Integrated sensitivity adjustment for 3D hall sensors

A three-dimensional Hall sensor with integrated coils for sensitivity control and volume testing is described in this article. A special way of operation allows for adjusting the sensitivities for all three magnetic flux components of the sensor, even during measurements. By exposing all orthogonal sensor directions to a magnetic field at the same time, the matching of the different sensitivities is guaranteed, even if the absolute value of the excitation current is unknown. This is of prime importance for further signal processing. In many applications such as rotary encoders, for example, the angle is calculated from two orthogonal flux components. A sensitivity mismatch between these orthogonal sensors of only 1 per cent leads, in worst instance, to an absolute error of 0.3 degrees. Measurements at our Institute show that even with sensitivities adjusted at room temperature the matching between the horizontal and vertical Hall sensors can vary by about ten per cent in a temperature range from -40 degrees C to 140 degrees C. This leads to an absolute error of 2.3 degrees. By adjusting the direction-dependent sensitivities versus temperature by means of the integrated coils, we reach an absolute error better than 0.2 degree.