New hardware and power efficient sporadic logarithmic shifters for DSP applications

Shifting an input data by variable amounts is commonly found in arithmetic operations, data encoding and bit-indexing. Although some shift amounts along the entire shift range are not required, the typical realization by a full-range logarithm shifter requires full implementation and therefore suffers from complexity and power overhead. In this paper, the notion of sporadic logarithmic shifter is introduced for the first time, and a new design methodology is proposed for its optimization. By reusing parts of existing substructure of conventional logarithmic shifter or post-multiplexing the hardwired shifts, contagious subranges of desirable shift amounts are successively realized. Synthesis results on 8-bit and 16-bit sporadic logarithmic shifters show average ASIC area and power savings of up to 73.24% and 63.90% respectively, over conventional logarithmic shifters. In addition, by applying the proposed sporadic logarithmic shifters to the DCT architecture, at least 47.5% area savings and 2.9% power savings can be achieved over two constant multipliers based DCT architectures reported in the literature.Accepted versio