The functionality of a unipolar switch is illustrated in Figure 3. Now, let’s examine the transfer function of the different types of digital (on/off) Hall devices. However, there are more sophisticated sensor ICs that employ more than one Hall element to support three axes of sensitivity (a three-dimensional sensor). If we present the magnet poles to the back side of the sensor package (not the branded face of the package), the above convention won’t be valid anymore!Ī final note to finish this discussion: Many Hall devices are one-dimensional and sense the B-field along only one axis of sensitivity (such as those shown in Figure 1). Similarly, a north pole will create a negative magnetic field. Considering the sensitivity axes shown in Figure 1, you can verify that presenting the south pole of the magnet to the branded face of the sensor will create a magnetic field in the direction of the sensitivity axis (positive field). The branded face is the front surface of the sensor where you can find the device part number, etc. This is based on the assumption that the branded face of the sensor is toward the magnet. They consider the magnetic field produced by a magnet south pole as positive and that of the north pole as negative. There is also a convention regarding the B-field polarity that is commonly used by Hall sensor manufacturers. Since the magnetic field lines of a magnet go from the north pole to the south pole, the B-field sensed by the device is negative. In the above example, we assume that the device sensitivity axis is in the z-axis direction. Figure 2 shows an example where the magnetic flux density has negative polarity at the sensor location (A). If the field produces a component in the opposite direction of the sensitivity axis, it is assumed to be negative. If the magnetic field applied to the device produces a component in the direction of the sensitivity axis, the B-field is assumed to be positive. Figure 1 shows the sensitivity axis of two common Hall device packages.įigure 1. It senses only the component of the magnetic flux density that is along its sensitivity axis. How Do We Define the Polarity of the B-field?Ī Hall effect device is directional. But, before that, I would like to clarify an important concept that will be commonly used in our discussion: the polarity of the magnetic flux density.
We’ll examine the transfer function of each type in detail.
There are four different categories of digital (on/off) Hall sensors: unipolar switches, bipolar switches, omnipolar switches, and latches. They compare the magnetic flux density, sometimes referred to as the B-field, with some pre-specified thresholds and output the comparison result as a 1-bit digital value. Hall effect switches and latches are magnetic field comparators.
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