Magnetic field sensor with shared path amplifier and analog-to-digital-converter

1. A magnetic field sensor comprising:

at least one magnetic field sensing element configured to generate a measured magnetic field signal responsive to an external magnetic field and to generate a reference magnetic field signal responsive to a reference magnetic field;

a signal path comprising an amplifier and an analog-to-digital converter for processing the measured magnetic field signal during a first time period to generate a sensor output signal indicative of the external magnetic field, and for processing the reference magnetic field signal during a second time period, the analog-to-digital converter comprising at least one integrator circuit having a first capacitor configured to process the measured magnetic field signal and a second capacitor configured to process the reference magnetic field signal, wherein the analog-to-digital converter is responsive to the measured magnetic field signal to generate a digital measured magnetic field signal and responsive to the reference magnetic field signal to generate a digital reference magnetic field signal;

a controller configured to switch the first capacitor with the second capacitor to enable the first capacitor to process the reference magnetic field signal; and

a comparator circuit to compare the reference magnetic field signal to a threshold value during the second time period to determine whether a fault is present;

wherein the first time period and the second time period are non-overlapping time periods.

2. The magnetic field sensor of claim 1 further comprising a reference coil proximate to the at least one magnetic field sensing element, wherein the reference coil is configured to carry a reference current to generate the reference magnetic field.

3. The magnetic field sensor of claim 1 wherein the at least one magnetic field sensing element is configurable to generate the measured magnetic field signal during the first time period and to generate the reference magnetic field signal during the second time period.

4. The magnetic field signal of claim 1 further comprising an output signal generator responsive to the measured magnetic field signal and to the diagnostic signal to generate the sensor output signal.

5. The magnetic field signal of claim 1 further comprising a diagnostic trim circuit configured to adjust a gain of the reference magnetic field, an offset of the reference magnetic field signal, or both.

6. The magnetic field sensor of claim 1 further comprising a built-in self-test circuit configured to detect an error in the magnetic field sensor.

7. The magnetic field sensor of claim 1 wherein the at least one magnetic field sensing element comprises a Hall effect element.

8. The magnetic field sensor of claim 1 wherein the at least one magnetic field sensing element comprises a magnetoresistance element.

9. A magnetic field sensor comprising:

at least one magnetic field sensing element configured to generate a measured magnetic field signal responsive to an external magnetic field and to generate a reference magnetic field signal responsive to a reference magnetic field;

a signal path comprising:

a shared portion for processing the measured magnetic field signal during a first time period to generate a sensor output signal indicative of the external magnetic field, and for processing the reference magnetic field signal during a second time period, wherein the first and second time periods are non-overlapping time periods;

a dedicated portion for processing the measured magnetic field signal during the first time period; and

at least one integrator circuit having a first capacitor configured to process the measured magnetic field signal and a second capacitor configured to process the reference magnetic field signal; and

a comparator circuit to compare the reference magnetic field signal to a threshold value during the second time period to determine whether a fault is present; and

a controller configured to switch the first capacitor with the second capacitor to enable the dedicated portion of the signal path to process the reference magnetic field signal.

10. The magnetic field sensor of claim 9 further comprising an analog-to-digital converter comprising at least one integrator and wherein the dedicated portion of the signal path comprises a capacitor of the at least one integrator.

11. The magnetic field sensor of claim 9 wherein the controller is configured to enable the dedicated portion of the signal path to process the reference magnetic field during a diagnostic mode of operation.

12. The magnetic field sensor of claim 9 further comprising a built-in self-test circuit configured to detect an error in the magnetic field sensor.

13. A magnetic field sensor comprising:

at least one magnetic field sensing element configured to generate a measured magnetic field signal responsive to an external magnetic field and to generate a reference magnetic field signal responsive to a reference magnetic field;

a signal path for processing the measured magnetic field signal during a first time period to generate a sensor output signal indicative of the external magnetic field and for processing the reference magnetic field signal during a second time period, the signal path comprising at least one integrator circuit having a first capacitor configured to process the measured magnetic field signal and a second capacitor configured to process the reference magnetic field signal, wherein the first time period and the second time period are non-overlapping time periods;

a controller configured to switch the first capacitor with the second capacitor to enable the second capacitor of the integrator circuit to process the reference magnetic field signal;

a comparator circuit to compare the reference magnetic field signal to a threshold value during the second time period to determine whether a fault is present; and

a diagnostic trim circuit configured to adjust a gain of the reference magnetic field signal, an offset of the reference magnetic field signal, or both.

14. The magnetic field sensor of claim 13 wherein the diagnostic trim circuit is configured to adjust at least one of the gain and the offset of the reference magnetic field signal based on a sensed temperature.

15. The magnetic field sensor of claim 13 further comprising an analog-to-digital converter responsive to the measured magnetic field signal to generate a digital measured magnetic field signal and responsive to the reference magnetic field signal to generate a digital reference magnetic field signal and wherein the diagnostic trim circuit is configured to adjust at least one of the gain and the offset of the digital reference magnetic field signal.

16. The magnetic field sensor of claim 13 further comprising a built-in self-test circuit configured to detect an error in the magnetic field sensor.

17. The magnetic field sensor of claim 13 wherein the at least one magnetic field sensing element is selected from a Hall effect element, a magnetoresistance element, or both.

18. A magnetic field sensor comprising:

means for generating a measured magnetic field signal responsive to an external magnetic field;

means for generating a reference magnetic field signal responsive to a reference magnetic field;

a signal path comprising:

means for processing the measured magnetic field signal during a first time period to generate a sensor output signal indicative of the external magnetic field;

means for processing the reference magnetic field signal during a second time period; and

means for converting the measured magnetic field signal and the reference magnetic field signal to digital signals, the means for converting comprising at least one integrator circuit having a first capacitor configured to process the measured magnetic field signal and a second capacitor configured to process the reference magnetic field signal; and

means for selectively coupling the first capacitor to the signal path during the first time period and coupling the second capacitor to the signal path during the second time period; and

means for detecting a fault and generating a signal indicative of whether a fault is present;

wherein the first time period and the second time period are non-overlapping time periods.