Analysis and Comparison on Full Adder Block in Sub-Micron Technology

In this paper the main topologies of one-bit full adders, including the most interesting of those recently proposed, are analyzed and compared for speed, power consumption and power-delay product. The comparison has been performed on two classes of circuits, the former with minimum transistor size to minimize power consumption, the latter with optimized transistor dimension to minimize power-delay product. The investigation has been carried out with properly defined simulation runs on a Cadence environment using a 0.35-m process, also including the parasitics derived from layout. Performance has been also compared for different supply voltage values. Thus design guidelines have been derived to select the most suitable topology for the design features required. This paper also proposes a novel figure of merit to realistically compare n-bit adders implemented as a chain of one-bit full adders. The results differ from those previously published both for the more realistic simulations carried out and the more appropriate figure of merit used. They show that, except for short chains of blocks or for cases where minimum power consumption is desired, topologies with only pass transistors or transmission gates are not attractive. In contrast, the most interesting implementations in terms of trade off between power and delay are the traditional CMOS and Mirror topologies. Moreover, the Dual-rail Domino and the CPL allow the best speed performance.