Mouser - White Papers

Mouser Electronics White Paper Figures 7–10 show the progression of the electrical transitions as the external magnetic field continues to rotate. In Figure 7, a domain wall appears at position 01, and the magnetization of the track from ground to 01 flips, raising its resistance. The position 01 electrical signal (green trace) transitions at that point in response to the resistance change. Figure 7: Appearance of a domain wall at position 01 with corresponding electrical transition. (Source: Analog Devices) In response to an additional 90° rotation of the external magnetic field, a domain wall reaches the VDD position on the inner part of the spiral, flipping the magnetization of the 01-to- VDD segment (Figure 8), but no electrical transition occurs. Figure 8: Domain wall at the VDD inner trace. (Source: Analog Devices) Another 90° rotation (Figure 9) results in a domain wall at position 02, causing the magnetization of the VDD-to-02 segment to flip and leading to a transition of the 02 electrical signal (blue trace). An additional 180° rotation (Figure 10) causes a domain wall to appear at position 03, resulting in the 03 electrical signal (purple trace) transitioning. The process continues until the 04 signal (red trace) transitions. If the magnetic field rotation reverses, the process reverses, and the sensor counts down, with the domain walls moving back through the spiral and reentering the DWG. Figure 9: Domain wall at position 02 with corresponding electrical transition. (Source: Analog Devices) Figure 10: Domain wall at position 03 with corresponding electrical transition. (Source: Analog Devices) From Theory to Reality The Analog Devices ADMT4000 sensor uses both AMR and GMR principles, combining a GMR multiturn sensor, AMR angle sensor, and signal conditioning in a single integrated circuit (IC). The AMR sensor measures fine-angle position within a single turn, while the GMR sensor uses domain walls within a spiral nanowire to retain multiturn counts (up to 46 turns), even when power is removed. The GMR sensor reads these positions via resistance changes. Figure 11 shows a typical application assembly, with the ADMT4000 positioned opposite a dipole magnet mounted on a rotating shaft. With GMR technology and AMR capability, the ADMT4000 spans more than 16,000°. For angle measurement, the device provides 12-bit resolution over 360° with a typical angle accuracy of ±0.25°. Data rates equal 0.5KSPS for turn counts and 100KSPS for angle measurements.

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