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Jun 25th, 2013
Voice controlled applications require more advanced microphones
Voice control of built environments, and of all devices used in and between them, is one of those concepts whose fate will be decided by whether people actually want it or not: do we really want to get to the stage of telling a light switch to turn on or off, rather than pressing it?
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The technologies behind the concept are essentially already here, although they need to be developed to meet some performance and power criteria. These developments are being made to meet the requirements of other related markets, an example being the progress being made with microphones.

Traditionally, every mobile device contained an ECM – an Electret Condenser Microphone. But, by this time, the market for mobile microphones will have topped $2billion. The remaining 75% will have been taken by the explosive growth in MEMS microphones, which have become popular for a number of reasons.

Most obviously, they are smaller than ECMs and, as smartphones require multiple microphones to be used, rather than the one required for a 'talk only' mobile phone, size is important. MEMS are also attributed as having other advantages in terms of performance consistency, operating temperature and orientation.

Mark Hesketh, general manager for MEMS technology at Wolfson Microelectronics, conceded that the acoustic signal chain was only as strong as its weakest link – and that could just as easily be a poor ECM or a poor MEMS microphone. However, he noted: "The performance of the MEMS microphone in terms of the signal to noise ratio and dynamic ranges has improved and that performance has been achieved with significantly smaller devices. Having a high performance, small package in your signal chain means that MEMS is helping us have the very best acoustic signal chain possible."

So how have MEMS devices moved ahead in the microphone race? At the heart of the microphone is the transducer. "We have a developed a transducer device that has a very linear performance and very low noise floor," explained Hesketh. "We not only design the MEMS transducer, but Wolfson also owns the process for their manufacture, so we can also tune the material design to get the very best performance from our transducers. We use silicon and variants – others use other materials – but we believe there are advantages in our material set, coupled with our design, that delivers the performance."

The other aspect is the associated asic that controls both input to transducer and the output of the device. The output can be either analogue or digital if converted to a pdm [pulse density modulation] stream.

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