Sensor devices with two differential magnetic field sensors

Abstract

Sensor device comprising: a magnet (2); a first differential magnetic field sensor (6) mounted on a first surface (4) of the magnet (2); and a second differential magnetic field sensor (10) mounted on a second surface (8) of the magnet (2) opposite the first surface (4), wherein the magnet (2) is magnetized in a first direction parallel to the first surface (4) and parallel to the second surface (8).

Description

Technical FieldThe present disclosure relates to sensor devices having two differential magnetic field sensors. The disclosure further relates to methods for producing such sensor devices.BackgroundMagnetic field sensors can be used in different (e.g. automotive) applications. In one example, magnetic field sensors may be used to sense a position or angle of a wheel or shaft. In another example, magnetic field sensors may be used to determine wheel speeds. Conventional magnetic field sensors may often suffer from a low accuracy of their measurement results and lack of interference resistance to stray magnetic fields. Manufacturers and designers of magnetic field sensors are constantly striving to improve their products. It may be of interest in particular to develop cost-effective magnetic field sensors with high measurement accuracy and insensitivity to magnetic stray fields.The document DE 10 2020 213 092 A1 relates to a magnetic detection device. The publication DE 10 2018 114 131 A1 relates to a magnetic position sensor arrangement which is robust in terms of stray fields. US 2010 / 0 134 095 A1 relates to an arrangement for scanning a linear or circular measuring rod made of ferromagnetic material. The document DE 10 2017 124 542 A1 relates to a magnetic field sensor arrangement and a method for measuring an external magnetic field. The document DE 10 2013 000 430 A1 relates to a measurement system with a magnetic field sensor arrangement. The document WO 2002 / 016 864 A1 relates to a device and a method for angle measurement. The document DE 10 2016 118 384 B4 relates to a magnetic angle sensor device and an operating method. The document JP 2006-084 416 A relates to a mobile body position detector. The publication US 2008 / 0 238 417 A1 relates to a sensor and an apparatus for detecting magnetic substances.SummaryVarious aspects relate to a sensor device. The sensor device includes a magnet, a first differential magnetic field sensor mounted on a first surface of the magnet, and a second differential magnetic field sensor mounted on a second surface of the magnet opposite the first surface. The magnet is magnetized in a first direction parallel to the first surface and parallel to the second surface.Various aspects relate to a method for producing a sensor device. The method includes providing a magnet, mounting a first differential magnetic field sensor on a first surface of the magnet, and mounting a second differential magnetic field sensor on a second surface of the magnet opposite the first surface. The magnet is magnetized in a first direction parallel to the first surface and parallel to the second surface.Brief Description of the DrawingsApparatuses and methods according to the disclosure are explained in more detail below with reference to drawings. Identical reference numerals may denote identical or similar components. The features of the various illustrated examples may be combined with each other unless they are mutually exclusive and / or may be selectively omitted unless described as essential. FIG. 1 includes FIGS. 1A to 1D, which show a side view, a perspective view, and two partial views of a sensor device 100 according to the disclosure. FIG. 2 shows a top view of a sensor device 200 according to the disclosure. FIG. 3 includes FIGS. 3A and 3B, which show a perspective view and a top view of an application of a sensor device 300 according to the disclosure. FIG. 4 includes FIGS. 4A and 4B, which show waveforms of output signals of a first differential magnetic field sensor of a sensor device according to the disclosure. FIG. 5 includes FIGS. 5A and 5B, which show waveforms of output signals of a second differential magnetic field sensor of a sensor device according to the disclosure. FIG. 6 includes FIGS. 6A and 6B, which show relative angle plots determined based on the output signals of FIGS. 4 and 5. FIG. 7 includes FIGS. 7A and 7B showing error patterns of the relative angles shown in FIG. 6. FIG. 8 includes FIGS. 8A and 8B, which show plots of a Vernier angle and its error determined based on the relative angles of FIG. 6 and a first Vernier operation. FIG. 9 includes FIGS. 9A and 9B, which show plots of a Vernier angle and its error determined based on the relative angles of FIG. 6 and a second Vernier operation. FIG. 10 shows a perspective view of an application of a sensor device 1000 according to the disclosure. FIG. 11 shows error patterns of a Vernier angle. FIG. 12 shows a perspective view of an application of a sensor device 1200 according to the disclosure. FIG. 13 shows a perspective view of an application of a sensor device 1300 according to the disclosure. FIG. 14 includes FIGS. 14A and 14B, which show waveforms of output signals of a first differential magnetic field sensor of a sensor device according to the disclosure. FIG. 15 includes FIGS. 15A and 15B showing waveforms of output signals of a second differential magnetic field sensor of a sensor device according to the disclosure. FIG. 16 shows a flow chart of a method for manufacturing a sensor device according to the disclosure.Detailed DescriptionThe sensor device 100 of FIG. 1 may include a magnet 2, a first differential magnetic field sensor 6 mounted on a first surface 4 of the magnet 2, and a second differential magnetic field sensor 10 mounted on a second surface 8 of the magnet 2 opposite the first surface 4. Furthermore, in the example shown, the sensor device 100 can optionally comprise a printed circuit board (or a PCB) 12 and a first encapsulation material 14. The magnet 2, the two differential magnetic field sensors 6 and 10 and the printed circuit board 12 can be at least partially encapsulated by the first encapsulation material 14.The magnet 2 may be magnetized in the y direction. In the side view of FIG. 1A, the north pole of the magnet 2 can be arranged to the right and the south pole of the magnet 2 to the left, or vice versa. The magnet 2 may be made of any suitable material. In one example, the magnet 2 may be made of sintered ferrite. The magnet 2 may be configured to provide a magnetic supporting field for the operation of the sensor device 100. The magnet 2 can be in particular a permanent block magnet, so that the magnet 2 can be referred to as a permanent back bias block magnet.The two differential magnetic field sensors 6 and 10 may be mounted on the opposing surfaces 4 and 8, respectively, of the magnet 2. The two magnetic field sensors 6 and 10 can be galvanically isolated from one another. The relative arrangement of the magnet 2 and the magnetic field sensors 6 and 10 shown in FIG. 1 can be referred to as a top read configuration. It can be seen from the side view of FIG. 1A that the two differential magnetic field sensors 6 and 10 can be arranged in a symmetrical manner relative to the magnet 2 and the printed circuit board 12.The differential magnetic field sensors 6 and 10 can each be an integrated circuit or a semiconductor chip, so that differential magnetic field sensor ICs or differential magnetic field sensor chips can also be mentioned. In the following, the first differential magnetic field sensor 6 is predominantly and exemplarily described, wherein corresponding embodiments can also be transmitted to the second differential magnetic field sensor 10. In one example, the two differential magnetic field sensors 6 and 10 can be of identical construction or have an identical or at least similar architecture. In further examples, the differential magnetic field sensors 6 and 10 may also differ in at least one feature.The differential magnetic field sensor 6 can have a first sensor element 16A, a second sensor element 16B and an optional third sensor element 16C situated between the two sensor elements 16A and 16B. In the example shown, the main surfaces of the differential magnetic field sensor 6 can lie in the x-y plane. The two sensor elements 6A and 6B can be spaced apart from one another in the x-direction, i.e. they can be arranged on a (straight) line running in the x-direction. The third sensor element 16C can likewise be arranged on this line running in the x direction and in this case can in particular be at the same distance from the first sensor element 16A and from the second sensor element 16B. In the example shown, in a plan view of the first surface 4, the first sensor element 16A is arranged on the left, the second sensor element 16B on the right and the third sensor element 16C in the middle. In the following, therefore, reference may also be made to the left, right and middle sensor elements.The sensor elements 16A- 16C may each be configured to sense one or more components of a magnetic field present at the location of the respective sensor element. For example, each of the sensor elements 16A to 16C may be implemented by itself as a resistor bridge having, for example, four resistors. In one example, the resistors can be arranged in the form of a Wheatstone bridge. The respective sensitivity directions of the sensor elements 16A to 16C may depend on the respective application. Exemplary applications having different sensitivity directions of the sensor elements 16A to 16C are described further below. In a general example, each of the sensor elements 16A- 16C may be sensitive to each of the three spatial directions. That is, each of the sensor elements 16A- 16C may be configured to sense the x, y, and z components of a magnetic field present at the location of the respective sensor element.The differential magnetic field sensor 6 or its sensor elements 16A to 16C are not limited to a specific sensor technology. In one example, the sensor elements 16A to 16C may be magnetoresistive xMR sensor elements, in particular AMR sensor elements, GMR sensor elements or TMR sensor elements. In further examples, sensor elements 16A- 16C may correspond to Hall sensor elements or fluxgate sensor elements. The sensor elements 16A to 16C may be integrated into a circuit of the chip. In such a circuit, signal amplification, analog-to-digital conversion, digital signal processing and / or offset and temperature compensation can also be carried out. In addition to the components of the respective sensor element, components for signal amplification and / or analog-to-digital conversion may or may not be considered part of the sensor elements 16A to 16C.The differential magnetic field sensor 6 may be mounted on a metal carrier 18, which may be made of copper, nickel, aluminum or stainless steel, for example. In an example, the metal carrier 18 may correspond to a leadframe (leadframe) having one or more die pads as well as one or more leads (leads or pins) 22. The differential magnetic field sensor 6 may be electrically connected to one or more of the leads 22. The metal carrier 18 and the differential magnetic field sensor 6 may be at least partially encapsulated in a second encapsulation material 20. The connection conductors 22 can protrude at least partially from the second encapsulation material 20, such that electrical contact can be made with the differential magnetic field sensor 6 from outside the second encapsulation material 20. The encapsulation materials 14 and 20 may be the same or different and each may be made of, for example, a laminate, an epoxy resin, a thermoplastic, and / or a thermosetting polymer.The circuit board 12 can be considered an optional component of the sensor device 100. For example, the sensor devices according to the disclosure described below and shown in FIGS. 2 and 3 do not necessarily have to include a printed circuit board. The circuit board 12 can have one or more conductor tracks 24 on its upper and lower sides. In the case shown, two linear conductor tracks 24 can be arranged, for example, on the upper side of the printed circuit board 12. In further examples, the number and geometry of the conductive traces 24 may be chosen differently depending on the application. The conductor tracks arranged on the underside of the printed circuit board 12 cannot be seen in FIGS. 1A to 1D on the basis of the selected perspectives. These conductor tracks 12 can be similar to the conductor tracks 24 arranged on the upper side of the printed circuit board 12.The two differential magnetic field sensors 6 and 10 may be electrically connected to the circuit board 12. More specifically, the first differential magnetic field sensor 6 may be electrically connected to conductive traces 24 on the upper surface of the circuit board 12 via the leads 22, and the second differential magnetic field sensor 10 may be electrically connected to conductive traces 24 on the lower surface of the circuit board 12 via the leads 22. In the example shown, the connection conductors 12 can be bent around edges of the magnet 2 for this purpose.The conductive traces 24 may be electrically connected to external terminal elements (not shown) of the sensor device 100. An electrical connection can thus be provided between the magnetic field sensors 6 and 10 and an external component (not shown) via these external connection elements, the conductor tracks 24 and the connection conductors 22. Such an external component may be, for example, a processing unit (or control unit, e.g. ECU) which may be configured to process measurement signals output by the differential magnetic field sensors 6 and 10. In one example, such a processing unit may include a microcontroller or a processor.The magnet 2 can have at least one cutout 26. A mechanical connection between the printed circuit board 12 and the magnet 2 can be provided by engaging a printed circuit board section 28 in the at least one cutout 26 of the magnet 2. In the case shown, the recess 26 may correspond, by way of example, to a groove which may extend along three mutually adjoining side surfaces of the magnet 2. The circuit board portion 28 may be bifurcated and have one or more tips engageable with the groove 26. In the example shown, the fork-shaped printed circuit board section 28 can have two laterally arranged tips. In further examples, the circuit board section 28 may have three peaks or even only a single (in particular) centered peak. In these cases, the magnet 2 may have one or more apertures for receiving the tip(s) to provide a mechanical connection between the magnet 2 and the circuit board 12.A connection to the printed circuit board sections described can be realized by cost-effective sintered magnets. With plastic-bonded (e.g. polyphenylene sulfide (PPS), polyamides (PA6, PA12)) magnets, it is also possible to realize more complex constructions, such as clip-on designs, in which the magnet 2 can have a cutout and the printed circuit board 12 can have a nose-shaped structure which can be latched into the cutout. Such plastic-bonded magnets can be produced, for example, on the basis of an injection molding process. In still further examples, a mechanical connection between the magnet 2 and the circuit board 12 may be provided simply by an adhesive agent or an adhesive.The sensor device 200 of FIG. 2 may include one or more features of the sensor device 100 of FIG. 1. In the plan view of FIG. 2, only the first differential magnetic field sensor 6 can be seen. In the example shown, the sensor device 200 does not necessarily have to have the first encapsulation material 14, which encapsulates the magnet 2 and the two differential magnetic field sensors 6 and 10. Further, the sensor device 200 does not necessarily have to include the circuit board 12. In such a case, an electrical connection between the magnetic field sensors 6 and 10 and an external component can be provided directly via the connection conductors 22. Since the sensor device 200 does not have a printed circuit board 12, the magnet 2 does not necessarily have to have a recess 26. In the example shown, the magnet 2 can be of cuboidal design.In particular, an arrangement of the sensor elements 16A to 16C relative to the magnet 2 can be seen from FIG. 2. A first side edge 30 of the magnet 2 running in the x-direction and the sensor elements 16A to 16C of the first differential magnetic field sensor 6 can be at least partially congruent in the plan view of the first surface 4 of the magnet 2 (i.e. viewed in the z-direction). More specifically, the centers of the sensor elements 16A to 16C and the side edge 30 of the magnet 2 may be arranged congruently with each other when viewed in the z direction. In this case, the first sensor element 16A and the second sensor element 16B can in particular have an identical distance from the center point of the side edge 30. In an analogous manner, a second lateral edge of the magnet 2 running in the x-direction and the sensor elements 16A to 16C of the second magnetic field sensor 10 can be at least partially congruent, as viewed in the z-direction.Due to the described congruent arrangement, the sensor elements 16A to 16C can be exposed to low magnetic fields. In particular, the sensor elements 16A to 16C can be exposed to low magnetic offsets, whereby saturation of the sensor elements 16A to 16C can be avoided or at least reduced. Further signal processing of the signals provided by the two differential magnetic field sensors 6 and 10 or a signal path design implemented for this purpose can therefore be simplified.FIGS. 3A and 3B show one possible application of a sensor device 300 according to the disclosure. The sensor device 300 may include one or more characteristics of sensor devices described above. The sensor device 300 may be disposed relative to a ferromagnetic target structure 32 and separated therefrom by an air gap 34. A size of the air gap 34 may be specified as a distance d between the target ferromagnetic structure 32 and the sensor elements 16A- 16C (or the side edge 30 of the magnet 2) measured in the y-direction, for example. The ferromagnetic target structure 32 may or may not be considered part of the sensor device 300. The ferromagnetic target structures described herein may be made of any suitable ferromagnetic material, such as a ferromagnetic metal or a ferromagnetic metal alloy. In a specific example, the ferromagnetic targets may be made of steel and / or iron.In the example shown, the ferromagnetic target structure 32 can have a ferromagnetic wheel or correspond to such a wheel. The ferromagnetic wheel 32 may be configured to rotate about an axis of rotation that may extend in the y-direction in the example shown. The sensor device 300 of FIG. 3 may be oriented as already shown in FIGS. 1 and 2, i.e. the magnet 2 may be magnetized in the y-direction (i.e. in the air gap direction), and the sensor elements 16A to 16C of the differential magnetic field sensors 6 and 10 may be spaced apart from each other in the x-direction.The ferromagnetic wheel 32 may include a first inner track having a first number N of apertures 36 and a second outer track having a second number M of apertures 38. The two tracks may be circular, and the radius of the inner track may be less than the radius of the outer track. The first number N and the second number M may differ, wherein the first number N of openings 36 may in particular be smaller by one than the second number M of openings 38, i.e. M=N+1. In the case shown, it may apply, without limitation and by way of example: N=30, and M=31.The sensor device 300 or its two differential magnetic field sensors 6 and 10 can be arranged offset with respect to the axis of rotation. In this case, the first differential magnetic field sensor 6 can be aligned with the openings 36 of the inner track. More specifically, the sensor elements 16A- 16C may be aligned with the apertures 36 so as to at least partially overlap with the ferromagnetic wheel 32 upon rotation thereof about the axis of rotation. When the ferromagnetic wheel 32 rotates, the openings 36 and the ferromagnetic material arranged between the openings 36 can alternately move past the sensor elements 16A to 16C of the first differential magnetic field sensor 6. The first differential magnetic field sensor 6 may be configured to sense the changing magnetic field at the positions of its sensor elements 16A to 16C. Similarly, the second differential magnetic field sensor 10 may be aligned with the outer track openings 38 and configured to sense the changing magnetic field at the positions of its sensor elements 16A- 16C.Each of the two magnetic field sensors 6 and 10 may be configured to output two differential signals. The generation of these differential signals and the sensitivity directions of the sensor elements 16A to 16C of the respective differential magnetic field sensor used in this context may differ depending on the application. Two examples are described below in this context.In a first example, all three sensor elements 16A to 16C of the differential magnetic field sensors 6 and 10 may be used. In this case, all three sensor elements 16A to 16C of the respective magnetic field sensor can be sensitive in the air gap direction (i.e. in the y direction). Thus, with such a configuration, all of the three sensor elements 16A to 16C have the same sensitivity direction, which can simplify a manufacturing process of the magnetic field sensors. For example, a corresponding magnetization can be generated in a furnace and a complete wafer can be magnetized in a single step.A first differential signal S 1 sine output by the first differential magnetic field sensor 6 may be based on a measurement of its first sensor element 16A and a measurement of its second sensor element 16B. In this context, the letter "L" may denote a measurement of the first (left) sensor element 16A and the letter "R" may denote a measurement of the second (right) sensor element 16B. A second differential signal S 1 cosine output by the first magnetic field sensor 6 can be based on measurements of its three sensor elements 16A to 16C. In this context, the letter "C" may denote a measurement of the third (middle) sensor element 16C. Differential signals S2 sine and S2 cosine output from the second differential magnetic field sensor 10 can be determined in an analog manner.In a second example, the first sensor element 16A and the second sensor element 16B of the differential magnetic field sensors 6 and 10 may be used. Here, the two sensor elements 16A and 16B may be sensitive in the connection direction of the two sensor elements (i.e., in the x direction) as well as in the air gap direction (i.e., in the y direction). The two sensitivity directions can be generated, for example, by a laser magnetization. In this case, a first bridge circuit may be sensitive in the y-direction and a second bridge circuit may be sensitive in the x-direction.A first differential signal S 1 sine output by the first differential magnetic field sensor 6 may be based on a measurement of its first sensor element 16A in the y-direction and a measurement of its second sensor element 16B in the y-direction. In this context, the same may applyA second differential signal S 1 cosine output by the first differential magnetic field sensor 6 may be based on a measurement of its first sensor element 16A in the x-direction and a measurement of its second sensor element 16B in the x-direction. In this context, the same may applyThe differential signals S2 sine and S2 cosine output by the second differential magnetic field sensor 10 can be determined in an analog manner.The differential signals S1 sine( and S2 sine) according to relations (1) and (3) can each have a sinusoidal profile. Exemplary curves of such signals are shown and described further below in connection with FIGS. 4A and 5A. The differential signals S1 cosine( and S2 cosine) according to relations (2) and (4) can each have a cosine-shaped profile. Exemplary curves of such signals are shown and described further below in connection with FIGS. 4B and 5B.The differential signals S 1 sine, S 1 cosine, S 2 sine and S 2 cosine provided by the two magnetic field sensors 6 and 10 can be used to determine a position or a rotation angle of the ferromagnetic target structure 32. In this context, it is noted that the ferromagnetic target structure 32 may be mechanically coupled to a component, such as a rotatable shaft. Based on the angle or position determination of the ferromagnetic target structure 32, a position or a rotation angle of the component coupled thereto can then also be determined. An exemplary scheme for determining the angle of rotation is described below. The calculations performed in this context may be provided by a processing unit (or control unit, e.g. ECU) which may include, for example, a microcontroller or a processor. The scheme described below can be carried out both on the basis of difference signals according to relations (1) and (2) and on the basis of difference signals according to relations (3) and (4).Differential signals S 1 sine and S 1 cosine provided by the first differential magnetic field sensor 6 may be used to determine a first relative angle α coarse. In an analog manner, differential signals S 2 sine and S 2 cosine provided by the second differential magnetic field sensor 10 may be used to determine a second relative angle α fine. The determination of the first relative angle α coarse and the second relative angle α fine can be based in each case on an arctangent operation. In this context, andExemplary curves of the relative angles α coarse and α fine are shown and described further below in connection with FIGS. 6A and 6B. It is noted that the difference signals prior to the arctangent operation may be normalized and the normalized signals used as input for the arctangent operation. Normalization may include offset and / or amplitude correction.The relative angles α coarse and α fine may be used to determine an (absolute) angle of rotation (or Vernier angle) α nonius of the ferromagnetic target structure 32. The determination of the vernier angle α nonius can be based on a vernier operation. In this context, the same may applyAn exemplary profile of the Vernier angle α nonius is shown and described further below in connection with FIG. 8A.The ascertained Vernier angle α nonius can have a residual error. By means of a further calculation scheme described below, such a residual error can be reduced and a new (absolute) Vernier angle α new with reduced angle error can be provided. A modulo operation can first be applied to the Nonius angle α nonius in order to correct overshoots:Next, a signal period associated with the outer trace having N+1 apertures 38 may be determined according to and using the rounding function (or Gaussian clip or floor function [·]) in equation (10).Knowing the signal period, the new and more accurate output angle α new can be calculated according toDue to a possible error of the Vernier angle α nonius the correct signal period may not always be correctly determined. In some cases, the calculated signal period may deviate by one. This can result in high error peaks with an amplitude of +1 threshold. The error peaks can be removed by comparing the new angle α new with the Nonius angle α nonius. If a difference of the two angles is greater than a maximum Nonius error, the threshold value Thresholdmay be subtracted from α new i.e.Conversely, the threshold value Threshold can be added if the difference between the two angles is less than the minimum Nonius error, i.e.In the following, in conjunction with FIGS. 4 to 9, simulation results of a determination of a position or a rotation angle of a ferromagnetic target structure based on the above-described scheme are shown and described. The simulations are based on an arrangement as shown in FIGS. 3A and 3B. Further, the simulations are based on the example and non-limiting parameter values given below.A radius of the inner track with the openings 36 has a value of about 10 mm and a radius of the outer track with the openings 38 has a value of about 27 mm. A thickness of the ferromagnetic wheel 32 in the y-direction has a value of about 1 mm. The first differential magnetic field sensor 6 is aligned with the inner track with a reading radius of approximately 14 mm and a number of N=330 openings 36. A distance or pitch between (directly) adjacent openings 36 is approximately 2.93 mm. The second differential magnetic field sensor 10 is aligned with the outer track with a reading radius of about 20 mm and N=31 openings 38. A distance or pitch between (directly) adjacent openings 38 is about 4.05 mm. A width of the openings is slightly greater than a width of the ferromagnetic material located between the openings. An associated division ratio has a value of approximately 0.4. the back bias magnet 2 is a cuboidal and sintered ferrite block magnet having approximate dimensions (x, y, z)=(6, 7, 5) mm. A residual magnetic field Br of the magnet 2 has a value of about 410 mT, and a coercive force Hcj of the magnet 2 has a value of about 271 kA / m.In the simulations, sensor elements 16A to 16C are modeled as 3 sensitive regions on the left (sensor element 16A), in the center (sensor element 16C) and on the right (sensor element 16B). The distance between the left sensor element 16A or the left region and the right sensor element 16B or the right region is approximately 1.546 mm. In real applications, the sensitive area may not be a single sensitive area, but the area may consist of TMR sensor elements, which may be connected in the form of a Wheatstone bridge. The bridge circuit may be either a spatially distributed bridge circuit (i.e. with two e.g. TMRs on the left side and the other two e.g. TMRs on the right side) or a double differential full bridge circuit (i.e. a Wheatstone full bridge on the left and a further bridge on the right side).The simulations proceed from two spatially distributed bridges, which are modeled by the left and right sensitive regions. One bridge circuit is sensitive to magnetic fields in the x-direction, while the other bridge circuit is sensitive to magnetic fields in the y-direction. In this way, each of the two differential magnetic field sensors 6 and 10 can provide two differential signals. One of the two difference signals may be representative of the Bx fields while the other difference signal may be representative of the By fields.FIGS. 4A and 4B show exemplary simulated curves of the output signals S 1 sine and. S1 cosine of the first differential magnetic field sensor 6. The signal strengths are plotted against the angle of rotation of the ferromagnetic wheel 32. The signal profiles for a full revolution of the ferromagnetic wheel 32 by 360 degrees are shown. FIG. 4A shows sinusoidal curves of the difference signal S 1 sine with a number of 30 oscillations, while FIG. 4B shows cosine curves of the difference signal S 1 cosine with a number of 30 oscillations.In an analogous manner, FIGS. 5A and 5B show exemplary simulated curves of the output signals S 2 sine and. S2 cosine of the second differential magnetic field sensor 10. FIG. 5A shows sinusoidal curves of the difference signal S 2 sine with a number of 31 oscillations, while FIG. 5B shows cosine curves of the difference signal S 2 cosine with a number of 31 oscillations.FIG. 6A shows exemplary simulated curves of a relative angle α ccerse. based on the output signals S 1 sine and S 1 cosine of the first differential magnetic field sensor 6. The signal curves are based on equation (5). In a preceding step, difference signals S1 sine and S1 cosine may be normalized (offset and amplitude correction) and used as input for the arctangent operation. The determined angle α ccerse is plotted against the angle of rotation of the ferromagnetic wheel 32. The profile of the relative angle α ccerse for a full revolution of the ferromagnetic wheel 32 by 360 degrees is shown. The signal curves shown each provide relative position information. During a full revolution of the ferromagnetic wheel 32, the signal curves have N=30 periods.FIG. 6B shows exemplary simulated curves of a relative angle α fine. based on the output signals S 2 sine and S 2 cosine of the second differential magnetic field sensor 10. The signal curves are based on equation (6). In a previous step, difference signals S2 sine and S2 cosine may be normalized (offset and amplitude correction) and used as input for the arctangent operation. The determined angle α fine is plotted against the angle of rotation of the ferromagnetic wheel 32. Curves of the relative angle α fine for a full revolution of the ferromagnetic wheel 32 by 360 degrees are shown. The waveforms shown represent relative position information. During a full revolution of the ferromagnetic wheel 32, the signal curves have N+1=31 periods.FIGS. 7A and 7B show error patterns of the relative angles shown in FIGS. 6A and 6B, respectively. In this case, FIG. 7A shows the error profile of the relative angle α coarse and FIG. 7B shows the error profile of the relative angle α fine over a full revolution of the ferromagnetic wheel 32.FIG. 8A shows exemplary simulated plots of the relative Nonius angle α coarse and α fine based on the relative angles α nonius. The angle curves shown are based on the Nonius operation of equation (7) and provide absolute angle information.FIG. 8B shows exemplary error characteristics of the Vernier angle α nonius of FIG. 8A. It can be seen from FIG. 8B that the angular error can be in a range of approximately ±3 degrees.FIG. 9A shows exemplary simulated curves of a modified Vernier angle α new with reduced angle error. The angle curves shown are based on the advanced calculation scheme according to equations (8) to (13).FIG. 9B shows exemplary error characteristics of the modified Vernier angle α new of FIG. 9A. It can be seen from FIG. 9B that the angular error can be in a range of approximately ±0.1 degrees and can thus be more significantly smaller than in FIG. 8B. In this connection, it is noted that a measurement accuracy of the application can be improved by adjusting and optimizing the geometric shape of the ferromagnetic target structure (e.g., its pitch and the associated pitch ratio) to the respective sensor device. An important optimization parameter may be a small root mean squared error (RMSE) deviation when comparing the normalized differential sensor signals to ideal sine and cosine signals.FIG. 10 shows a further possible application of a sensor device 1000 according to the disclosure. The sensor device 1000 may have one or more characteristics of sensor devices described above. The sensor device 1000 may be disposed relative to a ferromagnetic target structure 32 and separated therefrom by an air gap. The ferromagnetic target structure 32 may or may not be considered part of the sensor device 1000. In one example, the sensor device 1000 may be identical or similar to the sensor device 300 of FIG. 3. The arrangements of FIGS. 3 and 10 may differ in the design of the ferromagnetic target structure 32 in this case. In the example shown, the ferromagnetic target structure 32 may correspond to a ferromagnetic wheel that may rotate about an axis of rotation extending in the z-direction. The sensor device 1000 can be oriented analogously to the examples described above, i.e. the magnet 2 can be magnetized in the y-direction, and the sensor elements of the differential magnetic field sensors 6 and 10 can each be spaced apart from one another in the x-direction.The ferromagnetic wheel 32 may include a first upper track having a first number N of apertures 36 and a second lower track having a second number M of apertures 38. Each of the two tracks may have a circular shape. The first number N and the second number M may differ from one another, wherein the first number N of openings may in particular be smaller by one than the second number M of openings, i.e. M=N+1. In the case shown, it may apply, without limitation and by way of example: N=40 and M=41.The first differential magnetic field sensor 6 may be aligned with the top track openings 36 and the second differential magnetic field sensor 10 may be aligned with the bottom track openings 38. When the ferromagnetic wheel 32 rotates about its axis of rotation, the openings 36 and 38 can move past the sensor elements 16A to 16C of the first magnetic field sensor 6 and of the second magnetic field sensor 10, respectively. The magnetic field sensors 6 and 10 are each designed to detect the magnetic field changing at the positions of the respective sensor elements 16A to 16C upon rotation of the ferromagnetic wheel 32.Each of the two differential magnetic field sensors 6 and 10 may be configured to output two differential signals. Analogous to FIG. 3, for example, the sensor device 1000 may include a processing unit or control unit (e.g. ECU) (not shown) which may be configured to receive the output differential signals of the magnetic field sensors 6 and 10 and determine a first and second relative angle based thereon. The processing unit may further be configured to determine a position or a rotation angle of the ferromagnetic wheel 32 from the first and second relative angles. The stated variables can be determined in this case as already described in connection with FIG. 3. For the sake of simplicity, reference is made in this respect to the description of FIG. 3.FIG. 11 shows exemplary simulated error patterns of a modified Vernier angle α new for the arrangement shown in FIG. 10. The simulation results shown are based on the advanced calculation scheme of equations (8) to (13). It can be seen from FIG. 11 that the angular error can be in a range of approximately ±0.03 degrees.FIG. 12 shows another possible application of a sensor device 1200 according to the disclosure. The sensor device 1200 may include one or more characteristics of sensor devices described above. For example, the sensor device 1200 may be identical or similar to one of the sensor devices 300 and 1000 of FIGS. 3 and 10, respectively. The sensor device 1200 may be disposed relative to a ferromagnetic target structure 32 and separated therefrom by an air gap. The ferromagnetic target structure 32 may or may not be considered part of the sensor device 1200. In the example shown, the ferromagnetic target structure 32 may correspond to a linear ferromagnetic structure that may be configured to move past the two magnetic field sensors 6 and 10 in the x-direction. The sensor device 1200 may be oriented analogously to previous examples, i.e. the magnet 2 may be magnetized in the y-direction and the sensor elements of the differential magnetic field sensors 6 and 10 may be spaced apart from one another in the x-direction.The ferromagnetic target structure 32 may include a first upper track having a first number N of openings 36 and a second lower track having a second number M of openings 38. The two tracks may extend linearly along the x-direction. The first number N and the second number M may differ, wherein the first number N of openings may in particular be smaller by one than the second number M of openings, i.e. M=N+1. In the case shown, it may not apply in a restrictive and exemplary manner: N=40 and M=41.The sensor device 1200 may generate similar signals and determine similar sizes as the sensor devices described above according to the disclosure. For the sake of simplicity, reference is made in this respect to the description of preceding examples, in particular to the description of FIG. 3.FIG. 13 illustrates another possible application of a sensor device 1300 according to the disclosure. The sensor device 1300 may include one or more characteristics of sensor devices described above. The sensor device 1300 may be disposed relative to a ferromagnetic target structure 32 and separated therefrom by an air gap. The ferromagnetic target structure 32 may or may not be considered part of the sensor device 1300. The sensor device 1300 may be identical or similar to the sensor device 300 of FIG. 3, for example. The arrangements of FIGS. 3 and 13 may differ in the design of the ferromagnetic target structure 32 in this case. In the example shown, the ferromagnetic target structure 32 may correspond to a ferromagnetic wheel that may rotate about an axis of rotation extending in the z-direction. In FIG. 13, only a part of the ferromagnetic wheel 32 is shown. The sensor device 1300 can be oriented analogously to preceding examples, i.e. the magnet 2 can be magnetized in the y-direction and the sensor elements of the differential magnetic field sensors 6 and 10 can each be spaced apart from one another in the x-direction.The ferromagnetic wheel 32 may have a single circular trace of apertures 40. The number of openings 40 can be chosen according to the application and correspond, for example, to one of the values N or M mentioned in connection with the preceding examples. The two differential magnetic field sensors 6 and 10 may both be aligned with the single trace of apertures 40. When the ferromagnetic wheel 32 rotates about its axis of rotation, the openings 40 can move past the sensor elements 16A to 16C of the two differential magnetic field sensors 6 and 10. The magnetic field sensors 6 and 10 may each be configured to detect the magnetic field changing at the positions of the respective sensor elements 16A to 16C upon rotation of the ferromagnetic wheel 32. Each of the two differential magnetic field sensors 6 and 10 can be designed to output two differential signals, as already described in connection with FIG. 3. In one example, the difference signals output from the magnetic field sensors 6 and 10 may be based on the relations (1) and (2).In the following, in conjunction with FIGS. 14A to 15B, simulation results of a determination of a wheel speed or a rotational speed of a ferromagnetic wheel, as is shown by way of example in FIG. 13, are described. The simulation results are based on the relations (1) and (2) and the exemplary and non-limiting parameter values given below.The ferromagnetic wheel 32 has a radius of about 30 mm and a thickness in the z direction of about 1 mm. Furthermore, the ferromagnetic wheel 32 has a track with 40 openings and a spacing or pitch between (directly) adjacent openings 40 of approximately 4.7 mm. The ferromagnetic wheel 32 is made of iron and has a permeability μ r of about 4000. The back bias magnet 2 is a cuboidal and sintered ferrite block magnet having approximate dimensions of about (x, y, z)=(6, 7, 5) mm. A residual frequency Br of the magnet 2 has a value of approximately 410 mT, a coercive field strength Hcj of the magnet 2 has a value of approximately 271 kA / m. The sensor elements 16A to 16C are modeled in the simulations as 3 sensitive regions on the left (cf. sensor element 16A), in the middle (cf. sensor element 16C) and on the right (cf. sensor element 16B). The distance between the left sensor element 16A or the left region and the right sensor element 16B or the right region is approximately 1.546 mm.FIGS. 14A and 14B show exemplary simulated curves of output signals of the first differential magnetic field sensor 6 according to the relations (1) and (2), respectively, for different air gap sizes. FIG. 14A shows a sinusoidal profile of the output signal based on the relation (1). With a full revolution of the ferromagnetic wheel 32 through 360 degrees, the sinusoidal signal profile can have 40 oscillations. In the example shown, for the sake of simplicity, only a single oscillation is shown. It can be seen from FIG. 14A that the signal strength decreases with increasing air gap size. FIG. 14B shows waveforms based on the relation (2) from which the rotational direction of the ferromagnetic wheel 32 can be determined.FIGS. 15A and 15B show exemplary simulated curves of output signals of the second differential magnetic field sensor 10 according to the relations (1) and (2), respectively, for different air gap sizes. It can be seen from the signal curves of FIG. 15A that the second differential magnetic field sensor 10 provides the same information as the first differential sensor 6, but shifted (or inverted) by a phase of 180 degrees. This can be due in particular to the fact that the sensor elements 16A and 16B of the two magnetic field sensors 6 and 10 can be interchanged in a plan view of the surfaces 4 and 8 of the magnet 2 (i.e. viewed in the z direction). In this case, in the plan view, the first sensor element 16A of the first magnetic field sensor 6 can be congruent with the second sensor element 16B of the second magnetic field sensor 10 and the second sensor element 16B of the first magnetic field sensor 6 can be congruent with the first sensor element 16A of the second magnetic field sensor 10.Identical output information of the two magnetic field sensors 6 and 10 can be provided in different ways based on the inverted output signals. In one example, via e.g. an EEPROM (electrically erasable programmable read-only memory) bit, one of the two output signals can be switched from a rising edge to a falling flicker, whereby this signal can be inverted. In a further example, one of the two magnetic field sensors 6 and 10 can be realized with a reference magnetization of the sensor elements 16A and 16B (e.g. TMR elements) rotated by 180 degrees. In yet another example, one of the two magnetic field sensors 6 and 10 can be attached to the magnet 2 with its front side instead of with its rear side, i.e. the sensor can be mounted in an inverted manner. In this case, the first sensor elements 16A and the second sensor elements 16B of the two magnetic field sensors 6 and 10 would then each be congruent, as viewed in the z direction.The simulated waveforms of FIG. 15B may be identical or similar to the simulated waveforms of FIG. 14B. The two differential magnetic field sensors 6 and 10 can therefore provide identical information with respect to the present rotational direction of the ferromagnetic wheel 32.Analogous to examples described above, the sensor device 1300 may include a processing unit (or control unit, e.g. ECU) which may include or correspond to, for example, a microcontroller or processor. The processing unit can be designed to determine a speed of the ferromagnetic wheel 32 on the basis of the difference signals output by the two differential magnetic field sensors 6 and 10. In this connection, the processing unit may count the pulses of the output signals shown in FIGS. 14A and 15A and determine the rotational speed of the rotating ferromagnetic wheel 32 therefrom.As described, the sensor device 1300 of FIG. 13 may be configured to provide two identical and thus redundant output signals from which the rotational speed of the ferromagnetic wheel 32 may be determined. The sensor device 1300 can be used, for example, in automotive applications for determining wheel speeds, in particular in safety-related applications, such as ABS (anti-lock brake system), motors or transmissions. In this context, the sensor device 1300 or its processing unit can be designed to carry out an automotive safety test on the basis of the difference signals output by the two differential magnetic field sensors 6 and 10. The two redundant signals can be used for system-level safety plausibility checks and thereby provide a high degree of diagnostic coverage. As a result, potentially A-SIL stages up to ASIL-D can be achieved. The sensor device 1300 may be configured to be used as a wheel speed sensor in redundant brake systems, which may be prescribed for autonomous driving from the ADAS (Advanced Driver Assistance System) level 3 (L3, "Conditional Automation"). In this context, in particular two wheel speed sensors per wheel may be required.FIG. 16 shows a flow chart of a method for manufacturing a sensor device according to the disclosure. The method can be used, for example, to produce one of the sensor devices described herein according to the disclosure. The method may thus be read in connection with any of the preceding figures.At 42, a magnet may be provided. At 44, a first differential magnetic field sensor may be mounted on a first surface of the magnet. At 46, a second differential magnetic field sensor may be mounted on a second surface of the magnet opposite the first surface.By the sensor devices according to the disclosure described herein, the technical effects described below can be provided. Based thereon, sensor devices according to the disclosure may exceed conventional sensor devices in various aspects.Sensor devices according to the disclosure or their applications may use a low cost ferromagnetic wheel and a single bias magnet. In contrast, conventional sensing devices may require an expensive encoder wheel with alternating magnetic poles or a ferromagnetic wheel with two bias magnets. Thus, by using the sensor devices described herein, costs can be effectively saved.Sensor devices according to the disclosure are based on a differential measuring principle. The applications described herein are therefore insensitive to influences of magnetic stray fields and can thus provide a high measurement accuracy. The sensor devices are suitable for a large number of applications, for example in automotive, industrial and consumer electronics.Sensor devices according to the disclosure may have a small form factor. The magnet and the two differential magnetic field sensors may be encapsulated in a single common encapsulation material. In one example, the corresponding sensor package or sensor module can be configured cylindrically and have a comparatively small diameter of, for example, approximately 8 mm.Sensor devices according to the disclosure may be used in a variety of different applications. In the examples of FIGS. 3 and 10, example angle measurements for ferromagnetic wheels are described. In addition, the sensor device used in these measurements can also be used for a linear position measurement, as is shown and described by way of example in connection with FIG. 12. In this case, only the wheel-shaped ferromagnetic target structure has to be replaced by a linear ferromagnetic target structure.Identical sensor devices according to the disclosure may be used for position or angle measurements (see e.g. FIGS. 3, 10 and 12 ) as well as for speed measurements (see e.g. FIG. 13 ).Sensor devices according to the disclosure provide a simple structure with one magnet and two magnetic field sensors. Necessary calculations for angle determination and / or speed determination can be carried out by an external processing unit (e.g. a microcontroller).Sensor devices according to the disclosure may be used for measurement of an absolute position or an absolute angle. An "absolute" measurement can in this context mean, in particular, obtaining a unique signal over the entire mechanical stroke (linear movement or rotation of the ferromagnetic target structure or of a component, such as a shaft, for example), which is coupled thereto.Sensor devices according to the disclosure may provide redundant measurement signals for determining wheel speeds and therefore be used for (in particular automotive) safety checks, as described in connection with FIGS. 13 to 15.ExamplesHereinafter, sensor devices according to the disclosure and related manufacturing methods will be described by way of examples.Example 1 is a sensor device comprising: a magnet; a first differential magnetic field sensor mounted on a first surface of the magnet; and a second differential magnetic field sensor mounted on a second surface of the magnet opposite the first surface.Example 2 is a sensor device according to example 1, wherein: the magnet is magnetized in a first direction, and each of the two magnetic field sensors comprises a first sensor element and a second sensor element spaced apart from each other in a second direction perpendicular to the first direction.Example 3 is a sensor device according to example 1 or 2, wherein: the sensor device is arranged relative to a ferromagnetic target structure, and the sensor device and the ferromagnetic target structure are separated from each other by an air gap.Example 4 is a sensor device according to example 3, wherein: the ferromagnetic target structure comprises a linear ferromagnetic structure configured to move past the two magnetic field sensors in the second direction.Example 5 is a sensor device according to example 3, wherein: the ferromagnetic target structure comprises a ferromagnetic wheel configured to rotate about an axis of rotation, and the axis of rotation is either parallel to the first direction or in a third direction perpendicular to the first direction and perpendicular to the second direction.Example 6 is a sensor device according to example 5, wherein the two magnetic field sensors are arranged offset with respect to the axis of rotation.Example 7 is a sensor device according to one of Examples 2 to 6, wherein the following applies to each of the two magnetic field sensors: the first sensor element and the second sensor element are sensitive in the first direction and in the second direction, a first differential signal output by the magnetic field sensor is based on a measurement of the first sensor element in the first direction and a measurement of the second sensor element in the first direction, and a second differential signal output by the magnetic field sensor is based on a measurement of the first sensor element in the second direction and a measurement of the second sensor element in the second direction.Example 8 is a sensor device according to one of Examples 2 to 6, wherein: each of the two magnetic field sensors has a third sensor element which is arranged between the first sensor element and the second sensor element of the respective magnetic field sensor, all three sensor elements of the respective magnetic field sensor are sensitive in the first direction, a first differential signal output by the respective magnetic field sensor is based on a measurement of the first sensor element and a measurement of the second sensor element, and a second differential signal output by the respective magnetic field sensor is based on measurements of all three sensor elements.Example 9 is a sensor device according to any one of Examples 3 to 8, wherein: the ferromagnetic target structure comprises a first track having a first number of openings and a second track having a second number of openings, the first number and the second number are different from each other, and the first magnetic field sensor is aligned with the first track and the second magnetic field sensor is aligned with the second track.Example 10 is a sensor device according to example 9, wherein the first number of openings is smaller than the second number of openings by one.Example 11 is a sensor device according to any of Examples 7 to 10, further comprising: a processing unit configured to: receive the first differential signal and the second differential signal of each magnetic field sensor, determine a first relative angle based on the two differential signals of the first magnetic field sensor, and determine a second relative angle based on the two differential signals of the second magnetic field sensor.Example 12 is a sensor device according to example 11, wherein the determining of the first relative angle and the determining of the second relative angle are each based on an arctangent operation.Example 13 is a sensor device according to example 11 or 12, wherein the processing unit is configured to determine a rotation angle of the ferromagnetic target structure based on the first relative angle and the second relative angle.Example 14 is a sensor device according to example 13, wherein the determination of the angle of rotation is based on a Nonius operation.Example 15 is a sensor device according to any of Examples 3 to 8, wherein: the ferromagnetic target structure comprises a single track of openings, and both magnetic field sensors are aligned with the single track of openings.Example 16 is a sensor device according to example 15, further comprising: a processing unit configured to determine a speed of the ferromagnetic target structure based on the differential signals output by the two magnetic field sensors.Example 17 is a sensor device according to example 16, wherein the processing unit is further configured to perform an automotive safety check based on the differential signals output by the two magnetic field sensors.Example 18 is a sensor device according to one of Examples 2 to 17, wherein: a first side edge of the magnet running in the second direction and the sensor elements of the first magnetic field sensor are congruent in a plan view of the first surface of the magnet, and a second side edge of the magnet running in the second direction and the sensor elements of the second magnetic field sensor are congruent in a plan view of the second surface of the magnet.Example 19 is a sensor device according to one of the preceding examples, further comprising: a printed circuit board, wherein the first magnetic field sensor is electrically connected to a first surface of the printed circuit board via connection conductors and the second magnetic field sensor is electrically connected to a second surface of the printed circuit board opposite the first surface via connection conductors.Example 20 is a sensor device according to example 19, wherein: the magnet comprises at least one recess, and a mechanical connection between the printed circuit board and the magnet is provided by engaging a printed circuit board section in the at least one recess of the magnet.Example 21 is a sensor device according to one of the preceding examples, wherein the first magnetic field sensor and the second magnetic field sensor are identical in construction.Example 22 is a sensor device according to one of the preceding examples, wherein the magnet and the two magnetic field sensors are encapsulated in a common encapsulation material.Example 23 is a sensor device according to any of the preceding examples, wherein the magnet is a permanent back bias block magnet.Example 24 is a sensor device according to any of the preceding examples, wherein the magnetic field sensors are arranged in a top read configuration relative to the magnet.Example 25 is a method of manufacturing a sensor device, the method comprising: providing a magnet; mounting a first differential magnetic field sensor on a first surface of the magnet; and mounting a second differential magnetic field sensor on a second surface of the magnet opposite the first surface.Although specific embodiments are illustrated and described herein, it will be apparent to those of ordinary skill in the art that a variety of alternative and / or equivalent implementations may replace the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and their equivalents.

Claims

A sensor device comprising: a magnet (2); a first differential magnetic field sensor (6) mounted on a first surface (4) of the magnet (2); and a second differential magnetic field sensor (10) mounted on a second surface (8) of the magnet (2) opposite the first surface (4), wherein the magnet (2) is magnetized in a first direction parallel to the first surface (4) and parallel to the second surface (8).The sensor device according to claim 1, wherein: each of the two magnetic field sensors (6, 10) includes a first sensor element (16A) and a second sensor element (16B) spaced apart from each other in a second direction perpendicular to the first direction.The sensor device of claim 1 or 2, wherein: the sensor device is disposed relative to a target ferromagnetic structure (32), and the sensor device and the target ferromagnetic structure (32) are separated from each other by an air gap (34).The sensor device according to claim 2 and claim 3, wherein: the target ferromagnetic structure (32) comprises a linear ferromagnetic structure configured to move past the two magnetic field sensors (6, 10) in the second direction.The sensor device of claim 3 and claim 2, wherein: the ferromagnetic target structure (32) comprises a ferromagnetic wheel configured to rotate about an axis of rotation, and the axis of rotation is either parallel to the first direction or in a third direction perpendicular to the first direction and perpendicular to the second direction.Sensor device according to claim 5, wherein the two magnetic field sensors (6, 10) are arranged offset with respect to the axis of rotation.The sensor device according to any one of claims 2 to 6, wherein, for each of the two magnetic field sensors (6, 10), the first sensor element (16A) and the second sensor element (16B) are sensitive in the first direction and in the second direction, a first differential signal output from the magnetic field sensor (6, 10) is based on a measurement of the first sensor element (16A) in the first direction and a measurement of the second sensor element (16B) in the first direction, and a second differential signal output from the magnetic field sensor (6, 10) is based on a measurement of the first sensor element (16A) in the second direction and a measurement of the second sensor element (16B) in the second direction.The sensor device according to any one of claims 2 to 6, wherein: each of the two magnetic field sensors (6, 10) comprises a third sensor element (16C) arranged between the first sensor element (16A) and the second sensor element (16B) of the respective magnetic field sensor (6, 10), all three sensor elements (16A, 16B, 16C) of the respective magnetic field sensor (6, 10) are sensitive in the first direction, a first differential signal output from the respective magnetic field sensor (6, 10) is based on a measurement of the first sensor element (16A) and a measurement of the second sensor element (16B), and a second differential signal output from the respective magnetic field sensor (6, 10) is based on measurements of all three sensor elements (16A, 16B, 16C).The sensor device of any of claims 3 to 8, wherein: the ferromagnetic target structure (32) comprises a first track having a first number of apertures (36) and a second track having a second number of apertures (38), the first number and the second number being different from each other, and the first magnetic field sensor (6) is aligned with the first track and the second magnetic field sensor (10) is aligned with the second track.The sensor device of claim 9, wherein the first number of apertures (36) is less than the second number of apertures (38) by one.The sensor device according to claim 7 or 8, further comprising: a processing unit configured to: receive the first differential signal and the second differential signal of each magnetic field sensor (6, 10), determine a first relative angle based on the two differential signals of the first magnetic field sensor (6), and determine a second relative angle based on the two differential signals of the second magnetic field sensor (10).The sensor device of claim 11, wherein the determining of the first relative angle and the determining of the second relative angle are each based on an arctangent operation.The sensor device according to claim 11 or 12, wherein the processing unit is configured to determine a rotation angle of the ferromagnetic target structure (32) based on the first relative angle and the second relative angle.The sensor device of claim 13, wherein the determining of the angle of rotation is based on a Vernier operation.The sensor device of any of claims 3 to 8, wherein: the ferromagnetic target structure (32) has a single trace of apertures (40), and both magnetic field sensors (6, 10) are aligned with the single trace of apertures (40).Sensor device according to claim 15 and one of claims 7 and 8, further comprising: a processing unit configured to determine a speed of the ferromagnetic target structure (32) based on the differential signals output by the two magnetic field sensors (6, 10).Sensor device according to claim 16, wherein the processing unit is further configured to perform an automotive safety check based on the differential signals output by the two magnetic field sensors (6, 10).Sensor device according to one of Claims 2 to 17, wherein: a first lateral edge (30) of the magnet (2) running in the second direction and the sensor elements (16A, 16B, 16C) of the first magnetic field sensor (6) are congruent in a plan view onto the first surface (4) of the magnet (2), and a second lateral edge of the magnet (2) running in the second direction and the sensor elements (16A, 16B, 16C) of the second magnetic field sensor (10) are congruent in a plan view onto the second surface (8) of the magnet (2).The sensor device according to any one of the preceding claims, further comprising: a printed circuit board (12), wherein the first magnetic field sensor (6) is electrically connected to a first surface of the printed circuit board (12) via connection conductors (22) and the second magnetic field sensor (10) is electrically connected to a second surface of the printed circuit board (12) opposite the first surface via connection conductors (22).The sensor device according to claim 19, wherein: the magnet (2) has at least one recess (26), and a mechanical connection between the circuit board (12) and the magnet (2) is provided by engaging a circuit board portion (28) with the at least one recess (26) of the magnet (2).Sensor device according to one of the preceding claims, wherein the first magnetic field sensor (6) and the second magnetic field sensor (10) are structurally identical.Sensor device according to one of the preceding claims, wherein the magnet (2) and the two magnetic field sensors (6, 10) are encapsulated in a common encapsulation material (14).Sensor device according to one of the preceding claims, wherein the magnet (2) is a permanent back bias block magnet.Sensor device according to one of the preceding claims, wherein the magnetic field sensors (6, 10) are arranged in a top-read configuration relative to the magnet (2).A method of manufacturing a sensor device, the method comprising: providing a magnet (2); mounting a first differential magnetic field sensor (6) on a first surface (4) of the magnet (2); and mounting a second differential magnetic field sensor (10) on a second surface (8) of the magnet (2) opposite the first surface (4), wherein the magnet (2) is magnetized in a first direction parallel to the first surface (4) and parallel to the second surface (8).

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