Optimisation of RO-PUF Design Parameters for Minimising the Effective Area per PUF Bit

This work links Ring Oscillator (RO)-Physical Unclonable Function (PUF) specific design parameters with previously neglected area consumption per PUF bit. In prior art, the PUF specific design parameters such as number of ROs in a given RO collection that can be compared to one another and readout time are optimised in terms of e.g stability and/or power consumption. The influence of these design parameters on the effectively required area per bit remains overlooked, since optimization on area is mostly done simply by designing small ROs. This work establishes a relationship between the general design parameters and the area per bit for RO-PUFs. Using finite frequency readout resolution by means of a limited readout time, the RO-PUF is transformed into graph-theory and by finding a Minimum Spanning Tree (MST), the best possible yield of a given collection of ROs is determined. The given collection together with variable yield is then mapped to a certain demand on area per bit. An extensive yield analysis is performed which then is again mapped to a certain area per bit, leading to the proposed connection between readout time, amount of ROs in a collection and area per bit.The system-level analysis performed shows that a set of 8 ROs represents a sweet-spot in terms of area per bit as well as low read-out time.