Low-Power Color TFT LCD Display for Hand-Held Embedded Systems
ABSTRACT
An LCD (Liquid Crystal Display) is a standard display device for hand-held embedded systems. Today, color TFT (Thin-Film Transistor) LCDs is common even in cost-effective equipments. An LCD display system is composed of an LCD panel, a frame buffer memory, an LCD and frame buffer controller, and a backlight inverter and lamp. All of them are heavy power consumers, and their portion becomes much more dominant when running interactive applications. This is because interactive applications are often triggered by human inputs and thus result in a lot of slack time in the CPU and memory system, which can be effectively used for dynamic power management.
In this paper, we introduce low-power LCD display schemes as a system-level approach. We accurately characterize the energy consumption at the component level and minimize energy consumption of each component without appreciable display quality degradation. We develop several techniques such as variable-duty-ratio refresh, dynamic-color-depth control and backlight luminance dimming with brightness compensation or contrast enhancement. Each method exhibits power reduction of 260mW, 250mW and 480mW, respectively. The aggregate energy reduction ratio is 28% out of total energy consumption including the CPU and the main memory system when we execute a document viewer. We also demonstrate that we can extend the battery life about 38% and 20% for a text editor and an MPEG4 player, respectively.
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