Capacitive Sensor Testing via AC Coupling Path
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Solution Overview
Problem
Existing methods for testing capacitive sensors, particularly those using constant charge biasing schemes, face difficulties in applying test signals without disturbing the sensor's operation due to high impedances that act as filters, making it challenging to measure capacitances accurately.
Innovation Solution
A sensor device and method that apply a bias voltage through a high-impedance component while using an AC coupling path for the test signal, allowing the test signal to be applied without filtering effects, enabling independent measurement of capacitances without disturbing the sensor's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a test signal is applied to a capacitive sensor using constant charge biasing with high impedance connections, then the sensor operation is maintained, but the high impedance acts as a filter with slow time constant that prevents accurate capacitance measurement
Solution Approach 1:
The patent divides the biasing and testing functions into separate paths: a high-impedance path for maintaining constant charge biasing (sensor operation) and a separate low-impedance test signal path for accurate capacitance measurement. This segmentation allows each path to optimize its function without interference from the other.
Solution Approach 2:
The patent introduces a switch as an intermediary component that selectively connects either the high-impedance bias voltage source or the low-impedance test signal source to the capacitive sensor. This intermediary enables transition between measurement and operation modes without direct conflict between the two signaling paths.
2Stability of the object's composition
If a test signal is applied through the high impedance connection in constant charge biasing, then the sensor remains biased, but the slow time constant of the high impedance filter distorts the test signal and prevents accurate measurements
Solution Approach 1:
The patent makes the impedance characteristic dynamic by using a switch to change the connection configuration between measurement and operation modes. During measurement, a low-impedance path is established for fast signal response; during operation, the high-impedance path maintains constant charge. This dynamic switching resolves the contradiction between stable biasing and easy measurement.
Solution Approach 2:
The patent employs periodic switching between measurement mode and operation mode. The switch alternately connects the test signal generator and the bias voltage source to the capacitive sensor, allowing periodic capacitance measurements without continuously disrupting the constant charge biasing condition. This periodic action enables measurement while preserving operational stability.
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 allows for accurate measurement of capacitances and detection of capacitance imbalances, enabling calibration and optimization of sensor performance, including determining pull-in voltage and sensitivity, without affecting the sensor's operation.
Implementation Method 1
The voltage source is coupled to a terminal of the capacitive sensor via a high-impedance component providing an ohmic resistance of at least 1 MΩ
Implementation Method 2
an output of the test signal generator is coupled with a first terminal of an alternating current (AC) coupling capacitance, and a second terminal of the AC coupling capacitance is coupled with the second terminal of the first high impedance component
Data Source
AI summary
Sensor devices and methods are provided where a test signal is applied to a capacitive sensor. Furthermore, a bias voltage is applied to the capacitive sensor via a high impedance component. A path for applying the test signal excludes the high impedance component. Using this testing signal, in some implementations a capacity imbalance of the capacitive sensor may be detected.