US 9,810,519 B2
Arrangements for magnetic field sensors that act as tooth detectors
William P. Taylor, Amherst, NH (US); P. Karl Scheller, Bow, NH (US); and Paul David, Bow, NH (US)
Assigned to Allegro MicroSystems, LLC, Worcester, MA (US)
Filed by Allegro Microsystems, LLC, Worcester, MA (US)
Filed on Jul. 19, 2013, as Appl. No. 13/946,380.
Prior Publication US 2015/0022187 A1, Jan. 22, 2015
Int. Cl. G01B 7/14 (2006.01); G01R 33/07 (2006.01); G01R 33/09 (2006.01); G01D 5/14 (2006.01); G01R 33/06 (2006.01)
CPC G01B 7/146 (2013.01) [G01D 5/147 (2013.01); G01R 33/06 (2013.01); G01R 33/07 (2013.01); G01R 33/09 (2013.01)] 18 Claims
OG exemplary drawing
 
1. A magnetic field sensor for sensing motion of a ferromagnetic object, comprising:
a substrate, comprising:
a first major surface, wherein a first dimension across the first major surface of the substrate defines a width dimension of the substrate and a second dimension across the first major surface of the substrate perpendicular to the width dimension defines a length dimension of the substrate;
first and second substrate edges at ends of the width dimension of the substrate;
a second major surface parallel to the first major surface; and
a substrate center axis perpendicular to the first and second surfaces of the substrate, wherein the magnetic field sensor further comprises:
a magnet, comprising:
a first major surface proximate to the substrate and substantially parallel to the first major surface of the substrate, wherein a first dimension across the first major surface of the magnet defines a width dimension of the magnet and a second dimension across the first major surface of the magnet perpendicular to the width dimension defines a length dimension of the magnet;
a second major surface distal from the substrate and parallel to the first major surface of the magnet; and
a magnet axis perpendicular to the first and second major surfaces of the magnet and centered within the width dimension and length dimension of the magnet, wherein the magnet axis intersects the ferromagnetic object, wherein the magnetic field sensor further comprises:
a magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a first magnetic field signal, wherein the magnetic field sensing element comprises a sensing element center axis perpendicular to the first surface of the substrate and passing through a center of the magnetic field sensing element, wherein the sensing element center axis is parallel to the magnet axis and parallel to the substrate center axis, wherein a first distance between the sensing element center axis and a first end of the width dimension of the magnet is substantially smaller than a second distance between the first end of the width dimension of the magnet and the magnet axis, wherein a location of the magnetic field sensing element relative to the magnet is selected to achieve the magnetic field signal having a value less than a saturation value, wherein the center of the magnetic field sensing element is disposed proximate to a first end of the width dimension of the substrate, wherein there is no magnetic field sensing element disposed with a center proximate to a second different end of the width dimension of the magnet or proximate to a second different end of the width dimension of the substrate, wherein the sensing element center axis intersects a center of rotation of the ferromagnetic object, and wherein the substrate center axis and the magnet axis are offset from the sensing element center axis.