Power and area efficient sorting networks using unary processing

Sorting is a common task in a wide range of applications from signal and image processing to switching systems. For applications that require high performance, sorting is often performed in hardware. Hardware cost and power consumption are the dominant concerns. The usual approach is to wire up a network of compare-and-swap units in a configuration called a Batcher (or Bitonic) network. This paper proposes a novel area-and power-efficient approach to sorting networks based on 'unary processing.' Data is encoded as serial bit-streams, with values represented by the fraction of 1's in a stream of 0's and 1's. (This is an evolution of prior work on stochastic logic. Unlike stochastic logic, the unary approach is deterministic and completely accurate.) Synthesis results of complete sorting networks show up to 87% area and power saving compared to the conventional binary implementations. However, the latency increases. To mitigate the increased latency, the paper uses a novel time-encoding of data. The approach is validated with implementation of an important application of sorting: median filtering. The result is a low-cost, energy-efficient implementation of median filtering with only a slight accuracy loss.