Circuits and methods for limiting a smallest separation of thresholds in a magnetic field sensor

• US 9,778,326 B2
• Filed: 02/20/2015
• Issued: 10/03/2017
• Est. Priority Date: 03/11/2014
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Chen, Michael, Burdette, Eric, Fernandez, Devon, Snyder, Steven E., Harer, Jacob
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): Rodriguez, Douglas X
• Application Number:
  US14/626,963
• Publication Number:
  US 20150260803A1
• Time in Patent Office: 956 Days
• Field of Search: None
• CPC Class Codes: G01D 5/147 influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other
• CPC Class Codes: G01D 5/2448 Correction of gain, threshold, offset or phase control
• CPC Class Codes: G01R 33/0029 Treating the measured signals, e.g. removing offset or noise
• CPC Class Codes: G01R 33/07 Hall effect devices
• CPC Class Codes: G01R 33/09 Magnetoresistive devices

Abstract

A magnetic field sensor uses upper and lower thresholds. The upper and lower thresholds are limited such that they have a minimum separation distance between equivalent voltage levels of the upper and lower thresholds.

Claims

1. A magnetic field sensor, comprising:

at least one magnetic field sensing element configured to generate a magnetic field signal influenced by a ferromagnetic object;

peak finding circuitry operable to identify at least one of a positive peak value or a negative peak value of the magnetic field signal;

a threshold generation module coupled to receive the at least one of the positive peak value or the negative peak value, wherein the threshold generation module comprises;

a peak-to-peak calculation module operable to determine a peak-to-peak value by using the at least one of the positive peak value or the negative peak value;

a threshold calculation module operable to determine an upper threshold value and a lower threshold value based on the peak-to-peak value, wherein the upper threshold value is a first predetermined percentage of the peak-to-peak value and the lower threshold value is a second lower predetermined percentage of the peak-to-peak value; and

a threshold limiting module operable to identify a difference between the upper threshold value and the lower threshold value, and, if the difference is smaller than a minimum separation value based on a function of an RMS noise level associated with the magnetic field signal, operable to set the difference between the upper threshold value and the lower threshold value to a corrected difference value.

2. The magnetic field sensor of claim 1, wherein the corrected difference value is selected based upon an expected, but not measured, noise of the magnetic field signal.

3. The magnetic field sensor of claim 1, wherein the magnetic field sensor further comprises a noise measurement module operable to measure a noise of the magnetic field signal, wherein the corrected difference value is selected based upon the measured noise of the magnetic field signal.

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

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

6. The magnetic field sensor of claim 1, wherein the at least one magnetic field sensing element comprises a first magnetic field sensing element operable to generate a first magnetic field signal and a second magnetic field sensing element operable to generate a second magnetic field signal, the magnetic field sensor further comprising:

a selection module coupled to receive at least one of the positive peak value, the negative peak value, or the peak-to-peak value, operable to identify an amplitude of a magnetic field sensed by at least one of the first or second magnetic field sensing elements, operable to select one of a first signal indicative of the first magnetic field signal or a second signal indicative of the second magnetic field signal based upon the identified amplitude, and operable to generate a selected signal as the selected one of the first or second signals based upon the selection.

7. The magnetic field sensor of claim 6, wherein the first and second magnetic field sensing elements have first and second different sensitivities to a magnetic field, and wherein the magnetic field sensor has first and second different operating ranges in response to the first and second different sensitivities.

8. A method of sensing a magnetic field, comprising:

generating a magnetic field signal influenced by a ferromagnetic object with at least one magnetic field sensing element;

identifying at least one of a positive peak value or a negative peak value of the magnetic field signal;

determining a peak-to-peak value by using the at least one of the positive peak value or the negative peak value;

determining an upper threshold value and a lower threshold based on the peak-to-peak value, wherein the upper threshold value is a first predetermined percentage of the peak-to-peak value and the lower threshold value is a second lower predetermined percentage of the peak-to-peak value;

identifying a difference between the upper threshold value and the lower threshold value; and

if the difference is smaller than a minimum separation value based on a function of an RMS noise level associated with the magnetic field signal, setting the difference between the upper threshold value and the lower threshold value to a corrected difference value.

9. The method of claim 8, wherein the corrected difference value is selected based upon an expected, but not measured, noise of the magnetic field signal.

10. The method of claim 8, further comprising:

measuring a noise of the magnetic field signal, wherein the corrected difference value is selected based upon the measured noise of the magnetic field signal.

11. The method of claim 8, wherein the at least one magnetic field sensing element comprises a Hall element.

12. The method of claim 8, wherein the at least one magnetic field sensing element comprises a magnetoresistance element.

13. The method of claim 8, wherein the at least one magnetic field sensing element comprises a first magnetic field sensing element operable to generate a first magnetic field signal and a second magnetic field sensing element operable to generate a second magnetic field signal, the magnetic field sensor, the method further comprising:

identifying an amplitude of a magnetic field sensed by at least one of the first or second magnetic field sensing elements using at least one of the positive peak value, the negative peak value, or the peak-to-peak value;

selecting one of a first signal indicative of the first magnetic field signal or a second signal indicative of the second magnetic field signal based upon the identified amplitude; and

generating a selected signal as the selected one of the first or second signal based upon the selection.

14. The method of claim 13, wherein the first and second magnetic field sensing elements have first and second different sensitivities to a magnetic field, and wherein the magnetic field sensor has first and second different operating ranges in response to the first and second different sensitivities.

15. A non-transitory computer-readable storage medium having computer readable code thereon, the medium comprising:

instructions for determining a peak-to-peak value by using the at least one of a positive peak value or the negative peak value of a magnetic field signal generated by at least one magnetic field sensing element;

instructions for determining an upper threshold value and a lower threshold based on the peak-to-peak value, wherein the upper threshold value is a first predetermined percentage of the peak-to-peak value and the lower threshold value is a second lower predetermined percentage of the peak-to-peak value;

instructions for identifying a difference between the upper threshold value and the lower threshold value; and

instructions for, if the difference is smaller than minimum separation value based on a function of an RMS noise level associated with the magnetic field signal, setting the difference between the upper threshold value and the lower threshold value to a corrected difference value.

16. The non-transitory computer-readable storage medium of claim 15, wherein the corrected difference value is selected based upon an expected, but not measured, noise of the magnetic field signal.

17. The non-transitory computer-readable storage medium of claim 15, further comprising:

instructions for measuring a noise of the magnetic field signal, wherein the corrected difference value is selected based upon the measured noise of the magnetic field signal.

18. The non-transitory computer-readable storage medium of claim 15, wherein the at least one magnetic field sensing element comprises a Hall element.

19. The non-transitory computer-readable storage medium of claim 15, wherein the at least one magnetic field sensing element comprises a magnetoresistance element.

20. The non-transitory computer-readable storage medium of claim 15, wherein the at least one magnetic field sensing element comprises a first magnetic field sensing element operable to generate a first magnetic field signal and a second magnetic field sensing element operable to generate a second magnetic field signal, the magnetic field sensor, the non-transitory computer-readable storage further comprising:

instructions for identifying an amplitude of a magnetic field sensed by at least one of the first or second magnetic field sensing elements using at least one of the positive peak value, the negative peak value, or the peak-to-peak value;

instructions for selecting one of a first signal indicative of the first magnetic field signal or a second signal indicative of the second magnetic field signal based upon the identified amplitude; and

instructions for generating a selected signal as the selected one of the first or second signal based upon the selection.

21. The non-transitory computer-readable storage medium of claim 20, wherein the first and second magnetic field sensing elements have first and second different sensitivities to a magnetic field, and wherein the magnetic field sensor has first and second different operating ranges in response to the first and second different sensitivities.