A comparison of quasi-delay-insensitive asynchronous adder designs corresponding to return-to-zero and return-to-one handshaking

This paper makes a comparison between various quasi-delay-insensitive (QDI) asynchronous ripple carry adders (RCAs) realized using a delay-insensitive dual-rail code which correspond to 4-phase return-to-zero (RTZ) and 4-phase return-to-one (RTO) handshaking. The QDI RCAs considered are 32-bits in size and correspond to a variety of timing regimes viz. strong-indication, weak-indication, early output, and relative-timed, which are implemented using a 32/28nm CMOS process. The extensive comparisons show that, overall, QDI RCAs which correspond to the RTO protocol are optimized compared to their QDI RCA counterparts which correspond to the RTZ protocol in terms of area, power dissipation, latency, and cycle time.