WSEAS Transactions on Circuits and Systems
Print ISSN: 1109-2734, E-ISSN: 2224-266X
Volume 15, 2016
An Asynchronous Early Output Full Adder and a Relative-Timed Ripple Carry Adder
Authors: ,
Abstract: "This article presents the design of a new asynchronous early output full adder which when cascaded leads to a relative-timed ripple carry adder (RCA). The relative-timed RCA requires imposing a very small relative-timing assumption to overcome the problem of gate orphans associated with internal carry propagation. The relative-timing assumption is however independent of the RCA size. The primary benefits of the relativetimed RCA are processing of valid data incurs data-dependent forward latency, while the processing of spacer involves a very fast constant time reverse latency of just 1 full adder delay which represents the ultimate in the design of an asynchronous RCA with the fastest reset. The secondary benefits of the relative-timed RCA are it achieves good optimization of power and area metrics simultaneously. A 32-bit relative-timed RCA constructed using the proposed early output full adder achieves respective reductions in forward latency by 67%, 10% and 3.5% compared to the optimized strong-indication, weak-indication, and early output 32-bit asynchronous RCAs existing in the literature. Based on a similar comparison, the proposed 32-bit relative-timed RCA achieves corresponding reductions in cycle time by 83%, 12.7% and 6.4%. In terms of area, the proposed 32-bit relative-timed RCA occupies 27% less Silicon than its optimized strong-indication counterpart and 17% less Silicon than its optimized weak-indication counterpart, and features increased area occupancy by a meager 1% compared to the optimized early output 32-bit asynchronous RCA. The average power dissipation of all the asynchronous 32-bit RCAs are found to be comparable since they all satisfy the monotonic cover constraint. The simulation results obtained correspond to a 32/28nm CMOS process."
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Keywords: Asynchronous design, Relative-timing, Indication, Ripple Carry Adder, CMOS, Standard cells
Pages: 91-101
WSEAS Transactions on Circuits and Systems, ISSN / E-ISSN: 1109-2734 / 2224-266X, Volume 15, 2016, Art. #12