High-speed driving and pixel nonuniformity compensation method for active-matrix OLED display

Abstract

In this thesis, pixel nonuniformity compensation method and high-speed driving method are introduced to overcome two main obstacles of AMOLED display driving: temporal and spatial variation of TFT, and data-line RC delay. In Chapter 1, an active matrix organic light emitting diode (AMOLED) display driver IC, enabling real-time TFT non-uniformity compensation, is presented with a hybrid driving method to satisfy fast driving speed, high TFT current accuracy and a high aperture ratio. The proposed hybrid column driver IC drives a mobile UHD (3840x2160) AMOLED panel, with one horizontal time of 7.7$\mu$s at a scan frequency of 60Hz, and simultaneously senses the TFT current for back-end TFT variation compensation. Thanks to external compensation, a simple 3T1C pixel circuit is employed in each pixel. Accurate current sensing and high panel noise immunity is guaranteed by a proposed current sensing circuit. By reusing the hybrid column driver circuitries, the driver embodies an 8-bit current-mode ADC to measure OLED V-I transfer characteristic for OLED luminance degradation compensation. Measurement results show that the hybrid driving method reduces the maximum current error between two emulated TFTs with a 60mV threshold voltage difference under 1 gray-level error of 0.94 gray-level (37nA) in 8-bit gray scales from 12.82 gray-level (501nA). The circuit-reused current-mode ADC achieves 0.56LSB DNL and 0.75LSB INL. Chapter 2 presents a load-aware pre-emphasis column driver for large-size and high-resolution flat panel displays. The column driver self-calibrates a pre-emphasis factor (K) in a column-parallel fashion to achieve fast driving speed under column-to-column panel-load RC variation. A manufactured prototype IC of the column driver drives panel load of 3.87k$\Omega$ and 150.6pF within 1.8$\mu$s, which is a 1-H time of UHD (3840x2160) display at a scan frequency of 240Hz, with less than 0.7% error under $\pm$18% panel RC variation.