Technology flavor selection and adaptive techniques for timing-constrained 45nm subthreshold circuits

摘要

We investigate techniques to design 45nm minimum-energy subthreshold CMOS circuits under timing constraints, considering the practical case of an 8-bit multiplier. We first show that technology flavor and Vt selections shift minimum-energy point to different operating frequencies, thereby enabling minimum energy in either low- or mid-performance applications. However, we demonstrate that independent dual-Vt assignment to save leakage in non-critical paths is not feasible. We then show that reverse adaptive body biasing (ABB) is potentially more efficient to compensate for global process/temperature variations than adaptive voltage scaling and forward ABB. Nevertheless, its practical efficiency is limited by the affordable VBB range and the value of the body-effect coefficient.