A 0.002-mm², 2.9-μW Pulse-Frequency-Modulation-Based Temperature Sensor for Wide Sensing Range from -60 °C to 120 °C

This work presents a compact, low-power fully CMOS pulse-frequency-modulation (PFM) temperature sensor fabricated in 180 nm technology, supporting a wide -60 °C to 120 °C sensing range. Subthreshold biasing generates temperature-proportional current, while PFM converts current variations into digital pulse signals to bypass supply voltage swing limitations. The following two core optimizations are proposed: an improved cascode current mirror to suppress channel-length modulation and stabilize thermal current, and a temperature-insensitive monostable circuit eliminating extreme-temperature oscillation failure caused by variable reset pulse width. A four-point off-chip calibration model further compensates static and temperature-dependent loop delay errors. The prototype occupies only 2200 μm² core area and consumes 2.9 μW. With a 5 ms conversion time, it achieves 47 mK RMS temperature resolution, 32 pJ·K² resolution FoM and 0.06 pJ·K^-2·mm^-2 area FoM, with calibrated measurement inaccuracy limited to +1.8/-1.9 °C (3σ). This RC-free quasi-digital PFM architecture scales well to advanced process nodes and fits aerospace, cryogenic infrared detector and low-power industrial thermal sensing applications.