Variability-aware architecture level optimization techniques for robust nanoscale chip design

摘要

The design space for nanoscale CMOS circuits is vast, with multiple dimensions corresponding to process variability, leakage, power, thermal, reliability, security, and yield considerations. These design issues in the form of either objectives or constraints can be handled at various levels of digital design abstraction, such as architectural, logic and transistor. At the architectural level (a.k.a. Register-Transfer Level, RTL), there is a balanced degree of freedom for fast design exploration by exploring various values of design parameters. Correct design decisions at an early phase of the design cycle ensure that design errors are not propagated to lower levels of circuit abstraction, where it is costly to correct them. Moreover, design optimization at higher levels of abstraction provides a convenient way to deal with design complexity, facilitates design verification, and increases design reuse through intellectual property (IP) cores. To achieve power-performance trade-offs, different architectural-level techniques have been proposed in the existing literature. This paper will briefly discuss selected RTL techniques which account for process variation. These existing approaches handle the optimization of different power components independently but do not effectively account for the inherent variation of process and design parameters. Thus, in this paper, a novel process variation aware statistical RTL optimization approach is presented. Assuming dual values of T_(ox), V_(th), and V_(DD), gate-oxide leakage, subthreshold leakage, dynamic power, and performance are estimated for architectural units. Statistical variations in the parameters (T_(gate), V_(th), V_(DD), and L_(eff)), are explicitly taken into account by using Monte Carlo simulations while characterizing the architectural units. The proportion of values of gate-oxide and subthreshold leakage and dynamic power in the total power consumption of these units is then analyzed. This analysis in essence gives a relative and integrated perspective of various power-performance tradeoffs against the baseline case, thus serving as a guideline to help designers make appropriate decisions. Experiments on several benchmarks show a significant reduction in gate-oxide and subthreshold leakage, dynamic, and total power.