Run-time Configurable Approximate Multiplier using Significance-Driven Logic Compression

Abstract

Designing energy-efficient hardware continues to be challenging due to arithmetic complexities. The problem is further exacerbated in systems powered by energy harvesters as variable power levels can limit their computation capabilities. In this work, we propose a run-time configurable adaptive approximation method for multiplication that is capable of managing the energy and performance tradeoffsideally suited in these systems. Central to our approach is a Significance-Driven Logic Compression (SDLC) multiplier architecture that can dynamically adjust the level of approximation depending on the run-time power/accuracy constraints. The architecture can be configured to operate in the exact mode (no approximation) or in progressively higher approximation modes (i.e. 2 to 4-bit SDLC). Our method is implemented in both ASIC and FPGA. The implementation results indicate that our design has only a 2.3% silicon overhead, on top of what is required by a traditional exact multiplier. We evaluate the efficiency of the proposed design through a number of case studies. We show that our method achieves similar image fidelity as in the existing approximate methods, without a delay penalty. Further, the inclusion of the dynamic approximation techniques is justified by up to 62.6% energy savings when processing an image with a multiplier using 4-bit SDLC and 35% energy savings when using 2-bit SDLC. In addition, case study results show that the proposed approach incurs negligible loss in output quality with the worst PSNR of 30dB when using the 4-bit SDLC multiplier.