Reducing stray magnetic field effects using a magnetic field feedback
In one aspect, a magnetic-field sensor includes main coil circuitry configured to generate a first magnetic-field signal at a first frequency; a first channel; a second channel; a subtractor circuit configured to subtract a second channel output signal from a first channel output signal to form a subtraction signal; an adder circuit configured to combine the first channel output signal and the second channel output signal to form a summation signal; processing circuitry configured to receive the summation signal and to provide a magnetic-field sensor output signal indicating a position of the target; feedback circuitry configured to receive the subtraction signal and to provide a first feedback signal to the processing circuitry, and a second feedback signal; and a secondary coil circuitry configured to receive the second feedback signal and to generate, based on the second feedback signal, a second magnetic-field signal to reduce the first magnetic-field signal received.
1. A magnetic-field sensor comprising:
main coil circuitry configured to generate a first magnetic-field signal at a first frequency, wherein a reflected signal is generated from a target caused by the first magnetic-field signal;
a first channel comprising:
a first magnetoresistance circuitry configured to receive the reflected signal and the first magnetic-field signal;
a first analog circuitry configured to receive an output signal from the first magnetoresistance circuitry; and
a first filter configured to receive an output signal from the first analog circuitry and to provide a first channel output signal;
a second channel comprising:
a second magnetoresistance circuitry configured to receive the reflected signal and the first magnetic-field signal;
a second analog circuitry configured to receive an output signal from the second magnetoresistance circuitry; and
a second filter configured to receive an output signal from the second analog circuitry and to provide a second channel output signal;
a subtractor circuit configured to subtract the second channel output signal from the first channel output signal to form a subtraction signal;
an adder circuit configured to combine the first channel output signal and the second channel output signal to form a summation signal;
processing circuitry configured to receive the summation signal and to provide a magnetic-field sensor output signal indicating a position of the target;
feedback circuitry configured to receive the subtraction signal and to provide a first feedback signal to the processing circuitry and a second feedback signal to secondary coil circuitry; and
the secondary coil circuitry configured to receive the second feedback signal and to generate, based on the second feedback signal, a second magnetic-field signal to reduce the first magnetic-field signal received at the first magnetoresistance circuitry.
2. The magnetic-field sensor of claim 1 , wherein the second magnetic field signal reduces the first magnetic-field signal received at the first and the second magnetoresistance circuitries.
3. The magnetic-field sensor of claim 1 , wherein the first and second magnetoresistance circuitries each comprises a bridge comprising magnetoresistance elements.
4. The magnetic-field sensor of claim 3 , wherein the magnetoresistance elements comprise at least one tunneling magnetoresistance element (TMR).
5. The magnetic-field sensor of claim 3 , wherein the magnetoresistance elements comprise at least one giant magnetoresistance element (GMR).
6. The magnetic-field sensor of claim 3 , wherein the main coil circuitry comprises a first coil having inner loops and outer loops,
wherein a number of the inner loops differ from a number of the outer loops by no more than one loop, and
wherein the magnetoresistance elements are disposed between the inner loops and the outer loops.
7. The magnetic-field sensor of claim 6 , wherein the number of the inner loops is equal to the number of the outer loops.
8. The magnetic-field sensor of claim 6 , wherein the second coil circuitry comprises a second coil, and
wherein the magnetoresistance elements are within the second coil.
9. The magnetic-field sensor of claim 8 , wherein a distance between the second coil to the magnetoresistance elements is smaller than a distance between the first coil to the magnetoresistance elements.
10. The magnetic-field sensor of claim 8 , wherein the second coil is wound in a first direction and the first coil is wound in a second direction opposite the first direction.
11. The magnetic-field sensor of claim 6 , wherein the second coil circuitry comprises a second coil, and
wherein a distance between the second coil to the magnetoresistance elements is smaller than a distance between the first coil to the magnetoresistance elements.
12. The magnetic field sensor of claim 3 , wherein the bridge is one of a voltage bridge, a current bridge, a resistance bridge or a conductance bridge.
13. The magnetic-field sensor of claim 1 , wherein the feedback circuitry comprises a mixer configured to convert the subtraction signal from a baseband signal to an alternating current (AC) signal having a frequency equal to negative of the first frequency and to provide the AC signal to the secondary coil circuitry.
14. The magnetic-field sensor of claim 13 , wherein the feedback circuitry further comprises:
an integrator configured to receive the subtraction signal;
a digital-to-analog converter (DAC) configured to receive an output signal from the integrator, to convert the output signal, from the DAC, from a digital signal to an analog signal and to provide the analog signal to the mixer.
15. The magnetic-field sensor of claim 13 , wherein the first and second analog circuitries each comprises a mixer, wherein the mixer converts the output signal from the respective magnetoresistance circuitry into the baseband signal.
16. The magnetic-field sensor of claim 15 , wherein the first and second analog circuitries each further comprises an amplifier that amplifies the baseband signal received from the respective mixer.
17. The magnetic-field sensor of claim 15 , wherein the first and second analog circuitries each further comprises an analog-to-digital (ADC) converter configured to convert an output of the mixer to a digital signal and to provide the digital signal to a respective filter.
18. The magnetic-field sensor of claim 1 , wherein the magnetic-field sensor is fabricated in an integrated circuit.
19. The magnetic-field sensor of claim 1 , wherein the secondary coil circuitry is a first secondary coil circuitry,
further comprising a second secondary coil circuitry configured to receive a third feedback signal from the feedback circuitry and to generate, based on the third feedback signal, a third magnetic field signal to reduce the first magnetic-field signal received at the second magnetoresistance circuitry.
20. The magnetic-field sensor of claim 1 , wherein the feedback circuit comprises:
an integrator configured to receive the subtraction signal;
a first digital-to analog converter (DAC) configured to receive an output of the integrator;
a second DAC configured to receive the output of the integrator;
a first mixer configured to receive the output of the first DAC and to provide the second feedback signal to the first magnetoresistance circuitry; and
a second mixer configured to receive the output of the second DAC and to provide the third feedback signal to the second magnetoresistance circuitry.
21. The magnetic-field sensor of claim 1 , wherein the second magnetic-field signal does not generate a reflected signal from the target.
22. A magnetic-field sensor comprising:
main coil circuitry configured to generate a first magnetic-field signal at a first frequency, wherein a reflected signal is generated from a target caused by the first magnetic-field signal;
a first channel comprising:
a first magnetoresistance circuitry configured to receive the reflected signal and the first magnetic-field signal; and
a first analog circuitry configured to receive an output signal from the first magnetoresistance circuitry and to provide a first channel output signal;
a second channel comprising:
a second magnetoresistance circuitry configured to receive the reflected signal and the first magnetic-field signal; and
a second analog circuitry configured to receive an output signal from the second magnetoresistance circuitry and to provide a second channel output signal;
a subtractor circuit configured to subtract the second channel output signal from the first channel output signal to form a subtraction signal;
an adder circuit configured to combine the first channel output signal and the second channel output signal to form a summation signal;
a first additional analog circuitry configured to receive the subtraction signal and to provide a first digital output signal to processing circuitry and to provide an analog signal to feedback circuitry;
a second additional analog circuitry configured to receive the summation signal and to provide a second digital output signal to the processing circuitry;
the feedback circuitry configured to receive the analog signal and to provide a first feedback signal to the first additional analog circuitry and a second feedback signal to secondary coil circuitry;
the secondary coil circuitry configured to receive the second feedback signal and to generate, based on the second feedback signal, a second magnetic-field signal to reduce the first magnetic-field signal received at the first magnetoresistance circuitry; and
the processing circuitry configured to receive the first and second digital signals and to provide a magnetic-field sensor output signal indicating a position of the target.
23. The magnetic-field sensor of claim 22 , wherein the second magnetic field signal reduces the first magnetic-field signal received at the first and the second magnetoresistance circuitries.
24. The magnetic-field sensor of claim 22 , wherein the first and second magnetoresistance circuitries each comprises a bridge comprising magnetoresistance elements.
25. The magnetic-field sensor of claim 24 , wherein the magnetoresistance elements comprise a tunneling magnetoresistance element (TMR) or one giant magnetoresistance element (GMR).
26. The magnetic-field sensor of claim 24 , wherein the main coil circuitry comprises a first coil having inner loops and outer loops,
wherein a number of the inner loops differ from a number of the outer loops by no more than one loop, and
wherein the magnetoresistance elements are disposed between the inner loops and the outer loops.
27. The magnetic-field sensor of claim 26 , wherein the number of the inner loops is equal to the number of the outer loops.
28. The magnetic-field sensor of claim 27 , wherein the second coil circuitry comprises a second coil, and
wherein the magnetoresistance elements are within the second coil.
29. The magnetic-field sensor of claim 28 , wherein a distance between the second coil to the magnetoresistance elements is smaller than a distance between the first coil to the magnetoresistance elements.
30. The magnetic-field sensor of claim 28 , wherein the second coil is wound in a first direction and the first coil is wound in a second direction opposite the first direction.
31. The magnetic field sensor of claim 24 , wherein the bridge is one of a voltage bridge, a current bridge, a resistance bridge, or a conductance bridge.
32. The magnetic-field sensor of claim 22 , wherein the feedback circuitry comprises:
an integrator configured to receive the subtraction signal;
a mixer configured to convert the subtraction signal, received from the integrator, from a baseband signal to an alternating current (AC) signal having a frequency equal to negative of the first frequency and to provide the AC signal to the secondary coil circuitry.
33. The magnetic-field sensor of claim 32 , wherein the first and second analog circuitries each comprises:
a mixer, wherein the mixer converts the output signal from the respective magnetoresistance circuitry into the baseband signal; and
an amplifier that amplifies the baseband signal received from the respective mixer.
34. The magnetic-field sensor of claim 22 , wherein the first and second additional analog circuitries each comprises an analog-to-digital (ADC) converter configured to convert an output of the mixer to a digital signal and to provide the digital signal to a respective filter.
35. The magnetic-field sensor of claim 22 , wherein the magnetic-field sensor is fabricated in an integrated circuit.
36. The magnetic-field sensor of claim 22 , wherein the secondary coil circuitry is a first secondary coil circuitry,
further comprising a second secondary coil circuitry configured to receive a third feedback signal from the feedback circuitry and to generate, based on the third feedback signal, a third magnetic field signal to reduce the first magnetic-field signal received at the second magnetoresistance circuitry.
37. The magnetic-field sensor of claim 36 , wherein the feedback circuit comprises:
an integrator configured to receive the subtraction signal;
a first mixer configured to receive the output of the integrator and to provide the second feedback signal to the first magnetoresistance circuitry; and
a second mixer configured to receive the output of the integrator and to provide the third feedback signal to the second magnetoresistance circuitry.
38. The magnetic-field sensor of claim 22 , wherein the second magnetic-field signal does not generate a reflected signal from the target.