Design Exploration of Energy-Efficient Accuracy-Configurable Dadda Multipliers With Improved Lifetime Based on Voltage Overscaling

Abstract

This article investigates an energy-efficient accuracy-configurable Dadda (X-Dadda) multiplier. The structure employs the voltage overscaling and approximate width setting as the approximation knobs for improving the energy consumption as well as the reliability and lifetime of the multiplier. While the former may be set in the design time as well as the runtime, the latter may only be invoked in the design time. For a given accuracy level, the partial product columns and the overscaled voltage for optimizing the energy are determined. Normally, to have the error within a tolerable limit, the voltage overscaled columns are those at lower bit significances which have higher switching activities. The structure makes use of a low number of level shifters for a low-overhead realization. The approximate columns which start from the first column are contiguous. To further improve the efficiency of the multiplier, four-bit truncation of the multiplier output is also suggested. The efficiency of the X-Dadda structure is investigated using a 15-nm FinFET technology. The results indicate that, for example, when the approximate mode with the mean relative error distance (MRED) of 0.11 is considered, up to 43% energy saving is achieved. In addition, for this case, the Bias temperature instability (BTI)-induced delay degradation of the multiplier decreases up to 9.9% compared to 50% in the case of the exact mode. Also, the impact of process variations on the accuracy of the X-Dadda is studied. Finally, the efficacy of the X-Dadda multiplier, when used in neural networks for image classification and image-processing applications, is assessed.