A Compass in Every Smartphone

Cheaper, better electronic compasses bring augmented reality and other features to your handset

3 min read

An old axiom says that in order to know where you're going, you first have to know where you are. To that, add that you should know which way you're facing. Makers of wireless handsets, having already installed GPS receivers, are poised to flood the market with phones containing tiny electronic compasses that allow the gadget to sense exactly what direction it's facing.

According to electronics industry analysis firm iSuppli Corp., in El Segundo, Calif., we can expect to see an increasing number of cellphones containing electronic compasses. Analysts predict the market for magnetic compass sensors will grow from the 8.7 million manufactured in 2008 to more than 540 million in 2013.

Underlying the jump is a combination of consumer demand for the whiz-bang feature of the moment and a steep drop in price fueled by manufacturing process improvements.

"Navigation is emerging as a must-have feature in smartphones," says Richard Dixon, a senior analyst at iSuppli. Consumers are already looking to their phones for turn-by-turn directions. With the addition of compasses, the beginnings of location-based augmented reality are also emerging, wherein a street map or even the phone's camera image could be overlaid with highly detailed information about what's in front of you.

The component that handset makers are exploiting to make these feats possible is the three-axis magnetometer. The sensor system's job is to home in on Earth's magnetic field and use that as a reference for determining the handset's orientation along the x-, y-, and z-axes. Three axes are important "because that third sensor allows the handheld device to correct for the orientation of Earth's magnetic field at a given location, as well as the relative position of the device," says Mark Laich, vice president of worldwide sales at Memsic, a maker of electronic compasses based in Andover, Mass. "Otherwise users would have to hold the phone precisely parallel to the ground or in some other position that may not correspond to how they normally use it."

Like the rest of the electronics industry, electronic compass makers have been making their products smaller, cheaper, and more energy efficient. And they reached a watershed moment in 2009, when the price of three-axis magnetometers dipped below US $1 per device. "Six months ago, magnetic sensors were selling at $1.50 each, but the price is coming down rapidly," says Laich. "They're now at the sub-$0.50 point and look to get even cheaper as production volumes increase."

Memsic and other new entrants into the magnetometer market for mobile devices mostly sell sensors that take advantage of amorphous magnetic alloys whose resistances change when acted upon by the planet's magnetic field. Memsic, for example, uses three chips, each containing a thin film of the alloy. The chips, which are set at right angles to each other, are incorporated into a Wheatstone bridge circuit so that when you move the phone, the change in resistance resulting from the perceived change in the strength or direction of the magnetic field is output as a change in voltage.

Aichi Steel, Honeywell, Memsic, and Sensitec have all developed magnetoresistive sensors in an effort to take a bite out of AKM Semiconductor's 95 percent share of the mobile phone compass market. AKM, in San Jose, Calif., uses a technology that relies on the Hall effect, in which electrons racing through a conductor in the presence of a magnetic field are forced to one edge of the conductor, creating a voltage difference whose orientation is perpendicular to the magnetic field.

AKM's competitors claim their devices are power misers compared with Hall effect sensors, a really big deal in palm-size devices that barely have room for the batteries they stow. The companies also say that their sensors are more sensitive and have quicker response times.

Naturally, AKM disagrees with its competitors' assessment. "We make magnetoresistive components but don't think they're a good solution for cellphones," says Richard Kulavik, application engineering manager at AKM. "One good reason is that the steady-state current of one of our Hall effect sensors may be higher, but magnetoresistive sensors—in an object like a cellphone that is filled with metal and is constantly giving off pulses of current—take on their own magnetic signatures and have to be continually degaussed. And degaussing takes a huge amount of current."

Nevertheless, the competition is making important inroads. Geneva-based STMicroelectronics, a leading accelerometer maker, chose Honeywell's magnetoresistive technology over Hall sensors to make the first single-package combination accelerometer-magnetometer on the market. One reason ST cited was that Honeywell's device provides the same sensitivity in all three axes without the need for the magnetic flux concentrators that Hall effect sensors require. And as for the degaussing issue, ST found it required only a matter of microamperes.

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