Asynchronous Circuit and System Design Group

Welcome to the website of the Asynchronous Circuit and System Design Group of the CARV laboratory of FORTH-ICS!

The goal of our group is to perform world-class research into the field of Asynchronous Circuit and System Design and promote the industrial take-up of asynchronous design.

Our research ranges from transistor level modelling and understanding of asynchronous circuit phenomena to asynchronous design techniques and EDA tools for asynchronous design.

Asynchronous Design

Asynchronous design is not new. Asynchronous design methods date back to the 1950's. However, the clock signal, which is traditionally used by circuit designers, in order to enforce global timing to a digital circuit, has historically been considered as an essential device.

The following is a famous quote by Turing, who consided the clock signal as necessary for the operation of a digital computer and claimed that asynchronous circuits are hard to design:

"We might say that the clock enables us to introduce a discreteness into time, so that time for some purposes can be regarded as a succession of instants instead of a continuous flow. A digital machine must essentially deal with discrete objects, and in the case of ACE this is made possible by the use of the clock. All other computing machines except for human and other brains that I know of do the same. One can think up ways of avoiding it, but they are very awkward..."

Alan Turing, 1912-1954

More than 60 years later, asynchronous design has experienced important breakthroughs both in design methods and approaches and practical demonstrator designs from both academia and industry.

Advantages of Asynchronous Design

• Elimination of clock tree related problems (clock skew and clock power): as digital systems become larger, an increasing amount of effort is required to enforce the global timing model, with significant effort being paid to guarantee clock skew and even clock power are kept under control. In asynchronous systems, skew can be tolerated and power is well controlled.
• Average-case performance: in synchronous design, cycle time and performance are dictated by worst-case conditions, as clock period is set to be long enough to accomodate the slowest possible data propagation. Asynchronous circuits can change their speed dynamically and their performance is data-driven and governed by average-case delay.
• Adaptability to processing and environmental variations: the delay of a VLSI circuit varies significantly over processing runs, supply voltages and operating conditions. Synchronous circuit have a fixed clock rate set according to some allowed degree of variations. Asynchronous circuits are adaptive and can operate correctly under all variations with their speed increasing or descreasing, as is necessary.
• Modularity and re-use: asynchronous components have plug-and-play capabilities because of the absence of global timing assumptions.
• Lower power and lower Electromagnetic Emissions: asynchronous circuits reduce synchronisation power and automatically power-down unused components; asynchronous circuits are also quiet as they avoid unneeded signal transitions and spread out needed signal transitions.