Gear tooth sensor with peak and threshold detectors

Patent metadata

Field	Value
Publication number	US-9329057-B2
Application number	US-201213484501-A
Country	US
Kind code	B2
Filing date	May 31, 2012
Priority date	May 31, 2012
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

Presented herein is a magnetic field sensor architecture that uses outputs of a peak detector and threshold detector operating in parallel to detect magnetic anomalies that may be associated with the target being sensed, e.g., a rotational ferromagnetic object such as a toothed gear, and use such detection to prevent sensor malfunction. The sensor includes an edge detection circuit and an error detection circuit. In one embodiment, the edge detection circuit includes circuits to detect edges (or transitions) of the threshold and peak detector output signals and the error detection circuit includes circuits, responsive to the edge detection circuit, to indicate an error when a “missed transition” occurs or a peak-to-peak value of an input signal as detected by the peak detector for a current cycle differs from an expected peak-to-peak value by a predetermined amount.

First claim

What is claimed is:

1. A sensor comprising:
a magnetic field signal generating circuit comprising at least one sensing element, to generate a magnetic field signal indicative of features of a rotational ferromagnetic object as the features pass in front of the at least one sensing element;
a threshold detector, responsive to the magnetic field signal, to generate a threshold detector output signal having transitions associated with a comparison of the magnetic field signal to a first threshold that is a percentage of the peak-to-peak magnetic field signal;
a peak detector, responsive to the magnetic field signal, to generate a peak detector output signal having transitions associated with a comparison of the magnetic field signal to a second threshold that is related to a peak of the magnetic field signal; and
a circuit, coupled to the threshold detector and peak detector, to detect the transitions of the threshold detector output signal and peak detector output signal, and to use the detected transitions to detect an error if a sequence in which the transitions occur deviates from an expected sequence, wherein the expected sequence is based on the first and second thresholds.

2. The sensor of claim 1 wherein the circuit operates to generate an error signal having a level indicative of the error when such error is detected.

3. The sensor of claim 2 wherein the circuit comprises an edge detection circuit to detect the transitions of the peak and threshold output signals and an error detection circuit coupled to the edge detection circuit and responsive to the transitions detection to generate the error signal.

4. The sensor of claim 3 wherein the edge detection circuit comprises a first edge detector to detect each transition of the peak detector output signal and a second edge detector to detect each transition of the threshold detector output signal.

5. The sensor of claim 4 wherein the error detection circuit comprises a first circuit, responsive to the edge detection circuit, to monitor the sequence of the transitions of the peak detector output signal and the threshold detector output signal and to generate a first circuit output signal having a level indicative of a first error when the monitoring detects that the sequence has deviated from the expected sequence.

6. The sensor of claim 5 wherein the first circuit output signal is provided as the error signal.

7. The sensor of claim 5 wherein the first circuit comprises a counter configured to increment a count value in response to each detected peak detector output signal transition and reset the count value in response to each detected threshold detector output signal transition, and further comprising a comparator to compare the count value to a count limit and set the first circuit output signal level to the level indicative of the first error when the count value reaches the count limit.

8. The sensor of claim 5 wherein the first circuit comprises a counter configured to increment a count value in response to each detected threshold detector output signal transition and reset the count value in response to each detected peak detector output signal transition, and further comprising a comparator to compare the count value to a count limit and set the first circuit output signal level to the level indicative of the first error when the count value reaches the count limit.

9. The sensor of claim 5 wherein the error detection circuit further comprises a second circuit, responsive to the detected peak detector output signal transitions, to compare a peak-to-peak value of the magnetic field signal associated with the detected peak detector output signal transitions for a current cycle to an expected peak-to-peak value and to provide a second circuit output signal based on the comparison.

10. The sensor of claim 9 wherein the expected peak-to-peak value is a peak-to-peak value of the magnetic field signal for a corresponding cycle of a prior rotation of the target.

11. The sensor of claim 9 wherein the second circuit comprises a comparator to compare the peak-to-peak value to a predetermined percentage of the expected peak-to-peak value.

12. The sensor of claim 9 wherein the error detection circuit further comprises a logic circuit to generate the error signal based on the first circuit output signal and the second circuit output signal.

13. The sensor of claim 4 wherein each of the first and second edge detectors operates to generate an output signal that provides a pulse for each detected transition.

14. The sensor of claim 1 wherein the at least one sensing element comprises a pair of sensing elements and the magnetic field signal is a differential magnetic field signal based on differential sensing by the pair of sensing elements.

15. The sensor of claim 1 wherein each of the at least one sensing element is a selected one of a Hall-effect element, magnetoresistance (MR) element or other type of magnetic field sensitive element.

16. The sensor of claim 15 wherein material used to implement each of the at least one sensing element is a selected one of type IV semiconductor material or a type III-V semiconductor material.

17. The sensor of claim 1 wherein the ferromagnetic object is a hard ferromagnetic material.

18. The sensor of claim 1 wherein the ferromagnetic object is a soft ferromagnetic material magnetized by a biasing permanent magnet.

19. A sensor comprising:
a magnetic field signal generating circuit comprising at least one sensing element, to generate a magnetic field signal indicative of features of a rotational ferromagnetic object as the features pass in front of the at least one sensing element;
a threshold detector, responsive to the magnetic field signal, to generate a threshold detector output signal having transitions associated with cycles of the magnetic field signal;
a peak detector, responsive to the magnetic field signal, to generate a peak detector output signal having transitions associated with the cycles of the magnetic field signal; and
a circuit, coupled to the threshold detector and peak detector, to detect the transitions of the threshold detector output signal and peak detector output signal, and to use the detected transitions to detect an error if a sequence in which the transitions occur deviates from an expected sequence, wherein the circuit operates to generate an error signal having a level indicative of the error when such error is detected; and
an output signal selector having a first input responsive to the threshold detector output signal, a second input responsive to the peak detector output signal, and has a control signal to select one of the threshold and peak detector output signals as an output signal based on the error signal generated by the circuit.

20. The sensor of claim 19 wherein the threshold detector is configured to operate in a first mode followed by a second mode, and is caused to return to operating in the first mode when the level of the error signal indicates an error.

21. The sensor of claim 20 wherein the threshold detector operates in the first mode for a recalibration time period.

22. The sensor of claim 21 wherein, when the recalibration time period is complete, the threshold detector resumes operating in the second mode and generates a signal to reset the state of the control signal.

23. A sensor comprising:
a magnetic field signal generating circuit comprising at least one sensing element, to generate a magnetic field s

Assignees

• Foletto Andrea
• Morris Michael
• Drouin Mathew
• Fernandez Devon
• Friedrich Andreas P
• Scheller P Karl
• Allegro Microsystems Llc

Inventors

• Foletto Andrea
• Morris Michael
• Drouin Mathew
• Fernandez Devon
• Friedrich Andreas P
• Scheller P Karl

Classifications

• G01D5/145

  influenced by the relative movement between the Hall device and magnetic fields (see G01R33/06) · CPC title

• G01D5/2448 Primary

  Correction of gain, threshold, offset or phase control · CPC title