Methods and apparatus for generating a threshold signal in a magnetic field sensor

Patent metadata

Field	Value
Publication number	US-9970996-B2
Application number	US-201514600826-A
Country	US
Kind code	B2
Filing date	Jan 20, 2015
Priority date	Jan 20, 2015
Publication date	May 15, 2018
Grant date	May 15, 2018

Abstract

A magnetic field sensor for detecting motion of an object includes threshold generation circuitry and processing. Magnetic field sensing elements are configured to generate a magnetic field signal in response to a magnetic field associated with the object. A motion detector responsive to the magnetic field signal and to a threshold signal is configured to generate a detector output signal having edges occurring in response to a comparison of the magnetic field signal and the threshold signal. A speed detector responsive to the detector output signal generates a speed signal indicative of a speed of motion of the object. A threshold generator responsive to the speed signal generates the threshold signal having a level that varies in response to the speed signal.

First claim

What is claimed is:

1. A magnetic field sensor for detecting motion of an object, comprising:
one or more magnetic field sensing elements configured to generate a magnetic field signal in response to a magnetic field associated with the object;
a motion detector responsive to the magnetic field signal and to a threshold signal and configured to generate a detector output signal having edges occurring in response to a comparison of the magnetic field signal and the threshold signal and occurring at a rate corresponding to a speed of motion of the object;
a speed detector responsive to the detector output signal to generate a speed signal having a value corresponding to a duration between edges of the detector output signal; and
a threshold generator coupled to receive the speed signal from the speed detector and coupled to the motion detector and configured to generate the threshold signal comprising a threshold adjustment amount having a level related to the speed of motion of the object in response to the speed signal.

2. The magnetic field sensor of claim 1 , wherein the threshold signal is at a first signal level when the speed signal indicates a speed of motion of the object greater than a predetermined speed and wherein the threshold signal is at a second signal level when the speed signal indicates a speed of motion of the object less than the predetermined speed.

3. The magnetic field sensor of claim 1 , wherein the speed detector comprises a counter responsive to the detector output signal and configured to generate a count signal having a value corresponding to a duration between like edges of the detector output signal.

4. The magnetic field sensor of claim 3 , wherein the speed detector further comprises a filter responsive to the count signal and configured to generate the speed signal.

5. The magnetic field sensor of claim 4 , wherein the speed signal is generated as an average of a predetermined, number of count signal values and wherein the predetermined number of count signal values corresponds to a number of features of the object.

6. The magnetic field sensor of claim 1 , wherein the threshold generator comprises a memory device.

7. The magnetic field sensor of claim 6 , wherein the memory device is configured to store a plurality of threshold adjustment amounts corresponding to the speed of motion of the object.

8. The magnetic field sensor of claim 7 , wherein the threshold generator further comprises a summing circuit responsive to at least a stored threshold adjustment amount and configured to generate the threshold signal.

9. The magnetic field sensor of claim 1 , wherein the object is comprised of a magnetic material and wherein the magnetic field is generated by the object.

10. The magnetic field sensor of claim 1 , wherein the object is comprised of a ferromagnetic material and wherein the magnetic field is affected by movement of the object.

11. The magnetic field sensor of claim 10 , further comprising a magnet and wherein the magnetic field is generated by the magnet.

12. The magnetic field sensor of claim 1 , wherein the one or more magnetic field sensing elements comprise at least one Hall effect element.

13. The magnetic field sensor of claim 1 , wherein the one or more magnetic field sensing elements comprise at least one magnetoresistance element.

14. The magnetic field sensor of claim 13 , wherein the at least one magnetoresistance element is an anisotropic magnetoresistance (AMR) element, a giant magnetoresistance (GMR) element, a tunneling magnetoresistance (TMR) element, a magnetic tunnel junction (MTJ) element, or a spin valve element.

15. The magnetic field sensor of claim 1 , wherein the motion detector comprises a tracking circuit responsive to the magnetic field signal and configured to track peaks of the magnetic field signal and generate a tracking signal and wherein the threshold generator is further responsive to the tracking signal to generate the threshold signal.

16. The magnetic field sensor of claim 15 , wherein the detector output signal transitions when a difference between one or more tracked peaks of the magnetic field signal and the threshold signal exceeds a predetermined amount.

17. The magnetic field sensor of claim 15 , wherein the tracking signal tracks positive and negative peaks of the magnetic field signal and wherein the threshold signal is provided as a predetermined percentage of a peak-to-peak value of the tracking signal.

18. The magnetic field sensor of claim 1 , wherein the threshold generator is further responsive to a fixed threshold voltage to generate the threshold signal.

19. The magnetic field sensor of claim 1 , wherein the threshold generator comprises a threshold controlled configured to compute the threshold adjustment amount corresponding to a speed of motion of the object.

20. A method for generating a threshold signal in a magnetic field sensor for detecting motion of an object, comprising:
receiving a magnetic field signal generated in response to a magnetic field associated with an object;
generating a detector output signal in response to the magnetic field signal and a threshold signal, the detector output signal having edges occurring in response to a comparison of the magnetic field signal and the threshold signal and occurring at a rate corresponding to a speed of motion of the object;
generating a speed signal indicative of a speed of motion of the object in response to the detector output signal, wherein the speed signal has a value corresponding to a duration between edges of the detector output signal; and
generating the threshold signal in response to the speed signal, the threshold signal comprising a threshold adjustment amount having a level related to the speed of motion of the object.

21. The method of claim 20 , wherein generating the speed signal comprises generating a count signal having a value corresponding to a duration between like edges of the detector output signal.

22. The method of claim 20 , further comprising storing a plurality of threshold adjustment amounts corresponding to the speed of motion of the object.

23. The method of claim 22 , wherein generating the threshold signal comprises generating the threshold signal in response to a stored threshold adjustment amount.

24. The method of claim 23 , wherein generating the threshold signal comprises tracking peaks of the magnetic field signal, generating a tracking signal in response to the tracked peaks, and generating the threshold signal in response to the stored threshold adjustment amount and further in response to the tracking signal.

25. The method of claim 23 , wherein generating the threshold signal comprises generating the threshold signal in response to the stored threshold adjustment amount and further in response to a fixed threshold voltage.

26. The method of claim 20 , wherein generating the threshold signal in response to the speed signal comprises generating a threshold signal having a first signal level when the speed signal indicates a speed of motion of the object greater than a predetermined speed and generating a threshold signal having a second signal level when the speed signal indicates a speed of motion of the object less than the predetermined speed.

27. The method of claim 20 , wherein generating the threshold signal comprises computing the threshold adjustment corresponding to the speed of m

Assignees

• Allegro Microsystems Llc

Inventors

• Fernandez Devon
• Drouin Mathew

Classifications

• G01P13/045

  with speed indication · CPC title

• G01P3/487

  delivered by rotating magnets · CPC title

• F02P7/067

  Electromagnetic pick-up devices {, e.g. providing induced current in a coil} · CPC title

• G01R33/09 Primary

  Magnetoresistive devices · CPC title

• G01R33/07

  Hall effect devices · CPC title