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Mar 1st, 2011
ADI ups ante in high-precision MEMS gyros
Already known for its high-precision micro-electro-mechanical system (MEMS) accelerometers, gyroscopes and complete inertial navigation units (IMUs), Analog Devices Inc.
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Fig1: ADI"s new ADXRS64x.
Fig1: ADI's new ADXRS64x.

(ADI) has upped the ante for high-precision with its invention of quad-differential iMEMS gyros, which combine four separate sensing elements to cancel out the effects of vibration, noise and other environmental stimuli.

MEMS gyroscopes use a vibrating "proof mass" suspended on silicon springs which harnesses the Coriolis effect to detect rotation orthogonal to its motion with capacitive sensors around its edges. Unfortunately, vibration, shock and excessive linear acceleration can fool a single proof mass into falsely reporting rotational motion. To cancel out these effects, ADI already had dual-differential proof masses on its previous high-precision gyros, but now has taken a significant step forward by going quad.

Fig1: ADI's new ADXRS64x quad-differential iMEMS gyroscope family uses four separate proof masses (upper left, upper right and lower left, lower right) to cancel out the effects of vibration, noise and other environmental stimuli.

"We call it the quad-differential sensor, because there are four proof masses that prevent the gyro from being lured into sensing movement that is not really there," said Wayne Meyer, marketing and applications manager at ADI's MEMS/Sensors Technology Group. "Previously we used two proof masses in a differential configuration—moving in opposite directions—for our high precision gyros, but this new family takes that concept even further with four proof masses to cancel out erroneous signals."

Besides providing more accurate and more reliable automotive safety systems, ADI is also targeting its new quad-sensor at autonomous navigation systems—such as for auto-steering crop harvesting equipment—for more accurate navigation of surgical and other robots, more precise indoor navigation for everything from first-responders to factory automation, as well as for greater accuracy in remote guidance, sensing and instrumentation.

"The key specifications that distinguish high-precision applications are immunity to the environment, low noise and low drift," said Meyer. "For instance, the iPad's consumer-grade gyro drifts hundreds of degrees per hour, whereas for high-precision applications—from a Boeing 747 to an Apache helicopter—you need gyros that only drift a few degrees per hour."

The new iMEMS quad-differential sensor drifts as little as eight degrees per hour, plus provides immunity to vibration and shock at ultra-low noise levels and a plus or minus 50,000 degree-per-second measurement range, according to ADI. The quad-differential sensors are available in three models with various combinations of features and price points. All have analog outputs specifically tailored to providing accurate angular rate (rotational) sensing even in harsh environments rife with excessive vibration, linear acceleration and shock. The new models also offer startup times as short as three milliseconds, as well as 10-times lower power consumption than typical gyros, according to ADI (3.5 milliAmps).

The new line of ultra-precise quad-MEMS gyros uses ADI's patented BiMOS process and the same pin-out as its previous dual-MEMS sensors, for drop in replacement in existing sockets using ADI's standard BGA chip-scale package measuring 7-by-7-by-3 millimeters.



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