The research into ring oscillator physically unclonable functions (RO-PUF) continues to expand due to its simple structure, ease of generating responses, and its promises of primitive security. However, a substantial study has yet to be carried out in developing designs of the FPGA-based RO-PUF, which effectively balances performance and area efficiency. This work proposes a modified RO-PUF where the ring oscillators are connected directly to the counters. The proposed RO-PUF requires fewer RO than the conventional structure since this work utilizes the direct pulse count method. This work aims to seek the ideal routing density of ROs to improve uniqueness. For this purpose, five logic arrangements of a wide range of routing densities of ROs were tested. Upon implementation onto the FPGA chip, the routing density of ROs are varied significantly in terms of wire utilization (higher than 25%) and routing hotspots (higher than 80%). The best uniqueness attained was 52.71%, while the highest reliability was 99.51%. This study improves the uniqueness by 2% subsequent to the application of scenarios to consider ROs with a narrow range of routing density. The best range of wire utilization and routing hotspots of individual RO in this work is 3–5% and 20–50%, respectively. The performance metrics (uniqueness and reliability) of the proposed RO-PUF are much better than existing works using a similar FPGA platform (Altera), and it is as good as the recent RO-PUFs realized on Xilinx. Additionally, this work estimates the minimum runtimes to reduce error and response bit-flip of RO-PUF.

Thermal issues are rapidly evolving in the field‐programmable gate arrays (FPGAs) and are being intensely studied as these issues appear to significantly affect the delay performance of FGPAs. A ring oscillator has been widely used as a digital temperature sensor to sense this thermal effect on FPGAs. The delay generated by the ring oscillator will vary depending on the temperature environment due to negative bias temperature instability, hot carrier injection and electromigration. It is therefore critical to adopt an accurate ring oscillator design to effectively measure the delay in FGPAs. In this study, a digital temperature sensor with a stable ring oscillator is proposed. Measurement periods of 512 and 4096 clock cycles have been implemented and the relationship between temperature, delay and total count has been established. The results show that as the temperature increases to 100°C, the delay decreases by 3.99 and 33.98% for 512 and 4096 clock cycles, respectively. It has been found that in order to reduce the degradation effect on the Virtex‐6 FPGA, adopting a measurement period of 512 clock cycles is the best method. The measured data is successfully validated through a set of simulations. Thus, it may benefit a system designer and industrial player, especially in designing temperature‐based FPGAs.

The degradation effect of a field-programmable gate array becomes a significant issue due to the high density of logic circuits inside the field-programmable gate array. The degradation effect occurs because of the rapid technology scaling process of the field-programmable gate array while sustaining its performance. One parameter that causes the degradation effect is the delay occurrence caused by the hot carrier injection and negative bias temperature instability. As such, this research proposed a multipoint detection technique that detects the delay occurrence caused by the hot carrier injection and negative bias temperature instability degradation effects. The multipoint detection technique also assisted in signaling the aging effect on the field-programmable gate array caused by the delay occurrence. The multipoint detection technique was also integrated with a method to optimize the performance of the field-programmable gate array via an automatic clock correction scheme, which could provide the best clock signal for prolonging the field-programmable gate array performance that degraded due to the degradation effect. The delay degradation effect ranged from 0° to 360° phase shifts that happened in the field-programmable gate array as an input feeder into the multipoint detection technique. With the ability to provide closed-loop feedback, the proposed multipoint detection technique offered the best clock signal to prolong the field-programmable gate array performance. The results obtained using the multipoint detection technique could detect the remaining lifetime of the field-programmable gate array and propose the best possible signal to prolong the field-programmable gate array’s performance. The validation showed that the multipoint detection technique could prolong the performance of the degraded field-programmable gate array by 13.89%. With the improvement shown using the multipoint detection technique, it was shown that compensating for the degradation effect of the field-programmable gate array with the best clock signal prolonged the performances.