PORTLAND, Ore. — Electronic compasses can now be built with a magnetometer that Freescale Semiconductor claims is smaller and less power-hungry than competing devices. The new Xtrinsic MAG3110 is a three-axis device that can determine headings for navigation, dead-reckoning indoors and a range of emerging location-based services (LBSes) for smartphones and other mobile devices.
The Freescale magnetometer is four times smaller than the most commonly used magnetometer today, "plus it has the lowest power consumption available—25 microamps, compared with 100 microamps or more" for rival devices, said Stephane Gervais-Ducouret, Freescale's global marketing director for sensors.
A global positioning system can inform a smartphone of its location, but only a compass built from a three-axis magnetometer can let the device determine heading (direction in which it is facing) at that location. Using a magnetometer together with GPS services allows smartphones, touchscreen tablets and other mobile devices to determine heading even when a GPS signal—and, for that matter cell phone service—is unavailable. The Xtrinsic MAG3110 is compatible with currently available LBS apps such as Foursquare, Facebook Places and Google's Goggles. Juniper Research claims that these and other LBSes logged collective revenues of $3 billion in 2009 and predicts a rise to $12.7 billion by 2014.
Today, 85 percent of the compasses in smartphones, including the iPhone, use Hall-effect magnetometers made by Asahi Kasei Microdevices Corp. (Tokyo), according to iSuppli. The Freescale magnetometer uses three small magnetic tunnel junctions (MTJs) to sense changes in the magnetic field. "We do not call it a MEMS device, because there are no moving parts," said Gervais-Ducouret. That helped Freescale achieve device dimensions of 2 millimeters square, compared with 4 for the Asahi part.
A separate ASIC, wirebonded inside the package to the magnetometer die, provides the smarts to compensate for nearby magnetic fields from other components on the circuit board. Freescale's Sensor Toolbox software development environment includes algorithms for compensating for both hard-iron and soft-iron interference. The ASIC also converts the analog output from the magnetometer die into a digital signal using an I2C interface.
It would seem that the "killer application" would be to combine the magnetometer with an inertial guidance system. The magnetometer could orient the device when the earth's magnetic field is reliably sensed. Motion sensors (accelerometers) and rotation sensors (gyroscopes) would maintain orientation information when the electronic device was moving around an environment which blocked or distorted the magnetic field. Animals have been utilizing redundant orientation systems for millenia.
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