Post-layout comparison of high performance 64b static adders in energy-delay space

Our objective was to determine the most energy efficient 64 b static CMOS adder architecture, for a range of high-performance delay targets. We examine extensively carry-lookahead (CLA) and carry-select adders with a wide range of tradeoffs in logic levels, fanouts and wiring complexity. We propose sparse CLA adder architectures based on buffering techniques to reduce logic redundancy and improve energy efficiency. All the designs were implemented using an energy-delay layout optimization flow with full RC extraction. Our new 64 b adder designs have a relative delay as low as 9.9 F04 (fanout-offour inverter) delays and promise better scaling for smaller technology nodes. They yield the best energy efficiency for a wide range of delay targets and are 30%, 15% and 7% more energy efficient than full Kogge-Stone, sparse-2 Kogge-Stone and Han-Carlson, respectively, at the fastest points. They consume only about 1/3 the energy of dynamic adders.