Non-degenerate Mode MEMS Gyroscope Phase Error Immunity
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Solution Overview
Problem
Conventional microelectromechanical systems (MEMS) gyroscopes face challenges with sensitivity loss and phase errors due to manufacturing imperfections, which are difficult to compensate for in high-quality oscillators, especially under varying temperature conditions.
Innovation Solution
A MEMS gyroscope operates in non-degenerate bulk acoustic modes with controlled resonant frequency differences between drive and sense modes, using electrostatic signals to adjust stiffness and phase response, and employs split electrodes to minimize quadrature errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If degenerate mode operation is used to maximize sensitivity, then sensitivity is improved, but manufacturing imperfections cause phase errors and sensitivity loss
Solution Approach 1:
The patent intentionally creates asymmetric conditions by operating in non-degenerate modes where the drive and sense modes have different resonant frequencies. This asymmetric operation allows the system to reject phase errors caused by manufacturing imperfections while maintaining adequate sensitivity through controlled frequency separation between modes.
Solution Approach 2:
The patent changes the operating parameters by deliberately setting the drive and sense modes to have different resonant frequencies rather than identical frequencies. This parameter change allows the system to operate in non-degenerate modes, which provides immunity to phase errors while maintaining sensitivity through electrostatic coupling between the modes.
2Reliability
If high quality oscillators are used to improve performance, then oscillation quality is improved, but maintaining degeneracy becomes difficult under temperature variations
Solution Approach 1:
By operating in non-degenerate modes with intentionally different resonant frequencies for drive and sense modes, the patent creates an asymmetric operation that is inherently more stable against temperature variations. The frequency separation provides a buffer that prevents temperature-induced drift from causing phase errors, making the system more adaptable to temperature changes while maintaining oscillator quality.
3Reliability
If non-degenerate modes are used to reject phase errors, then phase error immunity is improved, but sensitivity may be reduced
Solution Approach 1:
The patent carefully controls the frequency separation parameter between drive and sense modes to optimize the trade-off between phase error immunity and sensitivity. By adjusting the resonant frequency difference within specific ranges, the system achieves adequate phase error rejection while maintaining sufficient sensitivity through strong electrostatic coupling between the non-degenerate modes.
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 bandwidth and signal-to-noise ratio while maintaining sensitivity, offering a better trade-off between reduced sensitivity and increased bandwidth compared to degenerate mode operation.
Implementation Method 1
a primary member configured to vibrate in a first bulk acoustic mode at a drive frequency in response to a varying electrostatic signal
Implementation Method 2
A drive circuit causes the proof mass to oscillate (translate back and forth) in a plane of oscillation
Implementation Method 3
When the support structure is rotated in the plane of oscillation, the proof mass tends to continue oscillating in the plane but, as a result of the Coriolis Effect, the proof mass is displace in a direction perpendicular to both the axis of oscillation and the axis of rotation
Implementation Method 4
Stationary electrodes capacitively detect the amplitude of the second oscillation
Data Source
AI summary
Bulk acoustic wave (BAW) gyroscopes purposefully operate using non-degenerate modes, i.e., resonant frequencies of drive and sense modes are controlled so they are not identical. The resonant frequencies differ by a small controlled amount (Δf). The difference (Δf) is selected such that the loss of sensitivity, as a result of using non-degenerate modes, is modest. Non-degenerate operation can yield better bandwidth and improves signal-to-noise ratio (SNR) over comparable degenerate mode operation. Increasing Q of a BAW resonator facilitates trading bandwidth for increased SNR, thereby providing a combination of bandwidth and SNR that is better than that achievable from degenerate mode devices. In addition, a split electrode configuration facilitates minimizing quadrature errors in BAW resonators.