Coherent Design of Hybrid Approximate Adders: Unified Design Framework and Metrics

Numerous approximate adders have been proposed in the literature in response to the languishing benefits of technology scaling. However, they have been obtained with an ad-hoc and non-systematic methodology which does not fully exploit the design space possibilities. This paper provides a conceptual framework for the systematic design of approximate adders, including hybrid and non-equally segmented approaches as well as more robust error metrics. The framework discriminates the scenarios, where approximate processing does not provide significant benefits from those where it does; in this later case, it aids to obtain optimal configurations for the adders. Experimental results with a commercial technology assess the significant improvements of our systematic approach. Furthermore, a case study with a processor enhanced with an approximate accelerator highlights the usability of the methods.