A circuit that produces an output signal having a frequency that is proportional to absolute temperature (PTAT) is disclosed. In one embodiment, the circuit includes a ring oscillator and a bias current circuit coupled thereto. The ring oscillator and the bias current circuit are implemented in close proximity to one another. During operation, the bias current circuit generates a bias current that is provided to the ring oscillator. The amount of bias current generated is dependent upon the temperature of the circuit. In turn, the frequency of an output signal provided by the ring oscillator is dependent on the amount of bias current received from the bias current circuit. Accordingly, the frequency of the ring oscillator output signal is dependent on the temperature of the circuit.