A Majority-based Approximate Adder for FPGAs

The most advanced ASIC-based approximate adders are focused on gate or transistor level approximating structures. However, due to architectural differences between ASIC and FPGA, comparable performance gains for FPGA-based approximate adders cannot be obtained using ASIC-based approximation ones. In this paper, we propose a method for designing a low-error approximate adder that effectively deploys the modern FPGA structure. We introduce an FPGA-based approximate adder, named as Majority Approximate Adder (MAA), with less error than the advanced approximate adders. MAA is constructed using an approximate part and an accurate one; i.e. the accurate part is based on a smaller carry-chain compared with the carry-chain of the corresponding accurate adder. In addition, approximate part is designed to use FPGA resources efficiently with a low mean error distance (MED). Experimental results based on Monte-Carlo simulation demonstrates that a 16-bit MAA has a 49.92% lower MED than the state of the art FPGA-based approximate adder. MAA also takes up less area and consumes less power than other FPGA-based approximate adders in the literature.