Statistically optimized asynchronous barrel shifters for variable length codecs

This paper presents low-power asynchronous barrel shifters for variable length encoders and decoders useful in portable applications using multimedia standards. Our approach is to create multi-level asynchronous barrel shifters optimized for the skewed shift control statistics often found in these codecs. For common shifts, data passes through one level, whereas for rare shifts, data passes though multiple levels. We compare our optimized designs with the straight-forward asynchronous and synchronous designs. Both pre- and post-layout HSPICE simulation results indicate that, compared to their synchronous counterparts, our designs provide over a 40% savings in average energy consumption for a given average performance.