Intrinsic NBTI-variability aware statistical pipeline performance assessment and tuning

Abstract

Random process variation and variability intrinsic to PMOS Negative Bias Temperature Instability (NBTI-induced statistical variation) are two major reliability concerns as transistor dimensions scales with technology. Previous works have studied these two sources of variation separately at device and circuit level. We study the impact of the interaction between intrinsic PMOS NBTI variability and time process variability on circuit delay spread. A statistical pipeline timing error model is proposed including both the variability sources to predict its impact on pipeline stage count. It is shown that a wide difference in statistical timing response to intrinsic NBTI variability exists among different circuits. Traditional design time NBTI-aware delay guard-banding is proved to be statistically insufficient in pipelines and an excess of 2x guard-band needs to be incorporated at the end of 10 years. However, the guard-band is shown to be reduced by 30% when the dynamic cycle time stealing technique is employed.