Differential Condenser Microphone Dual Capacitor Design
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Solution Overview
Problem
Conventional MEMS microphones suffer from poor linearity, sensitivity, frequency response, and high noise due to deformation caused by electric field interference, leading to suboptimal call quality in mobile devices.
Innovation Solution
A differential condenser microphone design featuring dual capacitors formed by first and second fixed electrodes and movable electrodes, arranged in a comb-tooth shape, which outputs differential electrical signals to enhance sensitivity and suppress linear distortion, improving signal-to-noise ratio and interference resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional MEMS microphone structure with single capacitor is used, then the device complexity is low, but the sensitivity is poor and linearity is poor due to diaphragm deformation from electric field interference
Solution Approach 1:
The single capacitor structure is segmented into two separate capacitors (first capacitor with first fixed electrode, second capacitor with second fixed electrode). Each capacitor independently measures diaphragm displacement, and their differential output cancels electric field interference effects, thereby improving sensitivity and linearity without requiring complex additional components beyond the electrode arrangement
Solution Approach 2:
The movable electrode on the diaphragm acts as an intermediary that interacts with both fixed electrodes simultaneously. This intermediary element enables the differential measurement mechanism where the same physical displacement is measured from two different fixed electrode positions, allowing cancellation of non-linear effects through differential processing
2Measurement precision
If the capacitor area is increased to improve sensitivity, then the sensitivity improves, but the diaphragm deformation from electric field interference increases causing worse linearity
Solution Approach 1:
The measurement function is segmented into two separate capacitor measurements. By taking the differential of these two measurements, the system achieves high sensitivity (equivalent to large area) while the symmetric arrangement cancels the non-linear deformation effects, maintaining linearity even with larger effective measurement area
Solution Approach 2:
The fixed electrodes are positioned asymmetrically relative to each other (one above, one below the diaphragm), creating an asymmetric measurement configuration that, when differentially processed, eliminates the symmetric non-linear deformation effects and preserves linearity while enhancing sensitivity
3Measurement precision
If the distance between diaphragm and backplate is reduced to increase capacitance value, then the capacitance increases, but the electric field interference increases causing greater diaphragm deformation and worse frequency response
Solution Approach 1:
The electric field interaction is segmented into two separate fields from the first and second fixed electrodes. The differential measurement cancels the harmful interference effects of these fields, allowing the use of smaller distances (higher capacitance) without suffering from the negative effects of electric field-induced diaphragm deformation, thus improving frequency response
Solution Approach 2:
The electric field interference, which normally causes harmful diaphragm deformation, is converted into a beneficial effect through differential measurement. The same electric fields that cause deformation produce equal and opposite effects in the two capacitors, which cancel out in differential mode, transforming the harmful interference into a null effect while maintaining the benefits of reduced plate distance
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 dual capacitor design significantly increases sensitivity, suppresses linear distortion, and enhances anti-interference capabilities, resulting in longer signal transmission distances and better audio performance.
Implementation Method 1
The diaphragm 12 and the backplate 11 are respectively provided with conductive layers and can be energized, but the energized parts are insulated from each other. As such, the diaphragm 12 and the backplate 11 form a capacitor.
Implementation Method 2
The backplate 11 is provided with sound holes 111, through which sound airflow is transmitted to the diaphragm 12 to cause the diaphragm 12 to vibrate.
Data Source
AI summary
A differential condenser microphone is provided, including: a base having a cavity passing through the base; a diaphragm connected to the base and covering the cavity; a mounting portion connected to the diaphragm through a connector, movable electrodes protruding from an outer edge of the mounting portion; first fixed electrodes connected to the base, the first fixed electrodes and the movable electrodes are spatially separated from and cross each other; second fixed electrodes connected to the base, the second fixed electrodes and the movable electrodes are separated from and cross each other, and the first fixed and second fixed electrodes are arranged opposite to and spaced from each other along vibration direction of the diaphragm. Compared to the related art, the microphone can achieve higher sensitivity, higher signal-to-noise ratio, better capacity in suppressing linear distortion, and improve anti-interference capacity, thereby achieving longer signal transmission distance and better audio performance.