Reduced power consumption for MPEG decoding with LNS

Abstract

By reducing the accuracy of the logarithmic number system (LNS) it is possible to achieve lower power consumption for multimedia applications, such as MPEG, without significantly lowering the visual quality of the output. An LNS wordsize of 8 to 10 bits produces a comparable MPEG output as a fixed-point wordsize of 14 to 16 bits. The switching activity of an LNS ALU that computes the inverse discrete cosine transform (IDCT) is one quarter that of fixed point, implying lower power consumption. By skipping inputs that are zero (which MPEG can do naturally with its run-length coding and zigzag ordering) the switching activity of LNS MPEG becomes one-tenth that of fixed point, in contrast to the minimal impact zero skipping has on fixed-point power consumption.