Methods, systems and devices related to authentication of chips using physical physical unclonable functions (PUFs) are disclosed. In preferred systems, differentials of PUFs are employed to minimize sensitivity to temperature variations as well as other factors that affect the reliability of PUF states. In particular, a PUF system can include PUF elements arranged in series and in parallel with respect to each other to facilitate the measurement of the differentials and generation of a resulting bit sequence for purposes of authenticating the chip. Other embodiments are directed to determining and filtering reliable and unreliable states that can be employed to authenticate a chip.