Magnetic field sensor having calibration circuitry and techniques

• US 9,841,485 B2
• Filed: 11/14/2014
• Issued: 12/12/2017
• Est. Priority Date: 11/14/2014
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Petrie, Craig S., Cadugan, Bryan
• Primary Examiner(s): Nguyen, Tung X
• Assistant Examiner(s): Alejnikov, Jr., Robert P
• Application Number:
  US14/541,735
• Publication Number:
  US 20160139230A1
• Time in Patent Office: 1,124 Days
• Field of Search: 3242072, 324225
• CPC Class Codes: G01D 2218/10 Testing of sensors or measuring arrangements
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/2448 Correction of gain, threshold, offset or phase control
• CPC Class Codes: G01D 5/2449 using hard-stored calibration data
• CPC Class Codes: G01R 31/2884 using dedicated test connectors, test elements or test circuits on the IC under test G01R31/2855 takes precedence
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration
• CPC Class Codes: G01R 33/072 Constructional adaptation of the sensor to specific applications
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

A magnetic field sensor includes at least one magnetic field sensing element configured to generate a measured magnetic field signal responsive to an external magnetic field and to generate a reference magnetic field signal responsive to a reference magnetic field and a calibration circuit configured to divide the measured magnetic field signal by the reference magnetic field signal to generate a calibrated magnetic field signal. The calibrated signal has reduced susceptibility to stress influences.

Claims

1. A magnetic field sensor, comprising:

at least one magnetic field sensing element configured to generate a measured magnetic field signal responsive to and representing an external magnetic field and to generate a reference magnetic field signal responsive to and representing a reference magnetic field;

at least one analog-to-digital converter responsive to the measured magnetic field signal to generate a digital measured magnetic field signal and responsive to the reference magnetic field signal to generate a digital reference magnetic field signal; and

a calibration circuit responsive to the digital measured magnetic field signal and to the digital reference magnetic field signal to combine the digital measured magnetic field signal and the digital reference magnetic field signal in order to generate a calibrated magnetic field signal that represents the external magnetic field;

wherein the calibration circuit comprises a divider configured to divide the digital measured magnetic field signal by the digital reference magnetic field signal to generate the calibrated magnetic field signal.

2. The magnetic field sensor of claim 1 wherein the divider comprises a multiplier configured to generate the calibrated magnetic field signal based on a Taylor series expansion.

3. The magnetic field sensor of claim 1 further comprising a reference coil proximate to the at least one magnetic field sensing element, wherein the reference coil is configured to carry a reference current to generate the reference magnetic field.

4. The magnetic field sensor of claim 1 wherein the at least one magnetic field sensing element is configurable to generate the measured magnetic field signal during a first time period and to generate the reference magnetic field signal during a second, non-overlapping time period.

5. The magnetic field sensor of claim 1 wherein the at least one magnetic field sensing element comprises a Hall effect element.

6. The magnetic field sensor of claim 1 wherein the at least one magnetic field sensing element comprises a magnetoresistance element.

7. The magnetic field sensor of claim 1 further comprising a built in built-in self-test circuit configured to detect an error in the magnetic field sensor.

8. The magnetic field sensor of claim 1 further comprising an output signal generator responsive to the calibrated magnetic field signal to generate an output signal of the magnetic field sensor indicative of the external magnetic field.

9. The magnetic field sensor of claim 1 wherein the calibration circuit comprises a manufacturing trim circuit configured to adjust at least one of a gain or an offset of the digital measured magnetic field signal based on a sensed temperature.

10. The magnetic field sensor of claim 1 wherein the calibration circuit comprises a calibration trim circuit configured to adjust a gain of the digital reference magnetic field signal based on a predetermined scale factor.

11. The magnetic field sensor of claim 10 wherein the calibration trim circuit is further configured to adjust at least one of the gain or an offset of the digital reference magnetic field signal based on a sensed temperature.

12. The magnetic field sensor of claim 1 wherein the at least two magnetic field sensing elements are selected from Hall effect elements, magnetoresistance elements, or both.

13. The magnetic field sensor of claim 1 wherein the analog-to-digital converter (ADC) is a dual-path ADC having a first path to process the measured magnetic field signal and a second path to process the reference magnetic field signal.

14. A magnetic field sensor, comprising:

at least one magnetic field sensing element configured to generate a measured magnetic field signal responsive to an external magnetic field and to generate a reference magnetic field signal responsive to a reference magnetic field; and

a calibration circuit configured to combine the measured magnetic field signal and the reference magnetic signal by dividing the measured magnetic field signal by the reference magnetic field signal to generate a combined, calibrated magnetic field signal that represents the external magnetic field.

15. The magnetic field sensor of claim 14 further comprising a reference coil proximate to the at least one magnetic field sensing element, wherein the reference coil is configured to carry a reference current to generate the reference magnetic field.

16. The magnetic field sensor of claim 14 further comprising at least one analog-to-digital converter responsive to the measured magnetic field signal to generate a digital measured magnetic field signal and to the reference magnetic field signal to generate a digital reference magnetic field signal, wherein the calibration circuit is configured to divide the digital measured magnetic field signal by the digital reference magnetic field signal to generate the calibrated magnetic field signal.

17. The magnetic field sensor of claim 16 further comprising a manufacturing trim circuit configured to adjust at least one of a gain or an offset of the digital measured magnetic field signal based on a sensed temperature.

18. The magnetic field sensor of claim 16 further comprising a calibration trim circuit configured to adjust a gain of the digital reference magnetic field signal based on a predetermined scale factor.

19. The magnetic field sensor of claim 18 wherein the calibration trim circuit is further configured to adjust at least one of the gain or an offset of the digital reference magnetic field signal based on a sensed temperature.

20. The magnetic field sensor of claim 14 wherein the at least one magnetic field sensing element is configured to generate the measured magnetic field signal during a first time period and is configured to generate the reference magnetic field signal during a second, non-overlapping time period.

21. The magnetic field sensor of claim 14 wherein the at least one magnetic field sensing element comprises a Hall effect element.

22. The magnetic field sensor of claim 14 wherein the at least one magnetic field sensing element comprises a magnetoresistance element.

23. The magnetic field sensor of claim 14 further comprising further comprising a built in self-test circuit configured to detect an error in the magnetic field sensor.

24. The magnetic field sensor of claim 14 further comprising an output signal generator responsive to the calibrated magnetic field signal to generate an output signal of the magnetic field sensor indicative of the external magnetic field.

25. The magnetic field sensor of claim 14 wherein the calibration circuit comprises a multiplier configured to generate the calibrated magnetic field signal based on a Taylor series expansion.

26. A method for calibrating a sensed magnetic field signal, comprising:

generating a measured magnetic field signal having an amplitude dependent on an external magnetic field;

generating a reference magnetic field signal having an amplitude dependent on a reference magnetic field;

converting the measured magnetic field signal into a digital measured magnetic field signal and converting the reference magnetic field signal into a digital reference magnetic field signal; and

combining the digital measured magnetic field signal and the digital reference magnetic field signal by dividing the digital measured magnetic field signal by the digital reference magnetic field signal to generate a combined, calibrated signal that represents the external magnetic field.

27. The method of claim 26 wherein dividing comprises multiplying a plurality of terms according to a Taylor series expansion.

28. The method of claim 26 further comprising adjusting at least one of a gain or an offset of the digital measured magnetic field signal based on a sensed temperature.

29. The method of claim 26 further comprising adjusting a gain of the digital reference magnetic field signal based on a predetermined scale factor.

30. The method of claim 29 wherein adjusting further comprises adjusting at least one of the gain or an offset of the digital reference magnetic field signal based on a sensed temperature.

31. The method of claim 26 wherein at least one of generating the measured magnetic field signal or generating the reference magnetic field signal comprises using at least one Hall effect element.

32. The method of claim 26 wherein at least one of generating the measured magnetic field signal or generating the reference magnetic field signal comprises using at least one magnetoresistance element.

33. The method of claim 26 further comprising detecting an error with a built in built-in self-test circuit.

34. A method for calibrating a sensed magnetic field signal, comprising:

generating, by one or more coils, a measured magnetic field signal having an amplitude dependent on an external magnetic field;

generating, by the one or more coils, a reference magnetic field signal having an amplitude dependent on a reference magnetic field; and

dividing, by a calibration circuit, the measured magnetic field signal by the reference magnetic field signal to generate a combined, calibrated signal that represents the external magnetic field.

35. The method of claim 34 further comprising converting the measured magnetic field signal into a digital measured magnetic field signal and converting the reference magnetic field signal into digital reference magnetic field signal and wherein dividing comprises dividing the digital measured magnetic field signal by the digital reference magnetic field signal to generate the calibrated signal.

36. The method of claim 34 further comprising adjusting at least one of a gain or an offset of the digital measured magnetic field signal based on a sensed temperature.

37. The method of claim 34 further comprising adjusting a gain of the digital reference magnetic field signal based on a predetermined scale factor.

38. The method of claim 37 wherein adjusting further comprises adjusting at least one of the gain or an offset of the digital reference magnetic field signal based on a sensed temperature.

39. The method of claim 34 wherein dividing comprises multiplying a plurality of terms according to a Taylor series expansion.

40. The method of claim 34 wherein at least one of generating the measured magnetic field signal or generating the reference magnetic field signal comprises using at least one Hall effect element.

41. The method of claim 34 wherein at least one of generating the measured magnetic field signal or generating the reference magnetic field signal comprises using at least one magnetoresistance element.

42. The method of claim 34 further comprising detecting an error with a built in built-in self-test circuit.