Asynchronous carry select adders

This paper discusses the standard cell based designs of asynchronous carry select adders (CSLAs) corresponding to strong-indication, weak-indication, and early output timing regimes realized using a delay-insensitive dual-rail code for data representation and processing, and a 4-phase return-to-zero protocol for handshaking. Many 32-bit asynchronous CSLAs corresponding to a uniform input partition viz. 8-8-8-8 and a non-uniform input partition viz. 8-7-6-4-3-2-2 were considered for implementation and comparison. All the asynchronous CSLAs were physically realized in semi-custom ASIC design style using a 32/28 nm CMOS process technology. The simulation results show that the 32-bit early output asynchronous CSLA based on the uniform input partition (8-8-8-8) enables optimized data path latency, area occupancy, and average power dissipation compared to the rest.