Subthreshold logic for low-area and energy efficient true random number generator

Abstract

This paper discusses the advantages of subthreshold logic for True Random Number Generators (TRNG). In this work, the entropy is modeled, and a lower bound of Shannon's entropy per output bit can quickly be estimated. Thanks to this model, sizing TRNGs in subthreshold logic is quite simple and defining design guidelines for low-energy and low-area TRNGs is straightforward. A TRNG in 180nm CMOS technology has been designed, demonstrating low complexity (305 gates) and energy efficacy (30pJ/bit) at 0.5 Kbit/s.