On the convergence to regime of ADC-based true random number generators

Reconfigurable circuits alternatively acting as random number generators (RNGs) or analog to digital converters (ADCs) represent a promising approach to true random bit generation since they can provide high quality random values almost for free whenever a system already embeds an ADC. In their usage, one needs to consider that entering the RNG-mode requires some minor interruption of operation, since the internal chaos-based random source gets initialised at the last ADC input. Hence, the first generated values maintain some dependence on a potentially known value and a few dead beats are needed by the chaotic system to reach a regime where this correlation vanishes. This delay has so far been quantified only empirically. Here, a formal bound is provided, with relation to the required performance level and the system noise floor.