ISBN 9783843951791

978-3-8439-5179-1, Reihe Mikrosystemtechnik

Sebastian Neßler
A Readout Circuit with Collocated Force Feedback for the Control of Micromachined Inertial Sensors Based on Continuous-Time Delta-Sigma Modulation - System-Level Design and Implementation

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

Zusammenfassung / Abstract

This work presents for the first time the implementation of a continuous-time collocated force feedback (CCFB) for the readout of capacitive inertial sensors embedded into an electro-mechanical delta-sigma modulator. Compared to discrete-time implementations, the concept relies exclusively on continuous-time techniques to avoid noise folding and to reduce the power consumption. An input common mode modulation of the charge-to-voltage converter is used to enable simultaneous sensing of the proof mass deflection and generation of electrostatic force feedback at the same set of electrodes.

The CCFB is implemented as part of a high-performance and low-power micromachined gyroscope readout using an electro-mechanical bandpass delta-sigma modulator. Compared to previous continuous-time gyroscope readout circuits, the CCFB allows separation of high-voltage bias and time-varying feedback signals, resulting in increased energy efficiency. Measurements of the system implemented as an application-specific integrated circuit confirm very good performance combined with low power consumption.

The CCFB is also investigated for the readout of wide bandwidth accelerometers for condition monitoring. An optimized system-level design for the lowpass modulator is presented and its performance is verified by numerical simulation. Especially for this wide bandwidth accelerometer design, higher modes in the mechanical sensor transfer function jeopardize the loop stability. The stability analysis considers different loop filter architectures of the modulator. Moreover, state-of-the-art techniques to stabilize the loop are investigated and limitations are identified. In this work, the influence of higher sensor modes is suppressed by a multi-tap finite impulse response filter in the feedback or in front of the quantizer of the modulator. This concept provides additional degrees of freedom that enable systematic stabilization of the electro-mechanical delta-sigma modulator.