MEMS Sensor Input Attenuator for Resonance Noise Control
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Solution Overview
Problem
Microelectromechanical systems (MEMS) sensors, particularly capacitive MEMS microphones, face challenges with noise and distortion due to high signal amplitudes and mechanical resonances, which can lead to intermodulation products within the audible frequency band, even when noise sources are outside this range, affecting signal quality and system noise ratio.
Innovation Solution
A frequency-dependent input attenuator is integrated into the MEMS sensor circuit, utilizing a feedback capacitor and low pass filter to attenuate signals above a specific corner frequency, reducing noise and distortion while maintaining unity gain within the audible frequency band, thereby minimizing the impact on desired signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If wideband attenuation of the input signal is applied, then noise and distortion are reduced, but the strength of the desired audio signal is weakened and system level signal to noise ratio decreases
Solution Approach 1:
The patent applies attenuation selectively at specific frequency bands rather than uniformly across the entire spectrum. The frequency dependent input attenuator targets specific resonance frequencies (mechanical and acoustic resonances) while maintaining unity gain in the desired audio bandwidth, thereby reducing noise and distortion without weakening the desired audio signal.
Solution Approach 2:
The patent changes the attenuation parameter dynamically based on frequency. The frequency dependent input attenuator adjusts the attenuation amount according to the input signal frequency, applying stronger attenuation at resonance frequencies and no attenuation (unity gain) in the desired audio bandwidth, thus resolving the contradiction between noise reduction and signal preservation.
2Object-affected harmful factors
If frequency dependent input attenuation is applied, then intermodulation distortion is reduced, but device complexity increases
Solution Approach 1:
The patent introduces a frequency dependent input attenuator as an intermediary component between the MEMS motor and the amplifier input stage. This attenuator acts as a mediator that selectively reduces the amplitude of specific frequency components (resonances) before they enter the amplifier, preventing intermodulation distortion without requiring complex processing in subsequent stages.
Solution Approach 2:
The patent applies attenuation in advance at the input stage of the amplifier, before the signal is amplified and processed further. The frequency dependent input attenuator pre-reduces the amplitude of resonance frequencies and potential intermodulation products before they can be amplified and cause distortion, simplifying the overall system design by addressing the problem at its source.
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 solution effectively reduces noise and distortion by attenuating unwanted signals outside the audible range before they form intermodulation products, preserving signal strength and improving the signal-to-noise ratio within the desired frequency band.
Implementation Method 1
an input attenuator low pass filter, the input attenuator low pass filter having an input coupled to the output of the amplifier input stage
Implementation Method 2
A frequency dependent input attenuator is integrated into the electrical circuit of MEMS sensors, using a feedback capacitor and low pass filters
Data Source
AI summary
A microelectromechanical systems (MEMS) sensor, a capacitive MEMS motor sensing circuit and a method are provided. The present application provides a microelectromechanical systems (MEMS) sensor. The MEMS sensor includes a housing having electrical contacts disposed on an exterior of the housing. The MEMS sensor further includes a capacitive MEMS motor disposed in the housing, and an electrical circuit disposed in the housing and being electrically coupled to the electrical contacts. The electrical circuit includes a bias voltage source having an output coupled to an input of the MEMS motor. The electrical circuit further includes a buffer circuit including an amplifier input stage having an input coupled to an output of the MEMS motor. The electrical circuit still further includes a frequency dependent input attenuator including a feedback capacitor and an input attenuator low pass filter, the input attenuator low pass filter having an input coupled to the output of the amplifier input stage and an output coupled to a first terminal of the feedback capacitor, where a second terminal of the feedback capacitor is coupled to the input of the amplifier input stage.