An MIT researcher has designed a cochlear implant (CI) that does virtually all of its processing in analog mode rather than digital. What this means is that it uses considerably less power than standard CIs that process in digital mode, and it appears to perform every bit as well as the digital versions.

Here are a few excerpts from the New York Times story. For the complete story, point your browser here.

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COCHLEAR implants that restore some hearing to the profoundly deaf have improved steadily over the past two decades. Although they are called implants, however, these systems still lie mainly outside the ear.

Most of the apparatus - including the microphone, processor and batteries that transform speech into electrical signals passed on to electrodes embedded in the cochlea - is still typically worn behind the ear or in a shirt pocket. Researchers hope that one day the entire apparatus, which is designed to stimulate the auditory nerves of people who have lost or damaged cells in the cochlea, can be implanted in the body. But before that goal can be reached, cochlear implants will need to use far less power. Currently the batteries must be changed as often as every four hours.

Now a researcher at the Massachusetts Institute of Technology has devised a processor for cochlear implants that he says consumes only about half a milliwatt, one-tenth of the processing power of current devices. Such an acoustic processing chip, if proven to be effective, might be suitable for next-generation cochlear devices that are fully implanted.

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To save power, the new processor reverses the traditional pattern for chips used in cochlear implants: it does most of the work with analog circuits, not digital ones.

"Most people digitize the signal immediately as it comes from the microphone," turning the information into bits that a digital signal processor then handles, Dr. Sarpeshkar said. "We did the opposite." The signal remains in analog form for most of the processing, including filtering the sound, and is digitized only at the last interface to drive the control circuitry of the electrodes.

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The project was underwritten by industry sponsors, and Dr. Sarpeshkar expects the chip to be available commercially within two years.

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While Dr. Sarpeshkar's processor is based on analog circuits, it includes digital outputs so that it can be used with other parts of the system like the programming interface. Being able to reprogram the processor is crucial because each patient has different auditory needs that are translated into instructions to each electrode that stimulates a nerve ending in the cochlea.