Electronic Design

Accelerometer Offers Economical Low-G Sensing

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.

Hide comments

Comments

  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Publish