Magnetic sensor with low electric offset

• US 8,664,941 B2
• Filed: 08/24/2011
• Issued: 03/04/2014
• Est. Priority Date: 08/24/2011
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Sebastiano, Fabio, van Veldhoven, Robert Hendrikus Margaretha
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US13/217,155
• Publication Number:
  US 20130049748A1
• Time in Patent Office: 923 Days
• Field of Search: 324/207.12, 324/207.2, 324/207.21, 324/174, 324/252, 324/225
• US Class Current: 324/207.12
• CPC Class Codes: G01R 33/0017 Means for compensating offset magnetic fields or the magnetic flux to be measured; Means for generating calibration magnetic fields
• CPC Class Codes: G01R 33/0029 Treating the measured signals, e.g. removing offset or noise
• CPC Class Codes: G01R 33/09 Magnetoresistive devices

Abstract

A magnetic sensing system, including: a magnetic component proximate a movable mechanical component; and a magnetic sensor configured to determine a movement of the mechanical component based on a magnetic field produced by the magnetic component. The magnetic sensor includes: a low-offset magnetic sensing element; a high-sensitivity magnetic sensing element; and an offset compensation circuit configured to: determine a zero-crossing of a sensing field from an output of the low-offset magnetic sensing element; sample an offset value of the high-sensitivity magnetic sensing element at the zero-crossing; and subtract the offset value from an output of the high-sensitivity magnetic sensing element.

Claims

1. A low-offset, high-sensitivity magnetic sensor device, comprising:

a low-offset magnetic sensor;

a high-sensitivity magnetic sensor; and

an offset compensation circuit configured to;

determining a zero-crossing of a sensing field from an output of the low-offset magnetic sensor;

sample an offset value of the high-sensitivity magnetic sensor at the zero-crossing; and

subtract the offset value from an output of the high-sensitivity magnetic sensor.

2. The magnetic sensor device of claim 1, wherein the offset compensation circuit is further configured to re-sample the offset value in response to detecting a variation in the offset value.

3. The magnetic sensor device of claim 2, wherein the variation in the offset value exceeds a predetermined threshold.

4. The magnetic sensor device of claim 3, further comprising a memory device configured to store a previous offset value, wherein the offset compensation circuit is further configured to:

compare a current offset value to the previous offset value to obtain an offset difference value; and

store the current offset value in the memory device in response to the offset difference value being larger than the predetermined threshold.

5. The magnetic sensor device of claim 1, wherein the offset compensation circuit comprises a comparator to obtain the zero-crossing of the sensing field from the output of the low-offset magnetic sensor.

6. The magnetic sensor device of claim 1, wherein the low-offset magnetic sensor is a modulated anisotropic magnetic resistance sensor.

7. A method, comprising:

detecting a sensing field using a low-offset magnetic sensor and a high-sensitivity magnetic sensor;

determining a zero-crossing of the sensing field from an output of the low-offset magnetic sensor;

sampling an offset value of the high-sensitivity magnetic sensor at the zero-crossing; and

subtracting the offset value from an output of the high-sensitivity magnetic sensor.

8. The method of claim 7, further comprising re-sampling the offset value in response to detecting a variation in the offset value.

9. The method of claim 8, wherein the variation in the offset value exceeds a predetermined threshold.

10. The method of claim 9, further comprising:

comparing a current offset value to a previous offset value to obtain an offset difference value; and

storing the current offset value in a memory device in response to the offset difference value being larger than the predetermined threshold.

11. The method of claim 7, wherein subtracting the offset value further comprises:

filtering the output of the high-sensitivity magnetic sensor using a discrete-time low-pass filter,

wherein the low-pass filter provides an offset estimation based on the offset value sampled from the output of the high-sensitivity magnetic sensor each time the offset compensation circuit determines a zero-crossing.

12. The method of claim 7, wherein determining the zero-crossing further comprises detecting a switching of a comparator at the output of the low-offset magnetic sensor, wherein the switching corresponds to the zero-crossing.

13. The method of claim 7, wherein the low-offset magnetic sensor is a modulated anisotropic magnetic resistance (AMR) sensor.

14. A magnetic sensing system, comprising:

a magnetic component proximate a movable mechanical component; and

a magnetic sensor configured to determine a movement of the mechanical component based on a magnetic field produced by the magnetic component, the magnetic sensor comprising;

a low-offset magnetic sensing element;

a high-sensitivity magnetic sensing element; and

an offset compensation circuit configured to;

determine a zero-crossing of a sensing field from an output of the low-offset magnetic sensing element;

sample an offset value of the high-sensitivity magnetic sensing element at the zero-crossing; and

subtract the offset value from an output of the high-sensitivity magnetic sensing element.

15. The magnetic sensing system of claim 14, wherein the offset compensation circuit is further configured to re-sample the offset value in response to detecting a variation in the offset value.

16. The magnetic sensing system of claim 15, further comprising a memory device configured to store a previous offset value, wherein the offset compensation circuit is further configured to:

compare a current offset value to the previous offset value to obtain an offset difference value; and

store the current offset value in the memory device in response to the offset difference value being larger than a predetermined threshold.

17. The magnetic sensing system of claim 14, wherein the offset compensation circuit comprises a discrete-time low-pass filter at the output of the high-sensitivity magnetic sensor, wherein the low-pass filter is configured to provide an offset estimation based on the offset value sampled from the output of the high-sensitivity magnetic sensor each time the offset compensation circuit determines a zero-crossing.

18. The magnetic sensing system of claim 14, wherein the offset compensation circuit comprises a comparator to obtain the zero-crossing of the sensing field from the output of the low-offset magnetic sensing element.

19. The magnetic sensing system of claim 14, wherein the low-offset magnetic sensing element is a modulated anisotropic magnetic resistance sensor.