MEMS Sensor Self-Test Asymmetry Switching
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Solution Overview
Problem
MEMS sensors with dual-use terminals for excitation and testing face challenges in producing output signals during tests due to symmetry issues, particularly in differential acceleration sensors where movable masses move in opposite directions, resulting in equal currents and no detectable signal change.
Innovation Solution
The implementation of a controller circuit with switches that alternately connect only a single input of the detector circuit with the MEMS sensor outputs during test modes, allowing asymmetric reading of sensor values and increasing sensitivity by connecting a single input to both sensor outputs, thereby enabling effective testing using the same terminals for both excitation and testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If dual-use terminals are used for excitation and testing in differential acceleration sensors, then space is saved and device complexity is reduced, but output signals cannot be produced during testing due to symmetry
Solution Approach 1:
The patent applies asymmetry by using switches to create asymmetric connection configurations during testing. Specifically, during test mode, one switch connects the detector circuit to the first sensor output while the other switch disconnects the second sensor output, breaking the symmetric dual-use terminal configuration and enabling detectable test signals to be generated.
Solution Approach 2:
The patent employs dynamic switching to transition between different operational states. The switches are controlled to dynamically reconfigure the terminal connections based on whether the device is in sensing mode or testing mode, allowing the same terminals to serve different functions at different times while maintaining signal output capability during testing.
2Adaptability or versatility
If movable bodies move in opposite directions during testing, then test coverage is improved, but no output signal is produced due to equal currents
Solution Approach 1:
The patent extracts one of the sensor outputs from the differential measurement path during testing. By using switches to connect only one output to the detector circuit while disconnecting the other output, the system isolates the measurement path, allowing detection of test signals even when movable bodies move in opposite directions and produce equal currents.
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 solution allows for meaningful output signals during testing by ensuring asymmetric input connections, overcoming the symmetry-induced signal suppression in differential MEMS sensors, thus enabling accurate sensor testing and calibration.
Implementation Method 1
MEMS acceleration sensors typically include capacitors constituted by cooperating pairs of surfaces, one surface of each pair being located on a movable body and the other surface of each pair being located on the body of the sensor. The movement due to the acceleration may, depending on its direction, result in a change in the capacitance values of the capacitors.
Implementation Method 2
This change in capacitance values can, in some types of acceleration sensors, be determined by applying excitation voltages to the capacitors and measuring any currents flowing into the movable mass.
Data Source
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AI summary
A micro-electro-mechanical system (MEMS) device comprises a micro-electro-mechanical system (MEMS) sensor; a detector circuit; a controller circuit coupled with the MEMS sensor; a first connection arranged between a first output of the MEMS sensor and a first input of the detector circuit; a second connection arranged between a second output of the MEMS sensor and a second input of the detector circuit; and a first switch arranged in the first connection. The controller circuit is configured to open the first switch during a first test mode so as to connect only a single input of the detector circuit with an output of the MEMS sensor. A further switch may be provided to connect two outputs of the MEMS sensor to a single input of the detector circuit.