A 0.35-V 5,200-μm2 2.1-MHz Temperature-Resilient Relaxation Oscillator With 667 fJ/Cycle Energy Efficiency Using an Asymmetric Swing-Boosted RC Network and a Dual-Path Comparator

Abstract

This article describes a 2.1-MHz relaxation oscillator (RxO) for energy-harvesting Internet-of-Things (IoT) sensor nodes. The RxO features an asymmetric swing-boosted <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> network and a dual-path comparator to surmount the challenges of sub-0.5-V operation while achieving temperature resilience. The former enables alternating the common-mode voltages at the output of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> network to facilitate the sub-0.5-V operation, while the latter is outfitted with a delay generator for tracking the temperature-sensitive delay of the comparator. Prototyped in 28-nm CMOS, the RxO occupies a tiny footprint of 5,200 <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> . The power consumption is 1.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> at 0.35 V. The measured temperature stability is 158 ppm/°C (average of seven chips) over −20 °C–120 °C. It scores the best energy efficiency (667 fJ/cycle) among the reported MHz-range RxOs and has a figure-of-merit (181 dB) that compares favorably with the state-of-the-art.