Capacitive Sensor Sensitivity Measurement via Dual Bias
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Solution Overview
Problem
Existing methods for determining the sensitivity of capacitive sensing devices, such as silicon microphones and pressure sensors, are cumbersome and inaccurate due to manufacturing tolerances, requiring lengthy calibration processes and being influenced by parasitic capacities and time constants.
Innovation Solution
A novel approach that determines sensitivity by performing two capacitance measurements at distinct electrical input signals, such as bias voltages or charges, allowing for the calculation of sensitivity without finding the pull-in voltage, using a measurement module and processor to analyze the capacitance difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration methods using reference pressure signals are used to determine sensitivity, then measurement precision may be maintained, but measurement time and device complexity increase significantly
Solution Approach 1:
The patent extracts the essential sensitivity determination from complex calibration procedures by measuring capacitance at only two distinct bias voltages. Instead of using reference pressure signals and multiple measurement points, the invention isolates the key parameter (capacitance difference) that directly relates to sensitivity, eliminating unnecessary calibration steps and equipment requirements.
Solution Approach 2:
The invention changes the measurement parameter from pressure-based calibration to voltage-based capacitance measurement. By applying two distinct bias voltages and measuring the resulting capacitance values, the system determines sensitivity through electrical parameters rather than mechanical pressure application, significantly reducing measurement time and equipment complexity.
2Ease of operation
If the pull-in voltage method is used to determine sensitivity, then sensitivity can be characterized, but measurement precision deteriorates due to influence from mechanical and electrical time constants
Solution Approach 1:
The patent segments the sensitivity determination process from the pull-in phenomenon by measuring capacitance at two distinct bias voltages below the pull-in point. Instead of attempting to measure the pull-in voltage directly (which is influenced by time constants), the invention divides the measurement into two separate static capacitance measurements, eliminating dynamic effects and time constant influences.
Solution Approach 2:
The invention performs preliminary capacitance measurements at two distinct bias voltages before the pull-in condition occurs. By establishing the capacitance difference at these predetermined voltage points, the system determines sensitivity in advance without needing to reach the problematic pull-in state, avoiding the accuracy issues associated with dynamic pull-in measurement.
3Measurement precision
If high accuracy in pull-in voltage determination is pursued by increasing measurement points, then measurement precision improves, but productivity decreases due to extended measurement time
Solution Approach 1:
The patent applies partial action by measuring capacitance at only two specific bias voltages rather than using a full ramp or multiple measurement points across the entire voltage range. This partial measurement approach provides sufficient information to determine sensitivity through the capacitance difference, achieving adequate precision without the excessive time required for comprehensive pull-in characterization.
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 method reduces measurement and calibration time, provides accurate sensitivity determination, and is not affected by parasitic capacities, enabling efficient calibration and operation of capacitive sensors.
Implementation Method 1
a measurement module which is configured to determine, in response to a first electrical input signal to the sensor capacitor, a first quantity indicative of a first capacitance of the sensor capacitor, and to determine, in response to a second electrical input signal to the sensor capacitor, a second quantity indicative of a second capacitance of the sensor capacitor
Implementation Method 2
An electrostatic force associated with the bias voltage is nonlinear due to its inverse square relationship with the air gap thickness between the capacitor electrodes
Data Source
AI summary
Embodiments relate to an apparatus for determining a sensitivity of a capacitive sensing device having a sensor capacitor with a variable capacitance. The apparatus includes a measurement module and a processor. The measurement module is configured to determine, in response to a first electrical input signal to the sensor capacitor, a first quantity indicative of a first capacitance of the sensor capacitor and to determine, in response to a second electrical input signal to the sensor capacitor, a second quantity indicative of a second capacitance of the sensor capacitor. The processor is configured to determine the sensitivity of the sensing device based on the determined first and second quantity.