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New High-Performance MEMS Microphones


New family of digital and analog output microphones delivers industry's best signal-to-noise ratio and frequency response


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) well-known to audiophiles for its high-fidelity audio technology, 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 with the industry's highest SNR (signal-to-noise ratio) 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 15k Hz-and with a package size and cost tailored to the design considerations of portable electronics manufacturers.

New High-Performance MEMS Microphones from Analog Devices “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.”

“Combining the power-saving and space-saving benefits of Class-D audio technology with ADI's linear IC expertise has enabled a portfolio of audio amplifiers that deliver exceptional sound for a range of applications-from portable devices such as cellular handsets and MP3 players, to thin flat panel advanced televisions and multi-channel surround-sound car stereos,” said Steve Sockolov, product line director, Precision Signal Processing. “While most Class-D amplifiers use some variation of pulse-width modulation (PWM), ADI's Class-D amplifiers use a sigma-delta pulse density modulation (PDM) to reduce the amplitude of spectral components at high-frequencies, thus significantly minimizing EMI emissions.”

“Analog Devices is combining more than 15 years experience as a supplier of high quality MEMS sensors to the automotive and industrial markets with a heritage of high-fidelity audio design,” said Mark Martin, vice president, Micromachined Products Division, Analog Devices. “ADI leveraged its proven iMEMS 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 compliment our audio codecs, Class-D amplifiers, and processors. Our customers now have a single source for all their audio signal chain design and support needs.”

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 new ADMP421 microphone provides high immunity to coupled noise from RF (radio frequency) and EMI (electromagnetic interference) emanating from sources such as WiFi antennas and LCD (liquid crystal displays) 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 80dB FS PSRR (power supply rejection ratio), Left/Right select, and integrated sleep mode.

In addition to providing the industry's best SNR and frequency response, Analog Devices' ADMP401 analog output MEMS microphone delivers superior PSRR of better than 50 dBV, simplifying power supply design requirements to the microphone for near-field and far-field applications.


The company's Web site address is www.analog.com.
[Reprinted with kind permission from Analog Devices]