Robust and Energy-Efficient Hardware: The Case for Asynchronous Design

The current technologies behind the design of semiconductor integrated circuits allow embedding billions of components in a singe silicon die, enabling the construction of very complex circuits in a tiny space, dissipating little energy and producing huge amounts of useful computational work. However, the current levels of integration for electronic components in silicon and similar materials are not easily managed, as parameter variations grow steadily, making the design tasks increasingly challenging. Synchronous techniques have dominated the digital system design landscape for many decades, but their costs are increasingly hard to cope with. Asynchronous design and particularly quasi-delay insensitive design promises to deal with the same challenges more gracefully in current advanced nodes, and possibly irrevocably in future technology nodes. This article proposes a review of the state of the art in using asynchronous circuit design techniques to achieve energy-efficient and robust digital circuit and system design. In particular, the definition of a robust digital circuit comprises addressing several aspects to which a digital system design is expected to be robust to, including: (1) voltage variations; (2) process variations; (3) temperature variations; (4) circuit aging. Besides addressing energy-efficiency and all the mentioned robustness aspects, this work also approaches some of the state-of-the-art tools available to deal with asynchronous design, and points to desirable research development to be conducted in these subjects in the future.