Methods, systems and devices related to authentication of chips using physical physical unclonable functions (PUFs) are disclosed. In accordance one such method, a test voltage is applied to a PUF system including a first subset of PUF elements that are arranged in series and a second subset of PUF elements that are arranged in series, where the first subset of PUF elements is arranged in parallel with respect to the second subset of PUF elements. In addition, the PUF system is measured to obtain at least one differential of states between the first subset of PUF elements and the second subset of PUF elements. Further, the method includes outputting an authentication sequence for the circuit that is based on the one or more differentials of states.