Energy-Efficient Bus Encoding for LCD Digital Display Interfaces

This paper presents a low-power encoding technique explicitly devised for the digital interface to Liquid Crystal Displays (LCDs). The proposed code, called Limited Intra-Word Transition (LIWT), exploits the existing inter-pixel correlation of typical images, by selectively transmitting a suitably encoded representation of the difference between adjacent pixels. Since all LCD transmission protocols are serial, the LIWT code specifically targets the reduction of intra-word transitions by defining codewords with limited intraword transition counts. Three are the main improvements of the proposed code with respect to previous solutions. First, it provides superior energy savings at a reduced complexity; second, it can adapt to the different signaling schemes of standard protocols; third, it can account for DC-balancing without requiring additional logic to implement it. The application of the encoding to a series of standard images resulted in transition savings over 60% on average with respect to the TMDS, LVDS and GVIF protocols. A DC-balanced version of the encoding achieves almost perfect balancing, with only a 2% reduction of the transition savings.