Magnetic induction clips last wire for iPhone 7 earbuds

Article By : R. Colin Johnson

Coincidentally, NXP has announced the most advanced NFMI system-on-chip to date, the NxH2280 NFMI radio for Bluetooth-free earbuds.

iPhone 7 buyers will get a pair of wireless earbuds that use near field magnetic induction (NFMI) to eliminate the last wire (the one between the left and right earbud for Bluetooth headsets).

Coincidentally, NXP announced the most advanced NFMI system-on-chip to date, the NxH2280 NFMI radio for Bluetooth-free earbuds. Earbuds are predicted to be a ₹2.01 lakh crore ($30 billion) market by 2020, according to WiFore Consulting.

"NXP created the NFMI technology 10 years ago, but now we have put it on a second-generation SoC for the huge emerging hearables market," NXP product manager Pieter Verschueren told EE Times. "On our second-generation NFMI chip we have also included a Cortex M0, an audio DSP [digital signal processor], an audio-codec, -latency controller, -sample rate converter, timers, non-volatile memory, every kind of I/O [input/output] and the magnetic induction transceiver itself."

__Figure 1:__ *The NxH2280 puts a second-generation near field magnetic induction SoC onto a die that also includes a Cortex M0, an digital signal processor, and audio-codec, -latency controller, -sample rate converter, timers, non-volatile memory, I/O and the magnetic induction transceiver itself. (Source: NXP)*

The tiny 10.4 square millimetre SoC running at 10.6MHz also uses 10X less power than the equivalent Bluetooth Low Power device, plus its signal is absorbed by body tissues 10,000-times less than a Bluetooth radio which critics claim slow-cooks human tissue by running at the same 2.4GHz frequency as a microwave oven.

The major downside to NFMI is that its range is limited to about a 1 metre (39 inches) making its primary use connecting two earbuds together. NXP suggests that an MP3 player could be fitted into one earbud—using its Cortex M0, DSP and audio signal processors to manage it—for Bluetooth-free music systems, but it could also be used with smartphones that are kept less that 1 metre from the user's head.

"The adoption of wireless earbuds is likely to increase substantially after Apple introduced the iPhone 7," said an NXP spokesman. "Many wireless earbuds currently on the market rely on Bluetooth for connectivity with the smartphone. But Bluetooth does not support streaming audio to two distinct earbuds, requiring a wire between the two for connection. Truly wireless earbuds, such as the Braggi Dash, utilise near field magnetic induction (NFMI) technology for wireless ear-to-ear connection, allowing the pair to function as a single headset."

In fact, hearing aids have been using NFMI for decades, to synchronise and control the signal quality of both units by pushing buttons on either one of the ear's units to control both. Many modern hearing aids have added Bluetooth, in order to stream music from smartphones in addition to their normal hearing aid function, unwittingly exposing their users to the controversial 2.4GHz microwave frequency. And most of the new smart earbuds powered by NXP's NxH2280 are expected to take the same tact, since very few in the public are afraid of 2.4GHz radiation.

__Figure 2:__ *NFMI works like a non-ideal transformer with less than the theoretically possible coupling coefficient depending on how far apart the earbud are located. (Source: NXP)*

However, NXP has created its NxH2280 to be 2.4GHz free, enabling the original equipment manufacturer (OEM) to make the decision as to whether to use Bluetooth or not. Since Bluetooth cannot be economically streamed separately to each earbud, the NxH2280 allows one stereo channel to be transmitted harmlessly to the other earbud which thus does not require a Bluetooth connection.

"The ear canal is also a very good place to locate other sensors to monitor bodily functions, such as vital signs such as heart rate," said Verschueren. "In fact, with the NxH2280 you could put in personal trainer functions that monitor your activities, then encourages you to increase the pace for more aerobics, for instance."

The iPhone 7 earbuds in fact already have a two axis accelerometer included, which could be used for such wellness applications. And NXP's NxH2280 is waterproof for fitness measurements underwater, which fits well with the iPhone 7's waterproof claims.

The NxH2280 is available now, in quantities that could satisfy iPhone 7 demand, but NXP would not confirm that it was being used by Apple.

This article first appeared on EE Times U.S.

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