AUTO-CALIBRATION OF MAGNETIC SENSOR

• US 20080238410A1
• Filed: 10/16/2007
• Published: 10/02/2008
• Est. Priority Date: 10/16/2006
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: AMI Semiconductor Belgium BVBA (ON Semiconductor Corporation)
• Inventors: Badaroglu, Mustafa, Laulanet, Francois, Charlier, Olivier
• Granted Patent: US 8,134,358 B2
• Time in Patent Office: Days
• US Class Current: 324/202
• CPC Class Codes: G01R 33/0017 Means for compensating offset magnetic fields or the magnetic flux to be measured; Means for generating calibration magnetic fields
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration
• CPC Class Codes: G01R 33/0206 Three-component magnetometers
• CPC Class Codes: G01R 33/07 Hall effect devices

Abstract

The present invention provides a method to compensate for the sensitivity drift of a magnetic field sensor for sensing a magnetic field. The magnetic field sensor comprises at least four electrodes. The method comprises a first step where a first set of two electrodes is used to bias the sensor and a second set of two electrodes is used to sense an output signal of the magnetic field sensor, and a second step where the second set of two electrodes is used to bias the sensor and the first set of two electrodes is used to sense an output signal of the magnetic field sensor. The method is characterized in that at least one of the first or the second step is subdivided in at least a first sub-step and a second sub-step. A reference magnetic field has first magnetic field parameters, e.g. a first amplitude and/or direction, in the first sub-step and second magnetic field parameters, a second amplitude and/or direction, in the second sub-step. An output signal is sensed in the first and in the second step, and within the first or the second step an output signal is sensed in the first and the second sub-step.

Claims

1. A method to compensate the sensitivity drift of a magnetic field sensor for sensing a magnetic field B_Ext, the sensor comprising at least four electrodes, the method comprising:

a first step where a first set of two electrodes is used to bias the sensor and a second set of two electrodes is used to sense an output signal of the magnetic field sensor; and

a second step where the second set of two electrodes is used to bias the sensor and the first set of two electrodes is used to sense an output signal of the magnetic field sensor;

the method being characterized in that;

at least one of the first or the second step is subdivided in at least a first sub-step and a second sub-step, a reference magnetic field having first magnetic field parameters in the first sub-step and second magnetic field parameters in the second sub-step;

an output signal is sensed in the first and in the second step; and

within the first or the second step an output signal is sensed in the first and the second sub-step.

2. A method according to claim 1, characterized in that the reference magnetic field generated during the first sub-step has the same amplitude as the reference magnetic field B_Cal generated during the second sub-step but the opposite direction.

3. A method according to claim 1, characterized in that the reference magnetic field generated during the first sub-step has the same direction as the reference magnetic field B_Cal generated during the second sub-step but a different amplitude.

4. A method according to claim 3, wherein the reference magnetic field generated during one of the first or second sub-steps has zero amplitude.

5. A method according to claim 1, wherein the reference magnetic field has a monotonically changing amplitude during the first or the second sub-step.

6. A method according to claim 1, furthermore comprising performing a correlated double sampling on the sensed output signal of the magnetic field sensor.

7. A computer program product for executing the method of claim 1 when executed on a processing device associated with a magnetic field sensor.

8. A machine readable data storage device storing the computer program product of claim 7.

9. Transmission of the computer program product of claim 8 over a local or wide area telecommunications network.

10. A control unit for a magnetic sensor device comprising at least four electrodes, the control unit comprising:

timing means providing a timing signal for controlling timing of biasing and sensing of the magnetic sensor device, a bias signal being applied to a first set of two electrodes of the magnetic sensor device and an output signal being measured between a second set of two electrodes during a first step, and a bias signal being applied to the second set of two electrodes and an output signal being measured between the first set of two electrodes during a second step;

means for switching the biasing and the sensing between the first and the second set of two electrodes, dependent on the provided timing signal; and

means for controlling changing of magnetic field parameters of a reference magnetic field so that it has first magnetic field parameters in a first sub-step and second magnetic field parameters during a second sub-step of at least one of the first and second steps.

11. A magnetic field measurement device, comprising:

a magnetic field sensor for sensing a magnetic field, the magnetic field sensor comprising at least four electrodes;

a biasing element for biasing the magnetic field sensor;

a measurement circuit for measuring an output signal of the magnetic field sensor;

a switch box for connecting a first set of electrodes to the biasing element and a second set of electrodes to the readout circuitry during a first time period, and for connecting the second set of electrodes to the biasing element and the first set of electrodes to the readout circuitry during a second time period;

a reference magnetic field generator for generating a reference magnetic field; and

a reference magnetic field biasing element for changing magnetic field parameters of the reference magnetic field;

wherein the magnetic field measurement device is adapted for changing the reference magnetic field parameters within at least one of the first or the second time period.

12. A magnetic field measurement device according to claim 11, wherein the measurement circuit is adapted to sense an output signal of the magnetic field sensor at least once during each of the first and the second time period, and during at least one of the first and the second time period before and after changing of the reference magnetic field parameters.