Advanced Delay-Insensitive 4-Phase Protocols

Delay-insensitive data encoding is very attractive for transmitting data in an energy efficient way over links with significant PVT variations. In this paper we analyze the potential of using multiple spacer words in the 4-phase protocol. In particular, we study how a careful choice of spacer words can help optimizing energy efficiency, and we introduce the idea of leveraging the choice of a specific spacer word, from a set of possible ones, for transmission of extra information. Starting from a formal analysis of the construction of possible spacers, we systematically elaborate the most efficient spacer selections for all commonly used m-of-n codes and determine the obtained increase in energy efficiency. This gives evidence for the competitiveness of our solution, while our implementation study illustrates how efficiently the required transmitter, receiver and completion detection circuits can be built.