MEMS Inertial Sensor Multi-Axis Sampling via Composite Signals
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Solution Overview
Problem
Microelectromechanical systems (MEMS) sensors face challenges in improving noise performance, specifically achieving a higher signal-to-noise ratio, while also reducing size and cost, particularly in capacitive transducers used for multiple axis inertial sensing.
Innovation Solution
The solution involves a sensor system with a transducer configured to sense physical stimuli along orthogonal axes, utilizing a movable mass and differential electrode pairs, where an excitation circuit provides voltage connections that combine information from all axes in each measurement cycle, allowing for composite output signals to be converted into standard axis values, thereby enhancing signal-to-noise ratio without increasing current consumption or die size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate sensing periods are used for each axis, then measurement precision for each axis is improved, but productivity is reduced due to increased measurement time
Solution Approach 1:
The patent combines multiple sensing operations for different axes into a single sensing period. By applying excitation voltages to multiple electrode pairs simultaneously and measuring composite output signals that contain information from all axes, the system achieves multi-axis measurement in parallel, thereby improving measurement speed while maintaining precision through signal processing to extract individual axis data from the composite signals
2Measurement precision
If more electrodes and sensing circuits are added for multiple axis sensing, then measurement precision and functionality are improved, but device complexity increases
Solution Approach 1:
The patent makes the excitation circuit and measuring circuit universal by enabling them to handle multiple axes through different connection configurations rather than requiring separate dedicated circuits for each axis. The same measuring circuit processes composite output signals from multiple electrode pairs by selectively connecting and disconnecting electrode pairs during different time intervals within a sensing period, reducing overall device complexity while maintaining multi-axis measurement capability
Solution Approach 2:
The patent employs periodic switching of electrode pair connections during the sensing period. The excitation circuit periodically connects different electrode pairs to the measuring circuit in a time-multiplexed manner, allowing the system to sequentially access multiple axes within a single sensing period. This periodic action enables multi-axis sensing without requiring permanently connected separate circuits for each axis, thereby reducing device complexity
3Productivity
If excitation voltage is applied to all electrode pairs simultaneously, then productivity is improved by reducing sensing time, but use of energy increases
Solution Approach 1:
The patent applies excitation voltage to electrode pairs periodically rather than continuously. Within each sensing period, different electrode pairs are excited in sequence through periodic switching of the connection configuration. This periodic excitation reduces the total energy consumption compared to continuous excitation of all electrode pairs, while still achieving fast multi-axis measurement by overlapping the excitation and measurement operations within the same sensing period
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 significantly improves signal-to-noise ratio and maintains low current consumption, allowing for efficient multiple axis sensing without increasing the sensor's size or altering its configuration, effectively addressing the limitations of existing MEMS sensors.
Implementation Method 1
first and second electrodes that are immovable relative to the movable mass, the first and second electrodes being configured as a first differential electrode pair for detecting a first displacement of the movable mass along the first axis
Data Source
AI summary
A sensor system includes a transducer for sensing a physical stimulus along at least two orthogonal axes and an excitation circuit. The transducer includes a movable mass configured to react to the physical stimulus and multiple differential electrode pairs of electrodes. Each of the electrode pairs is configured to detect displacement of the movable mass along one of the orthogonal axes. The excitation circuit is connectable to the electrodes in various electrode connection configurations, with different polarity schemes, that enable excitation and sampling of each of the orthogonal axes during every sensing period. For each sensing period, a composite output signal is produced that includes the combined information sensed along each of the orthogonal axes. The individual sense signals for each orthogonal axis may be extracted from the composite output signals.