Coil actuated sensor with sensitivity detection
A magnetic field sensor includes at least one coil responsive to an AC coil drive signal; at least one magnetic field sensing element responsive to a sensing element drive signal and configured to detect a directly coupled magnetic field generated by the at least one coil and to generate a magnetic field signal in response to the directly coupled magnetic field; a processor responsive to the magnetic field signal to compute a sensitivity value associated with detection of the directly coupled magnetic field and substantially independent of a reflected magnetic field reflected by a conductive target disposed proximate to the at least one magnetic field sensing element; and an output signal generator configured to generate an output signal of the magnetic field sensor indicative of the reflected magnetic field.
1. A magnetic field sensor comprising:
at least one coil responsive to an AC coil drive signal;
at least one magnetic field sensing element responsive to a sensing element drive signal and configured to simultaneously detect a directly coupled magnetic field generated by the at least one coil and a reflected magnetic field generated by an eddy current induced in a conductive target by the at least one coil, the conductive target disposed proximate to the at least one magnetic field sensing element, the at least one magnetic field sensing element further configured to generate a magnetic field signal comprising a first component having a first frequency in response to the directly coupled magnetic field and a second component having a second frequency that is different than the first frequency in response to the reflected magnetic field, the magnetic field signal having a sensitivity affected by one or both of a change in temperature and a level of the AC coil drive signal, wherein the first component of the magnetic field signal comprises a sensitivity value;
a coil driver configured to generate the AC coil drive signal with an adjustable magnitude;
a sensing element driver configured to generate the sensing element drive signal with an adjustable magnitude;
a separating circuit configured to separate the second component of the magnetic field signal from the magnetic field signal; and
an output signal generator configured to generate an output signal of the magnetic field sensor in response to the second component of the magnetic field signal and indicative of the reflected magnetic field, wherein the output signal generator comprises:
a temperature sensor configured to measure temperature;
a material type selector comprising parameters to compensate for temperature effects and for a type of material used for the conductive target;
a temperature compensator directly connected to the separating circuit, the temperature compensator configured to receive the second component of the magnetic field signal directly from the separating circuit and configured to generate an output signal in response to the temperature measured by the temperature sensor and to one or more of the parameters from the material type selector; and
a linearization module configured to perform a linear regression on the output signal generated by the temperature compensator,
wherein the coil driver and the sensing element driver are configured to receive the sensitivity value and are respectively configured to adjust the magnitude of one or both of the sensing element drive signal and the AC coil drive signal in response to the sensitivity value in order to permit detection of the conductive target in a manner that is substantially independent of the sensitivity of the magnetic field signal.
2. The magnetic field sensor of claim 1 , wherein the output signal of the linearization module is the output signal of the magnetic field sensor.
3. The magnetic field sensor of claim 1 , wherein the output signal generator is configured to adjust the output signal of the magnetic field sensor in response to the sensitivity value.
4. The magnetic field sensor of claim 1 , wherein the magnitude of one or both of the sensing element drive signal and the AC coil drive signal is adjusted in response to the sensitivity value in order to maintain the sensitivity value at a predetermined level.
5. The magnetic field sensor of claim 1 , wherein the AC coil drive signal has the first frequency and the second frequency.
6. The magnetic field sensor of claim 5 , wherein the first frequency of the AC coil drive signal is lower than the second frequency.
7. The magnetic field sensor of claim 5 , wherein the AC coil drive signal has the first frequency during a first time interval and has the second frequency during a second time interval.
8. The magnetic field sensor of claim 7 , wherein the first and second time intervals overlap.
9. The magnetic field sensor of claim 7 , wherein the first and second time intervals do not overlap.
10. The magnetic field sensor of claim 1 , wherein the AC coil drive signal and the sensing element drive signal have different frequencies.
11. The magnetic field sensor of claim 10 , wherein the coil driver and the sensing element driver are independent sources.
12. The magnetic field sensor of claim 11 , wherein the frequency of the sensing element drive signal is approximately DC.
13. The magnetic field sensor of claim 1 , wherein the at least one magnetic field sensing element is from group consisting of a Hall effect element, a giant magnetoresistance (MR) element, an anisotropic magnetoresistance (AMR) element, a tunneling magnetoresistance (TMR) element, Of and a magnetic tunnel junction (MTJ) element.
14. The magnetic field sensor of claim 1 , wherein the at least one magnetic field sensing element comprises two or more magnetic field sensing elements arranged in a bridge configuration.
15. The magnetic field sensor of claim 14 , wherein the bridge configuration provides a differential output signal.
16. A magnetic field sensor system comprising:
a conductive target configured to carry an eddy current, wherein the eddy current generates a reflected magnetic field; and
a sensor integrated circuit proximate to the conductive target, the sensor integrated circuit comprising:
at least one coil responsive to an AC coil drive signal to generate a directly coupled magnetic field and to induce the eddy current in the conductive target;
at least one magnetic field sensing element responsive to a sensing element drive signal and configured to simultaneously detect the directly coupled magnetic field and the reflected magnetic field and to generate a magnetic field signal comprising a first component having a first frequency in response to the directly coupled magnetic field and a second component having a second frequency different than the first frequency in response to the reflected magnetic field, the magnetic field signal having a sensitivity affected by one or both of a change in temperature and a level of the AC coil drive signal, wherein the first component of the magnetic field signal comprises a sensitivity value;
a coil driver configured to generate the AC coil drive signal with an adjustable magnitude;
a sensing element driver configured to generate the sensing element drive signal with an adjustable magnitude;
a separating circuit configured to separate the second component of the magnetic field signal from the magnetic field signal; and
an output signal generator configured to generate an output signal of the magnetic field sensor system in response to the second component of the magnetic field signal and indicative of the reflected magnetic field, wherein the output signal generator comprises:
a temperature sensor configured to measure temperature;
a material type selector comprising parameters to compensate for temperature effects and for a type of material used for the conductive target;
a temperature compensator directly connected to the separating circuit, the temperature compensator configured to receive the second component of the magnetic field signal directly from the separating circuit, and configured to generate an output signal in response to the temperature measured by the temperature sensor and to one or more of the parameters from the material type selector; and
a linearization module configured to perform a linear regression on the output signal generated by the temperature compensator,
wherein the coil driver and the sensing element driver are configured to receive the sensitivity value and are respectively configured to adjust the magnitude of one or both of the sensing element drive signal and the AC coil drive signal in response to the sensitivity value in order to permit detection of the conductive target in a manner that is substantially independent of the sensitivity of the magnetic field signal.
17. The magnetic field sensor system of claim 16 , wherein the AC coil drive signal has the first frequency and the second frequency.
18. The magnetic field sensor system of claim 16 , wherein the output signal of the linearization module is the output signal of the magnetic field sensor system.