Capacitive Pressure Sensor Circuit Stabilizes Diaphragm
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Solution Overview
Problem
Capacitive pressure sensors, particularly microphones, face challenges in miniaturization and sensitivity due to the need for large back volumes, which lead to instability and reduced performance under varying environmental pressures.
Innovation Solution
An electronic circuit that controls a capacitive pressure sensor by maintaining a constant average capacity of the capacitor formed by the diaphragm and back plate using a DC bias-voltage and an AC voltage signal, with the AC signal frequency set outside the operational range to avoid interference and stabilize the diaphragm's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the back volume is made large to achieve high sensitivity, then the sensitivity is improved, but the device size increases and miniaturization is limited
Solution Approach 1:
The patent changes the pressure parameter by introducing a vacuum or reduced pressure environment in the back volume, allowing the diaphragm to be positioned closer to the back plate while maintaining high sensitivity. This parameter change enables the system to achieve high sensitivity without requiring a large back volume, thus resolving the contradiction between sensitivity and device size.
2Measurement precision
If the diaphragm is positioned close to the back plate to improve sensitivity, then the sensitivity is improved, but the diaphragm becomes unstable and may collapse under environmental pressure variations
Solution Approach 1:
The patent applies a DC bias voltage across the diaphragm and back plate to create an electrostatic force that counteracts the mechanical restoring force of the diaphragm. This parameter change in the electrical domain stabilizes the diaphragm position, allowing it to maintain a critical distance from the back plate without collapsing, thus resolving the contradiction between sensitivity and stability.
Solution Approach 2:
The patent uses an AC voltage source to generate an AC signal that is applied across the capacitor, and the resulting output signal is used to control the DC bias voltage. This feedback mechanism dynamically adjusts the electrostatic force to maintain stable diaphragm operation, preventing collapse while preserving high sensitivity.
3Stability of the object's composition
If the DC bias voltage is increased to maintain diaphragm position, then the stability is improved, but the diaphragm may collapse when deflected due to increased electrostatic force
Solution Approach 1:
The patent employs a feedback control system where the AC signal output is used to dynamically adjust the DC bias voltage. This feedback mechanism ensures that the electrostatic force is optimized to maintain diaphragm stability without exceeding the threshold that would cause collapse during deflection, thus resolving the contradiction between position stability and operational reliability.
Solution Approach 2:
The patent makes the DC bias voltage dynamic by controlling it based on the AC signal output. This dynamic adjustment allows the system to adapt the electrostatic force in real-time, maintaining stability during normal operation while preventing collapse during diaphragm deflection, thus resolving the contradiction between stability and reliability.
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 enhances sensitivity and robustness to environmental pressure variations, reduces non-linearities, and automatically compensates for manufacturing tolerances, preventing diaphragm collapse and maintaining optimal sensitivity.
Implementation Method 1
the electrostatic force increases with a decreasing distance between diaphragm and back plate
Implementation Method 2
The diaphragm is deflected by a pressure difference between its front surface and its back surface
Implementation Method 3
Deflecting the diaphragm causes slight changes of the capacitance of the capacitor
Data Source
AI summary
An electronic circuit (10) for controlling a capacitive pressure sensor (1), which capacitive pressure sensor (1) comprises a plate electrode capacitor (C) with a capacity that varies in dependence on pressure changes exerted on a deflectable diaphragm (2) forming one plate electrode of the capacitor (C), wherein the electronic circuit (10) comprises a DC voltage source (12) being adapted to generate a DC bias-voltage (UDC) to be applied across the electrodes of the capacitor (C), an AC voltage source (13) being adapted to generate an AC voltage signal (UAC) to be applied across the electrodes of the capacitor (C) and a controller (18) being adapted to receive an output signal (OUT) of the capacitor (C) and to control the DC voltage source (12) such that the DC bias-voltage (UDC) applied to the capacitor (C) adopts a value that maintains the capacity of the capacitor (C) at a desired value.