Electronic Design

The Mic-On-A-Chip's Future Sounds Good To The Industry

The votes are in. Electronic Design's readers selected Akustica's AKU2000 microelectro-mechnical-system (MEMS) microphone on a chip as the most significant Leapfrog technology of the year (see "Breaking A New Sound Barrier: It's A Mic-On-A-Chip," April 27, 2006, p. 36, ED Online 12361). This CMOS device breaks new ground in size, cost, and performance parameters.

Akustica hasn't rested on this achievement, though. The first-generation AKU2000 features an acoustic hole on the package's underside, while the AKU2001 can multiplex two microphones in an array configuration. And released in September, the digital AKU2004 eases the integration into camera models with its port and user-selection option (Fig. 1).

These digital microphones provide much higher noise-free performance than other electret microphones. They're immune from noise sources like radio-frequency interference (RFI), electromagnetic interference (EMI), and power-supply variations.

The surface-mountable chips come in a 4- by 4- by 1.8-mm package. They feature less than 10% total harmonic distortion at 115 dB of sound pressure level. The output is pulse-density modulated, producing a single-bit digital stream that can be decimated by a digital filter in downconversion electronics like audio codecs, DSPs, or baseband circuits for a high degree of design flexibility.

The design enables the use of a digital-bus architecture for a variety of audio systems, simplifying system design and expediting time-to-market. With 10% lower parasitics than other microphones, the chips are immune to radio-frequency-interference and electromagnetic-interference signal effects. They operate from 2.8 to 3.6 V and consume less than 75 µA in power-down mode. In addition, they feature a clock frequency of 1 to 4 MHz and a signal-to-noise ratio of 55 dB.

The high performance is catapulting these devices into mass-market applications. Combined with the fact that these chips are totally made on a standard CMOS process, which translates into low unit costs in high volumes, this development marks a milestone in MEMS technology.

The growing need for high-quality audio in laptops and notebooks is driving the demand for MEMS microphone chips like Akustica's models. Voice over Internet Protocol (VoIP) phone calls and video conferencing are becoming more popular for personal and business communication.

These calls require a more sophisticated microphone, considering the distance between a laptop and its user. That's why Fujitsu chose the AKU2000 for its LifeBook Q2010 notebook (Fig. 2). "Communications capabilities are becoming increasingly important for notebook PC users," says Paul Moore, senior director of mobile product marketing for Fujitsu Computer Systems.

"VoIP, dictation, and other applications are placing demands on the recording and voice quality these devices are expected to deliver," Moore adds. "Deploying Akustica's AKU2000 in our Q2010 notebook provides us with a truly superior digital microphone solution in an extremely small form factor."

The pending launch of Microsoft's Windows Vista, which has an audio feature that can use up to four microphones in each computer, is certain to increase the demand for MEMS microphones. "All major notebook manufacturers have at least one VoIP platform in their designs for 2007 products," says Ed Pawlak, Akustica's product marketing manager.

The microphone chip market is potentially huge. Research firm Yole Developpement sees it growing from $100 million in 2005 to $800 million in 2010. With Akustica chips costing less than $4 in 1000-unit lots, the company has good reason to be upbeat about its MEMS microphone sales. "We're predicting the sale of tens of millions of Akustica digital microphones next year," says Davin Yuknis, Akustica's vice president of marketing and product management.

Fujitsu isn't the only company interested in Akustica's MEMS microphones. Ricoh Co. Ltd. is collaborating with Akustica to promote voice and VoIP applications. In fact, Ricoh has developed a new camera module for optimized audio and video performance via the Universal Serial Bus (USB) port.

Both companies will actively-promote a fully integrated audio/video USB camera solution to computer manufacturers. They're now offering a reference design that pairs an array of Akustica's AKU2004 microphones with Ricoh's R5U872 USB 2.0 audio/video interface controller, which features a four-channel digital microphone interface.

Meanwhile, IDT is the first codec manufacturer to attain certification in the Akustica Certified Codec program, which validates all of the functionality required for a successful integration of Akustica digital microphones into other products. " Participating in this program reflects our goal to help drive the ongoing improvements and innovations for the PC market," says Phil Bourekas, vice president and general manager of IDT's PC audio products.

There are other applications as well. Akustica foresees a vast market not only for its silicon microphones, but also for CMOS MEMS sensor technology across the board. It trademarked the term " Sensory Silicon" to describe a platform upon which monolithic analog and digital sensory systems will be built to hear, speak, and sense the world around them.

The company envisions CMOS MEMS that can deliver accelerometers, gyroscopes, RF components, signal-processing ICs, and microphones for voice input chips, hybrid sensors, acoustic portals to the wireless Internet, and smart microphone arrays. Potentially, cell phones can be the biggest market of all since they use the most MEMS devices in consumer apps.

Yet price is a factor, except in high-end cell phones. Most cell-phone users pay for the service provided by the cell phone company and little or nothing for the phone itself. Since the Akustica microphones are made on a standard CMOS process, though, even the most ordinary cell phone will be able to use these MEMS microphones when shipping volumes of these chips begin to increase in large numbers.


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