Energy parsimonious circuit design through probabilistic pruning

Inexact Circuits or circuits in which the accuracy of the output can be traded for energy or delay savings, have been receiving increasing attention of late due to invariable inaccuracies in designs as Moore´s law approaches the low nanometer range, and a concomitant growing desire for ultra low energy systems. In this paper, we present a novel design-level technique called probabilistic pruning to realize inexact circuits. Unlike the previous techniques in literature which relied mostly on some form of scaling of operational parameters such as the supply voltage (V_dd) to achieve energy and accuracy tradeoffs, our technique uses pruning of portions of circuits having a lower probability of being active, as the basis for performing architectural modifications resulting in significant savings in energy, delay and area. Our approach yields more savings when compared to any of the conventional voltage scaling schemes, for similar error values. Extensive simulations using this pruning technique in a novel logic synthesis based CAD framework on various architectures of 64-bit adders demonstrate that normalized gains as great as 2X-7.5X in the Energy-Delay-Area product can be obtained, with a relative error percentage as low as 10^-6% up to 10%, when compared to corresponding conventionally correct designs.