Anisotropic magneto-resistive (AMR) sensors are magnetic sensors that detect the direction of the magnetic field vector rather than the strength of the field. An AMR sensor determines the position of a rotating permanent magnet if the field is sufficiently strong. AMR sensors can typically only resolve up to 180°.
TMAG6180-Q1 and TMAG6181-Q1 both implement AMR sensing combined with a 2D Hall-effect latch to expand angle calculations to a full 360° for low-latency angle measurements. TMAG6180-Q1 produces outputs Q0 and Q1 which provides quadrature data for absolute angle measurements and TMAG6181-Q1 includes a turns counter function which tracks relative position even while operating in low power sleep mode. Understanding how to properly calibrate an end system when configuring these devices and possible sources of error is important.
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Unlike Hall-effect, Giant Magneto-Resistive (GMR), and Tunneling Magneto-Resistive elements (TMR), the Anisotropic Magneto-Resistive (AMR) sensing element does not have an output voltage proportional to the magnitude of the applied magnetic field in the direction of sensitivity. Rather, the AMR sensing element exhibits a change in resistance regarding the direction of the applied magnetic field vector.
Figure 1-1 demonstrates that there is no resulting change in impedance with the magnetic field applied parallel to the flow of current through the sensing element. However, if the applied field is orthogonal to the sensing element then the impedance varies up to a maximal saturation point (Figure 1-2).
For example, suppose that the resistive element is exposed to an oscillating magnetic field, then the resulting behavior of the AMR resistivity follows the expression in Equation 1.