Arrangements for magnetic field sensors that act as tooth detectors

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;
• and
• a second major surface parallel to the first major surface, 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 magnetic field sensor further comprises:
• a first 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 first magnetic field sensing element comprises a center;
• and
• a second magnetic field sensing element disposed upon the first major surface or the second major surface of the substrate and configured to generate a second magnetic field signal, wherein the second magnetic field sensing element comprises a center, wherein the center of the first magnetic field sensing element and the center of the second magnetic field sensing element are the same distance from the first major surface of the magnet, wherein the first and second magnetic field sensing elements are disposed on opposite sides of the magnet axis, wherein the first magnetic field sensing element is disposed proximate to the ferromagnetic object and beyond the magnet such that a first line perpendicular to the substrate and intersecting the center of the first magnetic field sensing element does not intersect the magnet, wherein a line passing through the first and second magnetic field sensing elements intersects the ferromagnetic object, wherein the line passing through the first and second magnetic field sensing elements is parallel to the width dimension of the substrate and parallel to the width dimension of the magnet, wherein the second magnetic field sensing element is substantially farther from the ferromagnetic object than the first magnetic field sensing element, resulting in the first magnetic field sensing element being substantially more responsive to the motion of the ferromagnetic object than the second magnetic field sensing element, wherein the magnet is offset from the line passing through the first and second magnetic field sensing elements in a direction perpendicular to the line passing through the first and second magnetic field sensing elements, wherein the line passing through the first and second magnetic field sensing elements is perpendicular to the magnet axis, and wherein the magnetic field sensor is operable to generate an output signal having a value that can distinguish between a tooth and a valley of the ferromagnetic object when the ferromagnetic object is moving and when the ferromagnetic object is not moving.