Efficient arithmetic using self-timing

Abstract

Recent advances in VLSI technology have facilitated high levels of integration and the implementation of faster circuits on a chip. Most of the improvements in the performance of digital systems have been brought about by such faster technologies. However, these improvements in technology have brought along with them a host of other constraints. In the faster deep submicron technologies, the wire delays constitute a significant portion of the overall delay of the system and hence some of the advantages of faster technologies are lost. The high level of integration necessitates clock distribution schemes which minimize skew across the die. These result in area penalties and adversely affect the level of integration possible at the chip level. Hence, changes in the basic architecture of computing elements of a system, which when implemented in silicon introduces reduced interconnect delays and simpler clock distribution networks, will result in more effective performance improvements. The work presented here examines the implementation of the most basic element in any datapath-an adder. The adder, a carry elimination adder (CEA), uses self-timing at both the algorithmic and implementation levels and presents a minimal hardware high speed addition mechanism. The adder exploits the nature of the input operands dynamically, which results in its average case convergence time approaching that of the ubiquitous carry lookahead adder (CLA) and the hardware complexity of a carry ripple adder (CRA). Use of self-timing results in the elimination of a global clock and hence clock-skew.