Dynamic Thermal Clock Skew Compensation using Tunable Delay Buffers

Abstract

The thermal gradients existing in high-performance circuits may significantly affect their timing behavior, in particular by increasing the skew of the clock net and/or altering hold/setup constraints, possibly causing the circuit to operate incorrectly. The knowledge of the spatial distribution of temperature can be used to properly design a clock network that is able to compensate such thermal non-uniformities. However, re-design of the clock network is effective only if temperature distribution is stationary, i.e., does not change over time. In this work, we specifically address the problem of dynamically modifying the clock tree in such a way that it can compensate for temporal variations of temperature. This is achieved by exploiting the buffers that are inserted during the clock network generation, by transforming them into tunable delay elements. Temperature-induced delay variations are then compensated by applying the proper tuning to the tunable buffers, which is computed off-line and, stored in a tuning table inserted in the design. We propose an algorithm to minimize the number of inserted tunable buffers, as well as their tunable range (which directly relates to complexity). Results show that clock skew is kept within original bounds with minimum area and power penalty. The maximum increase in power is 23.2% with most benchmarks exhibiting less than 5% increase in power