PORTLAND, Ore. -- Always-on voice-activated applications, from smartphones to wearables to industrial control headsets -- at the very least have to leave the microphone drawing power 24/7. Older dynamic microphones required no power to be "on," but those mammoth beasts will not fit inside today's pint-sized devices. To solve the problem, Knowles Corp. (Itasca, Ill.) claims to have designed a micro-electro-mechanical system (MEMS) microphone that uses three-times less power than other digital MEMS microphones -- just 235 microAmps. Other firsts claimed by Knowles is that its SPH0641LM4H-1 is 20-percent smaller, 3.50 x 2.65 x 0.98 millimeters, and has the highest signal-to-noise (SNR) of any low-power digital MEMS microphone, 64.3 dB (using A rating).
Knowles claims its world's lowest-power MEMS mic with a signal-to-noise (SNR) of 64.3 dB measures just 3.50 x 2.65 x 0.98 millimeters. (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 [Internet of Things] 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 an new 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 45 to 20-kHz and for multiple microphone set ups are matched within plus or minus 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, Advanced Technology Editor, EE Times