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MEMS Microphones Busting Out All Over
6/24/2014

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Akustica first to make CMOS-based MEMS mic
Akustica was the first company to produce a CMOS-based MEMS microphone, allowing it to place the signal processing electronic circuitry around the MEMS diaphragm (right) instead of the standard solution of wire bonding the two MEMS die side-by-side with the ASIC in the same package (left). Click here for larger image


 



Akustica's most original designs, since its first models in 2006, used a proprietary CMOS process to fabricate the MEMS microphone diaphragm on the same chip alongside the CMOS signal processing circuitry and analog-to-digital (A/D) converter. This patented technology, originating at nearby Carnegie Mellon University, enabled Akustica to deliver the worlds smallest MEMS microphone die. However, since its acquisition by Bosch in 2009, Akustica took advantage of the surface micro machining expertise and patent portfolio of its parent company. Using Bosch's process the MEMS diaphragm is fabricated in polysilicon on top of a silicon substrate using-+deposition and sacrificial etching to release the mechanical diaphragm. The ASIC is then fabricated using standard CMOS manufacturing techniques-+on a separate silicon die then wire-bonded to the MEMS die in the same package. As a result, the packages are slightly larger, but the ability to mix-and-match MEMS diaphragms with ASICs cuts costs and allows a bigger catalog to be built.


— R. Colin Johnson is the Advanced Technology Editor at EE Times, where he has written about MEMS microphones for over 10 years; in the early days of MEMS mics, his colleagues were baffled by his fascination with them, but his interest has since been vindicated. 

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- Graphene MEMS Outperforms Silicon
Akustica was the first company to produce a CMOS-based MEMS microphone, allowing it to place the signal processing electronic circuitry around the MEMS diaphragm (right) instead of the standard solution of wire bonding the two MEMS die side-by-side with the ASIC in the same package (left). Click here for larger image

 

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Seltech-USA
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digital MEMS microphones
Seltech-USA   10/30/2015 2:00:31 PM
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Knowles now has an I2S MEMS microphone available.  part number SPH0645LM4H-B Seltech can provide technical and sales support for the entire line of Knowles microphones.

Brakeshoe
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Re: Unidirectional MEMS Microphones
Brakeshoe   9/18/2015 2:43:55 PM
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You still need multiple microphones for directionality -- The wider you space them, the more accurate the beamforming. This is a problem we fight in hearing aids & cochlear implant speech processors due to limited size on the spine of BTE & RIC devices.

Dan Schwartz

Editor, The Hearing Blog

Brakeshoe
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Cited in The Hearing Blog
Brakeshoe   9/18/2015 2:40:23 PM
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Thank you for the article: I cited it in The Hearing Blog:
TSMC Announces CMOS MEMS Microphones

R_Colin_Johnson
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Re: Unidirectional MEMS Microphones
R_Colin_Johnson   7/29/2014 3:45:38 PM
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Not sure about the Harmon model, but have made inquiries. Will get back to you soon.

D Cowan
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Re: Unidirectional MEMS Microphones
D Cowan   7/29/2014 3:14:21 PM
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Yes, we'll definitely see SNR continue to improve and at lower price points. What is even more important, in my mind, is that a unidirectional MEMS microphone with high SNR can replace multiple-microphone arrays - today. That means, even if the per unit cost is still at a premium, the value prop still makes sense. At a high level, one device means the  total system is easier to design and manufacture, less space is taken up on an already tight motherboard, and there will be fewer points of failure (not to mention lower power, heat, etc., etc.). I'm just wondering about uptake of the Harman product though because I haven't seen much written about it to know how well it works.

R_Colin_Johnson
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Re: Unidirectional MEMS Microphones
R_Colin_Johnson   7/29/2014 2:53:42 PM
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According to the analysts, all the high-end smartphone makers are going for as much SNR as they can get, and are willing to pay the premium price they demand. The reason is that the voice recognition and noise canceling algorithms work so much better, low-volume voice calls are easier to understand and the quality of the soundtrack on video recordings is even more important than the video quality. Of course, like everything else, as volume production ramps up and prices go down the other-than-top-line-models will start to adapt HD mics too.

D Cowan
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Unidirectional MEMS Microphones
D Cowan   7/29/2014 1:07:11 PM
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In January Harman announced unidirectional analog and digital MEMS microphones with SNR (signal-to-noise ratio) up to 68 dBA. Have you come across anyone designing these in yet? If a single MEMS microphone can replace multi-mic arrays for noise cancelation, it should speed adoption by significantly reducing the cost and space required within the target device. Thoughts?

R_Colin_Johnson
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Re: What is the breakdown of AMICs vs DMICs?
R_Colin_Johnson   6/30/2014 12:12:08 AM
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All your arguements for digital outputs are valid, and in fact the first startup's first microphone (Akustica) had digital outputs. Unfortunately, its kind of like the VHS versus Beta video take war--if you can remember that far back--everybody was already set up for analog mics (electrets) so much so that even Akustica has had to acquiesce a prodeuce analog models. But I am with you, and think hat eventually all MEMS mics will be digital. 

AZskibum
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What is the breakdown of AMICs vs DMICs?
AZskibum   6/29/2014 3:57:51 PM
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It would be interesting to know how far digital microphones (DMICs) -- MEMS mics that include the A/D converter -- have penetrated within the overall MEMS mic market. From an interface perspective, integrating the A/D into the same package as the MEMS makes so much more sense -- especially for applications requiring many microphones (beam-forming arrays, etc.). From the perspective of the audio processor at the receiving end, the two-wire PDM data & clock interface from a DMIC is so much easier to handle than a low-level analog signal, that it's probably well worth the extra cost of the MEMS mics with built-in A/D converters.

Kinnar
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Re: Which is the major cunsuming applicaton of MEMS Mic?
Kinnar   6/26/2014 2:12:58 PM
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Oh that's an answer with fact figures; my estimation was based on the observation of my own. But yes it is very true that MEMS Mics will be having more chances of acceptance in other left out application with possible use of it for betterment.

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