Research On Low Power AMOLED Pixel Circles And Driving Method

Attributed to the attractive features including high contrast ratio, fast response, vivid color and being thin and flexible, active matrix organic light emitting diode(AMOLED) displays have entered the market for smartphone and TV applications. Reducing the power consumption becomes a very important topic to be addressed for further technology development. Currently, low power AMOLED display technologies are mainly on high efficiency and low voltage OLED devices, and some behavior-level power reduction methods. There is lack of systematic study on the pixel circuit and driving scheme for low power AMOLED displays. Moreover, AMOLED pixel circuit design needs to compensate the non-ideal effects of thin-film transistors(TFTs), IR-drop on the display panel and OLED aging. Therefore, this thesis focuses on low power strategies on the pixel circuit design and driving methods, to reduce the power consumption without sacrifice of the display performance, and also make it easier to combine high efficiency OLED device technologies and behavior-level power reduction methods. The following work will be covered in this thesis:1) The power consumption in AMOLED display panels is systematically analyzed, composed of dynamic power and static power, which can provide the theoretical basis for research on low power technologies for AMOLED displays.2) A pixel circuit composed of three TFTs and one capacitor(3T-1C) with external feedback compensation is proposed. Simulation results show the circuit and driving scheme can effectively suppress all the non-ideal effects of TFTs including threshold voltage and mobility changes, kink effect, and IR-drop. This pixel circuit of fewer TFTs will be useful for high resolution displays and manufacturing with high yield.3) Based on the developed 3T-1C pixel circuit, a driving scheme by biasing the driving TFT in non-saturation regime is proposed for reducing the power consumption. It is shown that, with external compensation, the OLED current is not influenced by the electrical property of the driving TFT. Therefore, the driving TFT can be biased in the non-saturation regime without affecting the display performance.4) A one-dimensional(1D) dynamic voltage scaling(DVS) driving scheme is proposed to adaptively scale down the power supply voltage of different regions in the panel according to the displayed content for power reduction. By combining the DVS and the 3T-1C pixel circuit with the driving TFT biased in the non-saturation regime, it is shown the power consumption can be significantly decreased.