A circuit having a fingerprint for identification of a particular instantiation of the circuit is disclosed. The circuit may include a plurality of digital circuits or gates. Each of the digital circuits or gates is responsive to a configuration voltage applied to its analog input for controlling whether or not the digital circuit or gate performs its intended digital function and each of the digital circuits or gates transitioning between its functional state and its at least one other state when the configuration voltage equals a boundary voltage. The boundary voltage varies between different instantiations of the circuit for a majority of the digital circuits or gates and these differing boundary voltages serving to identify (or fingerprint) different instantiations of the same circuit.