World’s First 3-axis Electronic Compass for Cellphones

The Asahi Kasei 3-axis electronic compass is the first ever adopted for cellphones and the first to employ a 3-axis geomagnetic sensor – which enables effective correction for cellphone tilting and thus the reliable determination of geomagnetic direction without the need to keep the cellphone horizontal.
It is the result of a three-part collaboration between Asahi Kasei Electronics, which holds 70% of the world market in Hall sensors for consumer applications, Asahi Kasei Microsystems, a world leader in signal processing ICs for digital audio equipment and cellphones, and the Devices and Sensors Laboratory of Asahi Kasei EMD, the creator of its direction-finding algorithms.

The Hall Sensor at the Heart of the Geomagnetic Sensor

The Hall sensor has become a ubiquitous and indispensable part of everyday life – in motor controllers for DVD decks, fans, and other equipment, in hatch switches for cellphones, game sets, and other handhelds, and in many other applications.
It is the small size of the Hall sensor, together with its inherent performance characteristics, that makes possible a 3-axis geomagnetic sensor compact enough to fit comfortably inside a cellphone. Even with three Hall sensors – one for each of the three x-axis, y-axis, and z-axis directions – the result is an electronic compass only 1.0 mm tall – the world’s smallest.
With three axes, in turn, it is possible to detect and correct for tilting of the cellphone body, thus eliminating the need to hold the handset level during direction finding.

Optimum Sensitivity, Linear Response, and Dynamic Range

The Hall sensor provides the optimum sensitivity, linearity, and dynamic range for cellphone and other handheld geomagnetic-sensor applications.
In some environments, other types of magnetic sensors can provide higher sensitivity for more precise measurement of the earth’s relatively weak geomagnetic field. Cellphones and other handsets, however, are constantly subjected to both internal and external sources of extraneous magnetic fields and distortions which would easily saturate high-sensitivity sensors.
In contrast, the Hall sensor provides the optimum level of sensitivity – together with a highly linear response and dynamic range – to enable effective measurement of the geomagnetic field and compensation for the extraneous fields and distortions, through advanced IC circuit technology for clean, efficient amplification of the Hall sensor signal.
This is the basic development concept of the Asahi Kasei electronic compass.

The Auto-adjust DOE Algorithm

The DOE (Dynamic Offset Estimation) algorithm* provides automatic adjustment of the compass for extraneous magnetic field changes, and thus eliminates the need for repeated manual adjustment.
In cellphones and other handhelds, the extraneous magnetic fields are strong and subject to frequent change and distortion. The levels of cellphone component magnetization may change in the strong magnetic fields often encountered around trains, stereo speakers, and other electrical equipment. The cellphone’s own speaker magnets will vary in strength under changing temperatures. The interior magnetic field is also significantly affected by the insertion of memory cards and other ancillaries.

Without the DOE algorithm, frequent and troublesome manual adjustment is essential. With it, the adjustment is automatic, efficient, and highly effective for the maintenance of accurate and reliable direction finding, whether walking along the street, getting off a bus, leaving a subway station, or passing through other environments.
This auto-adjust operation is made possible by the combination of the 3-axis sensor configuration and the DOE algorithm.

*Patents pending in Japan and other countries.