  Mission-critical and safety-critical applications generally tend to
incorporate triple modular redundancy (TMR) to embed fault tolerance in their
physical implementations. In a TMR realization, an original function block,
which may be a circuit or a system, and two exact copies of the function block
are used to successfully overcome any temporary fault or permanent failure of
an arbitrary function block during the routine operation. The corresponding
outputs of the function blocks are majority voted using 3-input majority voters
whose outputs define the outputs of a TMR realization. Hence, a 3-input
majority voter forms an important component of a TMR realization. Many
synchronous majority voters and an asynchronous non-delay insensitive majority
voter have been presented in the literature. Recently, quasi delay insensitive
(QDI) asynchronous majority voters for TMR applications were also discussed in
the literature. In this regard, this paper presents a new QDI asynchronous
majority voter for TMR applications, which is better optimized in area compared
to the existing QDI majority voters. The proposed QDI majority voter requires
30.2% less area compared to the best of the existing QDI majority voters, and
this could be useful for resource-constrained fault tolerance applications. The
example QDI TMR circuits were implemented using a 32/28nm complementary metal
oxide semiconductor (CMOS) process. The delay insensitive dual rail code was
used for data encoding, and 4-phase return-to-zero and return-to-one handshake
protocols were used for data communication.
