Asynchronous Ripple Carry Adder based on Area Optimized Early Output Dual-Bit Full Adder

TL;DR

This paper introduces an area-optimized asynchronous dual-bit full adder and constructs a ripple carry adder that significantly reduces area and latency compared to previous designs, using delay-insensitive encoding and early output techniques.

Contribution

The paper proposes a novel asynchronous dual-bit full adder with reduced area and latency, and demonstrates its effectiveness in a 32-bit ripple carry adder with substantial performance improvements.

Findings

28.6% less silicon area for the new dual-bit full adder

18.8% area reduction in 32-bit RCA compared to previous design

29.4% latency reduction in 32-bit RCA over SFA-only design

Abstract

This technical note presents the design of a new area optimized asynchronous early output dual-bit full adder (DBFA). An asynchronous ripple carry adder (RCA) is constructed based on the new asynchronous DBFAs and existing asynchronous early output single-bit full adders (SBFAs). The asynchronous DBFAs and SBFAs incorporate redundant logic and are encoded using the delay-insensitive dual-rail code (i.e. homogeneous data encoding) and follow a 4-phase return-to-zero handshaking. Compared to the previous asynchronous RCAs involving DBFAs and SBFAs, which are based on homogeneous or heterogeneous delay-insensitive data encodings and which correspond to different timing models, the early output asynchronous RCA incorporating the proposed DBFAs and/or SBFAs is found to result in reduced area for the dual-operand addition operation and feature significantly less latency than the asynchronous RCAs which consist of only SBFAs. The proposed asynchronous DBFA requires 28.6% less silicon than the previously reported asynchronous DBFA. For a 32-bit asynchronous RCA, utilizing 2 stages of SBFAs in the least significant positions and 15 stages of DBFAs in the more significant positions leads to optimization in the latency. The new early output 32-bit asynchronous RCA containing DBFAs and SBFAs reports the following optimizations in design metrics over its counterparts: i) 18.8% reduction in area than a previously reported 32-bit early output asynchronous RCA which also has 15 stages of DBFAs and 2 stages of SBFAs, ii) 29.4% reduction in latency than a 32-bit early output asynchronous RCA containing only SBFAs.