Three-Axis Accelerometers

Three-axis silicon-based accelerometers have been gaining momentum for the past 18 months, as equipment manufacturers have begun employing them on applications ranging from washing machines to cell phones to laptop computers.

The fingernail-sized sensors, which detect z-axis motion along with the traditional x- and y-axis motion, are enabling products to perform functions that would have been difficult or impossible before. Hard drive manufacturers, for example, have begun incorporating the devices as a means of detecting free fall. Using the z-axis sensing capability, a hard drive can "know" when it is falling and, as a result, place itself into a "park" mode to prevent data from being lost on impact.

"That could have been done before, but it would have taken two sensors to do it," notes Bob Tucker, operations manager for sensor solutions at Freescale Semiconductor, one of several companies producing the MEMS (micro-electromechanical systems) silicon sensors.

Kionix, Oki, MemSense, Hitachi, and STMicroelectronics have also placed products on the market, and Analog Devices will roll out a three-axis product later this year.

Freescale's MMA7260Q

Freescale Semiconductor's new three-axis sensor, rolled out on May 11, is the newest three-axis MEMS device and the first to include a "g-select" feature that allows engineers to program it to detect a prescribed force range. Freescale's device also boasts exceptionally low current draw: 500 µA normally; and 5 µA in a power save mode. The device resides in a 16-lead, 6-mm × 6-mm × 1.45-mm package.
For more information on Freescale's three-axis sensor, go to www.freescale.com.

Oki Electric's ML8950

Oki Electric Industry's tri-axis sensor measures just 5 mm × 5 mm × 1.4 mm, and incorporates built-in amplifiers and A/D converters, resulting in a serial digital output that can be directly connected to a CPU. In addition to detecting tri-axis acceleration, the ML8950 can also detect inclination and impact shock, as well as measure degree of vibration.
For more information on Oki's three-axis sensor, go to http://rbi.ims.ca/4391-534.

Kionix's KXP74

Kionix's new device is said to be the thinnest tri-axis sensor available, measuring a scant 1.2 mm thick and 5 mm × 5 mm square. Kionix representatives say that the product's real strength, however, lies in its low-noise performance, which makes it well suited for applications such as precision compass tilt correction. A Serial Peripheral Interface (SPI) also eliminates the need for an analog-to-digital (A/D) converter, thus reducing system component requirements.
For more information on Kionix's three-axis sensor, go to http://rbi.ims.ca/4391-535.

STMicroelectronics' LIS3L02

STMicro's three-axis product line combines a MEMS-based sensor and interface chip in a single package. The company's three versions of the technology include one that produces an analog output, another that provides an analog voltage and PWM output, and a third that produces a serial digital output. During transport, the devices can withstand accelerations up to 1,500g, making them sufficiently shock resistant for mobile phone applications.
For more information on STMicroelectronics's three-axis sensors, go to http://rbi.ims.ca/4391-536.