  One of the most common types of Physical Unclonable Functions (PUFs) is the
ring oscillator PUF (RO-PUF), in which the output bits are obtained by
comparing the oscillation frequencies of different ring oscillators. In this
paper we design a new type of ring oscillator PUF in which the different
inverters composing the ring oscillators can be supplied by different voltages.
The new RO-PUF can be used to (1) increase the maximum number of possible
challenge/response pairs produced by the PUF; (2) generate a high number of
bits while consuming a low area; (3) improve the reliability of the PUF in case
of temperature variations. We present the basic idea of the new RO-PUF and then
discuss its applications.
