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Characterization of IOBUF-based Ring Oscillators

Ring Oscillators (ROs) are fundamental primitives that are used as building blocks in many other types of circuits. This paper presents an in-depth characterization of ring oscillators which leverage the IOBUF primitive found in modern Xilinx FPGAs. This work first analyzes the impact of the drive strength and slew rate attributes of the IOBUFs on the ROs, and also characterizes the impacts of external temperature, internal voltage, and external voltage fluctuations on the frequency of the proposed ROs. This work further demonstrates that IOBUF-based ROs can detect whether electrical connections to the IOBUF pins have changed, including whether the DRAM module has been physically removed. Finally, the proposed ROs can be realized on cloud FPGAs, bypassing the restrictions that some cloud providers impose on combinatorial loops, and thus presenting a new security threat to remote FPGAs.