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MEMS Microphones Make the Grade

Thu, 12/04/2008 - 5:11am
Despite the proliferation of electronics devices that integrate voice, music, and video, the quality of sound produced by these handheld electronics has not lived up to consumer expectations. Analog Devices, Inc., (ADI) has created a microphone capable of high-fidelity audio/video playback, conference calling, TIA-920-compliant VoIP (voice-over-IP), voice recognition, and other functions.

ADI combined audio applications know-how with MEMS (micro-electromechanical systems) technology to design a new family of microphones which offers one of
MEMS Microphones Make the Grade
the highest SNR (signal-to-noise ratios) of greater than 61 dB A-weighted. Today, the highest quality sound available in a cell phone, for example, is just 55 dB. The new omni-directional input microphones are available with digital output or analog output and deliver the industry's flattest frequency response from 100 Hz to greater than 15 kHz — and with a package size and cost tailored to the design considerations of portable electronics manufacturers. After faithfully serving the electronics industry for nearly 50 years, electret condenser microphones are beginning to give way at the edges to silicon micromachined microphones.

"MEMS microphones have several advantages. They can be manufactured using surface mounting, withstand high reflow temperatures, are easily integrated with CMOS processes and other audio electronics, and they offer improved noise cancellation and immunity to RF and EMI," said Jeremie Bouchaud, director and principal analyst for MEMS at research firm, iSuppli Corp. " "Today, MEMS microphones account for a bit less than 10% of the total market in units, but we expect that shipment will increase by 32% yearly over the next 4 years to exceed 1 billion units in 2012."

"ADI leveraged its proven MEMS® Motion Signal Processing technology, which has shipped more than 400 million components to date, to develop a new family of high performance analog and digital output MEMS microphones that complement our audio codecs, Class-D amplifiers, and processors," said Mark Martin, vice president, Micromachined Products Division, Analog Devices.

The ADMP421 PDM (pulse density modulated) digital output MEMS microphone is designed for multimedia and VoIP-enabled cell phones, Bluetooth headsets and other systems that rely on high quality digitized voice and audio. The digital output of the ADMP421 microphone provides high immunity to coupled noise from RF and EMI emanating from sources such as WiFi antennas and LCD clock signals. By eliminating the need for analog signal conditioning, as well as the cable shielding materials commonly required to route analog signals, system designers can optimize the placement of the ADMP421 digital MEMS microphone to improve audio-enhancement features, such as stereo sound and array beam forming. The ADMP421 features 80 dB FS PSRR (power supply rejection ratio), Left/Right select, and integrated sleep mode.

Analog Devices' ADMP401 analog output MEMS microphone delivers impressive PSRR of better than 50 dBV, simplifying power supply design requirements to the microphone for near-field and far-field applications. The ADMP421 digital output MEMS microphone is sampling now in a 4.0 mm x 3.0 mm x 1.0 mm surface mount package.

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