MEMS Gyroscope Double-Edge Phase Detection for Low-Frequency Noise
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Solution Overview
Problem
Microelectromechanical system (MEMS) gyroscopes face accuracy degradation due to low-frequency noise, leading to duty cycle jitter and bias instability, which affects the accuracy of angular motion sensing and can result in significant errors over time.
Innovation Solution
The implementation of a double-edge phase detection technique with a switch to maintain a non-conductive state during ripple formation, controlling the frequency of the demodulating signal using a control signal generated from both rising and falling edges of the resonator and reference signals, and an enabling signal to prevent frequency fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a MEMS gyroscope uses conventional demodulation techniques, then the system is simpler to implement, but low-frequency noise causes duty cycle jitter that degrades measurement precision
Solution Approach 1:
The patent segments the demodulation process into two independent paths: a resonator path that generates a clean square wave reference signal free from low-frequency noise, and a sense path that processes the Coriolis signal. By separating these functions, the system achieves high measurement precision without requiring complex noise filtering in the demodulation path.
Solution Approach 2:
The patent introduces an intermediary square wave signal generated from the resonator path that serves as a clean reference for demodulation. This intermediary signal acts as a mediator between the noisy sense signal and the demodulation process, enabling accurate measurement without directly processing the noisy original signal.
2Measurement precision
If the system uses double-edge phase detection to reduce duty cycle jitter, then measurement precision improves, but device complexity increases due to additional circuitry
Solution Approach 1:
The patent merges the phase detection functionality into the existing resonator and sense paths by using the resonator's natural oscillation edges. The double-edge detection is achieved by utilizing both rising and falling edges of the square wave signal from the resonator path, combining timing information from both edges to generate the control signal without adding separate detection circuits.
Solution Approach 2:
The resonator path serves itself by generating the square wave signal that provides the reference for phase detection. The system uses its own resonator oscillation characteristics to create the timing reference, eliminating the need for external reference generators or additional calibration circuits.
3Reliability
If a switch is added to prevent ripple formation in the control signal, then bias instability decreases, but device complexity increases
Solution Approach 1:
The patent extracts and removes the harmful ripple component from the control signal by using a switch that selectively blocks the ripple portion while allowing the useful control signal to pass. The switch is positioned to remove only the problematic high-frequency ripple generated during phase detection, separating the harmful element from the useful signal.
Solution Approach 2:
The patent converts the harmful ripple effect into a beneficial filtering mechanism by deliberately allowing ripple to form and then using a switch to remove it. The controlled formation and subsequent removal of ripple demonstrates converting a potentially harmful phenomenon into a useful signal conditioning step that improves bias stability.
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 reduces duty cycle jitter and limits bias instability to less than 1 degree per hour, maintaining the accuracy of angular motion sensing by stabilizing the demodulating signal's frequency and preventing ripple-induced distortions.
Implementation Method 1
MEMS gyroscopes are configured to detect angular motion by sensing accelerations produced by Coriolis forces. Coriolis forces arise when a resonant mass of a MEMS gyroscope is subjected to angular motion.
Implementation Method 2
receiving, from the resonator path output terminal, a resonator signal generated in response to resonance of the MEMS gyroscope
Data Source
AI summary
Systems and methods for sensing angular motion using a microelectromechanical system (MEMS) gyroscope are described. These systems and methods may be useful for sensing angular motion in the presence of low-frequency noise, which may be noise below 1 KHz. In a system for sensing angular motion, low-frequency noise may give rise to duty cycle jitter, which may affect the demodulation of the sense signal and cause errors in angular motion estimates. The systems and methods described herein address this problem by relying on double-edge phase detection technique that involves sensing when the rising and falling edges of the resonator signal deviate from their expected values in the idealized 50% duty cycle scenario. To prevent the formation of ripples in the double-edge phase detection that may otherwise affect the demodulation of the sense signal, a switch may be used. The switch may be maintained in a non-conductive state when a ripple is received.