Methods and devices for using multi-turn magnetic sensors with extended magnetic windows

A system includes a magnetic sensor that can store a magnetic state associated with a number of accumulated turns of a magnetic target. The magnetic sensor may work in conjunction with a magnetic target. The magnetic target may produce a magnetic field that, at some positions, drops below a magnetic window of the magnetic sensor. The magnetic target may produce a magnetic field that is within the magnetic window when needed to update the magnetic state of the sensor to keep track of the accumulated turns of the magnetic target. The magnetic sensor may be initialized with one or more domain walls.

FIELD OF DISCLOSURE

The described technology relates to magnetic sensors and related systems and methods.

BACKGROUND

Rotation counters that can measure angles greater than 360° are used in a variety of applications and are often referred to as multi-turn counters. One implementation of a multi-turn counter uses the magnetoresistance phenomenon, in which ferromagnetic layers are separated by a thin non-magnetic film. A multi-turn counter based upon the magnetoresistance phenomenon has various desirable properties. It can be desirable to keep the strength of the magnetic field generated by a rotating magnetic target and sensed by the sensor remain within a relatively narrow magnetic window. If the strength of the magnetic field is too low, the sensor can be unable to properly record rotation of the magnetic target. Conversely, if the strength of the magnetic field is too high, the magnetic field can scramble the data recorded by the sensor. In either case, the rotation count from the sensor can no longer be trusted. The difference between the minimum and maximum acceptable magnetic field strengths can be referred to as a magnetic window.

In various applications, it can be difficult to provide a magnetic target that provides a magnetic field that remains within the magnetic window for all rotation angles of the target. As an example, applications where the magnetic target cannot be located on the end of a rotating shaft can involve impracticably large magnetic windows.

SUMMARY OF THE DISCLOSURE

One aspect of this disclosure is a method of recording a number of turns with a multi-turn magnetic sensor using an extended magnetic window. The method comprises applying a magnetic field to the multi-turn magnetic sensor, where the magnetic field is pointing outside of an area for which domain wall propagation in the multi-turn magnetic sensor is expected and where the magnetic field has a first strength below a range for which domain walls predictably propagate through the multi-turn magnetic sensor. The method includes, while the magnetic field is pointing outside of the area, increasing the strength of the magnetic field to a second strength within the range for which domain walls predictably propagate through the multi-turn magnetic sensor and, while the magnetic field has the second strength, turning the magnetic field such that the magnetic field vector is pointing within the area so as to adjust a state of the multi-turn magnetic sensor.

The method can include applying the magnetic field to the multi-turn magnetic sensor with a magnetic target and rotating the magnetic target relative to the multi-turn magnetic sensor or linearly translating the magnetic target relative to the multi-turn magnetic sensor.

The method can include applying, with an initialization magnet separate from the magnetic target and to the multi-turn magnetic sensor, an initialization magnetic field having a third strength that is within the range for which domain walls predictably propagate through the multi-turn magnetic sensor and turning the initialization magnetic field relative to the multi-turn magnetic sensor in order to produce at least one domain wall in the multi-turn magnetic sensor.

The method can include, while the magnetic field is pointing outside the area, reducing the magnetic field to a third strength below a range for which any propagation of domain walls through the multi-turn magnetic sensor is expected.

Another aspect of this disclosure is a multi-turn magnetic sensing system with an extended magnetic window. The multi turn magnetic sensing system comprises a multi-turn magnetic sensor having magnetoresistive elements and being configured to record a number of turns of a magnetic field based on domain wall propagation through the multi-turn magnetic sensor and a magnetic target configured to move between a first position relative to the multi-turn magnetic sensor and a second position relative to the multi-turn magnetic sensor. The magnetic target can be configured such that, in the first position, the magnetic target is configured to apply the magnetic field with a first strength to the multi turn magnetic sensor, the first strength being below a range for which domain walls predictably propagate through the multi-turn magnetic sensor and, in the second position, the magnetic target is configured to apply the magnetic field with a second strength to the multi turn magnetic sensor, the second strength being in the range for which domain walls predictably propagate through the multi-turn magnetic sensor.

The magnetic target can include a first portion of magnetic material that forms a first magnetic dipole and a second portion of the magnetic material that forms a second magnetic dipole, where the first magnetic dipole is reversed relative to the second magnetic dipole, where the first and second portions of the magnetic material are disposed along a substantially circular circumference, and where at least some the first portion of the magnetic material is disposed adjacent to the second portion of the magnetic material.

When the magnetic target is in the first position, the second portion of the magnetic material can be disposed away from the multi-turn magnetic sensor. When the magnetic target is in the second position, the second portion of the magnetic material can be disposed adjacent to the multi-turn magnetic sensor.

The substantially circular circumference of the magnetic material can define a circle having a center. The first magnetic dipole can be oriented such that the first magnetic dipole has a north magnetic pole pointing towards the center of the circle and a south magnetic pole pointing away from the center of the circle. The second magnetic dipole can be oriented such that the second magnetic dipole has a south magnetic pole pointing towards the center of the circle and a north magnetic pole pointing away from the center of the circle.

The substantially circular circumference of the magnetic material can define a circle that lies in a plane. The first magnetic dipole can be oriented such that the first magnetic dipole has a north magnetic pole pointing normal to the plane and a south magnetic pole pointing anti-normal to the plane. The second magnetic dipole can be oriented such that the second magnetic dipole has a south magnetic pole pointing normal to the plane and a north magnetic pole pointing anti-normal to the plane.

The magnetic target can comprise a ring having the substantially circular circumference, where the first and second portions of the magnetic material together span substantially the entire substantially circular circumference of the ring.

The magnetic target can comprises a third portion of the magnetic material that forms a third magnetic dipole, where the third magnetic dipole is reversed relative to the second magnetic dipole and where the second portion of the magnetic material is disposed between the first and third portions of the magnetic material.

When the magnetic target is in the first position, the second portion of the magnetic material can be disposed away from the multi-turn magnetic sensor. When the magnetic target is in the second position, the second portion of the magnetic material can be disposed adjacent to the multi-turn magnetic sensor.

The magnetic target can comprise a linear magnetic target having an elongated direction and at least one pole pair that is magnetized perpendicular to the elongated direction. The pole pair can be closer to the multi-turn magnetic sensor when the magnetic target is in the first position than when the magnetic target is in the second position.

Another aspect of this disclosure is a magnetic sensing system with an extended magnetic window. The magnetic sensing system includes a magnetic sensor comprising magnetoresistive elements and configured to record position data based on domain wall propagation through the magnetic sensor and a magnetic target arranged relative to the magnetic sensor such that, in a first position relative to the magnetic sensor, the magnetic target is configured to apply a magnetic field with a first strength to the magnetic sensor, the first strength being in a range for which domain walls propagate through the magnetic sensor with a non-zero probability of less than 95% and, in a second position relative to the magnetic sensor, the magnetic target is configured to apply the magnetic field with a second strength to the magnetic sensor, the second strength being in a range for which domain walls predictably propagate through the magnetic sensor.

The magnetic target can be arranged relative to the magnetic sensor such that, in a third position relative to the magnetic sensor, the magnetic target is configured to apply the magnetic field with a third strength to the magnetic sensor, the third strength being in a range for which domain walls are not expected to propagate through the magnetic sensor.

The magnetic target can be shaped in a ring and can have magnetic poles pointing radially inwards towards a center of the ring and pointing radially outwards from the center of the ring.

The magnetic target can be shaped in a ring that lies in a plane and have magnetic poles pointing normal to the plane of the ring and pointing anti-normal to the plane of the ring.

The magnetic target can comprise a linear magnetic target with an elongated direction and have magnetic poles pointing perpendicular to the elongated direction of the linear magnetic target.

For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the innovations have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, the innovations may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

DETAILED DESCRIPTION

Aspects of this disclosure relate to a magnetic sensing system that includes a multi-turn magnetic sensor and a magnetic target. Domain walls can predictably propagate though the multi-turn magnetic sensor when a first strength of a magnetic field generated by the magnetic target is within a range of magnetic field strengths. In a first position, magnetic target can apply the magnetic field having the first magnetic field strength to the multi-turn sensor. The magnetic target can rotate from the first position to a second position. In the second position, the magnetic target can generate a magnetic field having a second magnetic field strength within an area for which no domain wall propagation is expected, in which the second magnetic field strength is below the range of magnetic field strengths for which domain walls predictably propagate though the multi-turn magnetic sensor. The multi-turn magnetic sensor can maintain a state as the magnetic target rotates from the first position to the second position and then to the first position. Accordingly, the magnetic sensing system can operate with magnetic field strengths that have a larger range than various other magnetic sensing systems. Magnetic targets in magnetic sensing systems discussed herein can include less magnetic material than the various other magnetic sensing systems. This can save space and costs.

The magnetic field sensing systems described herein can provide a compact and modular arrangement for measuring turn count in various applications. An example application for the disclosed magnetic field sensors is measuring the turn count of a steering column. In some arrangements, the disclosed magnetic field sensors may be used with magnetic targets whose operating strength can go outside of the traditional magnetic windows of the sensors, while maintaining faultless operation of the sensors. Such arrangements may facilitate sensing turn count of a rotating shaft even if the magnetic sensor is not positioned at an end of the rotating shaft.

In some embodiments, a magnetic strip having a magnetic anisotropy is physically laid out in the shape of a spiral. A domain wall generator coupled to one end of the magnetic strip is configured to generate and transport one or more domain walls through the magnetic strip according to the orientation of a rotating magnetic field. A driving circuit can activate (e.g., provide a voltage and/or current to) a portion of the spiral and a sensing circuit can make an electromagnetic reading associated with the portion of the spiral. As such, the sensing circuit can sense a resistance of an isolated magnetoresistive element of the magnetic strip. A control circuit can control a sequence in which different parts of the spiral can be powered and sensed by a sensing circuit. For instance, the control circuit can control switches to select a particular magnetoresistive element of the spiral for which the sensing circuit can sense a value indicative of resistance. The sensing circuit can make a sequence of electrical readings of the various parts of the spiral associated with magnetic states of the various parts of the spiral. In some instances, the sensing circuit can perform a comparison of the electromagnetic readings. The output of the sensing circuit can be decoded to determine an accumulated turn state of the magnetoresistive elements of the magnetic strip.

FIG.1shows an example magnetic strip layout100with a corresponding circuit schematic representation150.FIG.1shows a magnetic strip101having corners105and segments103a-103nforming magnetoresistive elements R1-R14arranged in series with each other, and a domain wall generator107. The magnetoresistive elements can act as variable resistors that change resistances in response to a magnetic alignment state. The magnetic strip101illustrated inFIG.1can be implemented in a multiturn counter.

The magnetic strip101can be a giant magnetoresistance (GMR) track that is physically laid out in the shape of a spiral. As illustrated inFIG.1, such a spiral shaped magnetic strip101can have rounded corners105and segments103a-103n. The magnetic strip101can have a magnetic anisotropy, such as a high anisotropy, based on the material and cross sectional dimensions of the magnetic strip101. The magnetic strip101can store magnetic energy. A domain wall generator (DWG)107is coupled to one end of the magnetic strip101. The DWG107can have a magnetic anisotropy, such as a low anisotropy. The domain wall generator can generate domain walls in response to rotations in a magnetic field. The domain walls can be injected to the magnetic strip101.

The segments103a-103nof the magnetic strip101are shown as straight sides of the magnetic strip101in the example ofFIG.1. The segments103a-103ncan have a variable resistance based on the magnetic domain of the segment. As the magnetic domain of a segment changes, the resistance of that segment can change. Accordingly, the segments103a-103ncan operate as magnetoresistive elements, also referred to as variable resistors R1-R14herein. The magnetoresistive elements R1-R14can also function as nonvolatile, magnetic memory that can be magnetically written and electrically read. The magnetoresistive elements R1-R14, as laid out in the spiral shaped magnetic strip101, are coupled in series with each other. Corresponding circuit schematic representation150shows segments103a-103ndepicted as corresponding magnetoresistive elements R1-R14connected in series.

FIG.2shows an example magnetic strip layout representation200with explanatory symbols. The magnetic strip101with magnetoresistive element segments equivalents R1-R14ofFIG.1is shown, along with DWG107, an external magnetic field201, an arrow203indicating a rotation of the external magnetic field201, and a domain wall213. Domain orientations205,207,209, and211indicate an orientation of a domain inside of a segment of a magnetic strip.

The DWG107can be affected by the external magnetic field201. As the external magnetic field201rotates as indicated by arrow203, the DWG107can inject domain walls213through the magnetic strip101. The domain wall213can propagate through the segments as magnetic field201rotates and the domain orientations205,207,209, and211change. AlthoughFIG.2shows the external magnetic field201at perpendicular positions for clarity, the magnetic field can be pointed at any angle, such as a 45 degree angle toward the spiral corners.

The resistivity of segments of the magnetic strip101can be affected by the domain orientation within a magnetic strip segment. Each segment's domain orientation can cause that segment to have a high resistance (“H” or “HR”) or a low resistance (“L” or “LR”) depending on the orientation of the segment. Vertically illustrated magnetic strip segments having a domain orientation205have a higher resistivity than vertical magnetic strip segments having a domain orientation207, which have a low resistivity. Horizontally illustrated magnetic strip segments having a domain orientation213have a higher resistivity than horizontal magnetic strip segments having a domain orientation211, which have a low resistivity. The magnetic strip segments with domain orientations205and213can have comparable resistances. Similarly, the magnetic strip segments with domain orientations207and211can have comparable resistances.

The examples shown inFIG.1andFIG.2depict a spiral shaped magnetic strip101as an open spiral based on a quadrilateral. However, in some other embodiments, different polygon or elliptical spiral configurations are possible. Also, the spiral can be a closed spiral or a multi-layer spiral with overlapping parts.

As discussed above, it may be desirable for the strength of the magnetic field generated by a rotating magnetic target and sensed by a multi-turn magnetic sensor to remain within a relatively narrow magnetic window, referred to herein as a first magnetic window. The first magnetic window may include the range of magnetic field strengths for which domain walls predictably propagate through a multi-turn magnetic sensor. As such, the first magnetic window may include magnetic fields having strengths at the multi-turn magnetic sensor that are no stronger than a maximum magnetic field strength Hmax and no weaker than a minimum magnetic field strength for reliable domain wall propagation. If the strength of the magnetic field is too high (e.g., above the maximum magnetic field strength Hmax), the magnetic field can create new domain walls, even without rotation of the magnetic field. This can scramble the data recorded by the sensor. Conversely, if the strength of the magnetic field is too low (e.g., below a minimum magnetic field strength for reliable domain wall propagation Hmin), the domain walls may not reliably propagate and the sensor may lose track of the number of rotations of the magnetic target. Thus, it may be desired that the magnetic field stay within the first magnetic window (e.g., between Hmin and Hmax) to ensure faultless operation.

In the present disclosure, multi-turn sensing systems are provided that operate with magnetic fields that go outside the first magnetic window, while still providing faultless operation. As examples, the multi-turn sensing systems provided in the present disclosure may operate with magnetic fields that may be occasionally within a second magnetic window and that may be occasionally within a third magnetic window.

The second magnetic window may include the range of magnetic field strengths for which domain walls propagate through a multi-turn magnetic sensor, but in an unreliable manner. If the strength of the magnetic field is within a second magnetic window (e.g., between a minimum magnetic field strength for reliable domain wall propagation Hmin and a minimum magnetic field strength for domain wall propagation Hmin2, where Hmin2is less than Hmin), the domain walls may propagate with a certain probability (e.g., with a certainty or probability of less than 1, sometimes referred to as a certainty or probability of less than 95%).

The third magnetic window may include magnetic field strengths that are sufficiently weak that no propagation of domain walls in the multi-turn magnetic sensor is expected to occur. If the strength of the magnetic field is within the third magnetic window (e.g., lower than a minimum magnetic field strength for domain wall propagation Hmin2), the domain walls should not propagate within the sensor regardless of the direction of the magnetic field. The properties of the second and third magnetic window may be used in forming a sensor that operates outside the first magnetic window (e.g., by ensuring that the magnetic field strength is within the first magnetic window during certain periods of time).

FIG.3shows an example multi-turn magnetic sensor300that can be reliably operated with a magnetic target that produces a magnetic field strength at the sensor that is occasionally outside the first magnetic window (e.g., outside a magnetic window in which domain walls predictably propagate through the multi-turn magnetic sensor300).

The external magnetic field301can drop into the second magnetic window (e.g., a magnetic window where propagation of domain walls occurs, but with less than 100% probability) as long as the field direction stays within one of the four areas302a,302b,302c, or302d. In particular, if the direction of the external magnetic field301stays within one of the four areas302a,302b,302c, and302d, no domain wall propagation is expected. As such, the less than 100% probability of domain wall propagation within the second magnetic window is acceptable (e.g., since domain wall propagation is not expected within this regions, the reliability of its propagation is irrelevant). Before entering the second magnetic widow, the direction of the external magnetic field301should be within one of the four areas the four areas302a,302b,302c, and302dand the direction should remain within the same area as long as the field strength is within the second magnetic window (e.g., between Hmin2and Hmin).

Various properties of the magnetic windows of the magnetic sensor300, such as the magnetic field strengths corresponding to a maximum magnetic field strength Hmax, a minimum magnetic field strength for reliable domain wall propagation Hmin, and a minimum magnetic field strength for domain wall propagation Hmin2, may depend upon the geometry of the magnetic sensor300as well as the materials forming the magnetic strip. In particular, the thickness and width of the magnetic strip together with the materials forming the strip may serve to define the values of Hmax, Hmin, and Hmin2. Various materials such as iron and cobalt iron may be used to form the magnetic strip. By varying the selected material and/or the thickness and/or width of the magnetic strip, the values of Hmax, Hmin, and Hmin2can be adjusted. Typical values for the magnetic windows of the sensor300in a first implementation may include a maximum magnetic field strength Hmax of approximately 1000 Oersted and a minimum magnetic field strength for reliable domain wall propagation Hmin of approximately 700 Oersted. In a second implementation, the Hmax of sensor300may be about 350 Oersted, the Hmin may be about 150 Oersted, and the minimum magnetic field strength for domain wall propagation Hmin2may be about 50 Oersted. In some instances, the minimum magnetic field strength for reliable domain wall propagation Hmin may be approximately half the value of the maximum magnetic field strength Hmax, while the minimum magnetic field strength for domain wall propagation Hmin2may be approximately 20 percent of the value of the maximum magnetic field strength Hmax.

The location, size, and even number of the areas302a,302b,302c, and302din magnetic sensor300where the field strength can drop out of the magnetic window may depend at least in part of the physical attributes of the magnetic strip (e.g., spiral) forming the magnetic sensor300and may also depend on the materials forming the magnetic strip (which, as discussed herein, may partially determine the properties of the magnetic windows). In some embodiments, the areas302a,302b,302c, and302dmay each span roughly 60 degrees, with the gaps between the areas spanning roughly 30 degrees. In some other embodiments, the gaps between the areas302a,302b,302c, and302dmay span between 10 and 30 degrees.

Additionally, the external magnetic field301can drop from the second magnetic window into the third magnetic window (e.g., a magnetic window below a minimum magnetic field strength for domain wall propagation Hmin2, in which no propagation of domain walls is expected to occur). In the third magnetic window, the direction of the external magnetic field301can rotate in any direction without altering the recorded data of sensor300. However, before the strength of the external magnetic field301is adjusted from within the third magnetic window to within the second magnetic window, the magnetic field vector of the external magnetic field301should be within one of the four areas302a,302b,302c, and302d.

In some embodiments, the direction of the external magnetic field301should be pointing within the same one of the areas302a,302b,302c, and302dwhen its strength rises into the second magnetic window, as it was when its strength dropped out of the second magnetic window. As an example, the magnetic field301may, at a first time, be pointing somewhere within area302aand have a strength in the second magnetic window. Then at a second later time, the magnetic field301may drop into the third magnetic window and its direction may change without restriction. Finally at a third later time, the magnetic field301may rise back into the second magnetic window, while its direction is within the area302a.

In some other embodiments, the direction of the external magnetic field301may change from one of the areas302a,302b,302c, and302dto another, while the field strength is within the third magnetic window. In other words, the external magnetic field301may drop in strength from the second to the third magnetic window (while in one of areas302a,302b,302c, and302d); may shift to another one of the areas302a,302b,302c, or302d; and may then rise in strength from the third to the second magnetic window while in the new area. In such embodiments, there may be a predictable relation between the direction of the magnetic field301at the time it entered the third magnetic window and the direction of the magnetic field301when it returns to the second magnetic window. The predictable relation may be determined based on the physical layout of the sensor300and the rotating magnetic target. As an example, the magnetic field301may, at a first time, be pointing somewhere within area302a, have an initial strength in the second magnetic window, and then drop into the third magnetic window. Then, the direction of the magnetic field301may shift in a predictable manner to be pointing within area302cand, after shifting direction to area302c, have its strength rise into the second magnetic window. The change from area302ato302c, while in the third magnetic window, may be indicative of a turn of the magnetic target in at least some implementations.

FIG.4shows an example of a multi-turn magnetic sensing system that includes a multi-turn magnetic sensor400and a magnetic target402formed from a magnetic ring404with a reversed pole pair406. The magnetic ring404along with the reversed pole pair406may rotate relative to sensor400in concert with a target (e.g., a shaft or other object whose rotation is being tracked by sensor402). The magnetic ring404may be formed from concentric rings, where the outer ring forms a first magnetic pole and the inner ring forms a second magnetic pole. The concentric rings may form a magnetic dipole and the reversed pole pair406may form an additional magnetic dipole that is reversed relative to the concentric rings. In at least some embodiments, the magnetic target402may be formed from a ring magnetized differently in different areas. Thus, the magnetic target402may be a single ring, magnetic in a first direction away from the reversed pole pair406and magnetized in a second direction at the reversed pole pair406.

The multi-turn magnetic sensing system may include readout circuitry, such as readout circuitry430as shown inFIG.4, for reading data from the multi-turn magnetic sensors disclosed herein. The readout circuitry430may be provided separate from or integrated with the multi-turn magnetic sensor400. Readout circuitry, such as readout circuitry430ofFIG.4, may sense the position(s) and number of domain walls within the magnetic sensor (e.g., by sensing the resistance of one or more of the tracks that make up the magnetic sensor, whose resistance may vary due to magnetoresistive effects, such as the giant magnetoresistive (GMR), anisotropic magnetoresistive (AMR), tunnel magnetoresistive (TMR), colossal magnetoresistive (CMR), and extraordinary magnetoresistive (EMR) effects). The readout circuitry may analyze the sensed position(s) and number of domain walls and provide an output to an external circuit indicative of the rotation count (or linear position in embodiments utilizing targets that translate linearly) of the magnetic target.

The magnetic target402may induce a magnetic field at sensor400that varies with rotation of the magnetic target402relative to the magnetic sensor400, thus enabling sensor400to track rotation or a rotation count of the magnetic target402. As an example, there may be a reversed pole pair such as pole pair406at one or more locations along the magnetic ring404, where the positions of the magnetic poles are reversed relative to the magnetic ring404. As an example, the shaded regions ofFIG.4may represent magnetic north poles, while the unshaded regions may represent magnetic south poles, or vice-versa. Because of the reversed pole pair406, the magnetic ring404may generate a non-uniform magnetic field that can be used to keep track of the rotations of the magnetic ring404. If desired, structures other than reversed pole pair406may be included as part of magnetic ring404in order to induce a non-uniform magnetic field and enable tracking of the rotation and/or rotation count of magnetic ring404.

In the multi-turn magnetic sensing system ofFIG.4, the sensor400can count a number of turns with a full turn resolution. The sensor400can store a state corresponding to an accumulated number of turns, in which the accumulated number of turns can be greater than 1.

In at least some embodiments, the field strength of magnetic target402is high near the reversed pole pair406, but weak along other portions of the magnetic ring404. In other words, whenever rotation of the magnetic ring404moves the reversed pole pair406away from sensor400, the field strength received by sensor400may be low. In contrast, whenever rotation of the ring404moves the reversed pole pair406near sensor400, the field strength received by sensor400may be high.

In the example ofFIG.4, the south magnetic pole of magnetic rings404may be radial to the plane of the magnetic target402(e.g., be pointed inwards to the center of the ring), while the north magnetic pole of magnetic rings404may be anti-radial to the plane of the magnetic target402(e.g., be pointed inwards to the center of the ring), or vice-versa (e.g., the north and south poles may be swapped). Similarly, the north and south magnetic poles of the reversed pole pair406may be said to be radial and anti-radial (or vice-versa) to the plane of the magnetic target402.

Graphs that include a magnetic field strength curve502and magnetic field angle curve510(e.g., magnetic angle) induced by magnetic target402ofFIG.4at magnetic sensor400are shown inFIGS.5A and5B, respectively.FIGS.5A and5Brespectively show the field strength and angle as a function of the rotation angle of the magnetic target402relative to the magnetic sensor400.

As shown inFIG.5A, magnetic field strength may be above a minimum magnetic field strength for reliable domain wall propagation Hmin and in the magnetic window of magnetic sensor400between angles504and506. The peak of the magnetic field strength curve502, which occurs roughly at the midpoint between angles504and506, may generally correspond to the position of the reversed pole pair406of the magnetic target402being in proximity to the magnetic sensor400. In particular, the magnetic field strength curve502may generally be at its maximum when the magnetic target402is rotated such that the reversed pole pair406is adjacent to the magnetic sensor400, which may be the position illustrated inFIG.4. As the magnetic target402is rotated such that the reversed pole pair406moves away from the magnetic sensor400, the magnetic field strength curve502may decrease and drop below the minimum magnetic field strength for reliable domain wall propagation Hmin into the second magnetic window, in which propagation of domain walls with changing magnetic field direction is expected to occur, but with less than 100% probability.

As shown inFIG.5Band in at least some embodiments, the magnetic field direction may lie within a range of angles512, whenever target402is rotated below angle504or above angle506. The range of angles512may correspond to one of the four areas302a,302b,302c, and302dillustrated inFIG.3. In particular, the magnetic field produced by magnetic target402may be within one of the four areas302a,302b,302c, or302dwhen the magnetic target402is rotated to an angle below angle504or above angle506. As discussed in connection withFIG.3, no propagation of domain walls is expected while the magnetic angle remains within one of the four areas302a,302b,302c, and302d. Thus, while the magnetic target is at an angle below504or above angle506, the magnetic field strength may drop below the minimum magnetic field strength for reliable domain wall propagation Hmin into the second magnetic window and may even drop below the minimum magnetic field strength for domain wall propagation Hmin2into the third magnetic window, without loss of data.

As the magnetic target402rotates and the reversed pole pair406passes by the sensor400, the magnetic field strength is within the magnetic window and completes a full 360 degree rotation as illustrated inFIG.5B. The rotation in the magnetic field direction can be recorded by sensor400and used to track a rotation count of the magnetic target402.

As shown inFIGS.5A and5B, the magnetic field strength may be above the minimum magnetic field strength for reliable domain wall propagation Hmin and in the magnetic window of magnetic sensor400at all times that the magnetic field angle curve510is outside of the range of angles512. Thus, the magnetic target402may provide a magnetic field strength sufficient to cause reliable propagation of domain walls within magnetic sensor400whenever the direction of the magnetic field is substantially changing due to rotation of the magnetic target402.

In at least some embodiments, the magnetic sensors disclosed herein, such as magnetic sensors400,600,800, and900, may be preloaded and/or initialized with one or more domain walls prior to active operations in tracking the rotations of a magnetic target. As an example, magnetic fields from a source other than the magnetic target (e.g., a magnetic initialization source) may be applied to a magnetic sensor in order to generate one or more domain walls, such as domain wall213ofFIG.2, and to position those domain walls at suitable locations along the track. This initialization process may be beneficial in arrangements in which the rotation of a magnetic target is capable of moving a domain wall within a magnetic sensor, but unable to generate new domain walls.

FIG.6shows an alternative magnetic target602that can be tracked by a magnetic sensor such as sensor600. The magnetic target602may include three magnetic pole pairs604,606, and608, which may have alternating poles. In particular, magnetic pole pair606may be reversed relative to pole pairs604and608. Additionally, magnetic pole pairs604and608may be configured such that the magnetic field strength drops off, potentially to zero, with increasing distance from the middle pole pair606. The magnetic pole pairs604and608may be formed from magnetic materials that taper off in thickness, with the thickest regions adjacent to reversed pole pair606and a tapering thickness with increasing distance from the reversed pole pair606. In at least some embodiments, magnetic targets such as target602and the other targets disclosed herein may be formed from a single piece of magnetic material, with different regions having different magnetizations. As an example, regions of the single piece of magnetic material corresponding to the middle pole pair606may be magnetized in a first direction, while regions of the single piece of magnetic material corresponding to the pole pairs604and608may be magnetized in a second direction. In still other embodiments, magnetic targets such as target602and the other targets disclosed herein may be formed from multiple pieces of magnetic material joined together.

In contrast with the magnetic target402ofFIG.4, the magnetic target602may include substantially less magnetic material. In particular, the magnetic target602may be formed substantially from magnetic material forming the magnetic pole pairs604,606, and608integrated into, attached to, or otherwise disposed at one or more locations along target650. In at least some embodiments, the magnetic target602may be formed by attaching magnetic material forming the magnetic pole pairs604,606, and608onto a target650, in order to count rotations of the target650. The target650may be non-magnetic, if desired. A magnetic target602may also be provided in a linear shape with one or more groupings of two or three magnetic pole pairs spaced along the elongate direction of the linear target.

In the example ofFIG.6, the north magnetic pole of magnetic pole pairs604and608may be said to be radial to the plane of the magnetic target602(e.g., be pointed inwards to the center of the ring), while the south magnetic pole of magnetic pole pairs604and608may be said to be anti-radial to the plane of the magnetic target602(e.g., be pointed outwards from the ring), or vice-versa (e.g., the north and south poles may be swapped). Similarly, the north and south magnetic poles of the reversed pole pair606may be said to be respectively anti-radial and radial (or vice-versa) to the plane of the magnetic target602.

Graphs of the magnetic field strength curve702and magnetic field angle curve710(e.g., magnetic angle) induced by magnetic target602ofFIG.6at magnetic sensor600are shown inFIGS.7A and7B, respectively.FIGS.7A and7Brespectively show the field strength and angle as a function of the rotation angle of the magnetic target602relative to the magnetic sensor600.

As shown inFIG.7A, magnetic field strength may be above the minimum magnetic field strength for reliable domain wall propagation Hmin and in the magnetic window of magnetic sensor600between angles704and706. The peak of the magnetic field strength curve702, which occurs roughly at the midpoint between angles704and706, may generally correspond to the position of the reversed pole pair606of the magnetic target602. In particular, the magnetic field strength curve702may generally be at its maximum when the magnetic target602is rotated such that the reversed pole pair606is adjacent to the magnetic sensor600, which may be the position illustrated inFIG.6. As the magnetic target602is rotated such that the reversed pole pair606moves away from the magnetic sensor600, the magnetic field strength curve702may decrease and drop below the minimum magnetic field strength for reliable domain wall propagation Hmin into the second magnetic window, in which propagation of domain walls with changing magnetic field direction is expected to occur, but with less than 100% probability. As the magnetic target602is further rotated such that the pole pairs604and608move away from the magnetic sensor600, the magnetic field strength curve702may further decrease and drop below the minimum magnetic field strength for domain wall propagation Hmin2into the third magnetic window, in which no propagation of domain walls is expected to occur.

As shown inFIG.7Band in at least some embodiments, the magnetic field direction may lie within a range of angles712, whenever target602is rotated below angle704or above angle706. The range of angles712may correspond to one of the four areas302a,302b,302c, and302dillustrated inFIG.3. In particular, the magnetic field produced by magnetic target602may be within one of the four areas302a,302b,302c, or302dwhen the magnetic target is rotated to an angle below angle704or above angle706relative to the magnetic sensor600. As discussed in connection withFIG.3, no propagation of domain walls is expected while the magnetic angle remains within one of the four areas302a,302b,302c, and302d. Thus, while the magnetic target602is at an angle below704or above angle706, the magnetic field strength curve702may drop below the minimum magnetic field strength for reliable domain wall propagation Hmin into the second magnetic window and may drop below the minimum magnetic field strength for domain wall propagation Hmin2into the third magnetic window, without loss of data. It should be noted that while the magnetic field strength is in the third magnetic window, the direction of the magnetic field is irrelevant. Thus, stray magnetic fields or other changes in the magnetic field direction do not impact the operation of magnetic sensor600as long as the strength remains within the third magnetic window.

As the magnetic target602rotates and the reversed pole pair606passes by the sensor600, the magnetic field strength is within the magnetic window and completes a full 360 degree rotation as illustrated inFIG.7B. The rotation in the magnetic field direction can be recorded by sensor600and used to track a rotation count of the magnetic target602.

As shown inFIGS.7A and7B, the magnetic field strength may be above the minimum magnetic field strength for reliable domain wall propagation Hmin and in the magnetic window of magnetic sensor600at all times that the magnetic field direction is outside of the range of angles712. Thus, the magnetic target602may provide a magnetic field strength sufficient to cause reliable propagation of domain walls within magnetic sensor600whenever the direction of the magnetic field is substantially changing due to rotation of the magnetic target602relative to the sensor600.

If desired, the principles and advantages discussed herein may be applied to targets of different shapes. As an example, linear magnetic targets, such as the targets illustrated in the examples ofFIGS.12and13, may be provided instead of circular magnetic targets. In a linear application, a magnetic bar may be magnetized perpendicular to its elongate direction and may have one or more reversed poles disposed along its elongate direction. A multi-turn magnetic sensor can count the reversed poles (in a manner similar to that discussed herein in connection with circular targets) and thereby track linear movement of the magnetic target relative to the magnetic sensor. Alternatively or additionally, a multi-turn magnetic sensor can be arranged to rotate relative to a linear magnetic target and count turns of rotation of the multi-turn magnetic sensor.

As another example, the principles and advantages discussed herein may be applied to magnetic rings configured for axial sensing, as shown in the examples ofFIGS.8and9.

As shown in the example ofFIG.8, a magnetic target802may be configured for sensing by a magnetic sensor, such as sensor800, disposed above the plane of the magnetic target802. The magnetic target802may include magnetic rings804and a reversed pole pair804integrated into, attached to, or otherwise disposed on target850. The magnetic rings804may be magnetized as shown inFIG.8, where the magnetic poles are disposed on opposite faces of the ring, as opposed to the concentric arrangement ofFIG.4. The magnetic target802may rotate around axis of rotation810, in concert with target850, and the number of rotations of the magnetic target802, and hence of target850, may be recorded by magnetic sensor800using the techniques discussed herein.

In the example ofFIG.8, the north magnetic pole of magnetic rings804may be normal to the plane of the magnetic target802(e.g., be pointed above the plane of the ring), while the south magnetic pole of magnetic rings804may be anti-normal to the plane of the magnetic target802(e.g., be pointed below the plane of the ring), or vice-versa (e.g., the north and south poles may be swapped). Similarly, the north and south magnetic poles of the reversed pole pair806may be said to be anti-normal and normal (or vice-versa) to the plane of the magnetic target802.

The magnetic target802ofFIG.8can produce magnetic fields for magnetic sensor800, which can be any of the multi-turn magnetic sensors discussed above, that are similar to the magnetic fields of the magnetic target402ofFIG.4. In particular, the strength of the magnetic field produced by magnetic target802may be within the second or third magnetic window when the magnetic target802is rotated such that the reversed pole pair806is disposed away from the magnetic sensor800. Additionally, when the magnetic target802is rotated such that the reversed pole pair806passes by the magnetic sensor800, the magnetic field produced by magnetic target802may have a strength within the magnetic window of sensor800and may change direction in a manner that can be recorded by sensor800, thereby enabling sensor800to keep track of the rotation count of the magnetic target802.

As shown in the example ofFIG.9, a magnetic target902configured for axial sensing by magnetic sensor900may be formed from pole pairs904and908disposed on either side of reversed pole pair906. The pole pairs904,906, and908may be integrated into, attached to, or otherwise disposed at one or more locations along target950. The magnetic target902may rotate around axis of rotation910, in concert with target950, and the number of rotations of the magnetic target902, and hence of target950, may be recorded by magnetic sensor900using the techniques discussed herein. The magnetic target902may have benefits similar to those discussed herein in connection withFIG.6.

The magnetic target902ofFIG.9may produce magnetic fields for magnet sensor900that are similar to the magnetic fields of the magnetic target602ofFIG.6. In particular, the strength of the magnetic field produced by magnetic target902may be within the third magnetic window when the magnetic target902is rotated such that the reversed pole pair906is disposed away from the magnetic sensor900. Additionally, when the magnetic target902is rotated such that the reversed pole pair906passes by the magnetic sensor900, the magnetic field produced by magnetic target902may have a strength within the magnetic window of sensor900and may change direction in a manner that can be recorded by sensor900, thereby enabling sensor900to keep track of the rotation count of the magnetic target902.

In the example ofFIG.9, the north magnetic poles of magnetic pole pairs904and908may be normal to the plane of the magnetic target902(e.g., be pointed above the plane of the ring), while the south magnetic poles of pairs904and908may be anti-normal to the plane of the magnetic target902(e.g., be pointed below the plane of the ring), or vice-versa (e.g., the north and south poles may be swapped). Similarly, the north and south magnetic poles of the reversed pole pair906may be said to be anti-normal and normal (or vice-versa) to the plane of the magnetic target902.

FIG.10shows an example method1000for counting turns of a magnetic target with a magnetic sensor. The magnetic target and sensor may be any of the magnetic targets and sensors disclosed herein.

At block1002, a magnetic sensor may receive a magnetic field having a strength that is within a first magnetic window of the sensor. As an example, the magnetic field may be generated by a magnetic target that rotates (or otherwise moves) relative to the magnetic sensor. The magnetic field may have a strength sufficient to cause reliable propagation of domain walls with the magnetic sensor (e.g., be no smaller than the minimum magnetic field strength for reliable domain wall propagation Hmin), but not so strong as to create or nucleate new domain walls within the magnetic sensor without corresponding rotation of the magnetic field (e.g., be no larger than the maximum magnetic field strength Hmax).

At block1004, the magnetic sensor may receive a magnetic field having a strength below the magnetic window of the sensor (e.g., a field of less than the minimum magnetic field strength for reliable domain wall propagation Hmin). Additionally, the magnetic field may have a direction at block1004that is not associated with propagation of domain walls. As an example, the direction of the magnetic field may be within one of the areas302a,302b,302c, or302dofFIG.3. In at least some embodiments, block1004may involve the magnetic field strength dropping below the second magnetic window such that no propagation of domain walls is expected (e.g., a field of less than the minimum magnetic field strength for domain wall propagation Hmin2). In such embodiments, the direction of the magnetic field may be irrelevant and unrestricted while the field strength is below the minimum magnetic field strength for domain wall propagation Hmin2.

At block1006, the magnetic sensor may receive a magnetic field having a strength within the magnetic window of the sensor. Additionally, the magnetic field may have a direction at block1006that is not associated with propagation of domain walls, such as one of the areas302a,302b,302c, or302dofFIG.3.

At block1008and while the magnetic field is within the magnetic window, the magnetic sensor may track or record changes in the direction of the magnetic field produced by a magnetic target. In particular, the magnetic sensor may produce, erase, or move domain walls within a spiral track. The position(s) and number of domain walls may be used to keep track of changes in the direction of the magnetic field produced by the magnetic target.

At block1010, the magnetic sensor may be read out to obtain a rotation count of the magnetic target. In particular, readout circuitry coupled to the magnetic sensor may sense the position(s) and number of domain walls within the magnetic sensor (e.g., by sensing the resistance of one or more of the tracks that make up the magnetic sensor, whose resistance may vary due to the GMR effect). The magnetic sensor may keep track of how many times the magnetic target was turned relative to the sensor. The magnetic sensor may be able to add counts when the magnetic target rotates in a first direction and subtract counts when the magnetic target rotates in a second direction opposite the first. Thus, in block1010, the readout circuitry may determine how many times and in what direction the magnetic target has been rotated relative to some baseline state. Such information may be used, as an example, to determine if a car's steering wheel is straight, rotated 360 degrees clockwise, or rotated 360 degrees counter-clockwise.

In at least some embodiments, the magnetic sensors disclosed herein such as magnetic sensors400,600,800, and900may be preloaded or initialized with one or more domain walls prior to use in tracking the rotations of a magnetic target. As an example, magnetic fields from a source other than the magnetic target (e.g., an initialization magnet) may be applied to a magnetic sensor in order to generate one or more domain walls, such as domain wall213ofFIG.2, and to position those domain walls at suitable locations along the track. This initialization process may be beneficial in arrangements in which the rotation of a magnetic target is capable of moving a domain wall within a magnetic sensor, but where it is difficult for the magnetic target to generate new domain walls.

FIG.11shows an example method1100for initializing a magnetic sensor with one or more domain walls. The magnetic target and sensor referred to inFIG.11may be any of the magnetic targets and sensors disclosed herein.

At block1102, one or more magnetic sensors may be initialized to have at least one domain wall. As an example, a magnetic field from an initialization source (e.g., a source other than the magnetic target the sensor will eventually track) may be applied to the magnetic sensor in a manner that generates one or domain walls within the magnetic spiral of the sensor. The initialization process of block1102may involve applying an initializing magnetic field at a strength within the magnetic window of the sensor, then rotating the magnetic field through a partial revolution, a whole revolution, or more than one whole revolution.

At block1104, the magnetic sensor may be configured to sensing a magnetic target. As an example, the magnetic sensor may be installed in a device near a magnetic target, such that rotation (or linear movement) of the magnetic target can be tracked by the magnetic sensor.

At block1106, movement of one of more domain walls, which may include the domain wall(s) generated in block1102, may be recorded by the magnetic sensor in response to rotation of the magnetic target and corresponding changes in the magnetic field generated by the magnetic target and received by the magnetic sensor.

At block1108, the magnetic sensor may be read out to obtain a rotation count of the magnetic target. In particular, readout circuitry coupled to the magnetic sensor may sense the position(s) and number of domain walls within the magnetic sensor (e.g., by sensing the resistance of one or more of the tracks that make up the magnetic sensor, whose resistance may vary due to the GMR effect). The magnetic sensor may keep track of how many times the magnetic target was turned relative to the sensor. The magnetic sensor may be able to add counts when the magnetic target rotates in a first direction and subtract counts when the magnetic target rotates in a second direction opposite the first. Thus, in block1108, the readout circuitry may determine how many times and in what direction the magnetic target has been rotated relative to some baseline state. Such information may be used, as an example, to determine if a car's steering wheel is straight, rotated 360 degrees clockwise, or rotated 360 degrees counter-clockwise.

As discussed herein, the principles and advantages discussed herein may be applied to targets of different shapes including linear targets, such as the linear targets illustrated in the examples ofFIGS.12and13.

FIG.12shows an alternative magnetic target1202that can be tracked by magnetic sensor1200. As shown inFIG.12, the magnetic target1202may be formed from a linear magnetic member1204with at least one reversed pole pair. The example ofFIG.12illustrates the magnetic target1202with two reversed pole pairs1206aand160b, which may be located any desired locations along the length of the linear magnetic member1204. The linear magnetic member1204may be magnetized perpendicular to its elongate direction. As an example, the shaded regions ofFIG.12may represent magnetic north poles, while the unshaded regions may represent magnetic south poles, or vice-versa. Because of the reversed pole pairs such as1206aand1206b, the magnetic target1202may generate a non-uniform magnetic field that can be used to keep track of the linear movement of the magnetic target1202along axis1210relative to the sensor1200(or vice-versa). The magnetic target1202may move linearly with respect to the sensors1200, e.g., along axis1210. The magnetic sensor1200may keep track of the linear position of the magnetic target1202by recording the passages, in each direction, of the reversed pole pairs.

FIG.13shows an alternative magnetic target1302that can be tracked by a magnetic sensor such as sensor1300. As shown inFIG.13, a magnetic target1302configured for linear sensing by magnetic sensor1300may be formed from at least one grouping of pole pairs disposed on either side of a reversed pole pair.FIG.13illustrates two such groupings; including reversed pole pair1306adisposed between pole pairs1304aand1308aand reversed pole pair1306bdisposed between pole pairs1304band1308b. The pole pairs and reversed pole pairs ofFIG.13may be integrated into, attached to, or otherwise disposed at one or more locations along target1350. As an example, the shaded regions ofFIG.13may represent magnetic north poles, while the unshaded regions may represent magnetic south poles, or vice-versa.

The target1350may translate linearly with respect to sensor1300along axis1310. The linear position of target1350along axis1310may be recorded by magnetic sensor1300using the techniques discussed herein. The magnetic target1302may have benefits similar to those discussed herein in connection withFIG.6.

The technology disclosed herein can be implemented in a variety of electronic systems. Aspects of the disclosure are applicable to any systems and/or devices that could benefit from the magnetic sensing technology disclosed herein.

Aspects of this disclosure can be implemented in various electronic devices. For instance, aspects of this disclosure can be implemented in any electronic device or electronic component that could benefit from the technology disclosed herein. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products, electronic test equipment, vehicular electronics systems, etc. Examples of the electronic devices can include, but are not limited to, computing devices, communications devices, electronic household appliances, automotive electronics systems, other vehicular electronics systems, industrial control electronics systems, etc. Further, the electronic devices can include unfinished products.

While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel methods, apparatus, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods, apparatus, and systems described herein may be made without departing from the spirit of the disclosure. For example, circuit blocks and/or circuit elements described herein may be deleted, moved, added, subdivided, combined, and/or modified. Each of these circuit blocks and/or circuit elements may be implemented in a variety of different ways. The accompanying claims and their equivalents are intended to cover any such forms or modifications as would fall within the scope and spirit of the disclosure.