Contributing Editor, MEMS Investor Journal
A leading supplier of airbag sensors worldwide with more than 500 million units shipped, Analog Devices diversified from accelerometers, gyroscopes, and inertial measurement units with its first MEMS microphone over a year ago. Recently ADI (NYSE, constituent S&P 500) announced two new MEMS microphones aimed at high-fidelity audio applications such as voice-over-Internet protocol (VoIP), voice recognition and hands-free communicators, translators, and dictation applications.
"Poor microphone performance at the front end significantly increases requirements for downstream audio processing," said Mark Martin, vice president, MEMS and Sensor Group, Analog Devices. "These new MEMS microphones enable many new high performance capabilities for portable consumer and industrial applications."
ADI's analog-output bottom-ported omnidirectional MEMS microphone is claimed to have the lowest noise available with a SNR (signal-to-noise ratio) of 62 dB and a frequency response of 100 Hz to 15 kHz (ADMP404). Voice recognition applications using hands-free devices are particularly sensitive to background noise, including wind noise when operating outside with mobile handsets. To suppress wind-, fan- and similar noises right at the transducer, a second model (the ADMP405) was also announced with the same 15 kHz high-end frequency response, but with a 200 Hz roll-off at the low end.
Each chip has three internal components -- the MEMS microphone chip, an impedance converter, and an output amplifier, all in a reflow-solder compatible 3.35-by-2.50-by-0.88 millimeter package. ADI also claims both MEMS mics have low power consumption to extend battery life in both near-field and far-field portable applications.
One innovative aspect of ADI's halide-free packaging, is its built-in particle filter which allows sound to pass through holes in its backplate that are small enough to block dust thus protecting the silicon diaphragm from contamination.
The perforated backplate has thousands of six micron diameter holes etched 10 microns deep that admit sound directly into the silicon diaphragm's cavity, thus allowing the entire space inside the package to act as the microphone's back-volume, unlike competing MEMS microphones whose back-volume is confined to the diaphragm's cavity.
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