A 0.26-pJ·K<sup>2</sup> 2400-μm<sup>2</sup> Digital Temperature Sensor in 55-nm CMOS
Zhong Tang, Zhenyan Huang, Xiaopeng Yu, Zheng Shi, Nick Nianxiong Tan
Abstract
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}^{2}$ </tex-math></inline-formula> and achieves a resolution figure of merit (FoM) of 0.26 pJ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{K}^{2}$ </tex-math></inline-formula> . It has a measured inaccuracy of ±0.8 °C ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\sigma $ </tex-math></inline-formula> ) from −40 °C to 85 °C after a 1-point correlated calibration.