System design of a low-power three-axis underdamped MEMS accelerometer with simultaneous electrostatic damping control

Ciotîrcă Lavinia 1
1 LAAS-OSE - Équipe Optoélectronique pour les Systèmes Embarqués
LAAS - Laboratoire d'analyse et d'architecture des systèmes [Toulouse]
Abstract : Recently, consumer electronics industry has known a spectacular growth that would have not been possible without pushing the integration barrier further and further. Micro Electro Mechanical Systems (MEMS) inertial sensors (e.g. accelerometers, gyroscopes) provide high performance, low power, low die cost solutions and are, nowadays, embedded in most consumer applications. In addition, the sensors fusion has become a new trend and combo sensors are gaining growing popularity since the co-integration of a three-axis MEMS accelerometer and a three-axis MEMS gyroscope provides complete navigation information. The resulting device is an Inertial measurement unit (IMU) able to sense multiple Degrees of Freedom (DoF). Nevertheless, the performances of the accelerometers and the gyroscopes are conditioned by the MEMS cavity pressure: the accelerometer is usually a damped system functioning under an atmospheric pressure while the gyroscope is a highly resonant system. Thus, to conceive a combo sensor, a unique low cavity pressure is required. The integration of both transducers within the same low pressure cavity necessitates a method to control and reduce the ringing phenomena by increasing the damping factor of the MEMS accelerometer. Consequently, the aim of the thesis is the design of an analog front-end interface able to sense and control an underdamped three-axis MEMS accelerometer. This work proposes a novel closed-loop accelerometer interface achieving low power consumption. The design challenge consists in finding a trade-off between the sampling frequency, the settling time and the circuit complexity since the sensor excitation plates are multiplexed between the measurement and the damping phases. In this context, a patented damping sequence (simultaneous damping) has been conceived to improve the damping efficiency over the state of the art approach performances (successive damping). To investigate the feasibility of the novel electrostatic damping control architecture, several mathematical models have been developed and the settling time method is used to assess the damping efficiency. Moreover, a new method that uses the multirate signal processing theory and allows the system stability study has been developed. This very method is used to conclude on the loop stability for a certain sampling frequency and loop gain value. Next, a CMOS implementation of the entire accelerometer signal chain is designed. The functioning has been validated and the block may be further integrated within an ASIC. Finally, a discrete components system is designed to experimentally validate the simultaneous damping approach.
Document type :
Theses
Micro and nanotechnologies/Microelectronics. INP Toulouse, 2017. English
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https://hal.laas.fr/tel-01561758
Contributor : Lavinia Ciotirca <>
Submitted on : Thursday, July 13, 2017 - 11:52:10 AM
Last modification on : Thursday, January 11, 2018 - 6:26:30 AM

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  • HAL Id : tel-01561758, version 1

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Ciotîrcă Lavinia. System design of a low-power three-axis underdamped MEMS accelerometer with simultaneous electrostatic damping control . Micro and nanotechnologies/Microelectronics. INP Toulouse, 2017. English. 〈tel-01561758〉

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