Self compensating control circuit for digital magnetic sensors

• US 6,456,063 B1
• Filed: 11/03/2000
• Issued: 09/24/2002
• Est. Priority Date: 11/03/2000
• Status: Expired due to Fees

• Current Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Lin, Yingjie, Moreno, Daniel J.
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): KINDER, DARRELL D
• Application Number:
  US09/706,199
• Time in Patent Office: 690 Days
• Field of Search: 324/169, 324/173, 324/174, 324/167, 324/207.12, 324/207.21, 324/207.2, 324/207.25, 123/617
• US Class Current: 324/207.12
• CPC Class Codes: G01D 3/021 using purely analogue techniques
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06

Abstract

A self-compensating control circuit for use with a magneto-resistive sensor. The control circuit includes a first stage amplification and offset function that removes a DC component from the input signal and maximizes an AC component of the input signal within the dynamic range of the control circuit. Subsequent stages remove the remaining DC component, if any, and provide suitable additional amplification. A comparator provides a digital output based on the processed input signal and a threshold signal.

Claims

1. An apparatus for generating an output signal indicative of an angular position of a rotating member, comprising:

a target wheel having a plurality of teeth separated by slots angularly spaced around a periphery thereof, said target wheel being configured to be mounted to the rotating member for rotation therewith;

a sense assembly having a biasing magnet and magneto-resistive (MR) magnetic field sensor disposed between said magnet and said target wheel; and

a control circuit coupled to said MR sensor configured to generate said output signal having transitions between first and second states at the passage thereby of each leading and trailing edge of said teeth, said control circuit further including an arrangement for electrically biasing said MR sensor to produce an input signal having a direct-current component and an alternating current component superimposed thereon when said target wheel rotates, wherein said control circuit further includes a first amplifier circuit having a fixed DC offset configured to remove a fixed portion of said DC component from said input signal to generate a first signal, said control circuit further including a peak detector circuit responsive to said firs signal for generating a second signal representative of a maximum voltage level of said first signal, said control circuit further including a second amplifier circuit responsive to said first signal having an adaptive DC offset based on said second signal configured to remove a remaining portion of said DC component from said first signal.

2. The apparatus of claim 1 wherein said second amplifier circuit is configured to generate a third signal having said DC component substantially removed.

3. The apparatus of claim 2 wherein said control circuit further includes:

a threshold reference generator for producing a threshold signal that is a percentage of a peak level of said third signal; and

a comparator configured to generate said output signal in response to said third signal and said threshold signal.

4. The apparatus of claim 1 wherein said MR sensor is a first MR sensor, said sense assembly further including:

a second magneto-resistive sensor arranged in series with said first MR sensor to form a voltage divider having a common node on which said input signal is generated; and

a power supply connected across said voltage divider;

wherein said second MR sensor is disposed on said magnet so as to remain uninfluenced by rotation of said target wheel.

5. A method for generating an output signal indicative of an angular position of a rotating target wheel having a plurality of teeth separated by slots angularly spaced around a periphery thereof, comprising the steps of:

(A) producing an input signal by biasing a magneto-resistive magnetic field sensor disposed between a magnet and the rotating target wheel;

(B) reducing a DC component of the input signal by a fixed amount;

(C) amplifying an AC component of the input signal to maximize the AC component within a dynamic range of a control circuit, the reduced DC component and amplified AC component input signal defining a first signal;

(D) removing a remaining portion of said DC component using an adaptive DC offset determined based on a peak level of the first signal to produce a second signal; and

(E) generating the output signal having transitions between first and second states at the passage thereby of each leading and trailing edge of said teeth in accordance with said second signal.

6. The method of claim 5 wherein said generating step includes the substep of:

detecting a peak level of the first signal and outputting a second signal in response thereto.

7. The method of claim 6 wherein said generating step further includes the substep of:

removing a remainder of the DC component of the input signal using said second signal, and outputting a third signal in response thereto.

8. The method of claim 7 wherein said generating step further includes the substeps of:

producing a threshold signal that is a percentage of a peak level of the third signal; and

producing the output signal in one of the first and second states when the third signal exceeds the threshold signal.