Magnetic field sensors and systems with sensor circuit portions having different bias voltages and frequency ranges
Embodiments relate to Hall effect sensor circuits and devices that provide improved performance, such as reduced residual offset errors and/or improved S/N ratios. In an embodiment, a Hall effect sensor circuit comprises two circuit portions, a first with a higher bandwidth for higher frequencies and having an improved S/N ratio, and a second with a lower bandwidth for lower frequencies and having low residual offset. First and second Hall plates or devices are incorporated in the first and second circuit portions. The first Hall plate can be operated with a larger bias voltage and a larger, high-pass-filtered signal bandwidth, while the second Hall plate can be operated with a smaller bias voltage and a smaller, low-pass-filtered signal bandwidth. Individual output signals from each of the first and second Hall plates can be scaled and combined to provide an overall output signal with the benefits of each circuit portion, including reduced residual offset error and negligible increased noise.
1. A magnetic field sensor comprising:
a first magnetic field sensor element configured for a first bias voltage and coupled to first filter circuitry to provide a first signal of a first bandwidth;
at least one second magnetic field sensor element configured for a second bias voltage less than the first bias voltage and coupled to second filter circuitry to provide a second signal of a second bandwidth less than the first
circuitry configured to generate a combined signal based on the first signal and the second signal; and
comparator circuitry configured to:
compare the first signal from the first magnetic signal field sensor element and the combined signal; and
generate a magnetic field sensor output signal based on the comparison of the first signal and the combined signal.
2. The magnetic field sensor of claim 1 , wherein the first and at least one second magnetic field sensor elements are selected from the group consisting of: a Hall plate; a Hall probe; a vertical Hall effect element; and a magnetoresistive element.
3. The magnetic field sensor of claim 1 , wherein the first filter circuitry comprises high-pass filter circuitry, and the second filter circuitry comprises low-pass filter circuitry.
4. The magnetic field sensor of claim 1 , further comprising:
a first switch coupled to the first magnetic field sensor element, the first switch having a first switching frequency; and
a second switch coupled to the at least one second magnetic field sensor element, the second switch having a second switching frequency less than the first switching frequency.
5. The magnetic field sensor of claim 1 , further comprising:
a first analog-to-digital converter (ADC) coupled between the first magnetic field sensor element and the first filter circuitry; and
a second ADC coupled between the at least one second magnetic field sensor element and the second filter circuitry.
6. The magnetic field sensor of claim 5 , further comprising scaling circuitry coupled between the second ADC and the circuitry configured to combine the first signal and the second signal.
7. The magnetic field sensor of claim 6 , wherein the scaling circuitry is configured to apply a scaling factor related to a ratio between the first bias voltage and the second bias voltage.
8. The magnetic field sensor of claim 1 , wherein the first signal has a lower noise component than the second signal.
9. The magnetic field sensor of claim 1 , wherein the second signal has a lower residual offset error than the first signal.
10. A method comprising:
applying a first bias voltage to a first magnetic field sensor element;
applying a second bias voltage to a second magnetic field sensor element, the second bias voltage being less than the first bias voltage;
sensing a magnetic field by the first and second magnetic field sensor elements to obtain a first magnetic field sensor signal and a second magnetic field sensor signal;
generating a first filtered magnetic field sensor signal based on the first magnetic field sensor signal;
generating a second filtered magnetic field sensor signal based on the second magnetic field sensor signal;
combining the first filtered magnetic field sensor signal and the second filtered magnetic field sensor signal to generate a combined signal; and
comparing the combined signal and the first magnetic field sensor signal to generate a magnetic field sensor output signal based on the comparison of the combined signal and the first magnetic field sensor signal.
11. The method of claim 10 , further comprising scaling the second filtered magnetic field sensor signal before the combining.
12. The method of claim 11 , wherein the combining comprises summing the first filtered magnetic field sensor signal and the scaled second filtered magnetic field sensor signal.
13. The method of claim 10 , further comprising:
digitizing the first magnetic field sensor signal, wherein the first filtered magnetic field sensor signal is based on the digitized first magnetic field sensor signal; and
digitizing the second magnetic field sensor signal, wherein the second filtered magnetic field sensor signal is based on the digitized second magnetic field sensor signal.
14. The method of claim 13 , further comprising chopping the first magnetic field sensor signal at a first frequency before the digitizing, and chopping the second magnetic field sensor signal at a second frequency less than the first frequency before the digitizing.
15. A magnetic field sensor comprising:
a first magnetic field sensor element configured for a first bias voltage and coupled to a first switch having a first switching frequency;
a second magnetic field sensor element configured for a second bias voltage less than the first bias voltage and coupled to a second switch having a second switching frequency less than the first switching frequency;
circuitry configured to:
generate a first filtered signal based on a signal from the first switch;
generate a second filtered signal based the second switch; and
generate a combined signal based on the first filtered signal and the second filtered signal; and
an amplifier configured to:
receive the signal from the first switch and the combined signal as inputs; and
generate a magnetic field sensor output signal based on the signal from the first switch and the combined signal.
16. The magnetic field sensor of claim 15 , wherein the circuitry comprises at least one analog-to-digital converter (ADC) and at least one digital-to-analog converter (DAC).
17. The magnetic field sensor of claim 16 , wherein the circuitry comprises at least one low-pass filter.
18. The magnetic field sensor of claim 15 , wherein the magnetic field sensor output signal is an analog signal.
19. The magnetic field sensor of claim 15 , wherein the signal from the first switch has a lower noise component than the signal from the second switch.
20. The magnetic field sensor of claim 15 , wherein the signal from the first switch has a lower residual offset error than the signal from the second switch.