  A new asynchronous early output block carry lookahead adder (BCLA)
incorporating redundant carries is proposed. Compared to the best of existing
semi-custom asynchronous carry lookahead adders (CLAs) employing
delay-insensitive data encoding and following a 4-phase handshaking, the
proposed BCLA with redundant carries achieves 13% reduction in forward latency
and 14.8% reduction in cycle time compared to the best of the existing CLAs
featuring redundant carries with no area or power penalty. A hybrid variant
involving a ripple carry adder (RCA) in the least significant stages i.e.
BCLA-RCA is also considered that achieves a further 4% reduction in the forward
latency and a 2.4% reduction in the cycle time compared to the proposed BCLA
featuring redundant carries without area or power penalties.
