Reducing bus transition activity by limited weight coding with codeword slimming

Transitions on high capacitance busses in VLSI systems result in considerable power dissipation. Various coding schemes have been proposed in literature to encode the input signal in order to reduce the number of transitions. Number of transitions can be reduced by introducing redundancy in data transferred over the busses. For a given amount of redundancy there exists a lower bound on the average number of transitions. In this paper we de-rive a new coding scheme which leads to extremely practical tech-niques for bus transmission that reduce bus transitions to within 3:96-8:42 % of the lower bound depending on the redundancy em-ployed. There is also a net reduction in power dissipation rang-ing from 8:53-21:88 % over an uncoded bus transmission scheme. This savings in power dissipation is identical to that for bus-invert coding per word transmitted the higher efficiency brought about by codeword slimming, however, results in shorter codewords than bus-invert coding which in turn results in higher energy efficiency in word transmission. Applications suitable for this new tech-nique include systems relying on bit-serial implementation and systems with bit-parallel implementations where the cost of ex-tra parallel-to-serial and serial-to-parallel data-format converters is marginal compared to the power savings obtained. 1