MinAC: Minimal-Area Approximate Compressor Design Based on Exact Synthesis for Approximate Multipliers

Approximate multiplier is a fundamental arithmetic block for designing energy-efficient systems, which can be realized by approximate 4-2 compressors. However, the prior works all design approximate 4-2 compressors manually, so the area optimality of the circuits cannot be guaranteed. In this paper, given any input distribution and error bound, we propose MinAC, an exact synthesis-based method to automatically produce minimal-area approximate 4-2 compressors. To directly obtain an area-optimal circuit using an industrial gate library, gates with multiple outputs are taken into account during the exact synthesis. The experimental results show that compared with the existing methods, MinAC on average can produce approximate 4-2 compressors with 39.8%, 44.2%, and 7.9% reduction in area-delay-product, power-delay-product, and mean error distance, respectively. The code of MinAC is available at https://github.com/SJTU-ECTL/MinAC.

Automated summary

This paper proposes an exact synthesis-based method MinAC to automatically generate minimal-area approximate 4-2 compressors. Experimental results show that MinAC outperforms existing methods in terms of area-delay-product, power-delay-product, and mean error distance.