Guest Editorial: Special Section on Asynchronous Circuits and Systems

T HE SPECIAL Section in this issue covers different aspects of asynchronous design. This is an area of increasing interest in the last few years triggered by the new challenges dictated by the continuous miniaturization of integrated circuits. Variability, power, noise, and electromagnetic interference are some of the aspects that designers have to face today to make their circuits efficient, robust and with affordable manufacturing costs. Imposing a rigid clock to a circuit that internally experiments significant variability is like keeping a sparrow in a cage. The delay margins to ensure correctness are increasing as device and interconnect variability dominate in the timing characterization of the components of the circuits. In addition, power consumption is often becoming the most severe limitation to achieve the performance requirements of the specification. Asynchronous circuits, with their different forms of implementation , contribute to meliorate some of the features of circuits finding more favorable points in the power/performance/area design space. Some examples may help to illustrate these features. Synchronization in asynchronous circuits is local, thus increasing the spatial correlation between the circuit delays and the synchronization signals, usually implemented as handshakes between local clocks. Hence, the margins to cover the potential variability can be significantly reduced and the performance of the circuit can be naturally adapted to the operating conditions determined by the environment (e.g., voltage and temperature). In some classes of circuits, such as delay-insensitive circuits, the immunity to variability is complete. Asynchronous circuits also contribute to reduce dynamic power. The components of the circuit only work when some computation is needed and this can be implemented elegantly by simply associating computations with the handshake signals that indicate the availability of information. Electromagnetic interference is another concerning aspect of synchronous circuits that concentrate their switching activity close to the clock edges. Asynchronous circuits spread this activity more evenly across the spectrum since the activity is determined by local handshakes that have a lower timing correlation. This issue presents five regular papers and two short papers exposing recent advances in the design of asynchronous systems. Most of the contributions were originally presented at the 14th IEEE International Symposium on Asynchronous Circuits and Systems that was held in Newcastle upon Tyne, U.K., in April 2008. Out of 23 submissions for this Special Section, the papers were selected after a thorough evaluation process. The first paper, " Efficient Automatic Resolution of Encoding Conflicts Using STG Unfoldings …