Magnetic field sensor for sensing a movement of a ferromagnetic target object

Patent metadata

Field	Value
Publication number	US-9719806-B2
Application number	US-201414529577-A
Country	US
Kind code	B2
Filing date	Oct 31, 2014
Priority date	Oct 31, 2014
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

A magnetic field sensor operates as a motion detector for sensing a movement of a ferromagnetic target object having features. The magnetic field sensor has a plurality of magnetoresistance elements to generate, in a first channel, a feature signal indicative of a proximity of a feature of a ferromagnetic target object and, in a second channel, an edge signal indicative of a proximity of an edge of a feature of a ferromagnetic target object.

First claim

What is claimed is:

1. A magnetic field sensor for sensing a movement of a ferromagnetic target object having ferromagnetic target object features with a target feature width, comprising:
a substrate;
a first full bridge circuit disposed upon the substrate and proximate to the ferromagnetic target object, comprising:
a first magnetoresistance element;
a second magnetoresistance element, the first and second magnetoresistance elements proximate to each other forming a first proximate pair;
a third magnetoresistance;
a fourth magnetoresistance element, the third and fourth magnetoresistance elements proximate to each other forming a second proximate pair;
a first noninverting output node joining a selected two of the first, second, third and fourth magnetoresistance elements;
a first inverting output node joining a different selected two of the first, second, third and fourth magnetoresistance elements, wherein a first differential signal is generated between the first noninverting node and the first inverting node, wherein the magnetic field sensor further comprises:

a second full bridge circuit disposed upon the substrate and proximate to the ferromagnetic target object, comprising:
a fifth magnetoresistance element;
a sixth magnetoresistance element, the fifth and sixth magnetoresistance elements proximate to each other forming a third proximate pair;
a seventh magnetoresistance element;
an eighth magnetoresistance element, the seventh and eighth magnetoresistance elements proximate to each other forming a fourth proximate pair;
a second noninverting output node joining a selected two of the fifth, sixth, seventh, and eighth magnetoresistance elements; and
a second inverting output node joining a different selected two of the fifth, sixth, seventh, and eighth magnetoresistance elements, wherein a second differential signal is generated between the second noninverting node and the second inverting node, wherein the magnetic field sensor further comprises:

a first combining circuit disposed upon the substrate and configured to combine the first differential signal and the second differential signal to generate a feature signal having a largest value when a ferromagnetic target object feature is centered with the first and second full bridge circuits; and
a second combining circuit disposed upon the substrate and configured to combine the first differential signal and the second differential signal to generate an edge signal having a largest value when the first full bridge circuit is on one side of an edge of a ferromagnetic target object feature and the second full bridge circuit is on the other side of the same edge.

2. The magnetic field sensor of claim 1 , wherein the first, second, third, and fourth proximate pairs are disposed in a line parallel to a tangent to a direction of movement of the ferromagnetic target object.

3. The magnetic field sensor of claim 1 , wherein the first and fourth proximate pairs are disposed in a first line parallel to a tangent to a direction of movement of the ferromagnetic target object, and wherein the second and third proximate pairs are disposed in a second line parallel to the first line, wherein the second line is more distal from the ferromagnetic target object than the first line.

4. The magnetic field sensor of claim 1 , wherein first, second, third, and fourth proximate pairs are disposed in an arc.

5. The magnetic field sensor of claim 1 , further comprising a magnet for generating respective magnetic fields at the first and second magnetoresistance elements, wherein the ferromagnetic target object is disposed at a position such that movement of the ferromagnetic target object results in changes of the magnetic fields at the first and second magnetoresistance elements.

6. The magnetic field sensor of claim 1 , wherein the ferromagnetic target object comprises a ring magnet having alternating north and south poles, the ring magnet for generating respective magnetic fields at the first and second magnetoresistance elements, wherein the ring magnet is disposed at a position such that movement of the ferromagnetic target object results in changes of the magnetic fields at the first and second magnetoresistance elements.

7. The magnetic field sensor of claim 1 , further comprising:
an electronic circuit disposed upon the substrate, coupled to receive the feature signal and the edge signal, and configured to compute a sign of a phase difference between the feature signal and the edge signal to generate an indication of a direction of movement of the ferromagnetic target object.

8. The magnetic field sensor of claim 1 , wherein the substrate comprises first and second parallel largest surfaces, wherein the first, second, third, fourth, fifth, sixth, seventh, and eighth magnetoresistance elements are disposed in or over the first largest surface of the substrate, wherein the ferromagnetic target object has first and second parallel largest surfaces, wherein the first largest surface of the substrate is substantially parallel to the first largest surface of the ferromagnetic target object.

9. The magnetic field sensor of claim 1 , wherein the feature signal and the edge signal are analog signals.

10. The magnetic field sensor of claim 1 , wherein the second proximate pair is disposed between the first and third proximate pairs, and wherein the third proximate pair is disposed between the second and fourth proximate pairs.

11. The magnetic field sensor of claim 10 , wherein a spacing between the first and third proximate pairs is selected to be between about one half and about two times the target feature width, and a spacing between the second and fourth proximate pairs is selected to be between about one half and about two times the target feature width.

12. The magnetic field sensor of claim 1 , further comprising:
an electronic circuit disposed upon the substrate, coupled to receive the feature signal and the edge signal, wherein the electronic circuit is operable to compare the edge signal with one or more threshold values to generate a first two-state signal and operable to compare the feature signal with another one or more threshold values to generate a second two-state signal, wherein an output signal generated by the magnetic field sensor comprises a signal encoding that identifies an alignment of state transitions of a selected one of the first or the second two-state signal.

13. The magnetic field sensor of claim 12 , wherein the output signal comprises pulses with a pulse rate indicative of a speed of the movement of the target object and with pulse edges aligned with the state transitions of the selected one of the first or the second two-state signal.

14. The magnetic field sensor of claim 12 , wherein a relative phase between the first and second two-state signals is indicative of a direction of the movement of the ferromagnetic target object, and wherein the pulses comprise pulse widths indicative of a direction of the movement of the ferromagnetic target object.

15. The magnetic field sensor of claim 1 , wherein the second proximate pair is disposed between the first and third proximate pairs, and wherein the third proximate pair is disposed between the second and fourth proximate pairs, and wherein a spacing between the first and second proximate pairs is selected to be between about one half and about two times the target feature width, and a spacing between the third and fourth proximate pairs is selected to be between about one half and about two times the target feature width.

16. The magnetic field sensor of claim 15 , furthe

Assignees

• Allegro Microsystems Llc

Inventors

• Foletto Andrea
• Eagen Jeffrey
• David Paul A

Classifications

• G01D5/145 Primary

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

• G01R33/09

  Magnetoresistive devices · CPC title

• G01D5/2046 Primary

  by a movable ferromagnetic element, e.g. a core · CPC title