A temperature-independent PUF with a configurable duty cycle of CMOS ring oscillators

In this work we propose a Ring Oscillator PUF focused on the variability of the duty cycle instead of measuring the output frequency deviations. To achieve this goal, we replace the common ring oscillators, whose outputs are clock signals of 50% duty cycle, for ring oscillators with an asymmetric structure. The asymmetry confers the ability to configure the duty cycle of each individual node. Through the measurement of a relative value, such as the duty cycle, the robustness of the PUF is improved. For example, the output shift due to the temperature variation is decreased from 3% to less than 0,5%. Moreover, the potential input challenges are multiplied by the number of stages of each ring oscillator. Hence, with our design, the number of ring oscillators needed to build a robust PUF is decreased thanks to the addition of multiple and uncorrelated variables but with negligible area overhead.