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Chapter 10: Transmittance Scaling for Reducing Power Dissipation of a Backlit TFT-LCD
By Enrico Macii
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From Ultra Low-Power Electronics and Design
Wei-Chung Cheng Massoud Pedram, University of Southern California OVERVIEWAbstract This chapter presents transmittance scaling; a technique aimed at conserving power in a transmissive TFT-LCD with a cold cathode fluorescent lamp (CCFL) backlight by reducing the backlight illumination while compensating for the luminance loss. This goal is accomplished by adjusting the transmittance function of the TFT-LCD panel while meeting an upper bound on a contrast distortion metric. Experimental results show that an average of 3.7X power saving can be achieved for still images with a mere 10% contrast distortion. Keywords: CCFL; transmissive LCD; TFT-LCD; backlight luminance dimming; transmittance scaling; concurrent brightness and contrast scaling; power efficiency; low power design. 10.1 INTRODUCTIONTFT-LCD is the most popular flat-panel display used in today's consumer electronics and computer systems. TFT stands for "Thin Film Transistor" and describes the control elements that actively control the individual pixels. For this reason, one speaks of so-called "active matrix TFT's". LCD means "Liquid Crystal Display" and stands for monitors that are based on liquid crystals. To obtain a high image quality and low power dissipation in a TFT-LCD, low off-current and high on-current are necessary. Previous studies on battery-powered electronics point out that the display subsystem dominates the energy consumption of the whole system. In the SmartBadge system, for instance, the display consumes 29%, 29%, and 50% of the total power in the active, idle, and standby modes, respectively [1]. Direct-view LCDs can largely be categorized into reflective and transmissive displays which...
Copyright Kluwer Academic Publishers 2004 under license agreement with Books24x7
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