Magnetoresistive sensor with reduced output signal jitter

• US 6,300,758 B1
• Filed: 12/02/1999
• Issued: 10/09/2001
• Est. Priority Date: 12/30/1994
• Status: Expired due to Fees

• Current Assignee: Northstar Technologies Incorporated (Brunswick Corporation)
• Original Assignee: Northstar Technologies Incorporated (Brunswick Corporation)
• Inventors: Griffen, Neil C., Stokes, Richard S.
• Primary Examiner(s): Patidar, Jay
• Application Number:
  US09/452,450
• Time in Patent Office: 677 Days
• Field of Search: 324/207.21, 324/207.22, 324/207.25, 324/173, 324/174, 324/252, 324/207.24, 324/225, 324/207.12, 338/32.R, 327/510, 337/06, 337/08
• US Class Current: 324/207.21
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01P 3/487 delivered by rotating magnets

Abstract

A magnetoresistive sensor for use in detecting relative motion between the sensor and a further object bearing an alternating pattern of north/south magnetic poles. The sensor includes one or more pairs of magnetoresistive elements positioned so that each element within a pair magnetically complements the corresponding element in that pair. That is, whenever an element is exposed to a north pole of the magnetic pattern, a corresponding complementary element is exposed to a south pole so as to provide a magnetically complemented output. Such pair of complementary magnetoresistive elements are connected into a bridge circuit such that jitter effects caused by asymmetric magnetic fields and physical differences between sensor elements are cancelled. The quadrature sensor output is frequency multiplied to provide frequency multiplied output signals in quadrature. The sensing arrangement can be used, for example, in the context of a rotary encoder having a drum having a circumference covered with a magnetic track at a predetermined pitch, and may include a plurality of magnetoresistive elements positioned opposite the drum and connected in a bridge circuit such that when the drum rotates an output signal from the encoder indicates rotary motion of the drum.

Claims

1. A self-canceling low jitter magnetoresistive sensor for, in use, sensing a pattern of north and south magnetic poles carried by a carrier, said magnetoresistive sensor comprising:

at least first, second, third and fourth magnetoresistive elements for, in use, magnetically sensing said pattern on said carrier, said first, second, third and fourth magnetoresistive elements being arranged and spaced apart such that when said first element is exposed to a north pole said second element is exposed to a south pole and said third and fourth elements are each between north and south magnetic poles, and when said third element is exposed to a north pole said fourth element is exposed to a south pole and said first and second elements are each between north and south magnetic poles;

a first arrangement of electrical conductors that electrically connects said first and second elements together to form a first quarter-bridge circuit, electrically connects said third and fourth elements together to form a second quarter-bridge circuit, and electrically connects said first and second quarter-bridge circuits together to form a half-bridge circuit that, in use, produces a first substantially periodic signal having a first frequency;

a plurality of additional magnetoresistive elements; and

additional arrangements of electrical conductors that electrically connect said additional magnetoresistive elements together to form additional half-bridge circuits that, in use, produce additional substantially periodic signals having substantially said first frequency, said substantially periodic signals being phase shifted with respect to one another to facilitate production of responsive frequency multiplied outputs in quadrature.

2. The sensor of claim 1 wherein the said substantially periodic signals are substantially sinusoidal.

3. The sensor of claim 1 wherein the said first, second, third, fourth and additional magnetoresistive elements are disposed on a common substrate.

4. The sensor of claim 1 wherein the said pattern provides a periodic magnetic scale and, in use, the said substantially periodic signals produced provide speed and direction information related to the relative motion between said sensor and said periodic magnetic scale.

5. A self-canceling low jitter magnetoresistive sensor for detecting changing magnetic fields generated by relative motion between said sensor and a further object bearing a pattern of alternating magnetic poles separated by a predetermined pitch, said sensor comprising:

a first plurality of magnetoresistive sensor elements;

a second plurality of magnetoresistive sensor elements;

a mounting arrangement that spaces at least some elements of said second plurality of magnetoresistive elements by a predetermined spacing related to said pitch from corresponding elements of said first plurality of magnetoresistive sensor elements such that when an element of said second plurality is exposed to a north magnetic pole a corresponding element of said first plurality is exposed to a south magnetic pole;

electrical conductors electrically connecting at least some of the magnetoresistive elements within said second plurality of magnetoresistive elements to corresponding magnetoresistive elements within said first plurality of magnetoresistive elements to form a plurality of half-bridge circuits, wherein at least one of said plurality of half-bridge circuits includes a quarter-bridge circuit containing at least one of said second plurality of magnetoresistive elements and at least one corresponding element of said first plurality of magnetoresistive elements;

wherein, in use, said plurality of half-bridge circuits produce substantially periodic signals that are phase shifted with respect to one another such that when electronically conditioned and combined, at least a pair of frequency multiplied output signals in quadrature are produced.

6. The sensor of claim 5 wherein the said substantially periodic signals are substantially sinusoidal.

7. The sensor of claim 5 wherein the mounting arrangement comprises a common substrate on which said first and second pluralities of magnetoresistive sensors are disposed.

8. The sensor of claim 5 wherein the pattern defines a periodic magnetic scale and, in use, the periodic signals produced provide speed and direction information related to the relative motion between said sensor and the periodic magnetic scale.

9. A self-canceling low jitter magnetoresistive sensor for detecting changing magnetic fields generated by relative motion between said sensor and a further object bearing a pattern of alternating north/south magnetic poles separated by a predetermined pitch, said sensor comprising;

at least first, second and third magnetoresistive elements and at least first, second and third corresponding complementary magnetoresistive elements wherein, said first complementary magnetoresistive element is spaced apart by a predetermined spacing related to said pitch from the corresponding first magnetoresistive element so as to magnetically complement said first magnetoresistive element and thereby compensate for differences in magnetic pole response characteristics, said second complementary magnetoresistive element is spaced apart by a predetermined spacing related to said pitch from the corresponding second magnetoresistive element so as to magnetically complement said second magnetoresistive element and thereby compensate for differences in magnetic pole response characteristics, and said third complementary magnetoresistive element is spaced apart by a predetermined spacing related to said pitch from the corresponding third magnetoresistive element so as to magnetically complement said third magnetoresistive element and thereby compensate for differences in magnetic pole response characteristics,

wherein, in use, at least said first, second, and third magnetoresistive elements and said first, second and third complementary magnetoresistive elements magnetically sense said pattern on said object, said magnetoresistive elements being arranged and spaced apart from one another such that when said first element is exposed to a north pole said first complementary element is exposed to a south pole, when said second element is exposed to a north pole said second complementary element is exposed to a south pole, and when said third magnetoresistive element is exposed to a north pole said third complementary element is exposed to a south pole;

an electrical conductor arrangement that electrically connects said first element and said first complementary element together to form a first quarter-bridge circuit, electrically connects said second element and said second complementary element together to form a second guarter-bridge circuit, and electrically connects said third element and said third complementary element together to form a third guarter-bridge circuit, wherein, in use, said first, second and third guarter-bridge circuits produce substantially periodic signals phase shifted with respect to one another so as to facilitate production of responsive frequency multiplied outputs in quadrature,

wherein said first and second magnetoresistive elements are spaced apart by a first spacing, said second and third magnetoresistive elements are spaced apart by a second spacing different from said first spacing, and said first and third magnetoresistive elements are spaced apart by a third spacing that is different from said first spacing and said second spacing, to provide non-uniform spacing between said first, second and third magnetoresistive elements.

10. A self-canceling low jitter magnetoresistive sensing arrangement for, in use, detecting changing magnetic fields generated by relative motion between said sensing arrangement and a further object bearing a magnetic pole pattern providing alternating north/south magnetic poles separated by a predetermined pitch, said sensing arrangement comprising:

a substrate shaped and dimensioned to be magnetically coupled to said further object;

a first plurality of magnetoresistive sensing elements disposed on said substrate and spaced apart by a spacing related to said pitch;

a second plurality of magnetoresistive sensing elements disposed on said substrate and spaced apart by a spacing related to said pitch, at least some of said second plurality of magnetoresistive sensing elements being spaced by a predetermined spacing related to said pitch from a corresponding magnetically complementary one of said first plurality of magnetoresistive sensing elements such that when a magnetoresistive sensing element in the first plurality is moved to a north pole of said pattern, a further, complementary magnetoresistive sensing element in the second plurality of magnetoresistive sensing elements is exposed to a south pole of said pattern so as to provide a magnetically complemented output;

an electrical connecting circuit that electrically connects at least some of said first plurality of magnetoresistive elements to corresponding complementary magnetoresistive sensor elements in the second plurality of magnetoresistive sensing elements to form a plurality of quarter-bridge circuits, wherein at least one of said plurality of quarter-bridge circuits contains at least one of said second plurality of magnetoresistive elements and at least one corresponding element of said first plurality of magnetoresistive elements;

; and

a frequency multiplier circuit electrically connected to said quarter-bridge circuits that produces at least a pair of frequency multiplied output signals in quadrature.

11. A self-canceling low jitter magnetoresistive sensing arrangement as in claim 10 wherein said further object provides a circumferential surface, and said sensing arrangement is dimensioned to sense said magnetic pole pattern borne by said circumferential surface.

12. An encoder comprising:

an enclosure at least partially enclosing a carrier; and

a self-canceling low jitter magnetoresistive sensor operatively coupled to said enclosure for, in use, sensing a pattern of north and south magnetic poles carried by the carrier, said magnetoresistive sensor comprising;

at least first, second, third and fourth magnetoresistive elements for, in use, magnetically sensing said pattern on said carrier, said first, second, third and fourth magnetoresistive elements being arranged and spaced apart such that when said first element is exposed to a north pole said second element is exposed to a south pole and said third and fourth elements are each between north and south magnetic poles, and when said third element is exposed to a north pole said fourth element is exposed to a south pole and said first and second elements are each between north and south magnetic poles;

a first arrangement of electrical conductors that electrically connects said first and second elements together to form a first quarter-bridge circuit, electrically connects said third and fourth elements together to form a second quarter-bridge circuit, and electrically connects said first and second quarter-bridge circuits together to form a half-bridge circuit that, in use, produces a first substantially periodic signal having a first frequency;

a plurality of additional magnetoresistive elements; and

additional arrangements of electrical conductors that electrically connect said additional magnetoresistive elements together to form additional half-bridge circuits that, in use, produce additional substantially periodic signals having substantially said first frequency, said substantially periodic signals being phase shifted with respect to one another to facilitate production of responsive frequency multiplied outputs in quadrature.

13. An encoder comprising:

an enclosure at least partially enclosing an object bearing a pattern of alternating north/south magnetic poles separated by a predetermined pitch; and

a self-canceling low jitter magnetoresistive sensor operatively coupled to said enclosure for detecting changing magnetic fields generated by relative motion between said sensor and said object, said sensor comprising;

a first plurality of magnetoresistive sensor elements;

a second plurality of magnetoresistive sensor elements;

a mounting arrangement that spaces at least some elements of said second plurality of magnetoresistive elements by a predetermined spacing related to said pitch from corresponding elements of said first plurality of magnetoresistive sensor elements such that when an element of said second plurality is exposed to a north magnetic pole a corresponding element of said first plurality is exposed to a south magnetic pole;

electrical conductors electrically connecting at least some of the magnetoresistive elements within said second plurality of magnetoresistive elements to corresponding magnetoresistive elements within said first plurality of magnetoresistive elements to form a plurality of quarter-bridge circuits, wherein at least one of said plurality of quarter-bridge circuits contains at least one of said second plurality of magnetoresistive elements and at least one corresponding element of said first plurality of magnetoresistive elements;

additional electrical conductors electrically connecting additional elements with said plurality of quarter-bridge circuits to form a plurality of half-bridge circuits;

wherein, in use, said plurality of half-bridge circuits produce substantially periodic signals that are phase shifted with respect to one another such that when electronically conditioned and combined, at least a pair of frequency multiplied output signals in quadrature are produced.