System-Level Power Reduction Techniques for Color

Modern portable computing devices such as notebook computers, palm-size PCs, PDAs (Personal Data Assistants) and even cell phones are equipped with color TFT (Thin-Film Transistor) LCDs (Liquid Crystal Displays) as well as a high-performance CPU and a high-bandwidth, large-capacity mem-ory system as a demand on multi-media applications and quality graphical user interfaces increases. Despite the limited power available in a battery-operated mobile embedded system, a quality LCD system is now the default configuration for hand-held embedded systems. It is composed of a high-resolution (i.e. 640 × 480 pixels or above) and high-color (i.e. 16 bits per pixel or higher) LCD panel, a high-wattage backlight lamp and a large-capacity frame buffer memory. These display components lead to the high power consumption although they become much more energy-efficient than before thanks to previous component-level power optimizations. The energy reduction for the display technology is still immature al