Layout and radiation tolerance issues in high-speed links for TDAQ systems

High-speed optical links are often used in trigger and data acquisition (TDAQ) systems of high-energy physics (HEP) experiments for data transfer, triggering and fast control distribution. Requirements of system integration, flexibility and re-programmability suggest the use of SERDESes embedded in SRAM-based FPGAs as a communication layer for off-detector electronics. The most attractive link architecture, would deploy the same FPGAs and firmware also on-detector. However, at that side the electronics components need to withstand the expected level of radiation. In this work, we focus on a multi-gigabit bidirectional serial link architecture, which we implemented by means of Xilinx Virtex 5 FPGAs. We present the design issues related to the improvement of the radiation tolerance and their impact on the link performance in terms of speed, power consumption, area and latency. We performed several irradiation tests at INFN Laboratori Nazionali del Sud (Catania, Italy) with a 62-MeV proton beam. We report the results of the irradiation tests and we compare the accumulated configuration errors before failure for each implementation of the design.