MEMS Mirror Capacitance Sensing Parasitic Shunt
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Solution Overview
Problem
The sensitivity of MEMS mirrors in LiDAR systems is hindered by parasitic capacitance, which limits the accuracy of capacitance measurement and reduces the effectiveness of light beam steering in applications such as autonomous vehicles.
Innovation Solution
The introduction of an added capacitance, much larger than the parasitic capacitance, which is integrated around the MEMS mirror or added to the substrate, shunts the parasitic capacitance to ground, improving sensed voltage sensitivity and reducing noise by providing a low impedance element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If parasitic capacitance is present in the MEMS mirror structure, then the substrate provides mechanical support, but the parasitic capacitance limits the sensitivity of capacitance measurement
Solution Approach 1:
The patent introduces an intermediary component (added capacitance element) between the MEMS mirror structure and ground. This intermediary capacitance, being much larger than the parasitic capacitance, acts as a shunt to divert the parasitic capacitance current to ground, thereby isolating the parasitic capacitance from the measurement circuit and improving measurement precision without requiring direct elimination of the harmful factor
Solution Approach 2:
The patent converts the harmful parasitic capacitance into a beneficial element by intentionally adding a larger capacitance that shunts the parasitic capacitance to ground. The previously harmful parasitic capacitance is now utilized as part of the grounding path, and its effect is transformed from a measurement error source into a controlled part of the electrical circuit that improves signal-to-noise ratio
2Reliability
If the parasitic capacitance is large, then the substrate provides good mechanical support, but the change in fingers capacitance has minimum effect on the sensed voltage
Solution Approach 1:
The added capacitance serves as an intermediary that bridges the parasitic capacitance and ground, allowing the mechanical support function of the substrate to be maintained while providing an alternative current path that isolates the parasitic capacitance from the voltage sensing circuit, thereby preserving both mechanical reliability and electrical sensitivity
Solution Approach 2:
The patent segments the capacitance pathways by separating the mechanical support function (substrate) from the electrical measurement function (fingers capacitance). The added capacitance creates a distinct grounding path that isolates the parasitic capacitance effects from the sensing circuit, allowing independent optimization of mechanical and electrical performance
3Measurement precision
If electrical decoupling is attempted to reduce parasitic capacitance, then measurement sensitivity improves, but the substrate is a fundamental component and electrical decoupling is extremely difficult
Solution Approach 1:
Instead of attempting direct electrical decoupling of the substrate (which would be extremely complex), the patent uses an intermediary added capacitance element that provides a controlled grounding path. This intermediary approach achieves effective electrical isolation of parasitic capacitance from the measurement circuit while maintaining the substrate's fundamental mechanical support role, avoiding complex decoupling structures
Solution Approach 2:
The patent changes the electrical parameters of the system by introducing a large added capacitance that dominates the parasitic capacitance. By altering the capacitance value parameter, the system achieves effective electrical isolation without changing the physical structure or requiring complex decoupling mechanisms, thereby improving measurement precision while maintaining device simplicity
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 the sensitivity of the sensed voltage and reduces noise, thereby improving the accuracy and reliability of light beam steering in LiDAR systems, particularly in autonomous vehicle applications.
Implementation Method 1
An added capacitance is provided between the substrate and a DC/AC voltage source. The added capacitance is much larger than the parasitic capacitance, and shunts the parasitic capacitance to ground to minimize its effect on the measured capacitance.
Implementation Method 2
There is a parasitic capacitance between the MEMS mirror structure and the substrate. The most significant parasitic capacitance is observed across the substrate.
Data Source
AI summary
According to certain embodiments, a micro-electromechanical system (MEMS) apparatus has a MEMS mirror structure with a rotatable mirror. Rotation of the mirror produces a change in a measured capacitance corresponding to an angle of rotation. The MEMS structure sits on an oxide layer deposited on a substrate. There is a parasitic capacitance between the MEMS mirror structure and the substrate. An added capacitance is provided between the substrate and a DC voltage source. The added capacitance is much larger than the parasitic capacitance, and shunts the parasitic capacitance to ground to minimize its effect on the measured capacitance.