Tiny MEMS Microphone Boosts Audio Quality

Wider frequency response, better signal-to-noise could help next-generation cell phones

Charles J. Murray, Senior Technical Editor -- Design News, September 10, 2009

Known as the ADMP421, the new microphone measures a scant 1 mm think, thanks to its use of microelectromechanical systems (MEMS) technology. It also offers a flat frequency response to 15 kHz and a better signal-to-noise ratio than previous microphones. Analog Devices (ADI), maker of the microphone, says it is targeting the product toward the cell phone market, among others.

"Having a smaller and more efficient microphone allows manufacturers to build a better phone," notes Todd Borkowski, marketing manager for ADI.

ADI engineers believe that the new microphone is entering the market at the right time, especially since standards are changing to accommodate wideband telephony. "The old telephony standard only went to 3 kHz," says Alex Ahenkin, senior acoustics engineer for ADI. "But now that that the standard extends to 8 kHz, many of the older microphones won't have the frequency response to accommodate the higher bandwidth."

Along with the ADMP421's 15-kHz frequency response, ADI says it also delivers the industry's highest signal-to-noise ratio. The 61-dB signal-to-noise ratio is reportedly about 6 dB better than predecessors.

"That represents an effective doubling of the distance that the microphone can be used at," Ahenkin says.

As a result, the microphone offers an advantage in hands-free phones, which often must pick up sounds at a distance of several feet. It also could help in next-generation cell phones that incorporate video. ADI engineers say that until now phone-based video typically has suffered from lack of quality audio, but the new system could help because it provides quality audio at a size that's small enough for use in cell phones. 

"The emphasis today is on thinness," Borkowski says. "In a densely packaged cell phone, every millimeter makes a huge difference to the cell phone manufacturer."