HALL ELEMENT SIGNAL CALIBRATING IN ANGLE SENSOR

Abstract

In one aspect, an angle sensor includes a first Hall element disposed on a first axis, a second Hall element disposed on a second axis perpendicular to the first axis and a conduction path having a first portion extending parallel to the first axis and a second portion parallel to the second axis. The conduction path is configured to conduct a calibration current that generates a first magnetic flux density measured at the first Hall element and a second magnetic flux density measured at the second Hall element. The angle sensor also includes calibration circuitry configured to generate one or more compensation signals based on the first and second magnetic flux densities and to adjust an external magnetic flux density measured at the second Hall element due to an external magnetic field using the one or more compensation signals to reduce angle error of the angle sensor.

Description

BACKGROUND

Typically, a magnetic-field angle sensor measures a direction of a magnetic-field vector through 360° in an x-y plane. In one example, a magnetic-field angle sensor may be used to detect an angular position of a rotating magnet. Some magnetic-field angle sensors may include one or more Hall elements. When signals from Hall elements are not properly calibrated, angle error of the angle sensor increases. Generally, the angle error is defined to be the difference between an actual position of a magnet and a position of the magnet as measured by the angle sensor.

SUMMARY

In one aspect, an angle sensor includes a first Hall element disposed on a first axis, a second Hall element disposed on a second axis perpendicular to the first axis and a conduction path having a first portion extending parallel to the first axis and a second portion parallel to the second axis. The conduction path is configured to conduct a calibration current that generates a first magnetic flux density measured at the first Hall element and a second magnetic flux density measured at the second Hall element. The angle sensor also includes calibration circuitry configured to generate one or more compensation signals based on the first and second magnetic flux densities and to adjust an external magnetic flux density measured at the second Hall element due to an external magnetic field using the one or more compensation signals to reduce angle error of the angle sensor.

In another aspect, a method includes determining one or more compensation signals based on a first magnetic flux density measured at a first Hall element of an angle sensor disposed on a first axis and a second magnetic flux density measured at a second Hall element of the angle sensor disposed on a second axis perpendicular to the first axis and adjusting an external magnetic flux density measured at the second Hall element due to an external magnetic field using the one or more compensation signals.

In a further aspect, an angle sensor includes a first Hall element disposed on a first axis, a second Hall element disposed on a second axis perpendicular to the first axis, a first conduction path extending parallel to the first axis, a second conduction path extending parallel to the second axis, and calibration circuitry configured to generate one or more compensation signals based on the first and second magnetic flux densities and adjust an external magnetic flux density measured at the second Hall element due to an external magnetic field using the one or more compensation signals to reduce angle error of the angle sensor. The first conduction path is configured to conduct a first calibration current that generates a first magnetic flux density measured at the first Hall and the second conduction path is configured to conduct a second calibration current that generates a second magnetic flux density measured at the second Hall element.

In a still further aspect, an angle sensor includes a first Hall element disposed on a first axis; a second Hall element disposed on a second axis perpendicular to the first axis and a means for calibrating signals from the first and second Hall elements.

DESCRIPTION OF THE DRAWINGS

The foregoing features may be more fully understood from the following description of the drawings. The drawings aid in explaining and understanding the disclosed technology. Since it is often impractical or impossible to illustrate and describe every possible embodiment, the provided figures depict one or more illustrative embodiments. Accordingly, the figures are not intended to limit the scope of the broad concepts, systems and techniques described herein. Like numbers in the figures denote like elements.

FIG. 1 is a block diagram of an example of an integrated circuit (IC) to calibrate signals from Hall elements;

FIGS. 2A and 2B are diagrams of vertical Hall elements with a conduction path used to generate magnetic field flux densities;

FIG. 3 is a diagram of planar Hall elements with a conduction path arranged in a coil used to generate magnetic field flux densities;

FIG. 4 is a graph a magnetic field versus Hall voltage;

FIGS. 5A to 5C are circuit diagrams used to generate compensation signals;

FIGS. 6A to 6C are circuit diagrams to calibrate signals measured from Hall elements using the compensation signals from FIGS. 5A to 5C; and

FIG. 7 is a block diagram of an example of a circuit used to calibrate signals from Hall elements.

DETAIL DESCRIPTION

Described herein are techniques to improve angle accuracy of a magnetic-field angle sensor (e.g., on an integrated circuit (IC)) by calibrating signals, on the IC, from Hall elements used in an angle sensor as opposed to a one-time calibration done at an IC manufacturer.

Referring to FIG. 1, an example of an IC that performs calibration of signals from Hall element is an IC 100. The IC 100 includes an angle sensor 101 and power 110 that power components on the IC 100 including the angle sensor 101. The angle sensor 101 includes Hall elements 102, angle processing circuitry 104 and calibration circuitry 108.

In one example, the Hall elements 101 are planar Hall elements. In another example, the Hall elements 101 are vertical Hall elements.

The Hall elements 102 in this embodiment include at least two Hall elements that are orthogonal to each other and the angle sensor 101 is a 2D (two-dimensional) angle sensor. For example, at least one Hall element is along an x-axis and at least one Hall element is along a y-axis.

In other embodiments, the Hall elements 102 may include at least three Hall elements that are orthogonal to each other and the angle sensor 101 is a 3D (three-dimensional) angle sensor. For example, at least one Hall element is along an x-axis, at least one Hall element is along a y-axis and at least one Hall element is along a z-axis.

In one example, the Hall elements 102 provide a signal X 122 from at least one Hall element along the x-axis and a signal Y 122 from at least one Hall element along the y-axis. The signals X 122, Y 124 are sent to the angle processing circuitry 104 and to the calibration circuitry 108.

In one example, in a first mode, the calibration circuitry 108 provides a calibration current I_cal 126 used in calibrating signals from the Hall elements 102. The calibration current I_cal 126 is used to measure the sensitivity of the Hall elements 101. In particular, the calibration current I_cal 126 generates a magnetic flux density that is detected by the Hall elements 102. The signals X 122, Y 124, which are provided by the Hall elements 102, are used by the calibration circuitry 108 to generate one or more compensation signals 128. In one example, the calibration current I_cal 126 is an alternating current. In one example, a frequency of the calibration current I_cal 126 is 100 kHz.

In a second mode, without the calibration current I_cal activated, the Hall elements 102 detect a magnetic field and provide the signals X 122, Y 124. The angle circuitry 104 uses the compensation signals 128 to calibrate one or more of the signals X 122, Y 124. Based on the signals X 122, Y 124 and the compensation signals 128, the angle circuitry 104 provides an output signal 130 that includes an angle.

Referring to FIGS. 2A and 2B, an example of a circuit configuration used to generate magnetic field flux densities is a circuit configuration 200. In one example, the circuit configuration 200 includes at least two vertical Hall elements (e.g., a Hall element 202a and a Hall element 202b) and a conduction path 204. In one example, the conduction path 204 carries the calibration current 126 (FIG. 1) and generates a first magnetic field flux density B₁ along the first Hall element 202a and a second magnetic field flux density B₂ along the second Hall element 202b.

Each Hall element 202a, 202b includes at least five metal contacts. For example, the Hall element 202a includes a contact 206, a contact 208, a contact 210, a contact 212 and a contact 214, and the Hall element 202b includes a contact 216, a contact 218, a contact 220, a contact 222 and a contact 224.

The contacts 206, 214 are used to supply power to the Hall element 202a. The contacts 208, 212 are used to measure signals (e.g., a voltage signal) from the Hall element 202a and the contact 210 provides a ground to the Hall element 202a.

The contacts 216, 224 are used to supply power to the Hall element 202b. The contacts 218, 222 are used to measure signals (e.g., a voltage signal) from the Hall element 202b and the contact 220 provides a ground to the Hall element 202b.

The conduction path 204 is separated from the Hall plates 202a, 202b by a distance D. In one example, the distance D is 1 micron.

The magnetic field flux density generated by the calibration current is:

$B_{\mathrm{cal}}=\frac{1}{r}*\frac{\mu }{2\pi }*I_{cal}.$

Assuming a 1 micron distance between the Hall element and the conduction path and a 10 mA conduction current, the expected magnetic flux density is 20G and the coupling factor is

$\frac{B_{cal}}{I_{\mathrm{cal}}}\mathrm{or}2G\text{/}\mathrm{mA}.$

Referring to FIG. 3, another example of a circuit configuration to generate magnetic field flux densities is a circuit configuration 300. In one example, the circuit configuration 200 includes at least two planar Hall elements (e.g., a Hall element 302a and a Hall element 302b) and a conduction path 304 in a form of a coil. In one example, the conduction path 204 carries the calibration current 126 (FIG. 1) and generates a first magnetic field flux density B₁ along the first Hall element 302a and a second magnetic field flux density B₂ along the second Hall element 302b.

Each Hall element 302a, 302b includes at least five metal contacts. For example, the Hall element 302a includes a contact 306, a contact 308, a contact 310, a contact 312 and a contact 314, and the Hall element 302b includes a contact 316, a contact 318, a contact 320, a contact 322 and a contact 324.

The contacts 306, 314 are used to supply power to the Hall element 302a. The contacts 308, 312 are used to measure voltage from the Hall element 302a and the contact 210 provides a ground to the Hall element 302a.

The contacts 316, 324 are used to supply power to the Hall element 302b. The contacts 318, 322 are used to measure voltage from the Hall element 302b and contact 320 provides a ground to the Hall element 302b.

While FIGS. 2A, 2B and 3 show Hall elements with a single conduction path, in other embodiments, one or more Hall elements may have a separate conduction path from the other Hall elements and thereby have their own respective calibration current. In one example, each Hall elements has a separate conduction path from the other Hall elements. Each conduction path may have a separate or the same current source to generate the respective calibration current. In one example, the current sources that generate the respective calibration currents are current mirrors. In one example, the respective calibration currents are equal.

Referring to FIG. 4, typically a magnetic sensor detects magnetic flux densities between 100 Gauss (G) to 1,000 G. Therefore, applying 20G may vary the measured magnetic flux density by roughly 2% to 20%. If the calibration current I_cal 126 (FIG. 1) is bidirectional, + or −20G may be achieved doubling the signal variation. Using calibration currents with frequencies higher than a sampling frequency (e.g., >100 kHz) enables a measurement of the Hall element sensitivity, which is equal to a slope in FIG. 4 and shows Hall voltage with respect to magnetic field flux density. For example, the sensitivity of a first Hall element is:

${\mathrm{sensitivity}}_{He1}=\frac{\Delta V_{\mathrm{Hall}1}}{\Delta B_{\mathrm{ext}}},$

and the sensitivity of a second Hall element is:

${\mathrm{sensitivity}}_{He2}=\frac{\Delta V_{\mathrm{Hall}2}}{\Delta B_{\mathrm{ext}}},$

and a sensitivity mismatch is:

${\mathrm{sensitivity}}_{\mathrm{mismatch}}=\frac{{\mathrm{sensitivity}}_{He2}}{{\mathrm{sensitivity}}_{He1}}=\frac{\Delta V_{\mathrm{Hall}2}}{\Delta V_{\mathrm{Hall}1}},$

where ΔV_{Hall 1} is the change in voltage of the first Hall element, ΔV_{Hall 2} is the change in voltage of the second Hall element, and ΔB_ext is the change in magnetic field flux density.

Variances in the measured sensitivity causing a sensitivity mismatch lead to harmonic errors. By compensating the sensitivity mismatch by a change in the Hall element biasing current and/or a mathematical factor in angle processing, the angle accuracy may be improved.

Referring to FIGS. 5A to 5C, examples of circuits to generate compensation signals are circuits 500a, 500b, 500c. The circuits 500a-500c determine compensations signal 524a, 524b, 524c, which are in one embodiment, examples of compensation signals 128.

In one example, the circuit 500a provides a compensation signal in the x-direction. The circuit 500a includes a current source 502a that provides a calibration current I_{x cal} on a conduction path 504a to a coil 506a. The coil 506a generates a magnetic flux density B_{x cal} that is detected by a Hall element 510a that is aligned along an x-axis. The coupling factor F_x is equal to B_{x cal}/I_{x cal}.

The output signal of the Hall element 510a is amplified by an amplifier 514a and converted from an analog signal to a digital signal by an analog-to-digital converter (ADC) 518a. The digital signal is a calibration signal 524a and represented as B_{x cal, measure}.

In one example, the circuit 500b provides a compensation signal in the y-direction. The circuit 500b includes a current source 502b that provides a calibration current I_{y cal} on a conduction path 504b to a coil 506b. The coil 506b generates a magnetic flux density B_{y cal} that is detected by a Hall element 510b that is aligned along a y-axis. The coupling factor F_y is equal to B_{y cal}/I_{y cal}.

The output signal of the Hall element 510b is amplified by an amplifier 514b and converted from an analog signal to a digital signal by an ADC 518b. The digital signal is a calibration signal 524b and represented as B_{y cal, measure}.

In one example, the circuit 500c provides a compensation signal in the c-direction. The circuit 500c includes a current source 502c that provides a calibration current I_{y cal} on a conduction path 504c to a coil 506c. The coil 506c generates a magnetic flux density B_{z cal} that is detected by a Hall element 510c that is aligned along a z-axis. The coupling factor F_z is equal to B_{z cal}/I_{z cal}.

The output signal of the Hall element 510c is amplified by an amplifier 514c and converted from an analog signal to a digital signal by an ADC 518c. The digital signal is a calibration signal 524c and represented as B_{z cal, measure}.

In one embodiment, the current sources 502a-502c are the same current source. In other embodiments, the current sources 502a-502c are current mirrors.

Referring to FIGS. 6A to 6C, examples of circuits to calibrate signals measured from Hall elements using the compensation signals are circuits 600a, 600b, 600c. The circuits 600a-600c determine adjusted signals 612a, 612b, 612c, which are signals that have been calibrated using the compensation signals 524a-524c.

In one example, the circuit 600a provides the adjusted signal 612a in the x-direction. The circuit 600a includes the Hall element 510a, which receives a detected magnetic field, B_ext,x. The output signal of the Hall element 510a is amplified by the amplifier 514a and converted from an analog signal to a digital signal 602a by the ADC 518a. The digital signal 602a is represented as B_{x ext, measure}.

In this embodiment, the digital signal 602a is the adjusted signal 612a. In this embodiment, the Hall elements 510b, 510c that are aligned along the y-axis and the z-axis are calibrated with the Hall element 510a along the x-axis. In other embodiments, the Hall elements may calibrate to the Hall element along the y-axis or the z-axis. In other embodiments, two Hall elements may be calibrated to each other. In still further embodiments, the Hall elements may be calibrated to a low drift current source.

In one example, the circuit 600b provides the adjusted signal 612b in the y-direction. The circuit 600b includes the Hall element 510b, which receives a detected magnetic field, B_ext,y. The output signal of the Hall element 510b is amplified by the amplifier 514b and converted from an analog signal to a digital signal 602b by the ADC 518b. The digital signal 602b is represented as B_{y ext, measure}. The digital signal 602b is provided to a mixer 604b to be mixed with the compensation signal 524a, 524b. That is, the ratio of the compensation signal 524b to the compensation signals 524c (B_{x cal, measure}/B_{y cal, measure}) is mixed with the signal 602b to provide an adjusted signal 612b.

In one example, the circuit 600c provides the adjusted signal 612c in the z-direction. The circuit 600c includes the Hall element 510c, which receives a detected magnetic field, B_ext,z. The output signal of the Hall element 510c is amplified by the amplifier 514c and converted from an analog signal to a digital signal 602c by the ADC 518c. The digital signal 602c is represented as B_{z ext, measure}. The digital signal 602c is provided to a mixer 604c to be mixed with the compensation signals 524a, 524c. That is, the ratio of the compensation signal 524b to the compensation signal 524c (B_{x cal, measure}/B_{z cal, measure}) is mixed with the signal 602c to provide an adjusted signal 612c.

Referring to FIG. 7, an example of the IC 100 (FIG. 1) to calibrate signals from the Hall elements is an IC 100′. The IC 100′ includes an angle sensor 101′, which is an example of the angle sensor 101 (FIG. 1), and power 702 which powers the IC 100′.

The Hall elements 102′ includes Hall elements 102′, which are similar to Hall elements 102 (FIG. 1); angle processing circuitry 104′, which is similar to angle processing circuitry 104 (FIG. 1), and calibration circuitry 108′, which is similar to calibration circuitry 108 (FIG. 1).

The angle sensor 101′ includes a Hall element 702a aligned along the x-axis and a Hall element 702b aligned along the y-axis. The Hall elements 702a, 702b are biased by the Hall plate biasing 706.

The calibration circuitry 108′ includes a calibration biasing circuit 708, which supplies the calibration current I_cal on the conduction path 704 to generate magnetic field flux densities at the coils 702a, 702b adjacent to their respective Hall element 702a, 702b.

Each Hall element 702a, 702b provides a signal to a multiplexor 710 which is controlled by time multiplexor logic 714. The signals from the multiplexor are converted by an ADC 718 from analog to digital and sent to a multiplexor 712 controlled by the time multiplexor logic 714.

The calibration circuitry 108′ also includes calibration logic 726. The signals from the multiplexor 712 are sent to the calibration logic 726 to determine the compensation signals. The compensation signals are sent to compensation factor 730.

In this embodiment, the signals from the Hall plate 702a are calibrated to the Hall plate 702b. Thus, the signals from the Hall plate 702a are mixed by a mixer 737 of the angle processing circuitry 104′ with compensation signals from the compensation factor 730 and sent to an angle processor 742 while the signals from the Hall plate 702b are sent directly to the angle processor 742.

In one example, the angle processor 742 is a CORDIC (COordinate Rotation DIgital Computer). The angle processor 742 may perform various trigonometric functions that can be used to compute an angle of magnetic field. In one example, the angle processor 742 performs a function, α tan 2 (P1, P2) to determine α, the angle of the direction of the magnetic-field vector, where P1 and P2 are parameters. In one example, P1 may represent signals from the Hall element 702b and P2 represents signals from the Hall element 702a.

The angle determined by the angle processor 742 is sent to digital logic 748 and to an output stage 752. The update timer 734 is used to control the calibration logic and the compensation factor 730 to update the calibration signals on a regular basis.

The compensation circuitry 108′ also includes a non-volatile (NV) memory 758. In one example, the NV memory 758 stores parameters to control the update timer 734, the compensation factor 730, the digital logic 748 and the output stage 752.

In some examples, the NV memory 758 store time adjustment factors and amplitude adjustment factors (PID regulator logic) for the compensation block 730 and the update timer block 734 in order to control the speed in which the compensation factor is being adjusted.

In some examples, the NV memory 758 may be used to control the digital logic 748 to adjust the angle output to fit application requirements (e.g., adjust zero angle point, adjust angle gain, adjust angle saturation and so forth).

In some examples, the NV memory 758 may be used to store configuration values for the output stage 752, so that different interfaces may be used (e.g., SENT, PWM with various tick times, frequencies and so forth).

Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Various elements, which are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

1. An angle sensor comprising: a first Hall element disposed on a first axis;a second Hall element disposed on a second axis perpendicular to the first axis;a conduction path having a first portion extending parallel to the first axis and a second portion parallel to the second axis, wherein the conduction path is configured to conduct a calibration current that generates a first magnetic flux density measured at the first Hall element and a second magnetic flux density measured at the second Hall element; andcalibration circuitry configured to: generate one or more compensation signals based on the first and second magnetic flux densities; andadjust an external magnetic flux density measured at the second Hall element due to an external magnetic field using the one or more compensation signals to reduce angle error of the angle sensor.

2. The angle sensor of claim 1, further comprising a third Hall element disposed on a third axis, the third axis being perpendicular to the first axis and being perpendicular to the second axis, wherein the conduction path has a third portion parallel to the third axis.

3. The angle sensor of claim 2, wherein the calibration current generates a third magnetic flux density measured at the third Hall element; wherein the calibration circuitry is further configured to: generate the one or more compensation signals based on the third magnetic flux density; andadjust the magnetic flux measured at the third Hall element from an external magnetic field using the one or more compensation signals.

4. The angle sensor of claim 1, wherein the first and second Hall elements are vertical Hall elements.

5. The angle sensor of claim 1, wherein the first and second Hall elements are planar Hall elements.

6. The angle sensor of claim 5, wherein the conduction path is a coil.

7. The angle sensor of claim 1, wherein the calibration current is an alternating current.

8. The angle sensor of claim 7, wherein a frequency of the calibration current is 100 kHz.

9. The angle sensor of claim 1, wherein the conduction path is spaced apart from the first Hall element by about one micron.

10. The angle sensor of claim 9, wherein the conduction path is spaced apart from the second Hall element by about one micron.

11. The angle sensor of claim 1, wherein the calibration current is 10 milliamps.

12. A method comprising: determining one or more compensation signals based on a first magnetic flux density measured at a first Hall element of an angle sensor disposed on a first axis and a second magnetic flux density measured at a second Hall element of the angle sensor disposed on a second axis perpendicular to the first axis; andadjusting an external magnetic flux density measured at the second Hall element due to an external magnetic field using the one or more compensation signals.

13. The method of claim 12, further comprising applying a calibration current to a first conduction path that generates the first magnetic flux density.

14. The method of claim 13, further comprising applying a calibration current to a second conduction path that generates the second magnetic flux density.

15. The method of claim 14, wherein the first conduction path is equal to the second conduction path.

16. The method of claim 12, further comprising determining one or more compensation signals based on the first magnetic flux density, the second magnetic flux density and a magnetic flux density measured at a third Hall element orthogonal to the first and second Hall elements.

17. The method of claim 16, further comprising adjusting an external magnetic flux density measured at the third Hall element due to the external magnetic field using the one or more compensation signals.

18. The method of claim 12, further comprising spacing the conduction path about 1 micron from the first Hall element.

19. The method of claim 18, further comprising spacing the conduction path about 1 micron from the second Hall element.

20. An angle sensor comprising: a first Hall element disposed on a first axis;a second Hall element disposed on a second axis perpendicular to the first axis;a first conduction path extending parallel to the first axis, wherein the first conduction path is configured to conduct a first calibration current that generates a first magnetic flux density measured at the first Hall;a second conduction path extending parallel to the second axis, wherein the second conduction path is configured to conduct a second calibration current that generates a second magnetic flux density measured at the second Hall element; andcalibration circuitry configured to: generate one or more compensation signals based on the first and second magnetic flux densities; andadjust an external magnetic flux density measured at the second Hall element due to an external magnetic field using the one or more compensation signals to reduce angle error of the angle sensor.

21. The angle sensor of claim 20, further comprising: a third Hall element disposed on a third axis, the third axis being perpendicular to the first axis and being perpendicular to the second axis,a third conduction path parallel to the third axis.wherein the third conduction path conducts a third calibration current that generates a third magnetic flux density measured at the third Hall element;wherein the calibration circuitry is further configured to: generate the one or more compensation signals based on the third magnetic flux density; andadjust the magnetic flux measured at the third Hall element from an external magnetic field using the one or more compensation signals.

22. The angle sensor of claim 1, wherein the first and second Hall elements are vertical Hall elements or planar Hall elements.

23. The angle sensor of claim 20, wherein the first, second and third conduction currents are equal.

24. The angle sensor of claim 20, wherein each of the first, second and third conduction currents is an alternating current.

25. The angle sensor of claim 24, wherein a frequency of each of the first, second and third conduction currents is 100 kHz.

26. The angle sensor of claim 20, wherein each of the first, second and third conduction currents is an alternating current.

27. The angle sensor of claim 20, wherein the first conduction path is spaced apart from the first Hall element by about one micron; and wherein the second conduction path is spaced apart from the second Hall element by about one micron.

28. An angle sensor comprising: a first Hall element disposed on a first axis;a second Hall element disposed on a second axis perpendicular to the first axis; anda means for calibrating signals from the first and second Hall elements.