CAMBRIDGE, UK The BMA220 triaxial digital accelerometer is what manufacturer Bosch Sensortec claims to be the world's smallest at 2x2x0.98mm, a 55 percent reduction in surface area over current 3x3mm LGA housings.
This size reduction is no small feat as shrinking MEMS geometries often means shrinking sensitivity. “The challenge in designing smaller MEMS is to keep them structurally sound while achieving a good signal with low noise” explained Dr Leopold Beer, global marketing director for Bosch Sensortec.
“ There is a lot of know-how in the way you can manufacture these devices, a lot of tricks to make these structures reliable. Our engineers had to design a different kind of structure, the trick is in the details and there are many details” he added.
The BMA220 digital sensor which has already been delivered in large quantities to OEM customers, is a fully fledged, triaxial g-sensor with digital data output, four programmable measuring ranges from ±2 g to ±16 g, and integrated evaluation electronics for recognizing specific motion patterns.
For use in pedometers (step counters), the manufacturer wrote specific evaluation algorithms tailored to the BMA220, a service that substantially shortened development time for the end device.
Other applications include 3D spatial orientation in mobile telephones, PDAs and game controllers, as well as targeted reactions to movements, such as the ability to mute a ring tone by tapping twice on the mobile phone.
The evaluation electronics integrated in the sensor obsoletes the need for intensive signal evaluation by the host application's microcontroller. This greatly reduces energy use in the mobile device, which significantly extends battery life.
The algorithms for motion recognition run internally on an
ASIC, which enables the sensor to autonomously and automatically distinguish between a random movement, a change in its spatial position, a single tap, double taps, and between slow and fast changes in movement.
The motion recognition parameters can be programmed by the customer.
The sensor signals the availability of new data at the interrupt output; at the same time, the sensor also outputs them in conditioned form to the digital interface. This means that end product developers no longer have to
grapple with complex raw 3 axis acceleration data from the internal MEMS readings.
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