AxBMs: Approximate Radix-8 Booth Multipliers for High-Performance FPGA-Based Accelerators

Abstract

The focus of existing designs on approximate radix-8 Booth multipliers has been on ASIC-based platforms. These multipliers are based on an approximation as defined for ASIC-based systems, so they cannot achieve comparable performance gains when used for FPGA-based hardware accelerators. This is due to the inherited architectural differences between FPGAs and ASICs. This brief bridges this gap by proposing high-performance approximate radix-8 Booth multipliers whose designs target FPGA-based systems. Hence, two approximate radix-8 Booth multipliers (referred to as AxBM1 and AxBM2) are proposed. Approximation is implemented such that the 6-input lookup table (LUT) and the associated carry chains of the FPGAs are fully utilized. AxBM2 exhibits 49% improvement in delay compared to the previous best FPGA-targeted design (Booth-Approx). AxBM2 has the advantage of complementing errors; this feature has been combined with truncation to achieve up to 60% in energy savings. Moreover, the resolution of the previous state-of-the-art error-energy Pareto front is improved, such that better energy gains can be achieved for a given error constraint. As a case study, the proposed multipliers are applied to the application of Sobel edge detection, AxBM2 detected 98.45% edges with energy savings of 26.41%.