MEMS Angular Rate Sensor Quadrature Drive Frequency Modulation
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Solution Overview
Problem
Conventional MEMS angular rate sensors face challenges in accurately detecting small Coriolis forces due to high demands on sense detection and significant quadrature signals induced by manufacturing imperfections, particularly in frequency modulation-based systems.
Innovation Solution
The design incorporates first and second drive systems with parallel-plate capacitive drive and sense elements, enabling anti-phase motion of proof masses along both in-plane and vertical axes, which reduces common mode motion and improves sensitivity to angular velocity by modulating drive frequency in response to angular rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency modulation is used to detect angular rates, then the sensitivity to angular velocity improves, but the quadrature signal from manufacturing imperfections becomes hundreds of times larger than the signal to be detected
Solution Approach 1:
The patent applies quadrature drive to intentionally generate equal magnitude drive signals in both x and z directions, which creates controlled common mode motion. This deliberate introduction of symmetry transforms the harmful quadrature signal (caused by manufacturing imperfections) into a beneficial common mode signal that can be rejected by the detection system, thereby improving angular rate measurement accuracy
Solution Approach 2:
The patent changes the drive strategy from conventional single-axis driving to dual-axis quadrature driving, modifying the drive frequency and phase relationships. By driving the proof mass in both x and z directions with equal frequency and appropriate phase relationship, the system transforms the detection paradigm to enable common mode rejection of quadrature errors while maintaining sensitivity to angular rate
2Device complexity
If conventional amplitude modulation is used, then the device complexity is lower, but the sense detection demands are high due to small Coriolis forces
Solution Approach 1:
The patent replaces the conventional amplitude modulation detection method with frequency modulation detection. Instead of measuring small amplitude changes caused by Coriolis forces, the system measures frequency shifts of the driven oscillation. This substitution transforms the detection challenge from measuring tiny force-induced amplitude variations to measuring frequency modulations, which provides better signal-to-noise ratio and reduces detection system complexity
3Measurement precision
If proof masses are driven in orbital motion at high frequency, then the angular velocity sensitivity improves, but common mode motion increases measurement nonlinearity
Solution Approach 1:
The patent extracts and separates the common mode motion component from the angular rate signal. By intentionally creating symmetric quadrature drive, the common mode motion becomes a distinct, identifiable component that can be rejected by the detection algorithm, allowing the system to maintain high orbital drive frequencies for sensitivity while removing the nonlinear common mode interference from the measurement
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 configuration enhances the sensitivity and accuracy of angular rate detection by effectively reducing nonlinear measurement output and common mode motion, thereby improving the overall performance of frequency modulated MEMS angular rate sensors.
Implementation Method 1
first and second parallel-plate capacitive drive elements for enabling motion of the one of the first and second proof masses along the first axis perpendicular to the surface of the substrate
Implementation Method 2
detect angular rates by demodulating the force applied to a movable sense mass from Coriolis accelerations as a result of the sense mass velocity provided from the driven frequency and amplitude
Data Source
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AI summary
An angular rate sensor includes first and second proof masses spaced apart from a surface of a substrate. One each of first and second drive systems is interconnected with one each of the first and second proof masses. The first and second drive systems enable drive motion of the first and second proof masses along both of first and second axes in an orbital drive direction at a drive frequency, the first axis being perpendicular to the surface of the substrate and the second axis being parallel to the surface of the substrate. The sensor is sensitive to angular velocity about a third axis oriented parallel to the surface of the substrate and perpendicular to the second axis, and the drive frequency of the drive motion of the first and second proof masses changes in response to the angular velocity of the angular rate sensor about the third axis.