Soner Sonmezoglu

An Automatically Mode-Matched MEMS Gyroscope With Wide and Tunable Bandwidth

This paper presents the architecture and experimental verification of the automatic mode-matching system that uses the phase relationship between the residual quadrature and drive signals in a gyroscope to achieve and maintain matched resonance mode frequencies. The system also allows adjusting the system bandwidth with the aid of the proportional-integral controller parameters of the sense-mode force-feedback controller, independently from the mechanical sensor bandwidth. This paper experimentally examines the bias instability and angle random walk (ARW) performances of the fully decoupled MEMS gyroscopes under mismatched (~ 100 Hz) and mode-matched conditions. In matched-mode operation, the system achieves mode matching with an error frequency separation between the drive and sense modes in this paper. In addition, it has been experimentally demonstrated that the bias instability and ARW performances of the studied MEMS gyroscope are improved up to 2.9 and 1.8 times, respectively, with the adjustable and already wide system bandwidth of 50 Hz under the mode-matched condition. Mode matching allows achieving an exceptional bias instability and ARW performances of 0.54 °/hr and 0.025 °/√hr, respectively. Furthermore, the drive and sense modes of the gyroscope show a different temperature coefficient of frequency (TCF) measured to be -14.1 ppm/°C and -23.2 ppm/°C, respectively, in a temperature range from 0 °C to 100 °C. Finally, the experimental data indicate and verify that the proposed system automatically maintains the frequency matching condition over a wide temperature range, even if TCF values of the drive and sense modes are quite different.

Extended Bandwidth Lorentz Force Magnetometer Based on Quadrature Frequency Modulation

In this paper, a Lorentz force magnetometer demonstrates quadrature frequency modulation operation. The Lorentz force magnetometer consists of a conventional 3-port resonator, which is put into oscillation by electrostatic driving and sensing. The bias current flowing through the resonator is proportional to the displacement, and generates Lorentz force in quadrature with the electrostatic force. As a result, the Lorentz force acts as an equivalent spring and the magnetic field can be measured by reading the change in oscillation frequency. The sensor has a sensitivity of 500 Hz/T with a short-term noise floor of 500 nT

An automatically mode-matched MEMS gyroscope with 50 Hz bandwidth

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Force-rebalanced Lorentz force magnetometer based on a micromachined oscillator

Hz. The bandwidth of the sensor is increased to 50 Hz, a factor of 12 greater than that of the same resonator operating in amplitude-modulated mode. The short-term noise floor within 50-Hz bandwidth is comparable with CMOS Hall-effect sensors.

Single-Structure Micromachined Three-Axis Gyroscope With Reduced Drive-Force Coupling

This paper presents the architecture and experimental verification of an automatic mode matching system that uses the phase relationship between the residual quadrature and drive signals in a gyroscope to accomplish and maintain the frequency matching condition. The system also allows controlling the system bandwidth by adjusting the closed loop controller parameters of the sense mode. This study experimentally examines the angle random walk (ARW) and bias instability performances of the fully decoupled MEMS gyroscopes under mismatched (~100Hz) and mode-matched conditions. Moreover, it has been experimentally shown that the performance of the studied MEMS gyroscopes is improved up to 2.4 times in bias instability and 1.7 times in ARW with 50 Hz system bandwidth under the mode-matched condition reaching down to a bias instability of 0.83°/hr and an ARW of 0.026°/√hr.

Simultaneous detection of linear and coriolis accelerations on a mode-matched MEMS gyroscope

This paper presents a 3-axis Lorentz force magnetometer based on an encapsulated micromechanical silicon resonator having three orthogonal vibration modes, each measuring one vector component of the external magnetic field. One mode, with natural frequency (fn) of 46.973 kHz and quality factor (Q) of 14 918, is operated as a closed-loop electrostatically excited oscillator to provide a frequency reference for 3-axis sensing and Lorentz force generation. Current, modulated at the reference frequency, is injected into the resonator, producing Lorentz force that is centered at the reference frequency. Lorentz force in the first axis is nulled by the oscillator loop, resulting in force-rebalanced operation. The bandwidth and scale-factor of this force-rebalanced axis are independent of resonator Q, improving the sensors temperature coefficient from 20 841 ppm/ °C to 424 ppm/ °C. The frequencies of the other two modes are closely spaced to the first modes reference frequency and are demonstrated to track thi...

Off-resonance operation of a MEMS Lorentz force magnetometer with improved thermal stability of the scale factor

This letter presents a micromachined silicon three-axis gyroscope based on a triple tuning-fork structure utilizing a single vibrating element. The mechanical approach proposed in this letter uses a secondary “auxiliary” mass rather than a major “proof” mass to induce motion in the proof mass frame for Coriolis force coupling to the sense mode. These auxiliary masses reduce the unwanted mechanical coupling of force and motion from the drive mode to the three sense modes. The experimental data show that the bias error due to coupling is reduced by a factor up to 10, and the bias instability of each sense axis is reduced by a factor of up to 3 when the gyroscope is actuated using the auxiliary masses rather than the major masses. The gyroscope exhibits a bias instability of 0.016°/s, 0.004°/s, and 0.043°/s for the x-, y-, and z-sense modes, respectively. Furthermore, initial temperature characterization results show that the gyroscope actuated by the auxiliary masses ensures a better bias instability performance in each sense axis over a temperature range from 10 °C to 50 °C in comparison with the gyroscope actuated by the major masses.

Magnetic sensors based on micromechanical oscillators

This paper presents a novel “in operation acceleration sensing and compensation method” for a single-mass mode-matched MEMS gyroscope. In this method, the amplitudes of the sustained residual quadrature signals on the differential sense-mode electrodes are compared to measure the linear acceleration acting on the sense-axis of the gyroscope. By measuring the acceleration acting along the sense-axis, the g-sensitivity of the gyroscope output to these accelerations is mitigated without using a dedicated accelerometer. It has been experimentally demonstrated that the g-sensitivity of the studied gyroscope is substantially reduced from 1.08°/s/g to 0.04°/s/g, and the effect of the linear acceleration on the gyroscope output is highly-suppressed (by 96%) with the use of the compensation method proposed in this work.

Monolithic piezoelectric Aluminum Nitride MEMS-CMOS microphone

This paper presents a new method for improving thermal stability of the scale factor in resonator-based microelectromechanical systems (MEMS) Lorentz force magnetometers. The method uses two nominally-identical magnetometers. The first is operated off-resonance in open-loop to measure magnetic field, and the second is operated as a closed-loop oscillator to provide a frequency reference for driving current generation. The proposed operation significantly reduces the effect of the resonators temperature coefficient of frequency (TCF) on the output, improving the sensors temperature coefficient from 12177 ppm/°C to 508 ppm/°C in a temperature range of 10-60 °C. The sensor operated with a 50 Hz frequency split exhibits a resolution of 0.36 μT/√Hz and measurement bandwidth of 38 Hz, independent from the O-limited mechanical sensors bandwidth of 3.2 Hz.

Countering the Effects of Nonlinearity in Rate-Integrating Gyroscopes

This paper describes magnetic sensor technology based on the detection of Lorentz force on a micromechani-cal oscillator. Experimental results are presented based on a silicon resonator operating at 105.5 kHz with a quality factor of 13,000. Sensor operation is demonstrated using amplitude modulation (AM) and frequency modulation (FM) readout of the magnetic signal. In AM operation, the noise at the sensors output is equivalent to 128 nT/rt-Hz and the bandwidth is 4 Hz. In FM operation, the noise at the sensors output is equivalent to 500 nT/rt-Hz and the bandwidth is 50 Hz.