Multi-operand adder synthesis on FPGAs using generalized parallel counters

Abstract

Multi-operand adders usually consist of compression trees which reduce the number of operands per a bit to two, and a carry-propagate adder for the two operands in ASIC implementation. The former part is usually realized using full adders or (3; 2) counters like Wallace-trees in ASIC, while adder trees or dedicated hardware are used in FPGA. In this paper, an approach to realize compression trees on FPGAs is proposed. In case of FPGA with m-input LUT, any counters with up to m inputs can be realized with one LUT per an output. Our approach utilizes generalized parallel counters (GPCs) with up to m inputs and synthesizes high-performance compression trees by setting some intermediate height limits in the compression process like Dadda's multipliers. Experimental results show its effectiveness against existing approaches at GPC level and on Altera's Stratix III.