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MEMS mic gives 64.3dB SNR within 235µA

Posted: 07 Jul 2014  Print Version  Bookmark and Share

Keywords:MEMS  microphone  low-power  Knowles 

One of the big challenges in designing pint-sized smartphones and wearable devices is that in always-on voice-activated applications, MEMS microphones access power round-the-clock—contributing negatively to the battery performance. There are older dynamic microphones that require no power to be "on, only they cover larger footprint that will not fit in tiny devices. Knowles Corp. revealed a microphone that claims to bridge this gap between power consumption and size.

The SPH0641LM4H-1 uses 235µA, three times less power than other digital MEMS microphones. Other firsts claimed by Knowles is that it is 20 per cent smaller, 3.5mm by 2.65mm by 0.98mm, and has the highest signal-to-noise (SNR) of any low-power digital MEMS microphone, 64.3dB using A rating. Last month, the firm introduced a device of the same kind, featuring the exact size and low-power boon for accurate ultrasonic finger tracking (see MEMS mic enables contact-free gesture recognition).

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Knowles claims its world's lowest-power MEMS mic with a signal-to-noise (SNR) of 64.3dB measures just 3.5mm by 2.65mm by 0.98mm. Source: Knowles

"Our low-power multi-mode microphone is ideal for any voice-controlled applications that require a high SNR and low power consumption in the smallest form factor. This includes various IoT devices that rely on battery power. The product has received a positive response from consumer electronics manufacturers and began shipping in volume to manufacturers in January," Thibault Kassir, senior director, Product Management, Mobile Consumer Electronics at Knowles told EE Times.

According to Kassir, design engineers no longer have to trade-off between MEMS microphones that consume little power and ones with a high SNR. The feat is achieved, according to Knowles, by adding super-low-power mode (to sleep mode and standard modes) that simultaneously maintains the high SNR. Knowles calls its super low-power mode Always-On/Always Listening and claims it enables accurate voice recognition even with significant background noise, from cocktail parties to baseball games. Frequency response is 45kHz to 20kHz and for multiple microphone set ups are matched within ±1dB. The bottom port SPH0641LM4H-1 uses a serial pulse-density modulation (PDM) bit stream output and has been in volume production since the first quarter of 2014. Products using it will likely appear by the end of the year.

- R. Colin Johnson
  EE Times





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