MEMS Gyroscope Quadrature Cancellation Using Variable Capacitor Feedback
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Solution Overview
Problem
MEMS gyroscope systems face challenges in effectively cancelling quadrature components of sensed signals, which can significantly exceed the Coriolis signal in strength, leading to reduced signal-to-noise ratio and limited amplification of the signal of interest.
Innovation Solution
A method involving a capacitance-to-voltage (C2V) amplifier, demodulator, integrator, analog-to-digital converter (ADC), and digital processing circuitry to extract and cancel the quadrature portion of the sensed signal. This is achieved by generating a variable capacitor control signal based on the digitized integrated quadrature portion, which is then used to modify the capacitances of variable quadrature cancellation capacitors coupled to the C2V amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If quadrature cancellation is not performed, then the circuit complexity is reduced, but the signal-to-noise ratio deteriorates due to the strong quadrature component overwhelming the Coriolis signal
Solution Approach 1:
The patent extracts the quadrature component from the total sensed signal using a demodulator that separates the quadrature portion from the Coriolis signal. This extracted quadrature component is then processed independently through integration and digital conversion to generate a cancellation signal, effectively removing the harmful quadrature interference from the measurement path.
Solution Approach 2:
The patent introduces an intermediary variable capacitor controlled by digital processing circuitry as a mediator between the sensed signal and the quadrature cancellation path. This variable capacitor dynamically adjusts the quadrature component based on the digitized integrated quadrature portion, providing adaptive cancellation without requiring complex analog filtering circuits.
2Power
If the quadrature component is strong, then the sensed signal contains more information, but the Coriolis signal amplification is limited due to the dominant quadrature portion
Solution Approach 1:
The patent implements a feedback mechanism where the digitized integrated quadrature portion is used to generate a control signal that adjusts the variable capacitor in real-time. This closed-loop feedback system continuously monitors the quadrature component and dynamically compensates for it, enabling the C2V amplifier to focus its amplification on the Coriolis signal without being overwhelmed by quadrature interference.
Solution Approach 2:
The patent changes the capacitance parameter of the variable capacitor based on the digitized integrated quadrature portion. By dynamically adjusting the capacitance value through digital control, the system modifies the quadrature component's contribution to the sensed signal, effectively reducing its dominance and allowing for enhanced Coriolis signal amplification.
3Area of stationary object
If multiple MEMS sensors share processing components, then the device size is reduced, but the quadrature cancellation capability is compromised due to limited processing resources
Solution Approach 1:
The patent designs the quadrature cancellation processing circuitry to be universal and shareable across multiple MEMS sensors. The same C2V amplifier, demodulator, integrator, and digital processing circuitry can serve multiple sensor outputs by time-multiplexing or parallel processing, reducing the overall device area while maintaining adequate quadrature cancellation capability for each sensor channel.
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
The proposed solution effectively reduces the quadrature component of the sensed signal, allowing for increased amplification of the Coriolis signal, thereby improving the signal-to-noise ratio and overall performance of the MEMS gyroscope system.
Implementation Method 1
a capacitance-to-voltage (C2V) amplifier, comprising an input coupled to the MEMS structure to receive the sensed capacitive signal
Implementation Method 2
at least one variable capacitor coupled to an output of the ADC and the input of the C2V amplifier, wherein the at least one variable capacitor receives the variable capacitor control signal from the digital processing circuitry, and wherein the quadrature portion of the sensed signal is cancelled based on a capacitance of the at least on variable capacitors
Data Source
AI summary
A microelectromechanical system (MEMS) gyroscope includes a MEMS structure that outputs a capacitive signal that includes both a Coriolis signal used to determine an angular velocity and a quadrature signal 90 degrees out-of-phase with the Coriolis signal. A capacitance to voltage (C2V) amplifier receives and amplifies the capacitive signal for further processing. Quadrature cancellation circuitry processes the output of the C2V amplifier to isolate the quadrature signal and generate a signal to control variable capacitors coupled to the C2V amplifier input in a manner that removes the quadrature signal from the C2V amplifier output.