acquisitionZONE Products for the week of November 7, 2005
AKM Semiconductor, a leading supplier of mixed-signal ICs for portable and consumer applications, introduced the AK8970N, the industry's first fully integrated 3-axis electronic compass.
Developed primarily for portable GPS applications, including GPS-enabled mobile phones, the AK8970N is ued to orient the map even if the user is stationary. Combining three Hall-effect sensors and a mixed-signal processing chip, the AK8970N measures the magnetic field strength of the earth in all three azimuths to determine orthogonal orientation. It is accompanied by proprietary Dynamic Offset Estimation software, which performs continuous calibration to eliminate errors caused by stray magnetic fields. Accuracy of the compass is ±5°.
The AK8970N enhances the user experience with GPS applications by orienting the map in the direction that the user is heading. If the user is not in constant motion, a conventional GPS system simply orients the map with north at the top. It can also provide information about left and right turns when the device is stationary or in very slow motion. With 2-axis sensors, the user must keep the GPS device parallel to the earth. With the 3-axis AK8970N, the magnetic field measurements are correct even when the user is tilting the device.
The Dynamic Offset Estimation (DOE) software is used to minimize the
effect of stray magnetic fields. When DOE is used, calibration requirements
are substantially reduced for the device manufacturers. The software runs
on ARM processors, requiring just 0.1 MIPS and 10kB of PROM.
analogZONE Says . . .
Most handheld GPS users are unaware that the accuracy of the readings they get depends not just on the number of satellites that can be accessed, but also on the inclination of the instrument. The correct alignment is straightforward in a fixed vehicle installation, poorer in a handheld environment, and almost impossible in a GPS-equipped phone.
This AK8970N is straightforward enough; three Hall-effect sensors in x, y, z alignments with the appropriate mixed-signal processing to go with it The DOE software is a neat additional touch allowing for more accurate readings in the presence of stray magnetic fields, and its own leakage field.
There may be a data sheet on the USA AKM site, but I could not access it as the search facility on the site goes into a loop -- and I tried with three different browsers. However, I was able to extract some information from the home site of Asahi Kasei in Japan.
Measurement time for the part is about 38 ms with a 155 µA operating current from a rail between 2.5 V and 3.6 V. 8-bit conversion is used throughout and there are 32 directions of operation -- thus the ±5° accuracy. A temperature sensor is included and there is an auto power down function where the quiescent falls to 8.5 µA.
This is certainly the fastest acquisition Hall-effect compass that I have ever seen and the accuracy is more than good enough for a phone user. Power is also not a problem at all and the demands on the microprocessor are slight, but I don't know if the price will fly in these applications.
The AK8970N is in production in QFN-24 and is priced
at $5.24 in 25-k piece lots.