Circuits and Methods for Generating a Self-Test of a Magnetic Field Sensor

• US 20100211347A1
• Filed: 02/16/2010
• Published: 08/19/2010
• Est. Priority Date: 02/17/2009
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Friedrich, Andreas P., Taylor, William P., Doogue, Michael C., Scheller, P. Karl, Vig, Ravi, Foletto, Andrea
• Granted Patent: US 8,447,556 B2
• Time in Patent Office: Days
• US Class Current: 702/117
• 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 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

A magnetic field sensor includes built in self-test circuits that allow a self-test of most of, or all of, the circuitry of the magnetic field sensor, including self-test of a magnetic field sensing element used within the magnetic field sensor, while the magnetic field sensor is functioning in normal operation.

Claims

1. A magnetic field sensor, comprising:

a magnetic field sensing element supported by a substrate, the magnetic field sensing element for generating a composite magnetic field signal comprising a measured-magnetic-field-responsive signal portion and a self-test-responsive signal portion, wherein the measured-magnetic-field-responsive signal portion is responsive to a measured magnetic field and the self-test-responsive signal portion is responsive to a self-test magnetic field;

a self-test circuit comprising a self-test current conductor proximate to the magnetic field sensing element, the self-test current conductor for carrying a self-test current to generate the self-test magnetic field; and

a processing circuit coupled to receive a signal representative of the composite magnetic field signal, configured to generate a sensor signal representative of the measured-magnetic field-responsive signal portion, and configured to generate at least one of a diagnostic signal representative of the self-test-responsive signal portion or a composite signal representative of both the measured-magnetic-field-responsive signal portion and the self-test-responsive signal portion.

2. The magnetic field sensor of claim 1, wherein the self-test current conductor comprises a conductor supported by the substrate and proximate to the magnetic field sensing element.

3. The magnetic field sensor of claim 1, wherein the self-test current conductor comprises a conductor supported by the substrate and spanning more than one metal layer supported by the substrate.

4. The magnetic field sensor of claim 1, further comprising a circuit board proximate to the magnetic field sensing element, wherein the self-test current conductor comprises a conductor supported by the circuit board.

5. The magnetic field sensor of claim 4, wherein the self-test current conductor comprises a coil supported by the circuit board and spanning more than one metal layer supported by the circuit board.

6. The magnetic field sensor of claim 1, wherein the self-test current conductor comprises a conductor separate from but proximate to the substrate.

7. The magnetic field sensor of claim 1, further comprising a switching circuit configured to switch a direction of the self-test current and the associated self-test magnetic field in response to a magnitude of the measured magnetic field.

8. The magnetic field sensor of claim 7, further comprising an electromagnetic shield proximate to the self-test current conductor.

9. The magnetic field sensor of claim 8, wherein the electromagnetic shield comprises at least one feature configured to reduce an eddy current in the electromagnetic shield when the shield is exposed to an AC magnetic field.

10. The magnetic field sensor of claim 1, wherein the processing circuit is configured to receive the composite magnetic field signal and configured to generate at least one of the diagnostic signal or the composite signal, wherein the diagnostic signal is responsive to the self-test magnetic field and not responsive to the measured magnetic field, and wherein the composite signal is responsive to both the measured magnetic field and the self-test magnetic field.

11. The magnetic field sensor of claim 10, wherein the processing circuit is further configured to generate the sensor signal, wherein the sensor signal is responsive to the measured magnetic field and not responsive to the self-test magnetic field.

12. The magnetic field sensor of claim 11, further comprising a combining circuit configured to combine a signal representative of the sensor signal with a signal representative of the diagnostic signal to generate a combined output signal.

13. The magnetic field sensor of claim 1, wherein the self-test circuit further comprises a diagnostic request processor coupled to receive a diagnostic input signal, configured to decode the diagnostic input signal, and configured to generate a diagnostic control signal configured to control the self-test circuit.

14. The magnetic field sensor of claim 13, wherein the self-test circuit further comprises:

a current generator circuit having an output node at which self-test current pulses are generated, wherein the self-test current conductor is coupled to receive the self-test current pulses resulting in the self-test magnetic field having magnetic field pulses.

15. The magnetic field sensor of claim 14, wherein the current generator is configured to generate the self-test current pulses in response to the diagnostic control signal.

16. The magnetic field sensor of claim 13, wherein the diagnostic control signal comprises control pulses, each control pulse resulting in one self-test current pulse from the current generator.

17. The magnetic field sensor of claim 13, wherein the diagnostic control signal comprises control pulses, each control pulse resulting in a plurality of self-test current pulses from the current generator.

18. The magnetic field sensor of claim 13, wherein the diagnostic control signal comprises a first state during which the current generator generates self-test current pulses and a second state during which the current generator does not generate self-test current pulses.

19. The magnetic field sensor of claim 13, wherein the diagnostic control signal comprises first control pulses with a first duty cycle during which the current generator generates self-test current pulses, and wherein the diagnostic control signal comprises second control pulses with a second duty cycle during which the current generator does not generate self-test current pulses.

20. The magnetic field sensor of claim 13, wherein the diagnostic control signal comprises a binary digital word.

21. The magnetic field sensor of claim 13, wherein the processing circuit comprises a track-and-hold circuit having an input node, and output node, and a control node, wherein the track-and-hold circuit is coupled to receive a signal representative of the composite signal at the input node, coupled to receive a signal representative of the diagnostic control signal at the control node, and configured to generate a signal representative of the sensor signal at the output node.

22. The magnetic field sensor of claim 1, further comprising a diagnostic output formatting circuit coupled to receive the diagnostic signal and configured to generate a diagnostic output signal representative of the diagnostic signal, wherein the diagnostic output signal comprises a pulse indicative of a properly functioning magnetic field sensor.

23. The magnetic field sensor of claim 1, further comprising a diagnostic output formatting circuit coupled to receive the diagnostic signal and configured to generate a diagnostic output signal representative of the diagnostic signal, wherein the diagnostic output signal comprises a state indicative of a properly functioning magnetic field sensor.

24. The magnetic field sensor of claim 1, further comprising a diagnostic output formatting circuit coupled to receive the diagnostic signal and configured to generate a diagnostic output signal representative of the diagnostic signal, wherein the diagnostic output signal comprises a predetermined duty cycle indicative of a properly functioning magnetic field sensor.

25. The magnetic field sensor of claim 1, further comprising a diagnostic output formatting circuit coupled to receive the diagnostic signal and configured to generate a diagnostic output signal representative of the diagnostic signal, wherein the diagnostic output signal comprises a binary digital word indicative of a properly functioning magnetic field sensor.

26. The magnetic field sensor of claim 1, further comprising a sensor output formatting circuit coupled to receive the sensor signal and configured to generate a sensor output signal representative of the sensor signal, wherein the sensor output signal comprises a two state non-linear signal responsive to the measured magnetic field.

27. The magnetic field sensor of claim 1, further comprising a sensor output formatting circuit coupled to receive the sensor signal and configured to generate a sensor output signal representative of the sensor signal, wherein the sensor output signal comprises a continuous linear signal responsive to the measured magnetic field.

28. The magnetic field sensor of claim 1, further comprising an electromagnetic shield proximate to the self-test current conductor.

29. The magnetic field sensor of claim 28, wherein the electromagnetic shield comprises at least one feature configured to reduce an eddy current in the electromagnetic shield when the shield is exposed to an AC magnetic field.

30. The magnetic field sensor of claim 1, wherein the measured magnetic field is generated by a current carried by a measured-current conductor.

31. The magnetic field sensor of claim 1, further comprising a lead frame comprising a plurality of leads and a coupling of at least two of the leads proximate to the magnetic field sensor, wherein the measured-current conductor comprises the coupling of the at least two of the leads.

32. The magnetic field sensor of claim 1, wherein the self-test circuit further comprises:

a clock generator configured to generate a clock signal;

a diagnostic clock generator coupled to receive the clock signal and configured to generate a diagnostic clock signal; and

a pulse generator coupled to receive the diagnostic clock signal and configured to generate a pulse signal in response to the diagnostic clock signal, wherein the current generator is coupled to receive the pulse signal and configured to generate the self-test current in response to the pulse signal.

33. The magnetic field sensor of claim 1, wherein the magnetic field sensing element comprises a Hall effect element, wherein the magnetic field sensor further comprises a current or voltage generator coupled to the Hall effect element.

34. The magnetic field sensor of claim 1, wherein the magnetic field sensing element comprises a magnetoresistance element, wherein the magnetic field sensor further comprises a current generator coupled to the magnetoresistance element.

35. The magnetic field sensor of claim 1, further comprising an electronic switch coupled across the self-test current conductor.

36. The magnetic field sensor of claim 1, wherein the processing circuit comprises:

a comparator coupled to receive a signal representative of the composite magnetic field signal, coupled to receive a threshold signal, and configured to generate a non-linear output signal; and

a logic circuit configured to generate the threshold signal having a value dynamically selected from among four different threshold signal values.

37. A method of generating a self-test of a magnetic field sensor, comprising:

generating, with a magnetic field sensing element, a composite magnetic field signal comprising a measured-magnetic-field-responsive signal portion and a self-test-responsive signal portion, wherein the measured-magnetic-field-responsive signal portion is responsive to a measured magnetic field and the self-test-responsive signal portion is responsive to a self-test magnetic field;

generating a self-test current in a self-test current conductor proximate to the magnetic field sensing element, the self-test current conductor for carrying the self-test current to generate the self-test magnetic field;

generating a sensor output signal representative of the measured-magnetic-field-responsive signal portion; and

generating at least one of a diagnostic signal representative of the self-test-responsive signal portion or a composite signal representative of both the measured-magnetic-field-responsive signal portion and the self-test-responsive signal portion.

38. The method of claim 37, wherein the self-test current conductor comprises a conductor supported by the substrate and proximate to the magnetic field sensing element.

39. The method of claim 37, wherein the self-test current conductor comprises a coil supported by the substrate and spanning more than one metal layer supported by the substrate.

40. The magnetic field sensor of claim 37, switching a direction of the self-test current and the associated self-test magnetic field in response to a magnitude of the measured magnetic field.

41. The method of claim 40, further comprising electromagnetically shielding the self-test current conductor.

42. The method of claim 37, further comprising electromagnetically shielding the self-test current conductor.