A device for measuring an angle at which a magnetic field is aligned in a plane relative to a reference axis has at least two magnetic field sensors, which are aligned with their measurement axes in and/or parallel to the plane and oriented at right angles to each other. The device has a PLL phase control...http://www.google.com.tw/patents/US8125221?utm_source=gb-gplus-share專利 US8125221 - Method and device for measuring an angle at which a magnetic field is aligned in a plane relative to a reference axis
