Library tuning for subthreshold operation

Abstract

In this paper, the authors extend their work on the balancing-based subthreshold cell sizing methodology. The libraries were benchmarked against a library tuned for super-threshold operation. Two sets of standard cells have been properly sized for operation at 0.3V, and further characterized at different voltages. A super-threshold 90 nm low power library was chosen as a reference library to compare timing, power and voltage scaling ability. The resented libraries show a 31% timing improvement at 0.3 V without area penalty over the conventional library. The comparison of libraries at different voltages shows that with respect to the super-threshold library, the presented library with only transistor channel width tuning has on average 10% better timing from 0.3 V to 1.2 V, and that this library with both transistor channel width and length tuning show timing improvements of 31.4% and 6.9% when the supply voltage increases from 0.3 V to 0.6 V, respectively.