A Self-Checking TMR Voter for Increased Reliability Consensus Voting in FPGAs

Abstract

Nanoscale field-programmable gate array (FPGA) circuits are more prone to radiation-induced effects in harsh environments because of their memory-based reconfigurable logic fabric. Consequently, for mission- or safety-critical applications, appropriate fault-tolerance techniques are widely employed. The most commonly applied technique for hardening FPGAs against radiation-induced upsets is triple modular redundancy (TMR). Voting circuits used in TMR implementations are decentralized and consensus is calculated from the redundant outputs off-chip. However, if there are an insufficient number of pins available on the chip carrier, the TMR system must be reduced to an on-chip unprotected simplex system, meaning voters used at those locations become single point of failure. In this paper, we propose a self-checking voting circuit for increased reliability consensus voting on FPGAs. Through fault injection and reliability analyses, we demonstrate that the proposed voter, which utilizes redundant voting copies, is approximately 26% more reliable than an unprotected simplex voter when reliability values of voters over normalized time are averaged.