PUF-Entropy Extraction of DAC Intersymbol-Interference using Continuous-Time Delta-Sigma ADCs

This work proposes a new method of Physical-Unclonable-Function (PUF) entropy extraction and for ADC fingerprinting using a DAC's Intersymbol-Interference (ISI). The proposed method can e.g. be implemented as a side-product of a continuous-time (CT-) Delta-Sigma-Modulator (DSM) by utilizing ISI of it's feedback DAC as unique entropy-source. This extends the existing state of the art by extracting more entropy per DAC unit element. A source coding of the dynamic DAC error estimations is explained which transforms the Gaussian distributed errors into uniform distribution by using multi-valued DSM fingerprints and creating an interval-based symbol sorting. Transistor-level simulations show a superior normalized entropy given by 0.999 for up to a 7-bit extraction with read-out stability given by its Symbol-Error (SE) between
$< 10^{-5}$
for a 3-bit extraction up to 0.1 for 7-bit after correction over temperature and supplv-voltage variation.