MIT debuts 'bionic ear processor' for hearing impaired
By Mark LaPedus
Silicon Strategies
February 08, 2005 (1:02 PM EST)

SAN FRANCISCO At the International Solid-State Circuits Conference (ISSCC) here, a team from the Massachusetts Institute of Technology (MIT) described an analog "bionic ear processor" with zero-crossing detection for the hearing impaired.

Built around a 1.5-micron BiCMOS process from AMI Semiconductor Inc. (AMI), the processor is an analog device that is designed to replace traditional cochlear implant devices for those who are deaf or experience hearing loss.

Cochlear implant devices provide sound perception through direct electrical stimulation of the hearing nerve. The electrical stimulation bypasses the inner ear, which is the most common culprit of hearing loss.

A cochlear implant consists of internal and external devices. The internal device is surgically implanted under the skin and is comprised of a receiver, a magnet, and a bundle of fine wires. The external device includes the sound processor, a cable and a microphone, which is housed in an earpiece.

These devices are power-hungry products. They are also done in the digital domain by digitizing the output of a microphone front-end and feeding it to a digital signal processor (DSP).

MIT proposes a better solution in the analog domain, which is said to reduce power consumption for these applications. The "bionic ear processor" is based on a single chip that measures 9.23- x 9.58-mm2. The chip consists of a microphone front-end circuit, an automatic gain control circuit, bandpass filters, envelope detectors, a logarithmic A/D device and a digital output product.

The entire device could be implanted in a body and can run on a 100-mAh battery "with at most 1000 wireless recharges and no battery replacements for at least 30 years," according to MIT. "In this chip digitizing is delayed to the very end while there is still room for 750-microWatts of stimulation power," according to MIT. "The input to the chip is current from the drain of a Knowles FG3329 electret microphone and the output of the chip is a 7-bit number that represents the log spectral envelope energy of each of 16 channels with a sampling rate for each channel programmable from 500Hz to 2kHz."