MEMS Gyroscope Compensation Circuit for Quality Factor Drift
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Solution Overview
Problem
Fluctuations in temperature or outgassing/ingassing cause pressure changes in MEMS resonators, affecting the quality factor and zero-rate offset of MEMS gyroscope, leading to phase errors due to frequency mismatch between Coriolis and quadrature signals.
Innovation Solution
A circuit and method for open-loop compensation using drive ratio or drive amplitude to estimate changes in the quality factor of MEMS gyroscope, compensating for offset changes by digitally modifying the sense path signal or adjusting the demodulator phase to maintain accurate signal output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure changes in the MEMS resonator cavity occur due to temperature fluctuations or outgassing/ingassing, then the quality factor of the MEMS resonator changes, but this results in phase errors and zero-rate offset changes that degrade measurement accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the measured quality factor is used to generate a compensation signal that is fed back to the demodulator. The demodulator adjusts its phase based on the quality factor changes, creating a closed-loop system that automatically compensates for pressure-induced quality factor variations, thereby maintaining measurement accuracy despite environmental fluctuations
Solution Approach 2:
The patent introduces an intermediary compensation signal that mediates between the quality factor changes and the demodulator phase. This intermediate element (the compensation signal generated from quality factor measurements) acts as a buffer that translates quality factor variations into appropriate phase adjustments, preventing direct transmission of errors to the final measurement output
2Measurement precision
If the phase difference between Coriolis and quadrature signals deviates from 90° due to frequency mismatch, then zero-rate offset increases, but this deviation is caused by quality factor changes that are difficult to control
Solution Approach 1:
Instead of trying to maintain constant frequency to preserve phase difference, the patent inverts the approach by measuring quality factor changes and using them to adjust the demodulator phase. Rather than controlling the cause (frequency stability), the system responds to the effect (phase error) by using quality factor information to directly compensate the phase, achieving the desired 90° phase difference through reverse causality
3Adaptability or versatility
If temperature changes or outgassing/ingassing occur in the operating environment, then cavity pressure changes, but this leads to quality factor variations that impact gyroscope performance
Solution Approach 1:
The system performs self-diagnosis and self-compensation by continuously measuring its own quality factor and automatically adjusting the demodulator phase based on these measurements. The gyroscope system serves itself by using its own performance metrics (quality factor) to correct its own errors (phase deviations), eliminating the need for external calibration or intervention despite environmental variations
Data Source
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AI summary
A circuit comprising a microelectromechanical (MEMS) gyroscope and a gain circuit coupled with the MEMS gyroscope. The gain circuit is configured to receive a digitized drive signal based at least in part on a digitized drive voltage amplitude of the MEMS gyroscope. The gain circuit is also configured to determine a percentage change in quality factor of the MEMS gyroscope based at least in part on the digitized drive signal and a stored trim value of the MEMS gyroscope. The gain circuit is also configured to compensate for an effect of a change in the quality factor of the MEMS gyroscope based at least in part on the percentage change in quality factor.