Capacitive Microphone Dual Capacitor Segmentation
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Solution Overview
Problem
Capacitive microphones suffer from poor linearity, sensitivity, audio loudness, and high noise due to interference from electric field forces affecting the vibration deformation of the diaphragm in existing MEMS microphone designs.
Innovation Solution
A capacitive microphone design featuring a substrate with a cavity and step, stationary and movable electrodes arranged in a comb shape, and a backplate with sound transmission holes, forming dual capacitors to improve signal-to-noise ratio and reduce linear distortion through phase compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitance is increased by enlarging the capacitor plate area or reducing plate distance, then the sensitivity improves, but the electric field interference on diaphragm vibration increases, causing poor linearity and high noise
Solution Approach 1:
The single capacitor structure is segmented into two separate capacitors: a first capacitor with stationary and movable electrodes for sensing diaphragm vibration, and a second capacitor with stationary and movable electrodes for sensing backplate vibration. This segmentation allows independent optimization of each capacitor's function, reducing electric field interference on the diaphragm while maintaining high sensitivity through dual-capacitor differential measurement.
Solution Approach 2:
The backplate serves as an intermediary element that is capacitively coupled to both capacitors. The second capacitor measures backplate vibration separately, allowing the system to differentiate between diaphragm-driven sound signals and backplate interference, thereby reducing noise and improving linearity through differential signal processing.
2Object-generated harmful factors
If the diaphragm vibration deformation is increased to improve audio loudness, then the signal strength increases, but the electric field interference causes curvilinear distance change, resulting in poor linearity
Solution Approach 1:
The dual-capacitor configuration provides feedback information about backplate vibration through the second capacitor. By comparing the output of both capacitors, the system can compensate for non-linear effects and electric field interference, maintaining linearity even when diaphragm vibration amplitude is increased for higher audio loudness.
Solution Approach 2:
The interference signal caused by electric field effects on diaphragm vibration is extracted and measured separately through the second capacitor (which measures backplate vibration). This extracted interference component can then be subtracted from the total signal, leaving a cleaner, more linear representation of the actual sound input.
3Measurement precision
If the capacitor plate distance is reduced to increase capacitance, then the sensitivity improves, but the electric field force interference on diaphragm vibration increases, causing high noise
Solution Approach 1:
The measurement function is segmented into two independent capacitive sensing paths: one measuring diaphragm position relative to the stationary backplate, and another measuring backplate position relative to the stationary diaphragm. This segmentation allows the system to maintain small capacitor plate distances for high sensitivity while using differential measurement to cancel out electric field-induced noise.
Solution Approach 2:
The backplate acts as an intermediary that mediates between the two capacitors. By capacitively coupling the backplate to both capacitors, the system can measure backplate motion separately and use this information to cancel noise in the final output, enabling small plate distances without proportionally increasing noise.
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
The design achieves higher sensitivity, reduced distortion, and improved anti-interference capabilities, resulting in enhanced audio performance with good linearity and signal quality.
Implementation Method 1
the plurality of stationary electrodes and the plurality of movable electrodes form a capacitor
Implementation Method 2
The backplate and the diaphragm form electrode plates of a variable capacitor
Data Source
AI summary
A capacitive microphone includes a substrate, a plurality of stationary electrodes, a diaphragm, and a backplate. The substrate includes a cavity and a step disposed in the cavity, and the plurality of stationary electrodes is equally spaced on the step. A diaphragm is received in the step and includes a vibration portion and a connecting portion connected to the vibration portion. A plurality of movable electrodes protrudes from a periphery of the vibration portion, and one end of the connecting portion away from the vibration portion is connected to the substrate. The backplate is provided with a plurality of sound transmission holes, and a gap is formed between the backplate and the diaphragm to form electrode plates of a variable capacitor. The capacitive microphone can get a higher signal-to-noise ratio, improve the capability of suppressing linear distortion, and improve the anti-interference capability of the microphone.