A high-performance 64-bit adder implemented in output prediction logic

Abstract

Output Prediction Logic (OPL) is a technique that can be applied to conventional CMOS logic families to obtain considerable speedups. When applied to static CMOS, OPL retains the restoring character of the logic family. Speedups of 2/spl times/ to 3/spl times/ over (optimized) conventional static CMOS are demonstrated for a variety of circuits, ranging from chains of gates, to datapath circuits, and to random logic benchmarks. Such speedups are obtained using identical netlists without remapping. When applied to pseudo-nMOS and dynamic families in combination with remapping to wide-input NORs, OPL yields even greater speedups over static CMOS. In this paper we present a novel 64-bit adder design implemented in OPL, using a combination of 8-bit Carry Look Ahead (CLA) and Carry Select (CS). The very fast wide-input OPL NORs enabled the use of 8-bit CLA units instead of the usual 4-bit. Using a process-independent metric for comparison, this adder is twice as fast as previously published 64-bit adders.