MEMS Gyroscope Position-Control Drive for Resonance Drift Tracking
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Solution Overview
Problem
Existing microelectromechanical gyroscopes face challenges in maintaining precise oscillation control due to variations in resonance frequency over time and temperature, leading to inefficiencies in driving and sensing mechanisms, particularly in complex electromechanical structures with multiple movable masses.
Innovation Solution
A microelectromechanical gyroscope with a hybrid control loop incorporating a charge amplifier, phase-shift module, low-pass filter, variable gain amplifier, and phase-locked loop circuit, utilizing differential capacitive structures and correlated double sampling techniques to stabilize oscillations and track resonance frequency drifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback driving circuits based on sigma-delta modulators are used to stabilize oscillation at resonance frequency, then oscillation stability is improved, but device complexity and manufacturing cost increase due to multiple filtering and processing stages
Solution Approach 1:
The patent extracts and eliminates the complex filtering and decimation stages from the sigma-delta modulator circuit by using a simplified resonant frequency tracking approach that directly measures and adjusts the driving frequency without requiring multiple processing stages, thereby maintaining oscillation stability while reducing device complexity
Solution Approach 2:
The patent implements a feedback mechanism that continuously monitors the oscillation frequency and adjusts the driving frequency accordingly, using a phase-detector circuit to compare the actual frequency with the target resonance frequency and automatically correct deviations, achieving stable oscillation with simpler circuitry
2Ease of manufacture
If open loop periodic stresses are applied at resonance frequency, then driving mechanism is simple, but oscillation stability deteriorates due to process spreads and frequency variations over time
Solution Approach 1:
The patent converts the open-loop driving mechanism into a closed-loop system by adding a frequency detection circuit that measures the actual oscillation frequency and feeds this information back to a frequency adjustment circuit, which automatically tunes the driving frequency to match the resonant frequency, thereby maintaining oscillation stability while keeping the overall structure simple
Solution Approach 2:
The patent enables the gyroscope to self-adjust its operating frequency by incorporating a frequency-tracking mechanism that automatically detects resonance conditions and adjusts the driving frequency without external intervention, allowing the device to compensate for process variations and frequency drift autonomously
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
This solution enables precise and reliable control of microelectromechanical oscillations, improving signal-to-noise ratio and reducing complexity, while allowing for effective tracking of resonance frequency variations, thus enhancing the performance and scalability of microelectromechanical gyroscopes.
Implementation Method 1
The movable mass is moreover coupled to the fixed body via capacitive structures (capacitors). The movement of the movable mass with respect to the fixed body, for example on account of an external stress, modifies the capacitance of the capacitors
Implementation Method 2
Vice versa, by supplying appropriate biasing voltages, it is possible to apply an electrostatic force to the movable mass to set it in motion
Implementation Method 3
In the case of rotation of the microstructure with respect to a pre-determined axis with an angular velocity, is subject to a Coriolis force proportional to the angular velocity itself
Implementation Method 4
In addition, to produce electromechanical oscillators the frequency response of the inertial MEMS structures is exploited, which is typically of the second-order low-pass type
Data Source
Figure 1~4
Figure 2~5
Figure 6~7
AI summary
A MEMS gyroscope includes: a microstructure (2) having a fixed structure (6), a driving mass (7), movable with respect to the fixed structure (6) according to a driving axis (X), and a sensing mass (8), mechanically coupled to the driving mass (7) so as to be drawn in motion according to the driving axis (X) and movable with respect to the driving mass (7) according to a sensing axis (Y), in response to rotations of the microstructure (2); and a driving device (3), for keeping the driving mass (7) in oscillation with a driving frequency (ωD). The driving device (3) includes a discrete-time sensing interface (20), for detecting a position (x) of the driving mass (7) with respect to the driving axis (X) and a control stage (21, 23, 24, 25) for controlling the driving frequency (ωD) on the basis of the position (x) of the driving mass (7).