SET Effects on Quasi Delay Insensitive and Synchronous Circuits

Due to their unbounded data accepting windows asynchronous circuits seem to be more susceptible to environmental effects than their synchronous counterparts with their strict data latching protocol. The technology advancement makes single event transients (SETs) more of a concern towards reliable operation.To better understand the properties of the mentioned classes we present their behaviour under the influence of SETs in a more detailed view that helps to visualize their unseen characteristics. For comparison we propose a way of fault injection where the length of a fault pulse is not fixed, calculated based on maximum gate delay, but related to the circuit's computation steps instead.The analysis concludes that asynchronous quasi delay-insensitive (QDI) circuits show better resilience against SETs due to two main reasons: (1) if realized with a 4-phase handshake protocol they are 95 to 97% resilient to negative fault pulses (2) the susceptibility of a circuit is largely unchanged for increasing fault length because of the causality underlying the QDI principle.Our analysis provides insights leading towards more resilient QDI circuits: if we only make a circuit or specific gates better resist "1" faults, we are fully resilient towards the single event transient (SET)s because "0" faults are already filtered out by its inherent behaviour. This is also beneficial for area efficiency; as asynchronous circuits often require already double or more area and computation time compared to synchronous circuits, adding extra SET mitigation with double-up or other buffer redundant techniques tends to result in painful overheads. Being able to focus the protection to "1" faults, as indicated by our analysis, can hence yield important savings.