Self-Timed Section Carry Based Carry Lookahead Adders and the Concept of Alias Logic
P. Balasubramanian, D. A. Edwards, and W. B. Toms
Abstract
This paper makes two important contributions to the domain of self-timed computer arithmetic. Firstly, a gate-level synthesis of self-timed carry lookahead (CLA) adders based on the notion of section-carry is discussed. Three types of CLA adder architectures have been conceived and both homogeneous and heterogeneous delay-insensitive (DI) data encoding schemes are considered. In general, for higher-order additions, the self-timed CLA adder is found to result in reduced latency than the carry ripple version by 38.6%. However, the latter occupies less area and dissipates less power than the former by 37.8% and 17.4%, respectively. Secondly, a new concept of alias logic is introduced in this work which is useful for delay optimization of iterative circuit specifications — here; this concept is applied to effect latency reduction in self-timed CLA adders. By incorporating alias logic, the propagation delay of the intermediate carries in a CLA structure is further minimized to the tune of 27.2% on average, whilst accompanied by marginal area and power penalties of the order of just 2% and 1.5%, respectively.