  Electronic circuits and systems used in mission and safety-critical
applications usually employ redundancy in the design to overcome arbitrary
fault(s) or failure(s) and guarantee the correct operation. In this context,
the distributed minority and majority voting based redundancy (DMMR) scheme
forms an efficient alternative to the conventional N-modular redundancy (NMR)
scheme for implementing mission and safety-critical circuits and systems by
significantly minimizing their weight and design cost and also their design
metrics whilst providing a similar degree of fault tolerance. This article
presents the first FPGAs based implementation of example DMMR circuits and
compares it with counterpart NMR circuits on the basis of area occupancy and
critical path delay viz. area-delay product (ADP). The example DMMR circuits
and counterpart NMR circuits are able to accommodate the faulty or failure
states of 2, 3 and 4 function modules. For physical synthesis, two commercial
Xilinx FPGAs viz. Spartan 3E and Virtex 5 corresponding to 90nm and 65nm CMOS
processes, and two radiation-tolerant and military grade Xilinx FPGAs viz. QPro
Virtex 2 and QPro Virtex E corresponding to 150nm and 180nm CMOS processes were
considered for the NMR and DMMR circuit realizations which employ the 4-by-4
array multiplier as a representative function module. To achieve a fault
tolerance of 2 function modules, both the DMMR and the NMR schemes provide near
similar mean ADPs across all the four FPGAs. But while achieving a fault
tolerance of 3 function modules the DMMR features reduced ADP by 44.5% on
average compared to the NMR, and in achieving a fault tolerance of 4 function
modules the DMMR reports reduced ADP by 56.5% on average compared to the NMR
with respect to all the four FPGAs considered.
