Magnetoresistive sensor systems with stray field cancellation utilizing auxiliary sensor signals

A system includes first and second magnetic sense elements for producing first and second output signals, respectively, in response to an external magnetic field along a sensing axis parallel to a plane of the first sense element, a magnetization direction of the second element being rotated in the plane relative to a magnetization direction of the first element. The second output signal differs from the first output signal in dependency to a magnetic interference field along a non-sensing axis of the first magnetic field. A processing circuit, receives the first and second output signals, identifies from a relationship between the first and second output signals an influence of the magnetic interference field on the first output signal, and applies a correction factor to the first output signal to produce a resultant output signal in which the influence of the magnetic interference field is substantially removed.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to magnetoresistive sensors. More specifically, the present invention relates to magnetoresistive sensors and systems incorporating the magnetoresistive sensors for measuring magnetic fields while substantially cancelling an influence of stray magnetic fields along one or more axes.

BACKGROUND OF THE INVENTION

Magnetic field sensor systems are utilized in a variety of commercial, industrial, and automotive applications to measure magnetic fields for purposes of speed and direction sensing, rotation angle sensing, proximity sensing, and the like. A magnetoresistive sensor can be sensitive to interference magnetic fields, also known as stray magnetic fields. A stray magnetic field along a non-sensing axis of a magnetic field sensor may change the sensitivity and linearity range of the sensor, thus negatively affecting the magnetic field detection quality. A stray magnetic field along a sensing axis of a magnetic field sensor may additionally introduce an error component (e.g., a voltage shift) in the output signal of the sensor.

DETAILED DESCRIPTION

In overview, the present disclosure concerns magnetic field sensors, and systems incorporating the magnetic field sensors for measuring magnetic fields while substantially cancelling an influence of stray magnetic fields along one or more axes. More particularly, a system includes one or more primary magnetic field sense elements and one or more auxiliary magnetic field sense elements located in proximity to the primary magnetic field sense elements. The auxiliary magnetic field sense elements are rotated in a plane relative to the primary magnetic field sense elements. More particularly, the magnetization direction of the auxiliary magnetic field sense elements is rotated in the plane relative to the magnetization direction of the primary magnetic field sense elements. Setting auxiliary sensor signals output from the auxiliary magnetic field sense elements in relation with primary sensor signals output from the primary magnetic field sense elements enables the extraction of the magnetic field strength of stray magnetic fields along a non-sensing axis. Knowledge of this field strength can be used to compensate for, or otherwise cancel, an adverse signal contribution resulting from the stray magnetic field along a non-sensing axis. The primary and auxiliary magnetic sense elements may be incorporated in a gradient unit approach which additionally enables cancellation of an adverse signal contribution resulting from a homogeneous (i.e., uniform) stray magnetic field along the sensing axis. Thus, a uniaxial (i.e., single-axis) magnetic sense element may effectively be achieved. One or more magnetic field sense elements with one or more auxiliary sense elements can be implemented in various system configurations for purposes of speed and direction sensing, rotation angle sensing, proximity sensing, and the like.

The instant disclosure is provided to further explain in an enabling fashion the best modes, at the time of the application, of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

It should be understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Furthermore, some of the figures may be illustrated using various shading and/or hatching to distinguish the different elements produced within the various structural layers. These different elements within the structural layers may be produced utilizing current and upcoming microfabrication techniques of depositing, patterning, etching, and so forth. Accordingly, although different shading and/or hatching is utilized in the illustrations, the different elements within the structural layers may be formed out of the same material.

Referring toFIG. 1,FIG. 1shows, in a simplified and representative form, a half bridge structure20that includes a first magnetic sense element22and a second magnetic sensor element24. Each of first and second magnetic sense elements22,24is configured to detect (e.g., sense) an external magnetic field, represented by an arrow26oriented in a left-to-right direction on the page. In this example, external magnetic field26, is oriented substantially parallel to a Y-axis28within a three-dimensional coordinate system that also includes an X-axis30oriented in an up-down direction on the page. Y-axis28and X-axis30define a plane33of magnetic sense elements22,24, where plane33corresponds to the layer magnetization of magnetic sense elements22,24. A Z-axis32is oriented into and out of the page, and is thus perpendicular to plane33. External magnetic field26, oriented within plane33substantially parallel to Y-axis28, may be referred to as an HYexternal magnetic field26herein.

First and second magnetic sense elements22,24may be anisotropic magnetoresistive (AMR) sense elements capable of changing the value of their electrical resistance in response to an externally-applied magnetic field. For example, first magnetic sense element22may include permalloy (N180Fe20) stripes that are oriented positive forty-five degrees relative to a direction of external magnetic field26and second magnetic sense element24may include permalloy stripes that are oriented negative forty-five degrees relative to the direction of external magnetic field26. The orientation of the stripes may enable maximum sensitivity and quasi linear response of first and second magnetic sense elements22,24for small magnetic fields of up to a few kiloamperes per meter (kA/m). However, other angular orientations are also possible. Although AMR sense elements are mentioned herein. Alternative embodiments may include other magnetoresistive sensor technologies, such as giant magnetoresistive (GMR) sense elements, tunnel magnetoresistive (TMR) sense elements, and so forth.

Connection terminals for half-bridge magnetic sensor structure20include a VDDterminal34, a VSSterminal35, and a VOUTterminal36. VDDterminal34may be connected to a positive output terminal of a regulated internal voltage supply (not shown) and VSSterminal35may be connected to a negative output terminal of the regulated internal voltage supply or to a system ground. VOUTterminal36is an output terminal for half-bridge magnetic sensor structure20at which a first output signal38produced by half-bridge magnetic sensor structure20of first and second magnetic sense elements22,24in response to external magnetic field26is available for further processing.

FIG. 2shows a simplified top view of a single magnetic sense element. In this example,FIG. 2shows first magnetic sense element22. The following discussion applies to second magnetic sense element24(FIG. 1) as well. As mentioned above, first magnetic sense element22is configured to detect (e.g., sense) external magnetic field26along a sensing axis, which in this example is Y-axis28. However, first magnetic sense element22may also be sensitive to stray magnetic fields (magnetic interference fields) that are parallel to the layer magnetization of first magnetic sense element22. Thus, first magnetic sense element22may be subjected to interference from stray magnetic fields along the sensing axis (i.e., Y-axis28) and the non-sensing axis (i.e., X-axis30) parallel to plane33of the sensor.

In general, first magnetic sense element22is a magnetoresistive sensor having a very thin film or layer (e.g., a few nanometer up to a ten nanometer thickness in some applications) along Z-axis32. This very thin layer leads to a strong layer internal anisotropy field. This field generally prevents rotation of the magnetization into the Z-direction. Thus, magnetoresistive sensors (e.g., first and second magnetic sense elements22,24) are relatively insensitive to stray magnetic fields along Z-axis32. Therefore, stray magnetic fields along Z-axis32are not considered herein.

In this example, a stray magnetic interference field oriented along the non-sensing X-axis30is represented by an arrow40directed upward on the page and is labeled HXIHence, this stray magnetic interference field may be referred to as non-sensing axis stray magnetic field40. Similarly, a stray magnetic interference field oriented along the sensing Y-axis28is represented by an arrow42directed rightward on the page and is labeled HYI. Hence, this stray magnetic interference field may be referred to as sensing axis stray magnetic field42. Non-sensing and sensing axis stray magnetic fields40,42can corrupt first output signal38(FIG. 1) or reduce the signal-to-noise ratio (SNR) to unacceptable levels. This can have significant impact on safety-critical designs in, for example, the automotive industry.

FIG. 3shows a graph44of an example sensor response, in the form of a voltage response46, of a magnetic sense element (e.g., VOUT38of half-bridge magnetic sensor structure ofFIG. 1) with respect to a varying external magnetic field. More particularly, graph44depicts time48(TIME) on the horizontal axis and output voltage50(VOUT) on the vertical axis. In response to a varying external magnetic field (e.g., external magnetic field26ofFIG. 1), voltage response46of the magnetic sense element will also vary. In this illustration, voltage response46is sinusoidally varying. The depiction of voltage response46as sinusoidally varying inFIG. 3is an ideal or representative signal that can be distorted by non-sensing and sensing axis stray magnetic fields40,42.

FIG. 4shows a graph52of examples of the voltage response of a magnetic sense element (e.g., VOUT38of half-bridge magnetic sensor structure ofFIG. 1) in response to external magnetic field26(FIG. 2) along a sensing axis and the dependence of the voltage response on the field strength of non-sensing axis stray magnetic fields40(FIG. 2). More particularly, graph52shows a field strength54(HY) of an external magnetic field along the horizontal axis and an output voltage56(VOUT) along the vertical axis. Graph52provides an array of characteristic voltage response curves58(e.g., voltage responses) exemplifying a dependence (e.g., variance) of the sensed external magnetic field26(FIG. 1) in the presence of non-sensing axis stray magnetic field40(FIG. 2). That is, characteristic voltage response curves58change in response to a field strength59of non-sensing axis stray magnetic field40. In graph52, field strength54, output voltage56, and field strengths59of non-sensing axis stray magnetic field40are shown in arbitrary units (A.U.) for simplicity.

A solid curve within the array of characteristic curves58represents a condition in which field strength59of non-sensing axis stray magnetic field40is equal to zero (e.g., there is no non-sensing axis stray magnetic field40). The remaining curves within the array of characteristic curves58represent the variance (e.g., distortion) of voltage response of the magnetic sense element when a non-sensing axis stray magnetic field40of a certain field strength59is applied. Consequently, the presence of non-sensing axis stray magnetic field40, or a change in field strength59of non-sensing axis stray magnetic field40, results in a change of the output voltage from the magnetic sense element, which may be mistaken as a change in field strength54of external magnetic field26. The change in the characteristic voltage response curve caused by field strength59of non-sensing axis stray magnetic field40can be described as a function ƒ(HX1), and its effect on field strength54, HY, of an external magnetic field26along Y-axis28(FIG. 2) for a linearized system can be described as follows:
VOUT=f(HXI)*HY(1)

Thus, the distortion represented by the characteristic curves58in the presence of non-sensing axis stray magnetic fields40can be readily characterized and visualized in comparison with the absence of a non-sensing axis stray magnetic field40.

Magnetoresistive sensor technologies may achieve better jitter accuracy than, for example, Hall sensors. However, magnetoresistive sensor technologies are typically sensitive in two spatial axes and are thus more prone to magnetic interference (i.e., stray) field influences, even in combination with a gradiometer approach (discussed below). In accordance with embodiments described below, knowledge of the non-sensing axis stray magnetic fields40and knowledge of the dependency of the voltage response variations of external magnetic field26in dependency to non-sensing axis stray magnetic field40(e.g., due to characterization as indicated inFIG. 4) enables correction or cancellation of the effect of non-sensing axis stray magnetic fields40. In addition, a gradient unit approach (discussed below) can additionally enable correction or cancellation of the effect of sensing axis stray magnetic fields42(FIG. 2). Thus, a system that includes magnetoresistive sense elements gains the benefit of improved jitter accuracy over Hall sensors, while the stray magnetic field cancellation techniques described herein enables the reduction of distortion effects typically observed in magnetoresistive sensor technologies.

Referring now toFIG. 5,FIG. 5shows a top view of magnetic sense elements in accordance with an embodiment. In particular,FIG. 5shows a first magnetic sense element60and a second magnetic sense element62rotated in plane33relative to first magnetic sense element60. In an embodiment, first and second magnetic sense elements60,62are formed on a planar surface68of a substrate70. Plane33is parallel to planar surface68, and plane33corresponds to, i.e., is aligned with, a layer magnetization of first and second magnetic sense elements60,62. First and second magnetic sense elements60,62are represented as single structural elements for simplicity. In an implementation, first and second magnetic sense elements60,62may be connected in a half bridge configuration. Further, first sense element60may be formed having a first magnetization direction of the sense layer (e.g., permalloy stripes) that is oriented +/−45° and second sense element62may be formed having a second magnetization direction of the sense layer (e.g., permalloy stripes) that is oriented +/−25° so that the magnetization directions differ between the first and second magnetic sense elements60,62of the half bridge configuration by approximately 20°. Hence, phraseology used herein of second magnetic sense element62being rotated relative to first magnetic sense element60refers to the difference in the magnetization directions of the sense layer of first and second magnetic sense elements60,62.

First and second magnetic sense elements60,62may be magnetoresistive sense elements such as AMR, GMR, TMR sense elements, and so forth capable of detecting a magnetic field. Further, each of first and second magnetic sense elements60,62may be a single stripe or dot, as well as include an array of the former, and can be connected as in a single bridge, half bridge, or full bridge configuration. As will be discussed in significantly greater detail below, first magnetic sense element60may alternatively be referred to herein as a primary magnetic sense element60and second magnetic sense element62may alternatively be referred to herein as an auxiliary magnetic sense element62. Only one primary magnetic sense element60and one auxiliary magnetic sense element62are shown for simplicity. Other configurations may include multiple primary and auxiliary magnetic sense elements arranged in half-bridge or full bridge configurations.

As depicted inFIG. 5, primary and auxiliary magnetic sense elements60,62are suitably fabricated to have a sensing axis64, labeled “S,” and a non-sensing axis66, labeled “NS.” Each of primary and auxiliary magnetic sense elements60,62is configured to sense external magnetic field26in plane33parallel to Y-axis28. In some embodiments, auxiliary magnetic sense element62may be rotated in plane33by, for example, twenty degrees relative to primary magnetic sense element60. In other words, the magnetization direction of the sense layer of auxiliary magnetic sense element62is rotated relative to primary magnetic sense element. The rotation of the magnetization direction of auxiliary magnetic sense element62relative to primary magnetic sense element60changes the sensitivity/slope and possible maximum/minimum values attainable by auxiliary magnetic sense element62relative to primary magnetic sense element60. Although, an example rotation of twenty degrees is discussed herein, other magnitudes of rotation of the magnetization direction of auxiliary magnetic sense element62relative to primary magnetic sense element60may be implemented in alternative embodiments.

As discussed in detail above, magnetoresistive sense elements, such as primary and auxiliary magnetic sense elements60,62, are sensitive to interfering magnetic fields that are parallel to the layer magnetization of the magnetoresistive sense elements (e.g., non-sensing axis stray magnetic field40and sensing axis stray magnetic field42). In accordance with an embodiment, a differing sensor response of the rotated auxiliary magnetic sense element62relative to the sensor response of primary magnetic sense element60in the presence of non-sensing axis stray magnetic field40can be exploited to compensate for, or otherwise cancel, an adverse signal contribution resulting from stray magnetic field40along non-sensing axis (e.g., X-axis30).

Referring concurrently toFIGS. 5 and 6,FIG. 6shows a graph72of linearized voltage responses of the magnetic sense elements ofFIG. 5. More particularly, graph72shows field strength54(HY) of an external magnetic field on the horizontal axis and output voltage56(VOUT) on the vertical axis. Graph72provides an array of voltage responses74,76demonstrating a dependence (i.e., variance) of the voltage response from the sensed external magnetic field26(FIG. 1) in the presence of non-sensing axis stray magnetic field40at various field strengths59(HXI(n)), where n=1-5). In graph72, field strength54, output voltage56, and field strengths59of non-sensing axis stray magnetic field40are again represented by arbitrary units (A.U.) for simplicity. Further, the behavior of the magnetic sense elements is shown for a linear sensitivity working range or by linearized magnetic sense elements (e.g., by trimming). Other non-linear response curves may alternatively be used.

In graph72, a voltage response80(solid line) from primary magnetic sense element60represents a condition in which field strength59of non-sensing axis stray magnetic field40is equal to zero (i.e., there is no non-sensing axis stray magnetic field40) and a voltage response81(dashed line) from auxiliary magnetic sense element62. Thus, the slopes of voltage responses80,81from primary and auxiliary magnetic sense elements60,62may be different. Voltage responses74(solid lines) represent the variance (i.e., distortion) of the sensor signal from primary magnetic sense element60when non-sensing axis stray magnetic field40of a certain field strength59is applied. Similarly, voltage responses76(dashed lines) represent the variance (i.e., distortion) of the sensor signal from auxiliary magnetic sense element62when non-sensing axis stray magnetic field40of a certain field strength59is applied. It can be readily observed from graph72that voltage responses76differ from voltage responses74at the various field strengths59of non-sensing axis stray magnetic field40. This can be readily observed as the difference between the slope of voltage response76relative to voltage response74at the same field strength59. The difference in the slopes of voltage responses74,76is more pronounced at the higher values of field strength59of non-sensing axis stray magnetic field40. The linearized response represented in graph72yields the following:
VOUT=m1(HXI)×HY(2)
VAUX-OUT=m2(HXI)×HY(3)

In equation (2), VOUTrepresents voltage response74of primary magnetic sense element60at a particular field strength59of non-sensing axis stray magnetic field40and m1is the slope of the voltage response74. In equation (3), VAUX-OUTrepresents voltage response76of auxiliary magnetic sense element62at a particular field strength59of non-sensing axis stray magnetic field40and m2is the slope of the voltage response76. The slopes of voltage responses74,76are modified, or affected, by non-sensing axis stray magnetic field, HXI. Due to their proximity, field strength54, HY, of the sensed external magnetic field26is the same in each of equations (2) and (3). A quotient value, Q, can therefore be determined from equations (2) and (3), as follows:

Thus, in equation (4), the quotient value, Q, is a ratio of the output voltage (VOUT) of primary magnetic sense element60to the output voltage (VAUX-OUT) of auxiliary magnetic sense element62. More specifically, the quotient value, Q, represents the differences of the slopes of response curve74of primary magnetic sense element60and response curve76of auxiliary magnetic sense element62at a particular field strength59of non-sensing axis stray magnetic field40. In the absence of non-sensing axis stray magnetic field40, exemplified by response curve80, m1is equal to m2. Therefore, the quotient value, Q, for response curve80is 1. However, in the presence of non-sensing axis stray magnetic field40, m1is not equal to m2.

FIG. 7shows a graph82of plotted quotient value curves84. More particularly, graph82shows field strength54(HY) of an external magnetic field on the horizontal axis and quotient values88(Q) on the vertical axis. It can be observed that certain field strengths59(HXI) of non-sensing axis stray magnetic field40result in a distinct quotient value curve84that is in dependence upon (i.e., varies in response to) field strength54of external magnetic field26. Thus, field strength59of non-sensing axis stray magnetic field40may be determined from quotient values88. By using the knowledge of the dependency of the linearized response curves74,76,80(FIG. 6), a correction of the characteristic curve is possible and the error due to non-sensing axis stray magnetic fields40may be eliminated (discussed below).

To summarize, from the linearized responses presented in graph72(FIG. 6), a quotient value, Q, can be computed in accordance with equations (2)-(4) as the differences of the slopes of related VOUTand VAUX-OUT. Therefore, the quotient value, Q, is nearly constant for a given field strength59of non-sensing axis stray magnetic field40. The quotient factor, Q, may be associated with a particular field strength of the non-sensing axis stray magnetic field40and stored in memory (discussed below) during a final test and calibration process. Additionally, a correction factor which is an inverse of the slope of m1for the sensor output, VOUT, of primary magnetic sense element60can be stored in the memory in association with the quotient factor, Q, and a particular field strength59of the non-sensing axis stray magnetic field40.

As will be discussed in greater detail in connection withFIG. 8, in operation, a quotient value, Q, from received sensor signals VOUTand VAUX-OUTcan be computed. The computed quotient values can be compared with the quotient values stored in memory to extract field strength59of non-sensing axis stray field40. Additionally, the associated correction factor can be extracted from the memory and can be applied to the sensor output, VOUT, of primary magnetic sense element60to compensate for the effect of the particular field strength59of the non-sensing axis stray field40in order to obtain the measured field strength of external magnetic field26.

FIG. 8shows a simplified block diagram of a system92incorporating primary magnetic sense element60and auxiliary magnetic sense element62. The block diagram ofFIG. 8is provided to demonstrate the cancellation of the adverse signal contributions of non-sensing and sensing axis stray magnetic fields40,42to an output signal representing the external magnetic field26. Additional processing operations will not be described herein for brevity.

First magnetic sense element60(referred to herein as primary magnetic sense element60) is configured to produce a first (i.e., primary) output signal94, labeled VOUT(HY, HXI, HYI) and second magnetic sense element62(referred to herein as auxiliary magnetic sense element62) is configured to produce a second (i.e., auxiliary) output signal96, labeled VAUX-OUT(HY, HXI, HYI). Each of first and second output signals94,96reflects all magnetic field sources (i.e., external magnetic field26, non-sensing axis stray magnetic field40, and sensing axis stray magnetic field42). Accordingly, primary magnetic sense element60produces first output signal94(a voltage output in this instance) having a first magnetic field signal component98responsive to external magnetic field26. In the presence of stray magnetic interference fields, first output signal94will additionally have a non-sensing axis stray field signal component100and a sensing axis stray field signal component102. Similarly, auxiliary magnetic sense element62produces second output signal96(also a voltage output in this instance) having a second magnetic field signal component104responsive to external magnetic field26. In the presence of stray magnetic interference fields, second output signal96will additionally have non-sensing axis stray field signal component101and sensing axis stray field signal component103. Thus, the term “component” utilized herein refers to the parts or constituents (i.e., external magnetic field26, non-sensing axis stray magnetic field40, and sensing axis stray magnetic field42) that make up first output signal94. Further, non-sensing axis stray field signal component100,101and sensing axis stray field signal component102,103represent the adverse influence of non-sensing axis and sensing axis stray magnetic fields40,42, respectively, on first and second output signals94,96.

In the interest of clarity, external magnetic field26, first magnetic field signal component98, and second magnetic field signal component104share the same label, HY, in the illustrations. Non-sensing axis stray magnetic field40and non-sensing axis stray field signal component100,101share the same label, HXI. And, sensing axis stray magnetic field42and sensing axis stray field signal component102,103share the same label, HYI. In accordance with an embodiment, non-sensing axis stray field signal component100,101will largely be canceled utilizing information provided in second output signal96produced by auxiliary magnetic sense element62.

In some embodiments, primary magnetic sense element60and auxiliary magnetic sense element62may be fabricated on, or otherwise integrated with, an application specific integrated circuit (ASIC)106, designated by a dashed line box encircling blocks in the block diagram of system92. By way of example, primary magnetic sense element60and auxiliary magnetic sense element62may be fabricated in one or more top metal layers of ASIC106. ASIC106may implement, among other features, a processing circuit108that is customized to function with primary and auxiliary magnetic sense elements60,62. As will be discussed below, processing circuit108can encompass a wide variety of processing, control, or other structures. Further, the term “circuitry” utilized in conjunction with the structures of processing circuit108can encompass analog, digital, and/or mixed-signal electronic circuits. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts of the various embodiments, further discussion of such structures, if any, will be limited to the essentials with respect to the principles and concepts of the various embodiments.

First output signal94is provided to first analog-to-digital (AD) conversion and trimming circuitry110of processing circuit108. At first AD conversion and trimming circuitry110, first output signal94is converted from an analog to a digital signal. InFIG. 8, first output signal94retains the same reference numeral following AD conversion at first AD conversion and trimming circuitry110to emphasize its relationship to the signal output from primary magnetic sense element60. Additionally, first output signal94may undergo further processing such as temperature compensation, offset compensation, and so forth based upon, for example, trimming data. Similarly, second output signal96is provided to second AD conversion and trimming circuitry112of processing circuit108. At second AD conversion and trimming circuitry112, second output signal96is converted from an analog to a digital signal, and second output signal96may undergo temperature compensation, offset compensation, and so forth based upon, for example, trimming data. Again inFIG. 8, second output signal96retains the same reference numeral following AD conversion at second AD conversion and trimming circuitry112to emphasize its relationship to the signal output from auxiliary magnetic sense element62.

Following processing at first AD conversion and trimming circuitry110, first output signal94may be provided to quotient value extraction circuitry114. Likewise, second output signal96may be provided to quotient value extraction circuitry114following processing at second AD conversion and trimming circuitry112. Quotient value extraction circuitry114extracts a quotient value116, labeled Q, as a ratio of first output signal94relative to second output signal96as demonstrated in equations (2)-(4). Upon extraction of quotient value116at quotient value extraction circuitry114, quotient value116is provided to correction factor computation circuitry118. Correction factor computation circuitry118may have a memory element120associated with it containing calibration data. This calibration data can include a database of quotient values122, a unique magnetic field strength parameter124of non-sensing axis stray magnetic field40(HXI) associated with each quotient value122, and a unique correction factor (CF)126dependent upon each quotient value122, as discussed above in connection withFIGS. 6 and 7.

Correction factor126in turn is provided to non-sensing axis interference compensation circuitry128. Additionally, first output signal94produced by primary magnetic sense element60containing magnetic field signal component98, non-sensing axis stray field signal component100, and sensing axis stray field signal component102is provided from first analog-to-digital (AD) conversion and trimming circuitry110to non-sensing axis interference compensation circuitry128. Non-sensing axis interference compensation circuitry128applies correction factor126to first output signal94to produce a resultant output signal130in which non-sensing axis stray field signal component100, HXI, representing the influence of non-sensing axis stray magnetic field40is substantially removed. As shown, non-sensing axis interference compensation circuitry128outputs or otherwise provides resultant output signal130in which non-sensing axis stray field signal component100is canceled.

To summarize, methodology performed by system92entails producing a first output signal94at a first magnetic sense element60in response to external magnetic field26. The first output signal94has a first magnetic field signal component98and a magnetic interference field signal component (non-sensing axis stray field signal component100). The first magnetic field signal component98is in response to the external magnetic field directed along a sensing axis (y-axis28) parallel to a plane33of the first magnetic sense element60and the magnetic interference field signal component100is in response to a magnetic interference field (non-sensing axis stray magnetic field40) directed along a non-sensing axis (X-axis30) of the first magnetic sense element60. At a second magnetic sense element62that is rotated in the plane33relative to the first magnetic sense element60, the methodology further entails producing a second output signal96having a second magnetic field signal component104in response to the external magnetic field26and having the magnetic interference field signal component (non-sensing axis stray field signal component101). The methodology further entails, receiving at a processing circuit108, the first and second output signals94,96, identifying from the second output signal96an influence100(HXI) of the magnetic interference field40on the first magnetic field signal component98, and applying a correction factor126to the first output signal94to produce a resultant output signal130in which the magnetic interference field signal component100is substantially removed.

Still further, the methodology entails computing, at the processing circuit108, a quotient value116as a ratio of the first output signal94to the second output signal96and utilizing, at the processing circuit108, the quotient value116to determine the correction factor126, wherein the quotient value116is distinct for one of a plurality of magnetic interference fields59along the non-sensing axis (X-axis30) and is dependent upon a magnetic field strength54of the external magnetic field26.

In this example, resultant output signal130may thus include, or is otherwise a function, of magnetic field signal component98, HY, and sensing axis stray field signal component102, HYI. In accordance with some embodiments, resultant output signal130, as a first resultant output signal130, may be provided to sensing axis interference compensation circuitry132. Sensing axis interference compensation circuitry132compensates for or otherwise cancels sensing axis stray field signal component102from first resultant output signal130to yield a second resultant output signal134. As shown, sensing axis interference compensation circuitry132, provides second resultant output signal134in which sensing axis stray field signal component102is canceled. The cancellation of sensing axis stray field signal component102may be performed in accordance with a gradient unit configuration approach described below in connection withFIGS. 9-17. InFIG. 8, sensing axis interference compensation circuitry132is shown as having a single input for simplicity of illustration. However, in a gradient unit configuration, system92would be configured to include at least one additional input to sensing axis interference compensation circuitry132, as shown and discussed in connection withFIG. 13. Second resultant output signal134may thereafter undergo further processing operations, such as, offset correction, protocol generation, pulse-shaping, and so forth that are not described herein for brevity.

Subsequent discussion in connection withFIGS. 9-17applies to a gradient unit approach that may be employed to cancel or otherwise compensate for sensing axis stray magnetic field42at, for example, sensing axis interference compensation circuitry132, within system92.FIGS. 9-10will first be discussed to provide a generalized approach for cancelling or otherwise compensating for sensing axis stray magnetic field42.FIGS. 11-17are subsequently provided to describe a configuration for determining an angle of rotation that additionally includes the structure discussed above for canceling non-sensing and sensing stray magnetic fields40,42. Additionally,FIGS. 18-20are provided to describe a configuration for rotational speed measurement that additionally includes the structure discussed above for canceling at least non-sensing stray magnetic field40.

With reference now toFIG. 9,FIG. 9shows a simplified top view of a pair of magnetic sense elements arranged as a gradient unit140. Gradient unit140includes a first magnetic sense element142and a second magnetic sense element144. First and second magnetic sense elements142,144are laterally spaced apart along the sensing axis direction (i.e., Y-axis28). First and second magnetic sense elements142,144are configured to sense external magnetic field26along the sensing axis, which is Y-axis28herein. Thus, for purposes of clarity, first magnetic sense element142senses external magnetic field26(A), labeled HY(A), and second magnetic sense element144senses external magnetic field26(B), labeled HY(B). Any difference in the magnetic field strength measured by each of first and second magnetic sense elements142,144can be used to determine the magnetic field gradient in a direction parallel to Y-axis28.

Referring toFIG. 10in connection withFIG. 9,FIG. 10shows a graph146of a magnetic gradient field distribution148in a direction parallel to the sensing axis (i.e., Y-axis28) for gradient unit140and a magnetic gradient field distribution150modified in response to a spatial homogeneous interference magnetic field (i.e., sensing axis stray magnetic field42, HYI) directed along Y-axis28. More particularly, graph146depicts relative positions152(i.e., displacement relative to an origin) of first and second magnetic sense elements142,144along Y-axis28on the horizontal axis and field strength154on the vertical axis. As such, graph146shows magnetic gradient field distribution148without the presence of a magnetic interference field. In the presence of a magnetic interference field (i.e., field sensing axis stray magnetic field42), graph146additionally shows magnetic gradient field distribution150modified from the ideal condition represented by magnetic gradient field distribution148.

In general, multiplication of external magnetic field26(A) with the sensor sensitivity, S (discussed below), results in a first output signal component156, labeled VOUTA(HY(A)), represented inFIG. 9. Further, multiplication of sensing axis stray magnetic field42with sensor sensitivity, S, results in a first stray field signal component158, labeled VOUTA(HYI), represented inFIG. 9. Therefore, a voltage output signal160(generally represented by the term VOUTAinFIG. 10) from first magnetic sense element142can be characterized as VOUTA(HY(A)+HYI). Similarly, multiplication of external magnetic field26(B) with the sensor sensitivity, S (discussed below), results in a second output signal component162, labeled VOUTB(HY(B)). Again, multiplication of sensing axis stray magnetic field42with sensor sensitivity, S, results in a second stray field signal component164, labeled VOUTB(HYI). Therefore, a voltage output signal166(generally represented by the term VOUTBinFIG. 10from second magnetic sense element144can be characterized as VOUTB(HY(B)+HYI).

InFIG. 10, a dotted line depicts magnetic gradient field distribution148as a linear gradient range and the related field strength154that results in voltage output signals160,166at the relative positions of first and second magnetic sense elements142,144in the absence of sensing axis stray magnetic field42. InFIG. 10, a solid line depicts magnetic gradient field distribution150as a linear gradient range and related field strength154that results in first and second output voltage signals160,166at the relative positions of first and second magnetic sense elements142,144with an additional spatial homogenous interference magnetic field component, e.g., sensing axis stray magnetic field42, HYI.

In general, output voltages VOUTAand VOUTB(i.e., voltage output signals160,166) of first and second magnetic sense elements142,144of gradient unit140can be generally described as follows:
VOUTA=S×HY(A)(5)
VOUTB=S×HY(B)(6)

S is the sensitivity of the magnetic sense elements and is assumed to be equal for both of first and second magnetic sense elements142,144(e.g., achieved by fabrication accuracy or trimming). Thus, sensing axis stray magnetic field42, HYI, leads to the same voltage shift in both of first and second magnetic sense elements142,144as follows:
VOUTA=S×(HY(A)+HYI)=S×HY(A)+S×HYI(7)
VOUTB=S×(HY(B)+HYI)=S×HY(B)+S×HYI(8)

Equations (7) and (8) are valid only if magnetic sense elements142,144are linear (i.e., have a linear response curve, for example, by trimming, and are in non-saturation). Therefore, the sensitivity (S) does not depend upon the magnetic field amplitude for the sensing axis magnetic fields. Calculation of a differential output signal for gradient unit140entails taking the difference of the two voltage signals and thereby cancelling sensing axis stray field signal components158,164, as shown in the following equation:
DA,B=VOUTB−VOUTA=(S×HY(B)+S×HYI)−(S×HY(A)+S×HYI)=S×(HY(B)−HY(A))   (9)

As demonstrated in connection withFIGS. 5-8, the implementation of the rotated auxiliary magnetic sense element62along with the primary magnetic sense element60can counteract, or otherwise cancel, the effects of non-sensing axis stray magnetic field40. Additionally, the implementation of the gradient unit configuration discussed in connection withFIGS. 9-10can counteract, or otherwise cancel, the effects of sensing axis stray magnetic fields42in magnetoresistive sense elements. Accordingly, configurations described below combine the rotated auxiliary magnetic sense element and the gradient unit configurations to yield magnetoresistive sense elements that are robust against generally homogeneous stray magnetic fields from every direction.

Referring now toFIGS. 11-12,FIG. 11shows a simplified partial side view of a system170for rotation angle sensing andFIG. 12shows a simplified partial top view of system170. In the embodiment ofFIGS. 11-12, primary magnetic sense elements60with the rotated auxiliary magnetic sense elements62may be suitably configured to sense angular position of an object in a gradiometer configuration.

System170generally includes first and second gradient units172,174formed on a surface176of a substrate178and a magnet180vertically displaced away from first and second gradient units172,174along Z-axis32. Magnet180is not shown in the top view illustrated inFIG. 12in order to better visualize the features formed on surface176of substrate178. First gradient unit172includes a first primary magnetic sense element (labeled60A) and a first auxiliary magnetic sense element (labeled62A) and a second primary magnetic sense element (labeled60B) and a second auxiliary magnetic sense element (labeled62B). Likewise, second gradient unit174includes a third primary magnetic sense element (labeled60C) and a third auxiliary magnetic sense element (labeled62C) and a fourth primary magnetic sense element (labeled60D) and a fourth auxiliary magnetic sense element (labeled62D).

In accordance with an embodiment, second gradient unit174is rotated ninety degrees relative to first gradient unit172. That is, a longitudinal dimension of first and second primary magnetic sense elements,60A,60B and first and second auxiliary magnetic sense elements62A,62B is aligned with X-axis30. Additionally, a longitudinal dimension of third and fourth magnetic sense elements,60C,60D and third and fourth auxiliary magnetic sense elements62C,62D is aligned with Y-axis28. Thus, first and second primary magnetic sense elements60A,60B are configured to sense an in-plane external magnetic field182along a first sense axis, i.e., Y-axis28, oriented approximately parallel to surface176of substrate178. Any difference in the magnetic field strength measured by each of first and second primary magnetic sense elements,60A,60B can be used to determine the magnetic field gradient in a direction parallel to Y-axis28. Third and fourth primary magnetic sense elements60C,60D are configured to sense an in-plane measurement magnetic field184along a second sense axis, i.e., X-axis30, oriented approximately parallel to surface176of substrate178. Any difference in the magnetic field strength measured by each of third and fourth primary magnetic sense elements,60C,60D can be used to determine the magnetic field gradient in a direction parallel to X-axis30.

Second gradient unit174is spaced apart from first gradient unit172by ninety degrees relative to an axis of rotation186perpendicular surface176of substrate178. Additionally, first and second gradient units172,174may be located the same radial distance188away from axis of rotation186. Further, first primary magnetic sense element60A may be laterally spaced apart from second primary magnetic sense element60B by a distance190and third primary magnetic sense element60C may be laterally spaced apart from fourth primary magnetic sense element60D by the same distance190. In other embodiments, the distances between primary magnetic sense elements60A,60B,60C,60D may differ.

Magnet180may be a permanent magnet in the form of, for example, a disc, ring, rectangle, or bar shape. Magnet180is configured to rotate about axis of rotation186relative to first and second gradient units172,174. Magnet180produces a magnetic field192that rotates along with magnet180relative to first and second gradient units172,174. Magnetic field192has in-plane external magnetic field components182,184and an out-of-plane magnetic field component194with gradient properties. Out-of-plane magnetic field component194has a magnetic field strength that changes as a function of the distance from axis of rotation186, as represented by varying length arrows. By way of example, the magnetic field strength may be lowest at locations nearest to axis of rotation186and greatest at locations farthest from axis of rotation186, but inside the magnet dimension.

In an embodiment, out-of-plane magnetic field component194is detectable by first and second gradient units172,174, and thus may be referred to herein as a magnetic gradient field194. For example, system170may include magnetic field deflection elements, sometimes referred to as flux guides (not shown), that are configured to suitably redirect the out-of-plane magnetic field component194into X-Y plane33defined by X-axis30and Y-axis28for detection by primary magnetic sense elements60A,60B,60C,60D and auxiliary magnetic sense elements62A,62B,62C,62D.

Out-of-plane magnetic field component194detected by first and second gradient units172,174, may be suitably processed to identify a rotation angle,196, labeled φ, of magnet180relative to first and second gradient units172,174. Although only two gradient units (e.g., first and second gradient units172,174) are shown, alternative embodiments may include a multitude of gradient units. In such a configuration, the signals of the opposing gradient unit may be averaged or the like. Thus, possible errors from eccentricity and so forth may be mitigated. The provided example is for a configuration having out-of-plane gradient fields in a non-limiting manner. Alternative embodiments may be implemented with in-plane gradient field components.

Referring toFIG. 13in connection withFIGS. 11 and 12,FIG. 13shows a simplified partial block diagram of system92incorporating a gradient unit configuration for canceling sensing axis stray magnetic field component102from the voltage output signal. The features ofFIG. 13will be described in connection with first and second gradient units172,174of system170. However, ellipses between second gradient unit174and an “Nth” gradient unit198indicate that a system may include any predetermined quantity of gradient units in accordance with a particular design configuration. Further, the letter “M” in association with the voltage outputs, VOUTN1and VOUTN2, indicates an arbitrary axis. Still further, although two or more gradient units are specifically shown inFIG. 13, another embodiment may only implement a single gradient unit.

FIG. 13is provided to emphasize that system92may be adapted to process multiple sensor signals (e.g., voltage output signals) from multiple magnetic sense elements. In this example, the multiple voltage output signals have been processed through non-sensing axis interference compensation circuitry128to thereby largely cancel non-sensing axis stray field signal components resulting from non-sensing axis stray magnetic fields. Accordingly, sensing axis stray magnetic field compensation circuitry132may have multiple inputs. For illustrative purposes, a first compensation circuitry section128A of non-sensing axis interference compensation circuitry128is electrically connected to first magnetic sense element60A of first gradient unit172to provide a first voltage output signal200, VOUTA, having an external magnetic field component202, HY(A), as a function of in-plane external magnetic field182and having sensing axis stray magnetic field component102. Similarly, a second compensation circuitry section128B of non-sensing axis interference compensation circuitry128is electrically connected to second magnetic sense element60B of first gradient unit172to provide a second voltage output signal204, VOUTB, having an external magnetic field component206, HY(B), as a function of in-plane external magnetic field182and having sensing axis stray magnetic field component102,103.

It should be recalled fromFIG. 12that third and fourth primary magnetic sense elements60C and60D are configured to sense in-plane external magnetic field184along a second sense axis, i.e., X-axis30, oriented approximately parallel to surface176of substrate178. Thus, voltage output signals from third and fourth primary magnetic sense elements60C and60D may include a sensing axis stray magnetic field component208,209, labeled HXI, aligned with X-axis30. Again, for illustrative purposes, a third compensation circuitry section128C of non-sensing axis interference compensation circuitry128is electrically connected to third primary magnetic sense element60C of second gradient unit174to provide a third voltage output signal210, VOUTC, having an external magnetic field component212, HX(C), as a function of in-plane external magnetic field184and having sensing axis stray magnetic field component208. Similarly, a fourth compensation circuitry section128D of non-sensing axis interference compensation circuitry128is electrically connected to fourth primary magnetic sense element60D of second gradient unit174to provide a fourth voltage output signal214, VOUTC, having an external magnetic field component216, HX(D), as a function of in-plane external magnetic field184and having sensing axis stray magnetic field component209.

Thus, each of the voltage output signals200,204,210,214is a function of an external magnetic field signal component and a sensing axis stray magnetic field signal component. More particularly, each of the voltage output signals is a summation of the external magnetic field signal component and the sensing axis stray field signal component, as shown in equations (7) and (8). Still further, sensing axis stray magnetic field signal component102,103along the first sensing axis, e.g., Y-axis28, may differ from sensing axis stray magnetic field signal component208,209along the second sensing axis, e.g., X-axis30.

Sensing axis stray magnetic field compensation circuitry132is electrically coupled with first gradient unit172and is configured to produce a first differential output signal218(DA,B) as a difference between first and second voltage output signals200,204in accordance with equations (5) through (9) described above. Likewise, sensing axis stray magnetic field compensation circuitry132is electrically coupled with second gradient unit174and is configured to produce a second differential output signal220(DC,D) as a difference between third and fourth voltage output signals210,214. Of course, depending upon the configuration of gradient units, a multiplicity of differential output signals may be computed, as represented by DN1,N2. Second differential output signal220may be computed as follows:
VOUTC=S×HX(C)(10)
VOUTD=S×HX(D)(11)

S is the sensitivity of the magnetic sense elements and is assumed to be equal for both of third and fourth primary magnetic sense elements60C,60D (e.g., achieved by fabrication accuracy or trimming). Thus, sensing axis stray magnetic field208, HXI, leads to the same voltage shift in both of third and fourth magnetic sense elements60C,60D as follows:
VOUTC=S×(HX(C)+HXI)=S×HX(C)+S×HXI(12)
VOUTD=S×(HX(D)+HXI)=S×HX(D)+S×HXI(13)

Accordingly, calculation of a differential output signal for second gradient unit174entails taking the difference of the two voltage signals and thereby cancelling sensing axis stray field signal component228, as follows:
DC,D=VOUTD−VOUTC=(S×HX(D)+S×HXI)−(S×HX(C)+S×HXI)=S×(HX(D)−HX(C))   (14)

Referring toFIGS. 11-13, processing circuit108may include rotation angle determination circuitry222. By way of example, rotation angle determination circuitry222includes a combination of structural and software configured components to determine rotation angle196in accordance with the configuration of system170shown inFIGS. 11-12. In general, the magnetic field gradient, e.g., for out-of-plane magnetic field components194(FIG. 11), at the position of first and second magnetic sense elements60A,60B of first gradient unit172can be described as:
HY(A)=HmA×sin φ  (15)
HY(B)=HmB×sin φ  (16)

In equations (15) and (16) and the subsequent equations (17) and (18), Hmrepresents the amplitude of the redirected/deflected in-plane external magnetic field. Due to the ninety-degree rotated arrangement of first and second gradient units172,174, the mathematical relationship of third and fourth magnetic sense elements60C,60D of second gradient unit174can be described as:
HX(C)=HmA×cos φ  (17)
HX(D)=HmB×cos φ  (18)

The magnetic field gradient for first gradient unit172can therefore be described as:
HY(B)−HY(A)=HmB×sin φ−HmA×sin φ=(HmB−HmA)×sin φ=HmG1×sin φ  (19)

The operator HmG1is equal to (HmB−HmA). Similarly, the magnetic field gradient for second gradient unit174can be described as:
HX(D)−HX(C)=HmB×cos φ−HmA×cos φ=(HmB−HmA)×cos φ=HmG1×cos φ  (20)

By substituting equation (19) into equation (9), first differential output voltage218, DA,B, can be determined as follows:
DA,B=S×HmG1×sin φ  (21)

By substituting equation (20) into equation (14), second differential output voltage220, DC,D, can be determined as follows:
DC,D=S×HmG1×cos φ  (22)

Thus, the angular position (i.e., rotation angle196) φ, can be calculated at rotation angle determination circuitry222by division of the differential output voltages218,220, DA,Band DC,D, as follows:

Referring now toFIG. 14,FIG. 14shows various simplified top views showing positions of gradient units that may alternatively be incorporated into the system ofFIGS. 11-12. As mentioned previously, alternative embodiments of system170may include a multitude of gradient units. Further, these gradient units may be arranged differently. Each of the configurations of gradient units shown inFIG. 14include primary magnetic sense elements60and auxiliary magnetic sense elements62, both of which are formed in the same structural layer, and with auxiliary magnetic sense elements62located adjacent to the corresponding primary magnetic sense elements60in a one-to-one configuration. Alternative embodiments (discussed in connection withFIG. 18) may include more than one primary magnetic sense element60and only a single auxiliary magnetic sense element62.

FIG. 14includes a first configuration214having two primary magnetic sense elements60with two auxiliary magnetic sense elements62that are widely spaced apart along the sensing axis (e.g., Y-axis28) but form a single gradient unit216. Additionally, a second configuration218includes two primary magnetic sense elements60and two auxiliary magnetic sense elements62that are closely spaced apart along the sensing axis (e.g., Y-axis28) and form a single gradient unit216. A third configuration220includes three primary magnetic sense elements60and three auxiliary magnetic sense elements62that are spaced apart along the sensing axis (Y-axis28). In third configuration220, one of the magnetic sense elements60may be located at the center point and the remaining two magnetic sense elements60are spaced on opposite sides of and at an equal distance from the center point. Various pairs of magnetic sense elements60can be formed to yield three gradient units216, as shown. A fourth configuration222has four gradient units216each separated by 90°.

Referring toFIGS. 15-16,FIG. 15shows various simplified top views showing additional positions of gradient units that may alternatively be incorporated into the system ofFIGS. 11-12, andFIG. 16shows a partial side sectional view of one of the gradient unit configurations along section lines16-16ofFIG. 15. The configurations presented inFIG. 14depicted auxiliary magnetic sense elements62formed in the same structural layer as primary magnetic sense elements60. Further, each of the auxiliary magnetic sense elements62was immediately adjacent to a corresponding one of the primary magnetic sense elements60. In the alternative configurations presented inFIGS. 15-16, the primary magnetic sense elements60and auxiliary magnetic sense elements62are arranged in a stacked configuration224.

As shown, primary magnetic sense elements60may be formed in a first structural layer226on a planar surface228of a substrate230. Substrate230may include ASIC106discussed above in connection withFIG. 8. The corresponding auxiliary magnetic sense elements62may be formed in a second structural layer232that may be spatially separated from first structural layer226by, for example, an electrically insulating layer234. In some structures, another electrically insulating layer236may overlie second structural layer232. Additionally, primary and auxiliary magnetic sense elements60,62may be arranged in stacked configuration224such that a first center point238of primary magnetic sense element60is aligned with a second center point240of auxiliary magnetic sense element62along Z-axis32that is perpendicular to planar surface228of substrate230.

Stacked configuration224may be achieved by a stacked processing methodology, an interleaved in-plane geometry, or without stacked processing. In stacked configuration224, corresponding primary and auxiliary magnetic sense elements60,62may be subject to substantially the same magnetic field behavior. Additionally, stacked configuration224may facilitate a decrease in the system size relative to the adjacently located primary and auxiliary magnetic sense elements60,62shown inFIGS. 12 and 14. Although primary magnetic sense elements60are depicted as being located in first structural layer226closest to surface228of substrate230, in alternative embodiments, auxiliary magnetic sense elements62may be fabricated in first structural layer226and primary magnetic sense elements60may be fabricated in second structural layer232in a stacked configuration. Further, each of first and second structural layers may include multiple material sub-layers that combine to form the specific first or second structural layer.

Accordingly,FIG. 15includes a fifth configuration242having two primary magnetic sense elements60with two auxiliary magnetic sense elements62arranged in stacked configuration224that are widely spaced apart along the sensing axis (e.g., Y-axis28) but form a single gradient unit216. Additionally, a sixth configuration244includes two primary magnetic sense elements60and two auxiliary magnetic sense elements62in stacked configuration224that are closely spaced apart along the sensing axis (e.g., Y-axis28) and form a single gradient unit216. A seventh configuration246includes three primary magnetic sense elements60and three auxiliary magnetic sense elements62, arranged in stacked configuration224, that are spaced apart along the sensing axis (Y-axis28). In seventh configuration246, one of the magnetic sense elements60may be located at the center of substrate230and the remaining two magnetic sense elements60are spaced on opposite sides of and at an equal distance from the center point. Various pairs of magnetic sense elements60can be formed to yield three gradient units216, as shown. An eighth configuration248has four gradient units216each separated by 90°, and a ninth configuration250has two gradient units216separated by 90°.

FIG. 17shows various simplified top views showing still more positions of gradient units216that may alternatively be incorporated into the system ofFIGS. 11-12. The space savings achieved using stacked configuration224of primary magnetic sense element60and auxiliary magnetic sense element62may be exploited to incorporate a multiplicity of gradient units in a multiplicity of locations on planar surface228of substrate230.

InFIG. 17, a tenth configuration252is shown having eight gradient units216in stacked configuration224, each separated by 45°. An eleventh configuration254is shown having gradient units216in which the angles (e.g., a1, a2, and an) from parallel to the axes and the distances (d1, d2, dn) from the center can be different. In a twelfth configuration256, multiple pairs of primary magnetic sense elements60and auxiliary magnetic sense elements62that are laterally shifted along the Y-axis28(sensing axis) with the same distance between each magnetic sense element60, thereby forming a multiplicity of gradient units216. In a thirteenth configuration258, distances vary and pairs of primary and auxiliary magnetic sense elements60,62can be laterally shifted along X-axis30and/or Y-axis28to yield multiple gradient units216.FIGS. 12, 14, 15, and 17only show a few configurations of gradient units. Other configurations may be equivalently applicable.

FIG. 18shows a top view of magnetic sense elements in accordance with another embodiment. In particular,FIG. 18shows two primary magnetic sense elements60and a single auxiliary magnetic sense element62, in which the magnetization direction of the sense layer is rotated in plane33relative to both of the illustrated primary sense elements60. In such a configuration, each of the two primary magnetic sense elements60may produce voltage output signals260,262(labeled VOUTAand VOUTB, respectively) and the single auxiliary magnetic sense element62may produce a voltage output signal264(labeled VAUX-OUT). Processing circuit108(FIG. 8) may be adapted to receive voltage output signals260,262,264and apply the derived correction factors126(FIG. 8) to both of voltage output signals260,262to produce two resultant output signals in which the non-sensing axis interference field (e.g., non-sensing axis stray magnetic field40) is substantially removed from each of the two resultant output signals.

The configuration of two primary magnetic sense elements60and a single auxiliary magnetic sense element62may be incorporated into a gradient unit configuration, although such a configuration is not a limitation. By way of example, the configuration of two primary magnetic sense elements60and a single auxiliary magnetic sense element62may be incorporated in rotational speed sensor systems, as will be discussed below. Further, alternative configurations may have more than two primary magnetic sense elements60associated with a single auxiliary magnetic sense element62.

FIG. 19shows a simplified partial side view of a system266for rotational speed measurement incorporating the magnetic sense elements ofFIG. 18. In particular, system266includes primary magnetic sense elements60with at least one auxiliary magnetic sense element62, in which its magnetization direction is rotated relative to primary magnetic sense elements60. In this example, system266includes a magnetized encoder wheel268for generating a magnetic field, although alternative embodiments may implement a ferromagnetic gear wheel (seeFIG. 20) or other similar structure. The presented north (N) and south (S) pole configuration shown inFIG. 19is one example of an encoder wheel.

In this example configuration, primary magnetic sense elements60are configured to measure rotational speed of encoder wheel268. Thus, primary and auxiliary magnetic sense elements60,62are aligned with Y-axis28to detect external magnetic field26along the sensing axis (e.g., Y-axis28) generated as the alternating magnetic north and south poles of encoder wheel268as they pass by during rotation of encoder wheel262. Each of primary magnetic sense elements60converts the pole-sequence into a sinusoidal-like output voltage, and the rotational speed of encoder wheel268may be derived by counting, for example, the zero crossings. A bias magnet (not shown) may be used to adjust the sensitivity and measurement range of primary and auxiliary magnetic sense elements62. Auxiliary magnetic sense element62is implemented herein to compensate for non-sensing axis stray magnetic field40(FIG. 2) along the non-sensing axis, e.g., X-axis30, as discussed in detail above.

FIG. 19does not show primary and auxiliary magnetic sense elements60,62in a packaged form and attached to a corresponding structure for simplicity of illustration. Rather, primary and auxiliary magnetic sense elements60,62are shown displaced away from encoder wheel268relative to Z-axis32of the three-dimensional coordinate system. In an actual configuration, it should be readily apparent that magnetic sense elements60will be packaged and attached to a support structure in suitable proximity to encoder wheel268. Further, primary and auxiliary magnetic sense element60,62are visible inFIG. 19for illustrative purposes. In an actual configuration, one or more primary magnetic sense elements60may be laterally displaced away from auxiliary magnetic sense element(s)62along X-axis. In such a configuration, auxiliary magnetic sense elements62would be in front of or behind primary magnetic sense elements60so that one or the other would not be visible in the orientation ofFIG. 19. Still further, two primary magnetic sense elements60and a single auxiliary magnetic sense element62are shown for simplicity. These magnetic sense elements60,62may be arranged as gradient units. Alternatively, output signals from each of magnetic sense elements60may be combined via, for example, summation to enhance the accuracy of system260to external magnetic field26.

FIG. 19only shows a simplified configuration of a rotational speed measurement system. Other configurations may be equivalently applicable. Further, other systems may be envisioned that include magnetic sense elements with auxiliary magnetic sense elements positioned proximate the primary magnetic sense elements for providing auxiliary sensor signals along the sensing axis and utilizing the auxiliary sensor signals to compensate for non-sensing axis stray magnetic fields along the non-sensing axis.

FIG. 20shows a simplified partial side view of another system270for rotational speed measurement. System264includes many of the structural features described in connection with system266(FIG. 19). Thus, a description of those features will not be repeated for brevity. In the configuration of system270, an unmagnetized passive ferromagnetic encoder wheel272is implemented, in which case, a bias magnet (not shown) may be used to magnetize the passive ferromagnetic encoder wheel272.

Embodiments described herein entail magnetic field sensors and systems incorporating the magnetic field sensors for measuring magnetic fields while substantially cancelling the influence of stray magnetic fields along one or more axes. An embodiment of a system comprises a first magnetic sense element configured to produce a first output signal in response to an external magnetic field directed along a sensing axis parallel to a plane of the first magnetic sense element, the first magnetic sense element having a first magnetization direction. The system further comprises a second magnetic sense element having a second magnetization direction that is rotated in the plane relative to the first magnetization direction, the second magnetic sense element being configured to produce a second output signal in response to the external magnetic field, wherein the second output signal differs from the first output signal in dependency to a magnetic interference field directed along a non-sensing axis of the first magnetic field. The system further comprises a processing circuit coupled with the first and second magnetic sense elements, wherein the processing circuit is configured to receive the first and second output signals, identify from a relationship between the first and second output signals an influence of the magnetic interference field on the first output signal, and apply a correction factor to the first output signal to produce a resultant output signal in which the influence of the magnetic interference field is substantially removed.

An embodiment of a method comprises producing a first output signal at a first magnetic sense element in response to an external magnetic field directed along a sensing axis parallel to a plane of the first magnetic sense element, the first magnetic sense element having a first magnetization direction, producing a second output signal at a second magnetic sense element in response to the external magnetic field, the second magnetic sense element having a second magnetization direction that is rotated in the plane relative to the first magnetization direction, wherein the second output signal differs from the first output signal in dependency to a magnetic interference field directed along a non-sensing axis of the first magnetic field, and receiving the first and second output signals at a processing circuit. The method further comprises at the processing circuit, identifying from a relationship between the third and fourth output signals an influence of the magnetic interference field on the first magnetic field signal component and applying a correction factor to the first output signal to produce a resultant output signal in which the influence of the magnetic interference field is substantially removed.

Another embodiment of a system comprises a substrate, a first magnetoresistive element formed on the substrate, the first magnetoresistive element being configured to produce a first output signal in response to an external magnetic field directed along a sensing axis, the first magnetoresistive element having a first magnetization direction, and a second magnetoresistive element formed on the substrate and having a second magnetization direction that is rotated parallel to the planar surface relative to the first magnetization direction, the second magnetoresistive element being configured to produce a second output signal in response to the external magnetic field, wherein the second output signal differs from the first output signal in dependency to a magnetic interference field directed along a non-sensing axis of the first magnetic field, the sensing and non-sensing axes are parallel to a planar surface of the substrate, and the non-sensing axis is perpendicular to the sensing axis. The system further comprises a processing circuit coupled with the first and second magnetoresistive elements, wherein the processing circuit is configured to receive the first and second output signals, identify from the second output signal an influence of the magnetic interference field on the first output signal, and apply a correction factor to the first output signal to produce a resultant output signal in which the influence of the magnetic interference field is substantially removed.

Thus, a system includes one or more primary magnetic field sense elements and one or more auxiliary magnetic field sense elements located in proximity to the primary magnetic field sense elements. The auxiliary magnetic field sense elements are rotated in a plane relative to the primary magnetic field sense elements. More particularly, the magnetization direction of the auxiliary magnetic field sense elements is rotated in the plane relative to the magnetization direction of the primary magnetic field sense elements. Setting auxiliary sensor signals output from the auxiliary magnetic field sense elements in relation with primary sensor signals output from the primary magnetic field sense elements enables the extraction of the magnetic field strength of stray magnetic fields along a non-sensing axis. Knowledge of this field strength can be used to compensate for, or otherwise cancel, an adverse signal contribution resulting from the stray magnetic field along a non-sensing axis. The primary and auxiliary magnetic sense elements may be incorporated in a gradient unit approach which additionally enables cancellation of an adverse signal contribution resulting from a homogeneous (i.e., uniform) stray magnetic field along the sensing axis. Thus, a uniaxial (i.e., single-axis) magnetic sense element may effectively be achieved. One or more magnetic field sense elements with one or more auxiliary sense elements can be implemented in various system configurations for purposes of speed and direction sensing, rotation angle sensing, proximity sensing, and the like.