The frequency-to-digital converters (FDC) are ADC less smart temperature sensors, which use temperature sensitive CMOS ring oscillator. However, the ring oscillator consumes most of the area in the FDC. In this paper, first, we propose a novel temperature sensitive, simple PrMnO ₃ (PMO) device based oscillator to replace a complex CMOS ring oscillator in FDC. The oscillations are based on negative differential resistance (NDR) by efficient thermal runaway due to the high thermal resistivity of PMO. Second, using the NDR in PMO and a simple circuit, the temperature sensitive oscillations are demonstrated experimentally. Finally, a Verilog-A model of PMO is developed and used in FDC circuit implementation to capture the temperature sensitive oscillations. The high area efficiency along with comparable power and resolution with the state-of-the-art temperature sensors makes the PMO based oscillator attractive in an area critical temperature sensing application such as U-healthcare and smart dust.