Miniaturization of ALDs: How Small Can We Go?

A recent product release has me thinking about assistive listening devices (ALDs) — i.e., hearing aids. The press release was pushing a new MEMS-based microphone and preamplifier in a very small surface-mount package. The main selling points (besides small size) were low noise, very low current draw (17μA), and the ability to operate from a supply as low as 1V.

This is a nice device, but if you are manufacturing an ALD, you'll need more than a mic and a preamp. Of course, you'll need a tiny speaker, too. But in between the mic and the speaker is where the real magic occurs.

With any decent present-day ALD, low current draw is essential. The device operates from a very small single cell. That means 1V operation and a 17μA draw are just what's needed. Beyond that, an essential part is the audio equalizer (EQ) that is part of the audio chain.

Just as the home hi-fi EQ compensates for listening room frequency characteristics, the ALD EQ will tailor the frequency response to the user's ears. The intent is to create an inverse frequency response. Peaking (where it occurs) is nulled with notch filters. High-frequency content is boosted to account for age- or injury-induced hearing loss.

Of course, the correction can go only so far — typically not far enough to help with speech recognition. The EQ is tweaked by an audiologist based on frequency response tests administered to the user. Any sort of sophisticated interface has a microcontroller (MCU) keeping track of everything.

Since the user would balk at the prospect of an EQ that requires a 19-inch relay rack panel, miniaturization is the next important goal after power draw. Combining these functional blocks on one piece of silicon should keep it all small enough to create an in-ear device.

  • MEMS mic
  • Mic preamp
  • EQ
  • Speaker driver
  • Power supply (and power supply support)
  • MCU
  • A programming interface that the audiologist uses

Ultimately, the goal is to reduce power consumption to the point that the device can use energy harvesting techniques.

Have you worked on any projects that use this level of miniaturization and power consumption?

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11 comments on “Miniaturization of ALDs: How Small Can We Go?

  1. Karl Wiklund
    July 31, 2013

    Since I work in this product space, I certainly have.  Both on full-blown hearing aids, as well as a recently-released consumer oriented product (a body-worn device).  Most ALDs I've seen generally use the same form factor as a typical hearing aid, and largely similar hardware too.  In other words, the devices are typically all-digital, and run one of several special purpose DSPs.

  2. Dirceu
    July 31, 2013


      “Energy harvesting + Low power audio “: This reminds me of those old crystal radios without batteries.

  3. David Maciel Silva
    July 31, 2013

    This new device is minuscule!

    Brad, you have the value of this iten or estimate? Local suppliers have not found much information. Good perfomace, low voltage.

  4. Brad Albing
    July 31, 2013

    @Maciel – The price and availability info should be available from Analog Devices. I'll see if I can get it and post it here.

  5. Brad Albing
    July 31, 2013

    @Dirceu – In a way – tho' these sorts of design are just a little bit more sophisticated.

  6. Brad Albing
    July 31, 2013

    @Karl – I welcome any further thoughts you have on this. Maybe write a blog?

  7. Karl Wiklund
    August 1, 2013

    I expect it should be in line with similar devices from ADI ($1-2 per unit per thousand).  You may be able to do better than that though if you deal directly with ADI rather than a third-party distributor.  It's expensive for a lot of consumer applications, although much cheaper than existing hearing aid mics which usually go for around $20 a unit.

  8. Davidled
    August 2, 2013

    Prototype ALD might be built with small components to minimize the size, as consumer electronics is getting small with better performance. For example, small IC is highly integrated with a lot of IP blocks. I think that miniaturization of system is depending on how to integrate the existing IC, not inventive in some cases.  

  9. Brad_Albing
    August 3, 2013

    @Karl – I wonder about the current draw for such a device. It seems like it would be pretty power hungery.

  10. Karl Wiklund
    August 3, 2013

    Much less so than you'd think.  The two open-platform DSPs (Ezairo and Voyageur from ONSemi) both draw ~ 1 mA of current or less when operating.  Aside from some hardware acceleration, you get there by a low clock speed; 2 MHz for Voyageur, and about 5 MHz for the newest Ezairo. There are a few other manufacturers in this space as well, but their offerings should be in this range as well.






  11. SunitaT
    August 20, 2013

    Miniaturization of electronic devices could be probable by either introduction of high k-oxides as gate isolators or by growth of structures with a 3D architecture. The leakage current was decreased on this way by the two orders in size, opening chances for more miniaturization of ICs. Gate dielectric was dropped by the atomic layer deposition (ALD), due to exclusive properties of this growth technique.

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