Narrow bus encoding for low power systems

High integration in integrated circuits often leads to the problem of running out of pins. Narrow data buses can he used to alleviate this problem at the cost of performance degradation due to wait cycles. In this paper, we address bus coding methods for low power core-based systems incorporating narrow buses. Although the conventional bus-invert code performs well for completely random patterns, we show that transition signaling combined with bus-invert, which we call BITS coding, can achieve much more power saving for data patterns of typical DSP applications. The application of BITS coding to a real circuit design is limited by the overhead of the encoder and decoder circuits and the extra bus line introduced. We propose an approximate version of BITS coding, which does not require the extra bus line while retaining the advantage of BITS coding.