Impact of TMR design layouts on single event tolerance in SRAM-based FPGAs

For highly reliable applications in mission critical systems, the Triple Modular Redundancy (TMR) technique is believed to be a common and effective approach to mitigate Single Event Upsets (SEUs) in Field Programmable Gate Arrays (FPGAs). In one of our neutron test campaigns, we observed an increase of 53.8% in single event tolerance of our optimized Fast Fourier Transform (FFT) design compared with the baseline (i.e., the traditional FFT design), while the increase of the TMR'd optimized FFT design is only 30.8% compared with the baseline. Although it is believed that Multiple-Cell Upsets (MCUs) poses a negative impact on the single event performance of TMR, the results of the TMR'd optimized FFT design are far from our expectations. A large number of preliminary simulations confirm that layout changes have a significant impact on the Multiple-Bit Upsets (MBUs) sensitivity of TMR'd design. This is because in the layout obtained through automatic placement and routing, these replicated modules of the TMR are interlaced with each other. Therefore, MBUs are more likely to induce domain-crossing events and affect two or more TMR modules. To further harden the TMR'd design, either putting three identical circuits of the TMR'd design into three independent blocks or using Dynamic Partial Reconfiguration (DPR) is demonstrated effective in mitigating MBUs in Static Random-Access Memory (SRAM)-based FPGAs.