Ambient field rejection (AFR) is crucial to ensure measurements are accurate by rejecting interference from external magnetic fields close to the device. Having a device that has good AFR ensures accurate measurements and simplifies main design challenges. To test the magnetic rejection ratio a Helmholtz coil and cryotronics probe were used. Helmholtz coils generate a uniform magnetic field by having two parallel coils with an equal current flowing through both coils in the same direction. A current was given to the Helmholtz coils to establish a desired uniform field; the probe was used to measure the magnetic field in the Z-orientation, and the devices compared were positioned in close proximity to the probe. $V_{out}$ was then measured for each device and recorded as shown on Figure 2-11. Testing the open-loop current transducer (Comp4) had some limitations as the component requires external cables to connect to the PCB which might interfere with the results. Figure 9 shows that TI TMCS1143 has the best AFR as the $V_{out}$ is not affected as much as the other components, especially the open-loop transducer (Comp2).

Figure 2-11 Vout Across Magnetic Fields