SGER: Exploring Massive Chip Level Active Deskewing for VLSI Chips Beyond 20GHz

Colorado State University, Fort Collins CO

Investigators

Abstract

During the last several decades, the clock rate and the level of integration of VLSI chips have reached a level that distributing clocks has become an increasingly difficult task. The most recently released chips run at more than 2GHz-clock rate. The performance projection for future ULSI chips will be up to 20GHz in the next 5-10 years. This implies that the overall clock skew needs to be kept under 5ps across the chip in order to control the amount of clock skew to be within 10% of the total clock cycle. This problem will be further exacerbated by the steep increase in process variations in future processing technologies beyond 50nm generations. Furthermore, when chips contain more and more components (gates), the disparity of switching activities on chip will vary more widely resulting in greater on-chip variations of temperature and supply noise, which are time-variant. The research proposed here is intended to explore a dramatically different design paradigm for designing and distributing clock signals for the future where the clocking networks will be dynamically adapted to chip's operating environment to perform a deskewing function in real-time. Active deskewing uses on-chip active devices such as delay-locked loops (DLLs) to detect and reduce skews between any two points on the chip. The issues the proposed research addresses include: Given a chip architecture and the characteristics (switching, leakage, and density) of the blocks used on the chip, what is the optimal topology of the self-adjusting deskewing network that must be stable? Given the performance requirements for the chip, what is the maximum latency of the deskewing network the chip can tolerate? What is the resolution of deskewing circuits? And how does this affect the overall performance of the clock network? Research includes an extensive exploration theoretically to determine the practicality of such a deskewing approach. A mathematical model for the entire deskewing system is formulated as a multi-input, multi-output (MIMO) discrete-time dynamic system. A stability analysis based upon the model is being developed. This approach uses results from robust control theory that can guarantee stability even for perturbed systems.