Hardening QDI circuits against transient faults using delay-insensitive maxterm synthesis

The correct functionality of quasi-delay-insensitive asynchronous circuits can be jeopardized by the presence and propagation of transient faults. If these faults are latched, they will corrupt data validity and can make the whole circuit to stall, given the strict event ordering constraints imposed by handshaking protocols. This is particularly concerning for the delay-insensitive minterm synthesis logic style, widely adopted by asynchronous designers to implement combinatory quasi-delay-insensitive logic, because it makes extensive use of C-elements and these components are rather vulnerable to transient effects. This paper demonstrates that this logic style submits C-elements to their most vulnerable states during operation. It accordingly proposes the alternative use of the delay-insensitive maxterm synthesis for hardening QDI circuits against transient faults. The latter is a logic style based on the return-to-one 4-phase protocol. Although this style also relies on extensive usage of C-elements, the states where these components are most vulnerable are avoided. Results display improvements of over 300% in C-elements tolerance to transient faults, in the best case.