Enhanced Wallace Tree Multiplier via a Prefix Adder

Abstract

At the end of all fixed point multiplications is one last long addition that needs to be performed. In this paper, we show how the choice of this last adder has significant effect on the delay of the multiplier, in terms of time complexity. It is shown here that using a prefix adder for the final addition, causes the multiplication delay to increase as $\mathrm{O}({log}[N])$, as compared to the $\mathrm{O}(N)$ delay if a ripple carry adder is used instead. Simulations using spectre by Cadence, for 8,16,32, and 64 bit Wallace tree based multipliers, show that using a prefix adder instead of a ripple carry adder reduces the multiplier’s latency by up to 66% at the cost of minimal increase in power consumption.