A new CMOS Hall angular position sensor

The new angular position sensor consists of a combination of a permanent ma gnet attached to a shaft and of a two-axis magnetic sensor. The permanent m agnet produces a magnetic field parallel with the magnetic sensor plane. As the shaft rotates, the magnetic field also rotates. The magnetic sensor is an integrated combination of a CMOS Hall integrated circuit and a thin fer romagnetic disk. The CMOS part of the system contains two or more conventio nal Hall devices positioned under the periphery of the disk. The ferromagne tic disk converts locally a magnetic field parallel with the chip surface i nto a field perpendicular to the chip surface. Therefore, a conventional Ha ll element can detect an external magnetic field parallel with the chip sur face. As the direction of the external magnetic field rotates in the chip p lane, the output voltage of the Hall element varies as the cosine of the ro tation angle. By placing the Hall elements at the appropriate places under the disk periphery, we may obtain the cosine signals shifted by 90 degrees, 120 degrees, or by any other angle.