.0% mobility and ±0.3 V threshold voltage variations of pixel-driving TFTs, which means the proposed driving method is applicable to large-area high-resolution applications.

A luminance adjusting algorithm for high resolution and high image quality AMOLED displays of mobile phone applications

A luminance adjusting algorithm using light sensing scanner is proposed for small-sized high resolution and high image quality active matrix organic light emitting diode (AMOLED) displays such as smartphone applications. By using simple pixel structure with the proposed algorithm, high aperture ratio in high resolution display can be achieved. Experimental results show that the standard deviation of luminance improves from 7.07 to 1.81 LSB when the proposed adjusting method is used to 3.5-inch AMOLED display with 8-bit gray scale.

A Simple Pixel Structure Using Polycrystalline-Silicon Thin-Film Transistors for High-Resolution Active-Matrix Organic Light-Emitting Diode Displays

A simple pixel structure comprising two transistors and one capacitor and a novel driving method are proposed for small-sized and high-resolution active-matrix organic light-emitting diode displays on polycrystalline-silicon thin-film transistor (TFT) backplane. The proposed pixel increases the yield due to small number of TFTs and improves image quality by compensating threshold voltage variations of driving TFTs. The proposed pixel is designed as test pixels with 353 pixels per inch, and the measured emission current error range of -74.2% -60.6% is improved to the range of -2.5% -2.1% when the proposed pixel is used.

Voltage‐programming method with transimpedance‐feedback technique for threshold voltage and mobility compensations in large‐area high‐resolution AMOLED displays

— A voltage-programming method with transimpedance-feedback control technique is proposed for compensating threshold voltage and mobility variations of driving thin-film transistors (TFTs) in large-area high-resolution polycrystalline-silicon (poly-Si) active-matrix organic light-emitting-diode (AMOLED) displays. Those electrical characteristic variations of TFTs throughout a large-area high-resolution panel result in picture-quality non-uniformity of AMOLED displays. The simulation and experimental results of the proposed method show that the maximum emission-current error for 30-in. full-high-definition television (HDTV) applications is less than 1.9% when the mobility variation and the threshold-voltage variation are ±12.5% and ±0.3 V, respectively. The proposed method is the best programming method for large-area high-resolution AMOLEDs among the published methods.

Simple Pixel Structure Using Video Data Correction Method for Nonuniform Electrical Characteristics of Polycrystalline Silicon Thin-Film Transistors and Differential Aging Phenomenon of Organic Light-Emitting Diodes

A simple pixel structure using a video data correction method is proposed to compensate for electrical characteristic variations of driving thin-film transistors (TFTs) and the degradation of organic light-emitting diodes (OLEDs) in active-matrix OLED (AMOLED) displays. The proposed method senses the electrical characteristic variations of TFTs and OLEDs and stores them in external memory. The nonuniform emission current of TFTs and the aging of OLEDs are corrected by modulating video data using the stored data. Experimental results show that the emission current error due to electrical characteristic variation of driving TFTs is in the range from -63.1 to 61.4% without compensation, but is decreased to the range from -1.9 to 1.9% with the proposed correction method. The luminance error due to the degradation of an OLED is less than 1.8% when the proposed correction method is used for a 50% degraded OLED.

P-8: A Novel Feedback-Type AMOLEDs Driving Method for Large-Size Panel Applications

A novel feedback-type driving method for active matrix organic light diodes (AMOLEDs) is proposed for large-size poly-Si panel applications. The driver is composed of voltage and current DACs, current comparator, and feedback control circuits. We have performed the circuit simulations with 30-inch HDTV panel conditions with both mobility and threshold variations of the driving TFT, and confirmed the pixel-to-pixel OLED-current uniformity have been greatly improved compared to prior AMOLED pixels.

P‐166: Successive Cross Emission Driving for 3‐Dimensional Active‐Matrix Organic Light Emitting Diode Displays

We propose a pixel structure and its driving scheme for stereoscopic 3-dimensional (3D) active-matrix organic light emitting diode (AMOLED) displays. The proposed pixel structure and its driving scheme have merits that are longer emission and programming time than simultaneous emission scheme by successive cross emission of left and right images. Moreover, it can reduce flicker by reducing interval between emission times. For 3D AMOLED displays of 40-inch full high definition TV (1920×1080), the emission current error rate of the proposed pixel structure is from −0.961% to 1.013% when the threshold voltage variation of driving TFT varies from −0.8 V to 0.8 V, and that the error is less than 2% when the VDD-IR drop voltage becomes 2.0 V.