Distributed Locally Synchronous Grid Oscillator via Perpetual Token Exchange

Abstract

Providing a global time reference for System-on-Chips (SoCs) is a challenging task. Conventional clock trees suffer from skews that unavoidably grow with the circuit size, which render them inappropriate for large circuits. In order to provide a synchronous abstraction at least locally, the globally asynchronous locally synchronous (GALS) approach can be used, which splits a circuit into several independently clocked islands and resorts to asynchronous communication between these islands. Several alternative approaches for achieving global synchrony were proposed in the past, some harnessing physical effects or other techniques, which suffer from different drawbacks. Inspired by certain self-timed asynchronous circuits, we present a fully digital distributed oscillator based on perpetual token exchange, which considerably outperforms alternative solutions in terms of the achievable local skew and simplicity. Furthermore, we experimentally study the fault-tolerance properties of our approach.