Electronic Design

Tiny, Low-Cost MEMS Gyro IC Sets Performance Records

Using the Coriolis effect and its integrated MEMS (iMEMS) surface micromachined process, Analog Devices has produced the smallest, lowest-cost high-performance commercially available angular-rate sensor (gyroscope) with signal-conditioning electronics on the same chip.

Mounted on a small BGA package just 7 by 7 by 3 mm (147 mm3), the ADXRS is much smaller than available gyros, which range in overall size from 15,138 to 159,975 mm3. The Coriolis effect is a phenomenon in which a moving object, subject to a rotation, experiences linear acceleration that's proportional to the rate of rotation.

To make the gyro, an 8-µg polysilicon proof mass is suspended 2 µm over the silicon substrate containing the signal-conditioning electronics. Some 5000 interdigitated fingers, spaced 1.6 µm apart, move in response to the rate of angular rotation, allowing capacitance changes on the order of an incredible 12 zF (1 zeptofarad = 10−21 F) to be measured. The device senses acceleration with 30 µg of resolution and can detect deflection distances of a mere 0.00016 Å. It has a shuttle motion of 3000 g at 15 kHz.

A very important parameter is a high level of rejection for environmental shock and vibration. The gyro can withstand a force of 2000 g. It has a built-in self-test function and can operate over a range of 10,000°/s. It runs on a 5-V supply and draws just 5 mA.

The gyro's ruggedness and low-noise output enable its use in many applications to augment GPS receivers. Applications include triggering automotive airbags during rollovers, improving the accuracy and reliability of GPS systems, and stabilizing moving platforms like autos, airplanes, robots, antennas, and industrial equipment.

"We can offer a roadmap that will provide high-quality and high-performance gyros for as little as $10," says Micromachined Products Division vice president Franklin Weigold.

Two versions will be offered initially: the ADXRS300 with a 300º/s dynamic range, and the ADXRS150 with a 150º/s dynamic range. Pricing is $30 each in 1000-unit lots. Sampling begins this month, with full production by year's end.

Analog Devices Inc., (781) 937-1428; www.analog.com.

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