On the Use of Low-power Devices, Approximate Adders and Near-threshold Operation for Energy-efficient Multipliers

With the rising importance of power consumption in battery-powered devices, approximate computing techniques have emerged as a promising approach to strike a balance between exact computation and power savings, leading to improved delays. This paper investigates the combination of near-threshold operation and approximate adders to design power-efficient multipliers. We analyzed four multiplier architectures using 16 nm low-power and high-performance models. At the transistor level, three strategies for approximate full adders are explored, focusing on both partial product reduction and the final addition stage of the multipliers. Eleven test cases are thoroughly evaluated to identify the most suitable approximate circuit, considering the trade-offs among power, performance, and accuracy. The obtained results demonstrate a substantial reduction in power consumption at near-threshold operation. The replacement of exact full adders with the approximate copy strategy in the least significant bits of the multipliers leads to a reduction of up to 34.4% in power consumption and 19.2% in delay. The design-space exploration carried out in this study provides valuable insights for designers to choose the best approximate multiplier based on specific design requirements.