MEMS Microphone Back-Volume Design for SNR and Low-Frequency Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing MEMS microphones face challenges in achieving high signal-to-noise ratio (SNR) and low frequency cutoff enhancement due to limited back volume (BV) in their packaging, which affects their performance in applications like Active Noise Cancellation (ANC) systems.
Innovation Solution
The design incorporates a dual-port MEMS microphone assembly with configurable front and back volumes by positioning ports in both the substrate and lid, and utilizing additional back volume through the PCB or housing to enhance SNR and frequency response, allowing for customization and fine-tuning of microphone performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the microphone assembly uses a conventional single-port design with limited packaging volume, then the device complexity is reduced, but the signal-to-noise ratio (SNR) and low frequency cutoff performance deteriorate
Solution Approach 1:
The microphone assembly is segmented into two distinct ports: a first port for sound input and a second port for acoustic reference. This segmentation allows independent optimization of each port's function, enabling the back volume behind the diaphragm to be effectively utilized for noise cancellation while maintaining a compact form factor. The substrate is divided to accommodate both ports with proper acoustic isolation.
Solution Approach 2:
The patent implements nesting by placing the second port and its associated acoustic path within the existing packaging structure. The back volume that would traditionally be unused space is now nested into the design to provide acoustic reference for noise cancellation, effectively utilizing the available packaging volume without increasing overall device size.
2Reliability
If the back volume is increased to enhance low frequency cutoff and SNR performance, then the frequency response improves, but the packaging volume requirement increases
Solution Approach 1:
The patent applies local quality by creating a concentrated back volume region directly behind the diaphragm that is optimized for acoustic reference, rather than uniformly increasing the entire packaging volume. The second port is strategically positioned to access this localized back volume, allowing enhanced low frequency response without proportionally increasing the overall device footprint.
Solution Approach 2:
The design utilizes the third dimension (depth) by routing the second port through the substrate to access the back volume behind the diaphragm. This dimensional approach allows the acoustic reference path to extend into the packaging depth rather than requiring increased lateral dimensions, thereby improving frequency response without increasing the device's planar footprint.
3Reliability
If acoustic isolation between ports is enhanced to improve noise cancellation performance, then the SNR improves, but the manufacturing precision requirements increase
Solution Approach 1:
The patent merges the acoustic isolation function with the existing housing and gasket structures. The gasket that seals the housing is also configured to provide acoustic isolation between the first and second ports. This integration reduces the need for separate acoustic isolation components and simplifies the manufacturing process while maintaining effective noise cancellation performance.
Solution Approach 2:
The housing and gasket components are designed to serve multiple functions: structural enclosure, acoustic sealing, and acoustic isolation between ports. This multi-functionality reduces the overall component count and simplifies manufacturing by eliminating the need for specialized acoustic isolation elements, thereby reducing precision requirements while maintaining performance.
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3~4
AI summary
In at least one embodiment, a microphone assembly including a substrate, a printed circuit board (PCB), a micro-electro-mechanical systems (MEMS) transducer, a first lid, and a second lid is provided. The substrate defines a first port that extends completely therethrough. The PCB defines a sound opening that extends completely therethrough. The MEMS transducer is positioned on a first side of the substrate. The first lid defines a second port and covers the MEMS transducer and the first port. The first lid and the substrate define a front volume of air that surrounds the MEMS transducer. The second lid is positioned on the second side of the PCB. A cavity of the second lid, the sound opening of the PCB, the sound opening of the PCB, and the first port of the substrate define a back volume of air that is greater than the front volume of air.