A 0.26-pJ·K2 2400-μm2 Digital Temperature Sensor in 55-nm CMOS

This letter presents a compact and energy-efficient digital CMOS temperature sensor. A leakage-dominated ring oscillator (LDRO) with exponential temperature dependence and tunable supply sensitivity is proposed. A Schmitt-trigger with feedback power gating is used to minimize short-circuit currents in the delay cell. An adaptive frequency-to-digital converter is proposed in this work to improve flexibility and efficiency. It remains accurate while the reference clock can be higher or lower than the sensed frequency. Fabricated in a standard digital 55-nm CMOS process, this sensor has an active area of 2400 μm
²
and achieves a resolution figure of merit (FoM) of 0.26 pJ ·K
²
. It has a measured inaccuracy of ±0.8 °C ( 3σ) from -40 °C to 85 °C after a 1-point correlated calibration.