A MEMS Coriolis-Based Mass-Flow-to-Digital Converter for Low Flow Rate Sensing

• Published in: IEEE journal of solid-state circuits 2022-12, Vol.57 (12), p.3681-3692
• Main Authors: de Oliveira, Arthur Campos, Pan, Sining, Wiegerink, Remco J., Makinwa, Kofi A. A.
• Format: Article
• Language: English
• Subjects: Capacitive interface; Capacitors; Circuits; CMOS; CMOS readout interface; Coriolis force; Coriolis mass flow sensor; Delta-sigma modulation; delta–sigma modulator (ΔΣM); demodulator; Digitization; Flow control; flow rate; Flow velocity; flowmeter; Impulse response; Low flow; low noise; Mass flow; Microelectromechanical devices; Microelectromechanical systems; microelectromechanical systems (MEMS); Microfluidics; Micromachining; Mixers; Modulators; Phase locked loops; Quadratures; Readout electronics; Sensitivity; Sensors; Stability
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2022.3210003

This article presents a microelectromechanical system (MEMS) Coriolis-based mass-flow-to-digital converter ( \Phi DC) that can be used with both liquids and gases. It consists of a micromachined Coriolis mass flow sensor and a CMOS interface circuit that drives it into oscillation and digitizes the resulting mass flow information. A phase-locked loop (PLL) drives the sensor at its resonance frequency ( f_{D} ), while a low 1/ f noise switched-capacitor (SC) proportional-integral (PI) controller maintains a constant drive amplitude. Mass flow through the sensor causes Coriolis-force-induced displacements, which are detected by co-integrated sense capacitors. In-phase ( {I} ) and quadrature ( {Q} ) components of these displacements are then digitized by two continuous-time delta-sigma modulators (CT- \Delta \Sigma Ms) with finite impulse response (FIR)-DACs and passive mixers. Their outputs are used to accurately estimate and cancel sense path delay, thus improving sensor stability. To ensure constant sensitivity over a wide range of fluid densities, a background sensitivity tuning (BST) scheme adjusts the sense capacitors' bias voltage as a function of f_{D} , which is a good proxy for fluid density. Implemented in a standard 0.18- \mu \text{m} CMOS technology, the interface circuit consumes 13 mW from a 1.8-V supply. The proposed MEMS Coriolis \Phi DC achieves a state-of-the-art noise floor of 80 \mu \text{g} /h/ \sqrt {\text {Hz}} and a zero stability (ZS) of ±0.31 mg/h, which is at par with MEMS thermal flow sensors.