A mixed-signal control system for Lorentz-force resonant MEMS magnetometers
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This paper presents a mixed-signal closed-loop control system for Lorentz force resonant MEMS magnetometers. The control system contributes to 1) the automatic phase control of the loop, that allows start-up and keeps self-sustained oscillation at the MEMS resonance frequency, and 2) output offset reduction due to electrostatic driving by selectively disabling it. The proposed solution proof-of-concept has been tested with a Lorentz force-based MEMS magnetometer. The readout electronic circuitry has been implemented on a printed circuit board with off-the-shelf components. Digital control has been implemented in an FPGA coded with VHDL. When biased with 1 V and a driving current of 300 µArms, the device shows 9.75 pA/µT sensitivity and total sensor white noise of 550 nT/vHz. Offset when electrostatic driving is disabled is 793 µT, which means a 40.1% reduction compared when electrostatic driving is enabled. Moreover, removing electrostatic driving does not worsen bias instability, which is lower than 125 nT in both driving cases.
CitationJ.M. Sánchez-Chiva [et al.]. A mixed-signal control system for Lorentz-force resonant MEMS magnetometers. "IEEE sensors journal", 1 Setembre 2019, vol. 19, núm. 17, p. 7479-7488.