On Extra Delays Affecting I/O Blocks of an SRAM-Based FPGA Due to Ionizing Radiation

This paper aims at characterizing additional delays induced by ionizing radiation in Input/Output Blocks (IOBs) of Static Random-Access Memory Based Field Programmable Gate Arrays (SRAM-Based FPGAs), using measurement techniques based on ring oscillators (ROs). This characterization effort includes experiments performed with proton irradiation at TRIUMF on Xilinx devices (Virtex-5 and Artix-7). Results from these irradiation experiments show that RO period variations, up to 6.2 ns for Virtex-5 and 3.8 ns for Artix-7, could be induced. These results also reveal that the occurrence rate of events (namely delays and breaks) affecting ROs implemented in IOBs is approaching the rate observed when ROs are implemented in the FPGA core, even if the number of configuration bits dedicated to IOBs is significantly lower than for the FPGA core. These radiation test experiments are supported by emulation using similar RO-based measurement techniques and Xilinx SEU Controller as a fault injector. The fault injection experiments allow a better understanding of the behaviour of IOBs affected by additional delays due to configuration bit flips, which in many cases is similar to what can be observed with an incorrect parameter setting. Emulation experiments also reveal that many of the events modifying IOB behaviour are found to require multiple bit fault injection.