Accelerometer Offers Economical Low-G Sensing

May 12, 2005
Designed for consumer portable handhelds, this tri-axis device gets low in all the right places: footprint, cost, and power dissipation.

Portable handheld consumer electronics have proven successful market-wise for microelectromechanical-system (MEMS) sensors. This is particularly true for sensing low levels of gravity and protecting data in devices that fall and crash on the ground.

Low-g sensing is a tough technical challenge for design engineers, requiring extremely sensitive sensors with low noise levels and very small footprints. Because these sensors target consumer items, they also must be cost-conscious while dissipating very little power.

The MMA7260Q three-axis acceleration sensor combines low-level sensing (selectable), low power dissipation, low noise, low cost, and a very low profile (Fig. 1). Freescale Semiconductor's single-package, two-chip MMA7260Q features the sensing unit on top of the control chip. Cost is $4.25 each in 1000-unit lots.

In comparison, Oki Electric's ML8950 5- by 5- by 1.4-mm three-axis accelerometer, set to sense ±3-g acceleration, costs $50 each in sample quantities (Japanese market only). This includes an evaluation board. Kionix's KXP74 three-axis accelerometer, which measures 5 by 5 by 1.2 mm and senses ±2 g, goes for $7 each in 10,000-unit lots. (See the table for a comparative listing of commercially available three-axis MEMS IC sensors.)

Also, STMicroelectronics' three-axis LIS3L02D, measuring 7 by 7 by 1.8 mm while sensing ±2 g, costs about $5 each in 100,000-unit lots. This June, Analog Devices will release a three-axis single-chip MEMS sensor that's 4 by 4 by 1.45 mm. Hitachi Metals America Ltd. is developing a single-chip, three-axis, 3-g accelerometer in a 4.8 by 4.8 by 1.25 mm. European Technology for Business Ltd. is working on a three-axis single-chip accelerometer as well.

Housed in a 16-lead, 6- by 6- by 1.45-mm QFN package, the MMA7260Q features four selectable g ranges of 1.5, 2, 4, and 6. Also, it consumes 500 mA and operates from a 2.2- to 3.6-V supply. In power-saving mode, it dissipates a mere 5 mA. It can turn on in just 1 ms, and noise is rated at 4.2 mV rms (from 0.1 Hz to 1 kHz).

The four selectable g ranges suit it for various movement, vibration, shock, tilt, and positioning applications (Fig. 2). Set at 1.5 g, it can be used for freefalls and accurate tilt compensation. At 2 g, it fits handheld motion detection and gaming controllers. At 4 g, it can be used for low-vibration monitoring, shipping, and handling. And at 6 g, it suits high-vibration monitoring and high shock readings.

The development of low-cost and miniature three-axis accelerometers raises the possibility of putting gyroscopes in handheld consumer electronics, such as cell phones. Even though there may not seem to be a strong demand in today's consumer market, falling chip prices may soon change this scenario. Gyroscopes are primarily used to provide rotational detection in military, aviation, industrial, and biomedical applications.

About the Author

Roger Allan

Roger Allan is an electronics journalism veteran, and served as Electronic Design's Executive Editor for 15 of those years. He has covered just about every technology beat from semiconductors, components, packaging and power devices, to communications, test and measurement, automotive electronics, robotics, medical electronics, military electronics, robotics, and industrial electronics. His specialties include MEMS and nanoelectronics technologies. He is a contributor to the McGraw Hill Annual Encyclopedia of Science and Technology. He is also a Life Senior Member of the IEEE and holds a BSEE from New York University's School of Engineering and Science. Roger has worked for major electronics magazines besides Electronic Design, including the IEEE Spectrum, Electronics, EDN, Electronic Products, and the British New Scientist. He also has working experience in the electronics industry as a design engineer in filters, power supplies and control systems.

After his retirement from Electronic Design Magazine, He has been extensively contributing articles for Penton’s Electronic Design, Power Electronics Technology, Energy Efficiency and Technology (EE&T) and Microwaves RF Magazine, covering all of the aforementioned electronics segments as well as energy efficiency, harvesting and related technologies. He has also contributed articles to other electronics technology magazines worldwide.

He is a “jack of all trades and a master in leading-edge technologies” like MEMS, nanolectronics, autonomous vehicles, artificial intelligence, military electronics, biometrics, implantable medical devices, and energy harvesting and related technologies.

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