Methods and apparatus for magnetic sensors having highly uniform magnetic fields

• US 10,215,550 B2
• Filed: 05/01/2012
• Issued: 02/26/2019
• Est. Priority Date: 05/01/2012
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Metivier, Ryan, Taylor, William P.
• Primary Examiner(s): Patel, Paresh H
• Application Number:
  US13/461,164
• Publication Number:
  US 20130293220A1
• Time in Patent Office: 2,492 Days
• Field of Search: None
• CPC Class Codes: G01B 7/30 for measuring angles or tapers; for testing the alignment of axes

Abstract

Methods and apparatus for a magnetic sensor including an elliptical magnet to generate substantially circular concentric zones of similar flux density in a plane over and parallel to a surface of the magnet. The sensor can include a sensing element disposed a selected distance from the magnet and a substrate containing circuitry to process a signal from the sensing element to provide a sensor output.

Claims

1. A system, comprising:

a magnet having a length, width, and height, wherein the magnet has a substantially planar surface that defines an ellipse across the length and width to generate substantially circular concentric zones of similar flux density in a plane over and parallel to the elliptical planar surface of the magnet, wherein the ellipse is noncircular; and

a magnetic sensor IC package comprising;

a sensing element disposed a selected distance from the planar surface of the magnet, wherein the planar surface of the magnet and a surface of the magnetic sensor IC package define an airgap with respect to rotation of the magnetic sensor IC package and/or magnet, wherein a center of the sensing element is substantially aligned with a center of the magnet; and

a substrate containing circuitry to process a signal from the sensing element to provide an output of the magnetic sensor IC package.

2. The magnetic sensor IC package according to claim 1, wherein a center of the concentric zones is aligned with a center of the magnet surface.

3. The magnetic sensor IC package according to claim 1, wherein a gradient of the flux density across the concentric zones is less than for a cylindrical magnet of the same volume.

4. The magnetic sensor IC package according to claim 1, wherein the magnetic sensor IC package provides better accuracy than a magnetic sensor having a cylindrical magnet having the same volume as the elliptical magnet.

5. The magnetic sensor IC package according to claim 1, wherein the sensing element comprises a circular vertical hall element.

6. The magnetic sensor IC package according to claim 1, wherein a length to width ratio of the elliptical magnet surface is about 1.5.

7. The magnetic sensor IC package according to claim 1, wherein the elliptical magnet is not keyed for orientation.

8. The magnetic sensor IC package according to claim 1, wherein the magnetic sensor IC package senses angular position of a target.

9. The magnetic sensor IC package according to claim 1, wherein the sensing element comprises at least one of a Hall element, an anisotropic magnetoresistance (AMR) element and/or a giant magnetoresistance (GMR) element.

10. The magnetic sensor IC package according to claim 9, wherein the sensing element comprises a circular vertical hall element.

11. A system, comprising:

a magnet having a length, width, and height, wherein the magnet has a substantially planar surface that defines a noncircular ellipse to generate substantially circular concentric zones of substantially similar flux density in a plane parallel to the elliptical planar surface of the magnet; and

magnetic sensor IC package comprising

a circular implant region having a plurality of vertical Hall elements defining a center, wherein the Hall elements are located in a plane located a distance from the elliptical planar surface of the magnet, wherein the center of the vertical Hall elements is substantially aligned with a center of the elliptical planar surface of the magnet.

12. The magnetic sensor IC package according to claim 11, wherein a gradient of the flux density across the concentric zones is less than for a cylindrical magnet of the same volume.

13. The magnetic sensor IC package according to claim 11, wherein the sensor provides better accuracy than a magnetic sensor having a cylindrical magnet having the same volume as the elliptical magnet.

14. The magnetic sensor IC package according to claim 11, wherein a length to width ratio of the elliptical magnet is about 1.5.

15. The magnetic sensor IC package according to claim 11, wherein the elliptical magnet is not keyed for orientation.