Magnetic angular encoder using an automatic offset compensation technique

Quality and resolution of integrated microsystems using Hall sensors dedicated to an angular encoder are strongly dependent on the accuracy of relative position of Hall sensors and on the offset of electronic frontend circuitry. In this paper, we describe a CMOS microsystem built on two integrated circuits. This contactless encoder microsystem gives three sine and square signals with a phase shift of 120/spl deg/ and provides an angular error less than 4 degrees without external trimming or feedback. The Hall sensor assembly with the engine consists in fixing a small permanent magnet on the rear axis of the motor. Then the sensor is positioned in front of this magnet.