MEMS Gyroscope Parametric Amplification via Capacitance Modulation
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Solution Overview
Problem
MEMS gyroscopes face challenges with phase synchronization of AC pump voltages, leading to phase shifts and zero-rate bias errors due to misalignment of pump voltage phases with sensor mechanism motion, which affects the amplification of Coriolis rate signals and attenuation of quadrature-phase signals.
Innovation Solution
The solution involves designing MEMS capacitance modulation devices with sense electrodes that modulate capacitance at twice the motor frequency, synchronizing the parametric pump force with motor motion, thereby ensuring precise phase alignment and reducing quadrature-phase interference through modulation of the electrostatic force using DC bias voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC pump voltages are applied to sense electrodes for parametric amplification, then mechanical gain and electrical gain are increased, but phase shifts occur between pump voltages and sensor mechanism motion causing zero-rate bias errors
Solution Approach 1:
The patent applies periodic AC pump voltages at twice the motor resonant frequency to the sense electrodes. This periodic modulation creates time-varying electrostatic forces that parametrically amplify the Coriolis rate signal while maintaining phase coherence through synchronous detection, thereby achieving signal amplification without introducing zero-rate bias errors.
Solution Approach 2:
The patent employs phase-sensitive detection that provides feedback to maintain proper phase alignment between the pump voltages and the sensor mechanism motion. By detecting the phase relationship and adjusting accordingly, the system ensures that parametric amplification occurs only for the Coriolis rate signal component, rejecting quadrature-phase signals and eliminating zero-rate bias errors.
2Measurement precision
If sense resonant frequency is set close to motor resonant frequency to maximize scale factor, then sensitivity is improved, but bandwidth is limited and stability issues occur
Solution Approach 1:
The patent makes the sense electrode system dynamically可调 by applying time-varying AC pump voltages. This dynamic modulation allows the sense resonant frequency to be effectively tuned across a wider range, enabling the system to maintain high scale factor when needed while also achieving broader bandwidth and improved stability through parametric control mechanisms.
Solution Approach 2:
The patent changes the electrical parameters of the sense electrodes by applying AC voltages at twice the motor frequency. This parameter modulation creates a time-varying electrostatic stiffness that effectively shifts the sense resonant frequency, allowing the system to operate with high scale factor while maintaining adequate bandwidth and stability through controlled parameter variation.
3Measurement precision
If phase-sensitive detection is used to detect Coriolis rate signal in presence of quadrature signal, then detection capability is improved, but phase shifts in electronics and sensor cause quadrature-phase signal to produce errors
Solution Approach 1:
The patent converts the potentially harmful quadrature-phase signal into a beneficial reference for rejection. By using parametric amplification synchronized with the motor frequency, the system creates a detection scheme where quadrature-phase components are naturally attenuated, and any remaining quadrature errors can be rejected through the phase-sensitive detection mechanism, effectively turning phase sensitivity into an advantage for error rejection.
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 approach enhances the mechanical and electrical gains of the sensor, effectively amplifying Coriolis rate signals while suppressing quadrature-phase signals, thereby improving the accuracy and stability of MEMS gyroscope output.
Implementation Method 1
sense electrodes that modulate capacitance at twice the motor frequency
Implementation Method 2
modulation of the electrostatic force using DC bias voltages
Implementation Method 3
the velocity of the motor mode motion causes the proof masses to experience Coriolis forces perpendicular to the motor velocity and the rotation axis
Implementation Method 4
the motor mode resonant frequency can be in the range of 10 to 20 kHz
Data Source
Figure 1
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Figure 4~5
AI summary
Parametric amplification of the output of a MEMS gyroscope is achieved by modulating the sense capacitance, or an auxiliary capacitance having an applied DC voltage. The capacitance modulation is produced by the driven motion of the gyroscope mechanism, so the pump signal of the parametric amplifier is not subject to phase errors in the electronics. The capacitance modulation affects the mechanical gain of the sensor (transfer function from input force to sensor mechanism displacement), as well as the electrical gain of the sensor (transfer function from sensor mechanism displacement to output electrical signal). The mechanical and electrical gains of the sensor become phase-dependent, so the Coriolis rate signal can be amplified while the unwanted quadrature-phase signal is attenuated.