MEMS Gyroscope Startup Sequence Avoiding Frequency Hysteresis
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Solution Overview
Problem
MEMS gyroscope start-up processes face challenges in ensuring the driving mass oscillates at the desired resonant frequency while avoiding unstable operation regions characterized by frequency hysteresis, which can lead to incorrect amplitude and frequency responses.
Innovation Solution
A method involving a drive signal application with a kicking frequency offset from the desired resonant frequency, followed by frequency tracking and amplitude control to sustain oscillations at the desired resonant mode, using a sequence of phases including quiet down, kicking, frequency tracking, and automatic gain control to maintain oscillations within stable parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a drive signal is applied at the desired resonant frequency during start-up, then the driving mass should oscillate at the correct frequency, but the system may become trapped in unstable operation regions with frequency hysteresis and incorrect amplitude responses
Solution Approach 1:
The system performs preliminary actions by first exciting the driving mass at a kicking frequency offset from the desired resonant frequency to build up oscillation amplitude, then gradually sweeping the frequency toward the resonant frequency. This preliminary frequency sweep avoids the unstable operation region and ensures reliable start-up before precise frequency locking is achieved.
Solution Approach 2:
The system dynamically adjusts the drive frequency during start-up, transitioning from a static kicking frequency to a dynamically swept frequency that approaches the resonant frequency. The frequency tracking process continuously adapts the drive frequency based on the system's response, enabling the system to navigate through stable and unstable regions dynamically.
2Measurement precision
If the oscillation amplitude is increased to improve signal strength, then the measurement sensitivity improves, but the system enters unstable operation regions with frequency hysteresis
Solution Approach 1:
The system employs feedback through frequency tracking that continuously monitors the system's oscillation response and adjusts the drive frequency accordingly. This feedback mechanism detects when the system approaches unstable regions and adjusts the frequency to maintain stable operation, while still achieving the desired oscillation amplitude for sensitive measurements.
Solution Approach 2:
The system changes operating parameters by adjusting the drive frequency as a function of oscillation amplitude. At lower amplitudes, the system operates at frequencies that build up oscillation, then transitions to the resonant frequency as amplitude increases. This parameter change strategy allows the system to achieve high amplitude for sensitivity while maintaining frequency stability through coordinated frequency adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Ensures the MEMS gyroscope starts up in the desired resonant mode, avoiding unstable operation regions and maintaining precise frequency and amplitude control, thus enhancing operational stability and accuracy.
Implementation Method 1
A first one of the mobile masses (referred to as the driving mass) is dedicated to driving and is kept in oscillation at a resonance frequency
Implementation Method 2
In the case of a rotation of the structure with respect to a predetermined gyroscope axis with an angular velocity, the sensing mass is subjected to a Coriolis force proportional to the angular velocity itself
Implementation Method 3
The two mobile masses are both capacitively coupled to the stator body. A change in capacitance with respect to the sensing mass is sensed in order to detect the angular motion (rotation)
Data Source
AI summary
A drive signal is applied to a MEMS gyroscope having several intrinsic resonant modes. Frequency and amplitude of mechanical oscillation in response to the drive signal is sensed. At startup, the drive signal frequency is set to a kicking frequency offset from a resonant frequency corresponding to a desired one of the intrinsic resonant modes. In response to sufficient sensed amplitude of mechanical oscillation at the kicking frequency, a frequency tracking process is engaged to control the frequency for the drive signal to sustain mechanical oscillation at the frequency of the desired one of the plurality of intrinsic resonant modes as the oscillation amplitude increases. When the increasing amplitude of the mechanical oscillation exceeds a threshold, a gain control process is used to exercise gain control over the applied drive signal so as to cause the amplitude of mechanical oscillation to match a further threshold. At that point start-up terminates.