MEMS Accelerometer Self-Test With Variable Excitation Voltage
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Solution Overview
Problem
There is a need for a self-test technique to ensure proper functioning of MEMS accelerometer sensors, particularly in safety-critical applications like automobile passenger safety systems, to verify their operation and detect mechanical faults.
Innovation Solution
A self-test method for MEMS accelerometers using a variable duty cycle or variable voltage level self-test signals is implemented, which applies a differential voltage to stator nodes to displace the mobile mass, allowing for the detection of any functional issues without interfering with normal sensing operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a self-test signal is applied to the stator nodes to displace the mobile mass, then the functionality of the MEMS accelerometer can be verified, but the normal sensing operations may be interfered with
Solution Approach 1:
The patent implements self-test at specific periodic intervals (e.g., every 1000th sensing frame) rather than continuously, allowing the sensor to alternate between normal sensing mode and self-test mode. This periodic switching verifies sensor functionality while minimizing interference with ongoing sensing operations.
Solution Approach 2:
The patent extracts the self-test function as a separate, independent operation from the normal sensing function. By isolating self-test into distinct time periods with dedicated excitation signals, the harmful interference with sensing operations is eliminated while maintaining verification capability.
2Adaptability or versatility
If a variable duty cycle self-test signal is used to control the displacement force, then the testing flexibility is improved, but the timing complexity increases
Solution Approach 1:
The patent varies the duty cycle parameter of the self-test excitation signal to control the magnitude of displacement force applied to the mobile mass. By adjusting the duty cycle (ratio of high-state time to total period), the system achieves flexible testing across different force levels while maintaining a fixed, simple timing framework.
Solution Approach 2:
The patent makes the duty cycle dynamic and adjustable during self-test operations, allowing the system to adapt the excitation characteristics based on testing requirements. This dynamic parameter control provides versatility without requiring complex timing changes, as the frequency and period remain fixed.
3Measurement precision
If a variable voltage level self-test signal is applied to the stator nodes, then the displacement control precision is improved, but the power consumption increases
Solution Approach 1:
The patent varies the voltage level parameter of the self-test excitation signal to precisely control the displacement force applied to the mobile mass. By adjusting the voltage magnitude while maintaining a fixed duty cycle, the system achieves precise displacement control with predictable and manageable power consumption characteristics.
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 self-test method effectively verifies the functionality of MEMS accelerometers by applying controlled forces to displace the mobile mass, ensuring proper operation and detecting faults without perturbing the sensing axes, thus enhancing reliability in safety-critical systems.
Implementation Method 1
A self-test signal is applied to two stator nodes of the MEMS accelerometer sensor. The self-test signal comprises a first voltage component applied to a first stator node and a second voltage component applied to a second stator node
Data Source
Figure 1~2
Figure 3A~4A
Figure 4B~5A
AI summary
A microelectromechanical system (MEMS) accelerometer sensor (12x, 12y, 12z) has a mobile mass and a sensing capacitor. To self-test the sensor, a test signal having a variably controlled excitation voltage and a fixed pulse width is applied to the sensing capacitor. The leading and trailing edges of the test signal are aligned to coincide with reset phases of a sensing circuit (32-36) coupled to the sensing capacitor. The variably controlled excitation voltage of the test signal is configured to cause an electrostatic force which produces a desired physical displacement of the mobile mass. During a read phase of the sensing circuit, a variation in capacitance of sensing capacitor due to the actual physical displacement of the mobile mass is sensed for comparison to the desired physical displacement.