A variability-tolerant feedback technique for throughput maximization of TRBGs with predefined entropy

In this paper a probabilistic feedback technique to maximize the throughput of a generic True Random Bit Generator (TRBG) circuit, under a given constraint on the entropy, is discussed. In the proposed solution, the throughput of the device is dynamically and adaptively varied by an on-line entropy detector, such to obtain, with an arbitrary confidence level, an entropy greater than a given worst-case value. The approach, which has a general validity, introduces a method for making maximum use of the TRBG random bit generation capabilities, maximizing the generation throughput while preserving its entropy. It is different from the classical "open loop" TRBG design approach, in which the circuit parameter variability determines an uncertainty about the actual entropy of the device, with the proposed techniques the TRBG generation speed is varied under a given constraint on the entropy. The method can be applied to all those integrated TRBG circuits proposed in the literature and based on the uniform sampling of, e.g., random physical processes or chaotic dynamical systems.