MEMS Microphone Module Offset Asymmetry for Stereo Noise Reduction
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Solution Overview
Problem
Stereo noise interference occurs when two microphones are connected to a DSP via a single line, causing power loss and deterioration in signal-to-noise ratio due to charge reversal effects and thermo-acoustic effects in stereo operation.
Innovation Solution
A microphone module with two MEMS microphones, each equipped with a modulator and an offset generator that applies a defined offset to shift the limit cycles of the modulators by a specific frequency difference, thereby damping stereo noise through the thermoacoustic frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If two MEMS microphones are connected to a DSP via a single line in stereo operation, then the device complexity is reduced, but stereo noise interference occurs causing deterioration in signal-to-noise ratio
Solution Approach 1:
The patent applies asymmetry by intentionally introducing different offset values to the limit cycles of the two microphones. This creates an asymmetric frequency difference between the limit cycles, which shifts the stereo noise to higher frequencies where it can be effectively damped by the thermoacoustic frequency response, thereby resolving the SNR deterioration while maintaining the single-line connection structure
Solution Approach 2:
The patent changes the parameter of limit cycle frequency by applying different offset values to each microphone's modulator. This parameter change creates a frequency difference that moves the stereo noise interference to a different frequency range, allowing it to be dampened without requiring separate connection lines, thus maintaining low device complexity while improving signal quality
2Use of energy by moving object
If charge reversal effects are reduced to minimize power loss, then energy efficiency improves, but stereo noise interference is exacerbated
Solution Approach 1:
The patent converts the harmful stereo noise into a beneficial effect by shifting it to higher frequencies through offset-based limit cycle frequency adjustment. The noise energy is redirected to frequency ranges where it can be naturally damped by the thermoacoustic frequency response, transforming the harmful interference into a manageable condition that doesn't require additional power consumption for mitigation
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 solution effectively shifts and damps stereo noise towards high frequencies, improving the signal-to-noise ratio by ensuring the limit cycles of the modulators differ by a significant frequency, thereby reducing interference and enhancing performance.
Implementation Method 1
Charge reversal effects give rise to additional power loss that causes interference (stereo noise) in the audio band by way of the thermo-acoustic effect
Data Source
AI summary
A microphone module includes a first MEMS microphone and a second MEMS microphone, wherein the first MEMS microphone includes a first modulator, and wherein the second MEMS microphone includes a second modulator. For the purpose of noise reduction, a defined offset can be applied to an input of the first modulator or of the second modulator. Alternatively, for the purpose of noise reduction, the first modulator and the second modulator can be operated with different modulation frequencies.