MEMS Capacitive Sensor Non-Linearity Elimination
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Solution Overview
Problem
Parallel plate capacitors in MEMS devices exhibit non-linear capacitance variation with distance, leading to reduced signal detection accuracy due to increased non-linearity as the distance between plates increases, which affects the symmetry and common mode signal rejection.
Innovation Solution
A MEMS device is designed with a sensing element comprising two capacitors connected to differential and common mode detection modules, and a non-linearity elimination module that eliminates non-linear relationships between capacitance variation and displacement, using operational amplifiers, feedback capacitors, and demodulation/filtering modules without requiring an additional reference capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the distance between parallel plates of the parallel plate capacitor is increased, then the sensing range is improved, but the non-linearity of capacitance variation increases, leading to reduced signal detection accuracy
Solution Approach 1:
The sensing element is divided into two separate capacitors (first capacitor and second capacitor) with electrode plates arranged on opposite sides of the movable electrode plate. This segmentation allows independent measurement and processing of capacitance variations from each capacitor, enabling the system to handle larger plate distances while maintaining measurement accuracy through differential processing.
Solution Approach 2:
The patent transforms the non-linear capacitance-displacement relationship into a linear output signal through parameter changes in the detection circuit. By using differential mode detection to extract the difference signal and common mode detection to extract the sum signal, the system converts the non-linear capacitance variation into a linear voltage output that is directly proportional to the displacement of the movable electrode plate.
2Stability of the object's composition
If differential parallel plate capacitors are used to perform common mode signal rejection, then the symmetry of scale factor is improved, but the non-linear capacitance variation with distance remains, affecting detection accuracy
Solution Approach 1:
The system segments the detection process into differential mode and common mode detection pathways. The differential mode detection module processes the difference between the two capacitors to reject common mode signals, while the common mode detection module processes the sum to maintain symmetry. This segmented approach allows both common mode rejection and symmetry maintenance while addressing non-linearity through subsequent linearization processing.
Solution Approach 2:
The patent implements feedback mechanisms through the differential and common mode detection modules that continuously monitor and adjust the output signals. By feeding back the capacitance variation information from both capacitors and processing them through operational amplifiers and demodulation circuits, the system compensates for non-linear effects and maintains accurate linear measurement output.
3Measurement precision
If additional reference capacitors are added to eliminate non-linearity, then the detection accuracy is improved, but the device complexity increases
Solution Approach 1:
The first and second capacitors serve multiple functions simultaneously: they act as sensing elements for displacement measurement, provide common mode signal rejection through differential detection, and enable non-linearity elimination through their combined differential and common mode processing. This multi-functionality eliminates the need for separate reference capacitors, reducing device complexity while maintaining high detection accuracy.
Solution Approach 2:
The sensing element itself provides the means for non-linearity elimination by using its own two capacitors in a differential configuration. The system self-corrects for non-linear effects through the inherent symmetry and differential processing of the two capacitors, without requiring external reference capacitors or additional compensation components, thereby reducing overall device complexity.
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 effectively eliminates non-linearity in detection, improving signal accuracy and temperature stability, and can be applied to MEMS accelerometers and gyroscopes, enhancing their performance by making the output signal linear with displacement.
Implementation Method 1
the first electrode plate and the movable electrode plate form a first capacitor, the second electrode plate and the movable electrode plate form a second capacitor
Implementation Method 2
Parallel-plate capacitors are easy to be fabricated, and have the advantages of high sensitivity
Data Source
AI summary
Disclosed is a MEMS device, comprising: a sensing element, including a movable electrode plate, a first electrode plate and a second electrode plate, the first electrode plate and the movable electrode plate forming a first capacitor; the second electrode plate and the movable electrode plate forming a second capacitor; the first capacitor and the second capacitor forming a detection capacitor of the sensing element; a differential mode detection module, performing differential mode detection on the first capacitor and the second capacitor; a common mode detection module, performing common mode detection on the first capacitor and the second capacitor; and a non-linearity elimination module, performing elimination of the non-linear relationship between the capacitance variation of the detection capacitor and the displacement of the movable electrode plate using the differential mode detection module output and the common mode detection module output.