Accelerometer Residual Voltage Self-Test via Auxiliary Signal
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Solution Overview
Problem
MEMS sensors, such as accelerometers and gyroscopes, suffer from errors due to residual charges on proof masses and sense electrodes, leading to inaccurate motion parameter measurements, as the residual voltage introduces undesired electrostatic forces and movement, affecting the reliability of the sensor readings.
Innovation Solution
The implementation of an auxiliary signal with a first harmonic frequency different from the operating signal allows for the detection of residual voltage by measuring the movement induced at this frequency, enabling compensation procedures to correct for the error, such as recalibration or discharge of the residual charge, thereby ensuring accurate motion parameter determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If residual charge is present on proof masses or sense electrodes, then the MEMS sensor can operate, but measurement accuracy deteriorates due to undesired electrostatic forces and movement
Solution Approach 1:
The system performs a self-test before normal operation to detect residual voltage on proof masses or sense electrodes. By measuring the voltage at the resonant frequency of the proof mass, the system identifies residual charge conditions before they degrade measurement accuracy, allowing preventive compensation or correction actions to be taken.
Solution Approach 2:
The system continuously monitors the voltage characteristics of the proof masses and sense electrodes during operation. By measuring the response at the resonant frequency and comparing it against expected values, the system provides feedback about residual voltage conditions, enabling real-time compensation to maintain measurement precision while preserving sensor operation.
2Measurement precision
If an auxiliary signal at first harmonic frequency is applied to detect residual voltage, then measurement accuracy is maintained, but device complexity increases
Solution Approach 1:
The same drive electrodes that normally drive the proof mass for sensing are also used to apply the auxiliary signal at the first harmonic frequency for residual voltage detection. The sense electrodes serve dual purposes: normal capacitance measurement and detecting the response to the auxiliary signal. This multi-functionality approach maintains measurement precision while minimizing additional device complexity.
Solution Approach 2:
The MEMS resonator structure itself serves as the detection mechanism for residual voltage. By exciting the proof mass at its known resonant frequency and measuring its response, the system uses the sensor's own mechanical properties to detect electrical conditions, eliminating the need for separate detection hardware and 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 approach effectively mitigates the impact of residual voltage on MEMS sensor accuracy, allowing for reliable motion parameter measurement and enabling timely warnings or corrective actions to maintain sensor reliability.
Implementation Method 1
residual voltage introduces undesired electrostatic forces and movement
Implementation Method 2
distance between the movable proof masses and sense electrodes, which form capacitors for sensing the movement
Data Source
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AI summary
A sensor such as an accelerometer includes a proof mass located opposite a plurality of electrodes located on a substrate. Some of the electrodes are auxiliary electrodes that apply an alternating current auxiliary signal to the proof mass while other electrodes are sense electrodes that sense movement of the proof mass. When a residual voltage is not present on the proof mass or on the sense electrodes, the forces imparted by the auxiliary signal onto the proof mass are substantially balanced. When the residual voltage is present on the proof masses, forces at a first harmonic frequency of the auxiliary signal are sensed by a sense electrode of the sensor. A self-test is failed if the sensed forces exceed a threshold.