READING CIRCUIT FOR A MAGNETIC FIELD SENSOR WITH SENSITIVITY CALIBRATION, AND RELATED READING METHOD

• US 20120153936A1
• Filed: 11/22/2011
• Published: 06/21/2012
• Est. Priority Date: 11/26/2010
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Romani, Carlo Alberto, Bottinelli, Fabio, Pozzati, Enrico
• Granted Patent: US 9,013,175 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 33/0023 Electronic aspects, e.g. circuits for stimulation, evaluation, control; Treating the measured signals; calibration G01R33/0017 takes precedence
• CPC Class Codes: G01R 33/0035 Calibration of single magnetic sensors, e.g. integrated calibration
• CPC Class Codes: G01R 33/06 using galvano-magnetic devices
• CPC Class Codes: G01R 33/09 Magnetoresistive devices
• CPC Class Codes: G01R 33/096 anisotropic magnetoresistance sensors
• CPC Class Codes: G01R 35/00 Testing or calibrating of apparatus covered by the other groups of this subclass

Abstract

A reading circuit for a magnetic-field sensor, generating an electrical detection quantity as a function of a detected magnetic field and of a detection sensitivity, is provided with an amplification stage, which is coupled to the magnetic-field sensor and generates an output signal as a function of the electrical detection quantity and of an amplification gain. In particular, the amplification gain is electronically selectable, and the reading circuit is moreover provided with a calibration stage, integrated with the amplification stage and configured so as to vary a value of the amplification gain in such a way as to compensate a variation of the detection sensitivity with respect to a nominal sensitivity value.

Claims

1. A reading circuit, comprising:

an amplification stage configured to receive a magnetic field detection signal of a magnetic field sensor and to generate an output signal as a function of the magnetic field detection signal and of an amplification gain of the amplification stage; and

a calibration stage configured to control the amplification gain of the amplification stage based on an indication of a detection sensitivity of the magnetic field sensor.

2. The circuit according to claim 1 wherein said calibration stage is configured to:

measure a value of the output signal associated with a controlled magnetic field having a known value;

determine an effective value of said detection sensitivity as a function of said measured value; and

control the amplification gain based on said effective value of said detection sensitivity.

3. The circuit according to claim 2 wherein said calibration stage is configured to generate an excitation current to excite a magnetization element of the magnetic field sensor and the amplification stage is configured to electrically couple to a first magnetoresistive element of the magnetic field sensor.

4. The circuit according to claim 1 wherein said calibration stage is configured to:

measure at least a first value of said output signal, in the presence of an external magnetic field and in the absence of a controlled magnetic field;

measure at least a second value of said output signal, in the presence both of said external magnetic field and of said controlled magnetic field;

determine an effective value of said detection sensitivity as a function of said first and second measured values; and

control the amplification gain based on said effective value of said detection sensitivity.

5. The circuit according to claim 4 wherein said calibration stage is configured to determine a difference between said first measured value and said second measured value of said output signal.

6. The circuit according to claim 1 wherein said amplification stage comprises an amplifier, having at least one input configured to receive said magnetic field detection signal and at least one output configured to supply said output signal;

and wherein said calibration stage comprises a gain-variation unit, coupled to said amplifier and configured to vary a gain of the amplifier between the at least one input and the at least one output of the amplifier.

7. The circuit according to claim 6 wherein said amplifier comprises a gain network, coupled to said at least one input and to said at least one output, and said gain-variation unit comprises an adjustable-impedance unit coupled to said gain network and having a selectable impedance value, wherein said calibration stage is configured to provide a gain-control signal to said gain-variation unit for selecting a value of said selectable impedance.

8. The circuit according to claim 1 wherein the magnetic field sensor is an anisotropic magnetoresistive (AMR) magnetic sensor, the amplification stage is configured to electrically couple to a bridge detection structure formed from a plurality of magnetoresistive elements of the magnetic field sensor, and said magnetic detection signal is an unbalancing signal of said bridge detection structure.

9. A system comprising:

a magnetic-field sensor configured to generate a magnetic field detection signal as a function of one or more magnetic fields; and

a reading circuit having;

an amplification stage coupled to the magnetic-field sensor and configured to generate an output signal as a function of the magnetic field detection signal and of an amplification gain of the amplification stage; and

a calibration stage configured to control the amplification gain of the amplification stage based on an indication of a detection sensitivity of the magnetic field sensor.

10. The system of claim 9, further comprising a control unit, coupled to said reading circuit and configured to receive said output signal.

11. The system according to claim 9 wherein said reading circuit is an application-specific integrated circuit housed in a same package together with a die comprising said magnetic-field sensor.

12. The system of claim 9 wherein said calibration stage is configured to:

measure a value of the output signal associated with a controlled magnetic field having a known value;

determine an effective value of said detection sensitivity as a function of said measured value; and

control the amplification gain based on said effective value of said detection sensitivity.

13. The system of claim 12 wherein said calibration stage is configured to generate an excitation current to excite a magnetization element of the magnetic field sensor and the amplification stage is configured to electrically couple to a first magnetoresistive element of the magnetic field sensor.

14. The system of claim 9 wherein said calibration stage is configured to:

measure at least a first value of said output signal, in the presence of an external magnetic field and in the absence of a controlled magnetic field;

measure at least a second value of said output signal, in the presence both of said external magnetic field and of said controlled magnetic field;

determine an effective value of said detection sensitivity as a function of said first and second measured values; and

control the amplification gain based on said effective value of said detection sensitivity.

15. The system of claim 14 wherein said calibration stage is configured to determine a difference between said first measured value and said second measured value of said output signal.

16. A method, comprising:

receiving a signal of a magnetic-field sensor, the received signal being a function of a detected magnetic field and of a detection sensitivity of the magnetic-field sensor;

controlling an amplification gain of a reading circuit to compensate for a variation of said detection sensitivity from a nominal detection sensitivity value; and

generating an output of the reading circuit as a function of said received signal and of said amplification gain.

17. The method of claim 16 wherein said controlling the amplification gain comprises:

measuring a value of the output signal associated with a controlled magnetic field having a known value;

determining an effective value of said detection sensitivity as a function of said measured value; and

controlling the amplification gain based on said effective value of said detection sensitivity.

18. The method of claim 17 wherein said measuring a value of the output signal associated with a controlled magnetic field comprises generating an excitation current to excite a magnetization element of the magnetic field sensor.

19. The method of claim 16 wherein said controlling the amplification gain comprises:

measuring at least a first value of said output signal, in the presence of an external magnetic field and in the absence of a controlled magnetic field;

measuring at least a second value of said output signal, in the presence both of said external magnetic field and of said controlled magnetic field;

determining an effective value of said detection sensitivity as a function of said first and second measured values; and

controlling the amplification gain based on said effective value of said detection sensitivity.

20. The method of claim 19 wherein said determining said effective value comprises determining a difference between said first measured value and said second measured value of said output signal.

21. A system comprising:

means for generating a magnetic field detection signal as a function of one or more magnetic fields;

means for generating an output signal as a function of the magnetic field detection signal and an amplification gain; and

means for controlling the amplification gain based on an indication of a detection sensitivity of the means for generating the magnetic field detection signal.

22. The system of claim 21 comprising an application-specific integrated circuit including the means for generating the output signal and the means for controlling the amplication gain in a same package together with a die comprising said means for generating the magnetic field detection signal.

23. The system of claim 21 wherein said means for controlling the amplification gain is configured to:

measure at least a first value of said output signal, in the presence of an external magnetic field and in the absence of a controlled magnetic field;

measure at least a second value of said output signal, in the presence both of said external magnetic field and of said controlled magnetic field;

determine an effective value of said detection sensitivity as a function of said first and second measured values; and

control the amplification gain based on said effective value of said detection sensitivity.

24. The system of claim 23 wherein said means for controlling the amplification gain is configured to determine a difference between said first measured value and said second measured value of said output signal.