Robust Near-Threshold Design With Fine-Grained Performance Tunability

Abstract

Lowering supply voltage is still the most effective technique to reduce dynamic power, and Vdd is being pushed toward the threshold voltage for ultra-low power applications. However, near-threshold circuit leakage power is comparable to the switching power and performance is highly sensitive to static and dynamic threshold voltage variations. This makes designing circuits for a target performance very difficult, and post-silicon tunability is required to achieve performance targets without taking huge design margins. In this work, we tackle this problem by proposing a novel dual-Vdd technique for near-threshold operation and show that one can tune the performance of a circuit in a fine-grained manner by powering an optimal sub-set of rows with a slightly higher supply voltage than the rest, without incurring the large cost of distributed level shifters. By varying the percentage of rows at a slightly higher voltage, one can trade off performance and power in a fine-grained manner. This style is fully compatible with state-of-the-art commercial physical design flows and imposes minimal area blow-up. It can be applied without any placement disruption on a fully placed design. Experimental results show that by employing our dual-Vdd technique, we can improve the performance of several benchmarks up to 45% while achieving more than 50% lower power as compared to single- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vdd</i> implementations.