A Hybrid Self-calibration Technique to Mitigate the Effect of Variability in TRNG

In this work, we briefly study the effect of variability in process and operating conditions on the statistics and performance of on-chip True Random Number Generator (TRNG), using the cryptographic measure of bit entropy. Circuits designed in deep submicron technologies are susceptible to variation in process. The variability may affect the circuit performance, power and reliability. Numerous pre-silicon design methodologies and post-silicon circuit tuning mechanisms have been proposed in literature. We propose a hybrid self-detection and calibration technique based on algorithmic post processing and circuit tuning to mitigate the effects of variability. Results show that variation in fabrication process and varying on-chip temperature affect the reliability of these circuits. On employing the proposed self calibration technique in 45nm technology, an improvement of close to 4X in the bit entropy is seen across a range of 10% intra-die variation. The proposed technique also mitigates the effect of variation in operating temperature. The simple control logic has an estimated area of 128 um and results in a negligible energy overhead of 0.82 fJ/bit.