Method of auto calibrating a magnetic field sensor for drift and structure therefor
View Patent ↗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.
1. A method to compensate a 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 of the at least our electrodes is used to bias the sensor and a second set of two electrodes of the at least four 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 another output signal of the magnetic field sensor;
the method being characterized in that:
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 wherein during both the first step and one of the first and second sub-steps of the second step the reference magnetic field has a first amplitude and a first phase for both the first step and the one of the first and second sub-steps and during only one of the first or second sub-steps the reference magnetic field has one of a) a greater amplitude than the first amplitude and has the first phase, or b) a zero amplitude;
the output signal is sensed in the first step and the another output signal is sensed in the second step; and
the another output signal is sensed within the first and second sub-step.
2. A method according to claim 1 , characterized in that the only one of the first and second sub-steps is the second sub-step.
3. A method according to claim 1 , wherein the only one of the first and second sub-steps is the first sub-step.
4. A method according to claim 1 , wherein the reference magnetic field has a linearly increasing amplitude during the first or the second sub-step.
5. A method according to claim 1 , furthermore comprising performing a correlated double sampling on the output signal of the magnetic field sensor.
6. The method of claim 1 further including performing, within a processing system coupled to the magnetic field sensor, at least a portion of the steps of claim 1 .
7. The method of claim 6 further including providing for the processing system, a machine readable data storage device for storing information related to the steps of claim 1 .
8. The method of claim 7 further including transmitting any of the information over a local or wide area telecommunications network.
9. 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 at least four electrodes of the magnetic sensor device and an output signal being measured between a second set of two electrodes of the at least four 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 the reference magnetic field has first magnetic field parameters having a first amplitude and a first phase in a first sub-step of the first step and having the first amplitude and the first phase in a second sub-step of the first step, the reference magnetic field has the first amplitude and the first phase in a first sub-step of the second step, and the reference magnetic field has second magnetic field parameters having a second amplitude and a second phase during a second sub-step of the second step, wherein the second magnetic field parameters include one of a) an amplitude that is different than an amplitude of the first magnetic field parameters, or b) a zero amplitude.