M-AxPPA: An Accurate and Energy-Efficient Modified Approximate Parallel Prefix Adder

This work introduces a combined version of approximate adders (AxAs), joining approximate parallel prefix adders (AxPPA) with other AxAs from the literature (COPY, Truncation - TRUNC, and lower-part OR adder - LOA). We call this approach M-AxPPA (modified approximate parallel prefix adder) and investigate three specific versions: M-AxPPA-COPY, M-AxPPA-TRUNC, and M-AxPPA-LOA. We evaluate 315 different configurations, comparing our novel M-AxPPA to other AxAs proposed in the literature. We present pseudocode examples and investigate the accuracy quality, incorporating metrics like SSIM, NCC, MAE, MRE, and MRED. Additionally, we perform a trade-off analysis between accuracy quality and logic synthesis outcomes, underscoring the advantages of our M-AxPPA, notably the outstanding accuracy achieved by M-AxPPA-LOA (approaching 100%), with a substantial energy-saving.