Improved Bus-Shift Coding For Low-Power I/O

In low-power VLSI design good amount of power can be saved by using coding scheme such as Bus-Invert (BI). Such a coding scheme looks at successive words on a data bus and applies transformation to minimize the number of transitions. In this paper we propose Bus-Shift (BS) coding scheme that circularly shifts the data to minimize transitions. Power saving of BI is poor on average cases, and even that deteriorates with wider bus width. In comparison the proposed BS scheme performs better in both maximum and average cases. For wide bus the savings from BS gets slightly worse, but still performs better than BI. Simulation results show a saving margin of 14% in average cases for a 32 bit bus. Comparison is also made with Shift-Invert (SINV), another reported coding scheme. An implementation of BS in Cadence is presented.