Can QDI Combinational Circuits be Implemented without C-elements?

Quasi-Delay insensitive (QDI) circuits are the most robust and practical circuits that can be built and are resilient to process, temperature and voltage variations. It is a common belief that QDI circuits should be implemented with C-elements to prevent timing violation from internal unstable signals and they suffer from high area overhead due to the C-elements. This paper proposes a novel cost-efficient QDI model without C-elements and presents an automatic synthesis scheme to translate any Boolean function into our model with 4-phase handshaking and dual-rail encoding. Experimental results in FPGAs indicate significant cost reduction over NCL_D and NCL_X design.