MEMS Microphone Balanced Bias Circuit for Equal Differential Signals
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Solution Overview
Problem
Existing MEMS microphones face challenges in generating differential signals with equal amplitudes and suppressed distortion due to unequal capacitances of variable capacitors, leading to increased circuit scale and cost when separate voltage generation circuits are used.
Innovation Solution
The microphone employs two equal-area fixed electrodes facing a common diaphragm, with a bias voltage applied to one electrode and a reference voltage to the diaphragm, generating equal capacitance changes and using a ½ bias generation circuit to apply positive and negative voltages without a separate negative voltage generation circuit, thus maintaining circuit scale and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate voltage generation circuits are used for each variable capacitor, then differential signals with equal amplitudes can be generated, but circuit scale and cost increase
Solution Approach 1:
The patent merges the voltage generation function into a single shared circuit that supplies voltage to both variable capacitors. Instead of using separate voltage generation circuits for each capacitor, a unified voltage generation circuit generates a single voltage that is distributed to both capacitors, thereby reducing circuit scale and component count while maintaining the ability to generate differential signals with equal amplitudes
Solution Approach 2:
The voltage generation circuit is designed with universal functionality to serve multiple variable capacitors simultaneously. The circuit generates voltage that can be applied to any number of variable capacitors connected in parallel, making the circuit multi-functional and eliminating the need for separate dedicated voltage generation circuits for each capacitor
2Measurement precision
If separate voltage generation circuits are used for each variable capacitor, then differential signals with equal amplitudes can be generated, but manufacturing cost increases
Solution Approach 1:
The patent merges the voltage generation function into a single shared circuit that supplies voltage to both variable capacitors. Instead of using separate voltage generation circuits for each capacitor, a unified voltage generation circuit generates a single voltage that is distributed to both capacitors, thereby reducing circuit scale and component count while maintaining the ability to generate differential signals with equal amplitudes
Solution Approach 2:
The patent uses a single voltage generation circuit design that can be replicated or scaled to accommodate multiple variable capacitors. By creating one master voltage generation circuit that serves all capacitors, the manufacturing cost is reduced compared to producing and assembling separate voltage generation circuits for each capacitor
3Device complexity
If unequal capacitances are used in variable capacitors, then circuit design is simplified, but distortion increases and sound pressure detection sensitivity decreases
Solution Approach 1:
The patent applies local quality by ensuring that each variable capacitor has equal capacitance value and is positioned symmetrically with respect to the diaphragm. This local equality in capacitance values at specific locations (each capacitor's relationship to the diaphragm) ensures balanced differential signal generation and minimizes distortion, while the overall circuit design remains manageable through the shared voltage generation approach
4Device complexity
If unequal capacitances are used in variable capacitors, then circuit design is simplified, but sound pressure detection sensitivity decreases
Solution Approach 1:
The patent applies local quality by ensuring that each variable capacitor has equal capacitance value and is positioned symmetrically with respect to the diaphragm. This local equality in capacitance values at specific locations (each capacitor's relationship to the diaphragm) ensures balanced differential signal generation and minimizes distortion, while the overall circuit design remains manageable through the shared voltage generation approach
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 generation of differential signals with inverted phases while reducing circuit scale and cost, enhancing sound pressure detection sensitivity and expanding the range of sound pressure levels without distortion.
Implementation Method 1
a first variable capacitor including a first fixed electrode facing the diaphragm, a capacitance of the first variable capacitor being changed in accordance with a vibration of the diaphragm
Data Source
AI summary
A MEMS microphone includes a diaphragm having conductivity, first and second variable capacitors respectively including first and second fixed electrodes, a first voltage output section that outputs a first voltage changed according to a change in a capacitance of the first variable capacitor, and a second voltage output section that outputs a second voltage changed according to a change in a capacitance of the second variable capacitor. The first and second fixed electrodes face the diaphragm. The capacitances of the first and second variable capacitors are changed in accordance with a vibration of the diaphragm. A first bias voltage is applied to the first fixed electrode. A reference voltage is applied to the second fixed electrode. A second bias voltage is applied to the diaphragm. A difference between the second bias voltage and the reference voltage is half of a difference between the first bias voltage and the reference voltage.