One-chip two-axis fluxgate compass

One-chip two-axis fluxgate compassSteve Bush  
 
A fully integrated one-chip two-axis fluxgate compass in almost standard CMOS was the subject of a paper presented jointly by a Swiss laboratory and a Japanese university.
The chip uses the fluxgate principle which is well know in electronic compasses but, according to the presenters, has only been integrated using special semiconductor processes.
The fluxgate presented was based on a standard CMOSprocess with the addition of single-mask ferromagnetic layer applied at room temperature to act as a core for the sensing coils.
The resulting compass is sensitive in the plane of the chip and is linear within ?1.5 ?T up to ?50?T (the Earths magnetic field strength) and is only slightly less linear up to ?100?T.
Two fluxgates remove ambiguity and give full 360 degree sensitivity and mechanical alignment is only limited by the accuracy of the lithograph process.
Compared with magneto-resistive sensing, the other electronic compass technology that can be integrated, the micro-fluxgates are said to have a “much larger” signal to noise ratio.
Alongside the sensors are all the excitation and sensing electronics including the ? modulators that seem an inevitable part of all analogue circuits at this year’s ISSCC. Chip output is digital.
The compass was fabricated on 0.8?m CMOS resulting in a 3.4 x 5.6mm chip. Power consumption is325mW at 5V.
The organisations involved were the Physical Electronics Laboratory, ETH Zurich and Department of Information and Computer Science, Toyohashi University of Technology.


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