Understanding and Comparing the Capabilities of On-Chip Voltage Sensors against Remote Power Attacks on FPGAs

This paper presents a study of two types of on-chip FPGA voltage sensors based on ring oscillators (ROs) and time-to-digital converter (TDCs), respectively. The performance of these sensors is evaluated in the presence of circuits that deliberately waste power, resulting in localized voltage drops. The effects of FPGA power supply features and sensor sensitivity in detecting voltage drops in an FPGA power distribution network (PDN) are evaluated for Xilinx Artix-7 and Zynq UltraScale+ FPGAs. We show that the two sensor types are both able to detect supply voltage drops, and that their measurements are consistent with each other. However, we find that TDC-based sensors are more sensitive and can detect voltage drops that are shorter in duration, while RO sensors have a higher dynamic range and are easier to implement because calibration is not required.