In many applications including space missions, Anisotropic Magnetoresistors (AMR) based magnetometers raised their popularity [1,2] as they are solid-state off-the-shelf components with good radiation immunity [3]. One of the issues they suffer is low sensitivity and thus high noise induced by their bridge thermal noise as well as by preamplifier stage noise [4]. To overcome this problem, higher supply voltage of an AMR bridge can be used to raise the sensitivity. This seems to be straightforward but power dissipated on the sensor raises quadratically with bridge voltage and thus it can’t be operated in "classical" continuous mode (due to overheating and excessive power consumption).<br/>In our research we propose novel method of powering bridge by pulses allowing to obtain better sensitivity and less noise with AMR sensors. During these short pulses (100 us width and 4.5 ms period) we also perform flipping pulses (both S/R) while measuring bridge response with an analog-to-digital converter. Acquired data are then signal-processed on the fly by a microcontroller. In traditional method, 10 V in continuous mode with HMC1021 AMR sensor will dissipate 91 mW of power, while cycling power with a duty cycle of 1:45 means only 2 mW (considering zero overhead power). In mostly used triaxial version it is 273 mW vs 6 mW preserving other main parameters of the magnetometer unchanged.<br/>To verify this idea we have developed single axis magnetometer (Fig. 1) with adjustable both bridge voltage as well as flipping current, with possibility of precise timing of all events. In the first trial/test, we have tried to obtain similar noise with pulsed 10 V bridge as we were able to get in our previous research with continuous supply of 10V [4], (see Fig 2.) After achieving this milestone (solving a lot of technical troubles) we tried 20 V bridge supply to verify expected noise reduction (as sensitivity doubles), but for now without result – at this voltage, AMR's electrical offset saturates the preamplifier. In the near future we aim to tackle this issue and to test the noise drift with temperature in different flipping current configurations.

![](https://assets.underline.io/uploads/markdown_image/1/image/f21d8768f1f6f2a671e16af4a0ec4b66.jpg)

Fig.1 - Photo of the experimental prototype

![](https://assets.underline.io/uploads/markdown_image/1/image/56f845d2e47285017dd6de7e45a96175.jpg)

Fig.2 - PSD of noise with pulsed 10 V bridge voltage

Low-Power AMR Magnetometer Operated in Discontinuous Mode

**Session chair:** Sho Muroga, Akita University



IPB - Sensors: Materials, Devices and Applications II

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Low-Power AMR Magnetometer Operated in Discontinuous Mode

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