ISBN 978-3-8439-5173-9

978-3-8439-5173-9, Reihe Mikrosystemtechnik

Maximilian Marx
Readout Circuits for Micromachined Gyroscopes Based on Continuous-Time Delta-Sigma Modulation - System Analysis, Power-Aware Design and Automatic Tuning

303 Seiten, Dissertation Albert-Ludwigs-Universität Freiburg im Breisgau (2022), Softcover, B5

Zusammenfassung / Abstract

Angular rate sensors based on cost-efficient micromachined gyroscopes must be low-noise, low-power, and highly stable to enable emerging high-accuracy applications. Sensor readout architectures using continuous-time electromechanical delta-sigma modulation provide a good basis for approaching the required performance. However, this concept also suffers from non-idealities, including the variation of time constants. Moreover, drive and auxiliary error compensation circuits need to be improved, as these components consume high power due to the high voltages required. Furthermore, with respect to the analysis of error mechanisms that limit the system’s accuracy, fundamental research questions are still open.

To overcome time constant variation, this work presents a novel analog filter tuning circuit solely based on noise observation. The circuit works in the background with input signals up to the full scale and over a temperature range of 115 °C. The power and area overhead to the system is less than 2 %. An extended tuning circuit additionally enables tuning of the mechanical sense resonator and other circuit components.

To reduce power consumption on the drive side, an optimized high-voltage interface is developed. The circuit efficiently exploits the fact that ac signals below the chip supply voltage are sufficient when combined with a high dc bias voltage. Furthermore, the systematic optimization of auxiliary error compensation amplifiers is investigated.

Studies with respect to bias stability allow the identification of an effect that couples offset signals from the quadrature to the Coriolis channel and originates from uncoupled sense resonators. Moreover, Allan variance analyses using a configuration that avoids this effect are presented to identify further relevant influences.

The developed prototype achieves an in-band noise of 0.015 °/s and a bandwidth of 50 Hz while consuming only 1.71 mW. The bias instability reaches values as low as 0.5 °/h.