Monitoring circuit for a magnetic-field sensor circuit

Abstract

The invention relates to a monitoring circuit (3) for monitoring the functionality of a magnetic-field sensor circuit (2) which contains magnetic-field sensor elements all of which or at least some of which have a pinning layer having a predefined magnetic orientation, wherein the monitoring circuit (3) contains correspondingly designed magnetic-field sensor elements which each have a pinning layer having a magnetic orientation which corresponds to the predefined magnetic orientation of the pinning layer of the associated magnetic-field sensor element within the monitored magnetic-field sensor circuit (2).

Description

[0001] Description

[0002] Monitoring circuit for a magnetic field sensor circuit

[0003] The invention relates to a monitoring circuit for monitoring the functionality of a magnetic field sensor circuit and a method for monitoring the functionality of a magnetic field sensor circuit.

[0004] State of the art

[0005] Conventional magnetic field sensors can be implemented based on the Hall, AMR, GMR, or TMR effect. For high-performance applications, GMR- or TMR-based sensors are preferred.

[0006] DE 600 25 146 T2 describes a method for producing a magnetic field sensor or magnetic memory with at least two magnetoresistive bridge elements, wherein each magnetoresistive element has a free and a pinned ferromagnetic layer.

[0007] These magnetic field sensors based on GMR or TMR effects require a so-called "pinning layer" for measuring the magnetic field. A "free layer" contained in the magnetic field sensor changes its magnetic orientation according to an external magnetic field. A "pinning layer" contained in the magnetic field sensor, on the other hand, is fixed in its magnetic orientation. The different magnetic orientations of the "free layer" and the "pinning layer" of the magnetic field sensor are measured via the TMR or GMR effect and evaluated for the sensory detection of the external magnetic field. The magnetic field sensor elements of the magnetic field sensor change their electrical resistance depending on the two aforementioned magnetic orientations. The orientation or magnetic orientation of the pinning layer of the magnetic field sensor is determined during the manufacturing process (usuallyThe magnetic alignment of the pinning layer of the magnetic field sensor is adjusted by applying a (locally) high temperature and a (locally) high, defined magnetic field to the pinning layer of the magnetic field sensor. This establishes a defined initial state for the magnetic alignment of the pinning layer.

[0008] However, a later change (during operation or upon delivery) in the orientation or magnetic alignment of the pinning layer of the magnetic field sensor results in an undefined operating state of the magnetic field sensor.

[0009] Disclosure of the invention

[0010] The present invention provides a monitoring circuit according to claim 1 and a method according to claim 15.

[0011] According to a first aspect, the invention provides a monitoring circuit for monitoring the functionality of a magnetic field sensor circuit which contains magnetic field sensor elements, each of which has a pinning layer with a predetermined magnetic orientation, wherein the monitoring circuit contains correspondingly designed magnetic field sensor elements, each of which or at least partially has a pinning layer with a magnetic orientation that corresponds to the predetermined magnetic orientation of the pinning layer of the associated magnetic field sensor element within the monitored magnetic field sensor circuit.

[0012] According to a further aspect, the invention provides a method for monitoring the functionality of a magnetic field sensor circuit which contains magnetic field sensor elements, each of which has a pinning layer with a predetermined magnetic orientation, wherein a monitoring circuit of the magnetic field sensor circuit automatically generates an error message as soon as the magnetic orientation of a pinning layer of at least one magnetic field sensor element within the magnetic field sensor circuit changes.

[0013] Advantages of the invention

[0014] A basic idea of ​​the invention is to electrically detect and evaluate changes in the sensor behavior of the magnetic field sensor. If the magnetic field sensor delivers potentially erroneous output signals due to a disturbance in a pinning layer caused by external influences, this can be detected with the monitoring circuit according to the invention and an appropriate response can be triggered.

[0015] An advantage of the monitoring circuit according to the invention is that it enables reliable detection during operation of the magnetic field sensor as to whether a pinning layer is disturbed and thus there is a risk of a faulty sensor output.

[0016] A further advantage of the monitoring circuit according to the invention is the avoidance of false signals and faulty operating states resulting from possible disturbances in the pinning layer through early detection and reporting to a higher-level system.

[0017] A further advantage of the monitoring circuit according to the invention is that it uses a circuit which is similar in structure and design to the monitored sensor circuit of the magnetic field sensor.

[0018] There is therefore only a minor additional circuit effort for providing the monitoring circuit.

[0019] According to a possible embodiment of the monitoring circuit, the magnetic field sensor elements of the monitoring circuit are designed such that the monitoring circuit has no sensitivity to an external magnetic field.

[0020] According to a possible embodiment of the monitoring circuit, the magnetic field sensor elements comprise GMR sensor elements or TMR sensor elements.

[0021] These sensor elements are reliable and easy to integrate.

[0022] According to a possible embodiment of the monitoring circuit, the magnetic field sensor elements of the monitoring circuit are connected in a detection circuit, in particular in a bridge circuit.

[0023] This circuit requires a small number of sensor elements and provides an electrical detection signal that can be easily evaluated.

[0024] According to a possible embodiment of the monitoring circuit, the detection circuit comprises a full-bridge circuit comprising two half-bridge circuits.

[0025] According to a possible embodiment of the monitoring circuit, the two half-bridge circuits of the full-bridge circuit are spatially separated from each other and are thus exposed to different external magnetic fields.

[0026] According to a possible embodiment of the monitoring circuit, the two half-bridge circuits of the full-bridge circuit are not spatially separated from each other and are exposed to the same external magnetic field.

[0027] According to a possible embodiment of the monitoring circuit, the detection circuit comprises a half-bridge circuit.

[0028] According to a possible embodiment of the monitoring circuit, the half-bridge circuits each have two magnetic field sensor elements connected in series between supply voltage terminals.

[0029] According to a possible embodiment of the monitoring circuit, the pinning layers of the two magnetic field sensor elements connected in series within a half-bridge circuit have the same magnetic orientation.

[0030] According to a possible embodiment of the monitoring circuit, the pinning layers of the two magnetic field sensor elements connected in series within a half-bridge circuit have an opposite magnetic orientation.

[0031] According to a possible embodiment of the monitoring circuit, the two half-bridge circuits of the full-bridge circuit each have an at least partially shielded magnetic field sensor element and an unshielded magnetic field sensor element connected in series therewith.

[0032] According to a possible embodiment of the monitoring circuit, the two half-bridge circuits of the full-bridge circuit each have an ohmic resistor and an unshielded magnetic field sensor element connected in series therewith.

[0033] This allows for simplified circuit implementation and simplified integration on a chip.

[0034] According to a possible embodiment of the monitoring circuit, the detection circuit of the monitoring circuit has a signal output which is connected to a signal input of a signal evaluation circuit of the monitoring circuit.

[0035] According to a possible embodiment of the monitoring circuit, the magnetic field sensor elements connected in the bridge circuit are designed such that the detection circuit does not generate any output signal, no signal, in particular no bridge output signal, at its signal output when an external magnetic field is applied and the magnetic alignment of the pinning layers of the magnetic field sensor elements contained therein remains unchanged.

[0036] According to one possible embodiment of the monitoring circuit, the monitoring circuit and the associated monitored magnetic field sensor circuit are integrated on one chip.

[0037] This minimizes the additional circuitry effort required to provide the monitoring circuit.

[0038] Furthermore, the monitoring circuit can thereby be manufactured in its structure and design in a simple manner during the manufacturing process similar or identical to the monitored magnetic field sensor circuit of the magnetic field sensor.

[0039] A magnetic field sensor element (bridge resistor) can consist of a single TMR or GMR sensor element or of a connection of a large number of such sensor elements (e.g. connected in series and / or parallel).

[0040] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings.

[0041] Short description of the drawings

[0042] The present invention is explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing.

[0043] Shown are: Fig.1 a block diagram for the schematic representation of a possible embodiment of a magnetic field sensor with a monitoring circuit according to the invention;

[0044] Fig.2 in block diagram for the schematic representation of a possible embodiment of a monitoring circuit according to the invention;

[0045] Figs. 3a to 3c show various bridge circuits which can be used in embodiments of the monitoring circuit according to the invention;

[0046] Fig.4a to 4c different embodiments of an inventive

[0047] monitoring circuit;

[0048] Fig.5a, 5b different embodiments of an inventive

[0049] monitoring circuit;

[0050] Fig.6 shows another possible embodiment of a monitoring circuit according to the invention;

[0051] Fig.7 shows another possible embodiment of a monitoring circuit according to the invention;

[0052] Fig.1 shows schematically in a block diagram a possible embodiment of a magnetic field sensor 1, which has a magnetic field sensor circuit 2 and an associated monitoring circuit 3.

[0053] The monitoring circuit 3 of the magnetic field sensor 1 is provided for monitoring the functionality of the magnetic field sensor circuit 2 within the magnetic field sensor 1. The magnetic field sensor circuit 2 contains a plurality of magnetic field sensor elements. The magnetic field sensor elements of the magnetic field sensor circuit 2 each have a pinning layer with a predetermined magnetic orientation. The monitoring circuit 3 contains correspondingly designed magnetic field sensor elements, each of which, or at least partially, has a pinning layer with a magnetic orientation that corresponds to the predetermined magnetic orientation of the pinning layer of the associated magnetic field sensor element within the monitored magnetic field sensor circuit 2.

[0054] The functionality is given if the pinning orientation during operation of the magnetic field sensor 1 corresponds to the pinning orientation after manufacture of the magnetic field sensor.

[0055] The monitoring circuit 3 preferably comprises an electrical detection unit 3A and a signal evaluation unit 3B, as shown in Fig. 2. The monitoring circuit 3 can monitor the functionality of the magnetic field sensor circuit 2 contained therein in the background or at specific intervals during normal operation of the magnetic field sensor 1. The detection circuit includes a test structure for detecting the pinning state of the magnetic field sensor elements of the magnetic field sensor circuit 2. The monitoring circuit 3 can also be activated to test the magnetic field sensor circuit 2 in a test mode.

[0056] In one possible embodiment, the monitoring circuit 3 and the associated monitored magnetic field sensor circuit 2 are integrated on a chip of the magnetic field sensor 1. The monitored magnetic field sensor circuit 2 delivers a sensor signal to a control unit of a device or system. A faulty sensor signal can trigger an erroneous response from the control unit. The monitoring unit 3 can report a possible malfunction of the magnetic field sensor circuit 2 to the control unit with a warning signal.

[0057] In a preferred embodiment of the monitoring circuit 3, the magnetic field sensor elements of the detection unit 3A of the monitoring circuit 3 are designed such that the monitoring circuit 3 has no sensitivity to an external magnetic field MF.

[0058] In one possible embodiment of the monitoring circuit 3, the magnetic field sensor elements connected in the detection circuit 3A of the monitoring circuit 3 of the magnetic field sensor 1 are designed such that the detection circuit 3A does not generate an output signal at the signal output of the detection circuit 3A when an external magnetic field MF is applied and the magnetic alignment of the pinning layers (= error-free sensor operation) of the magnetic field sensor elements contained therein remains unchanged.

[0059] The monitoring circuit 3 is capable of electrically detecting the sensor behavior of the magnetic field sensor circuit 2 of the magnetic field sensor 1 using the detection circuit 3A and evaluating it using the signal evaluation circuit 3B. The detection circuit 3A is preferably designed as a bridge circuit. If one or more magnetic field sensor elements of the magnetic field sensor circuit 2 of the magnetic field sensor 1 deliver faulty output signals due to a disturbance in its pinning layer caused by external influences, this can be detected by the associated monitoring circuit 3. In this case, the monitoring circuit 3 can generate a warning signal and thus trigger an appropriate response. The detection unit 3A contains magnetic field sensor elements whose circuit implementation corresponds (essentially or entirely) to the magnetic field sensor elements of the magnetic field sensor circuit 2 and is also interconnected accordingly.

[0060] The monitoring circuit 3 can have an interface to a higher-level control of a device, for example, a vehicle, or a system, for example, an automation system. The output signal supplied by the electrical detection circuit 3A, in particular a bridge output signal, is digitized by an AD converter of the signal evaluation circuit 3B in one possible embodiment. The acquired data samples can be processed by a data processing unit or a processor of the signal evaluation unit 3B and locally buffered in a data memory of the signal evaluation unit 3B.

[0061] The monitoring circuit 3 can reliably recognize or detect during the ongoing operation of the magnetic field sensor 1 whether a pinning layer of one or more magnetic field sensor elements of the magnetic field sensor circuit 2 is disturbed, and thus there is a risk of a faulty sensor output of the magnetic field sensor 1.

[0062] The monitoring circuit 3 thus allows the prevention of faulty measurement or sensor signals and faulty operating states resulting from potential disturbances in the pinning layers of magnetic field sensor elements of the monitored magnetic field sensor circuit 2. The monitoring circuit 3 can detect a potential disturbance early on and report it to a higher-level system.

[0063] The monitoring circuit 3 and the monitoring method according to the invention make it possible to detect or recognize any subsequent change in the orientation of the pinning layer after the production of the magnetic field sensor 1. This detection is performed electrically during the operation of the magnetic field sensor 1 by the detection circuit 3A of the monitoring circuit 3. If the orientation of the pinning layer changes, the change or disturbance is detected in the signal evaluation circuit 3B of the monitoring circuit 3, which leads to the output of a warning / error message and / or a change in the operating mode of the magnetic field sensor 1 from "function" to "error."

[0064] The monitoring circuit 3 according to the invention uses a circuit internally that is similar in structure and design to the monitored magnetic field sensor circuit 2 of the magnetic field sensor 1. The additional circuitry effort for providing the monitoring circuit 3 is therefore minimal.

[0065] In one possible embodiment of the monitoring circuit 3, its magnetic field sensor elements comprise GMR sensor elements, ie magnetic field sensor elements based on the giant magnetoresistance effect.

[0066] In one possible embodiment of the monitoring circuit 3, its magnetic field sensor elements comprise TMR sensor elements, i.e., magnetic field sensor elements based on the tunnel magnetoresistance effect. In one possible embodiment of the monitoring circuit 3, the magnetic field sensor elements of the monitoring circuit 3 are connected in a bridge circuit, as schematically shown in Fig. 3.

[0067] The monitoring circuit 3 shown in Fig.2 has a detection circuit 3A, in particular a bridge circuit, with a signal output which is connected to a signal input of a signal evaluation circuit 3B of the monitoring circuit 3

[0068] Fig.3a to 3c show various bridge circuits which can be used as detection circuit 3A in embodiments of the monitoring circuit 3 according to the invention.

[0069] Electrical detection is achieved, for example, via Wheatstone bridge circuits, e.g., full-bridge circuits (Fig. 3a) or half-bridge circuits (Fig. 3c). The pinning orientations of the individual resistors R of the magnetic field sensor elements are adjusted such that an external magnetic field MF leads to a bridge output signal Vout (output voltage between poles C and D or at pole C). This signal is then evaluated.

[0070] In one possible embodiment of the monitoring circuit 3, the detection circuit 3A comprises a full-bridge circuit 4 comprising two half-bridge circuits 5-1, 5-2, as shown in Figs. 3a, 3b.

[0071] In the embodiment shown in Fig. 3a, the two half-bridge circuits 5-1, 5-2 of the full-bridge circuit 4 are not spatially separated from one another and are exposed to the same external magnetic field MF. Fig. 3a shows a full-bridge circuit 4 with two half-bridge circuits 5-1, 5-2 connected in parallel between the supply terminals A, B. Terminals A and B are used to supply a constant voltage. Terminals C and D form the signal output of the full-bridge circuit 4 and thus of the detection circuit 3A and supply a bridge output signal of the full-bridge circuit 4, which is evaluated by the signal evaluation circuit 3B of the monitoring circuit 3. The resistors R1 to R4 of the full-bridge circuit 4 shown in Fig. 3a can be implemented entirely or partially as GMR or TMR resistors.

[0072] In the embodiment of the detection circuit 3A of the monitoring circuit 3 shown in Fig. 3b, the two half-bridge circuits 5-1, 5-2 of the full-bridge circuit 4 are spatially separated from each other and are exposed to different external magnetic fields MF1, MF2, as shown in Fig. 3b.

[0073] Fig. 3b shows a full-bridge circuit 4 analogous to Fig. 3a, but the two half-bridge circuits 5-1, 5-2 are spatially divided or separated. For example, the magnetic field sensor elements R1, R3 of the first half-bridge circuit 5-1 and the magnetic field sensor elements R2, R4 of the second half-bridge circuit 5-2 are located on opposite chip edges of a chip.

[0074] In the embodiment of the detection circuit 3A of the monitoring circuit 3 shown in Fig. 3c, the detection circuit 3A has only one half-bridge circuit 5.

[0075] The half-bridge circuits 5-1, 5-2 of the full-bridge circuit 4 shown in Fig. 3a, 3b and the half-bridge circuit 5 according to Fig. 3c each have two magnetic field sensor elements connected in series between supply voltage terminals A, B, which preferably each have a magnetic field-sensitive resistor R.

[0076] In one possible embodiment of the detection circuit 3A of the monitoring circuit 3, the pinning layers of the two magnetic field sensor elements connected in series within a half-bridge circuit 5-1, 5-2, 5 have the same magnetic orientation, as shown schematically in Fig.4a, 4b, 4c.

[0077] Fig. 4a to 4c show an embodiment of the three bridge variants (analogous to Fig. 3a to 3c) related to the circuitry according to the invention. The magnetic orientation or magnetic alignment of the pinning layer of a magnetic field sensor element is adjusted and magnetically "frozen" during the manufacture of the respective magnetic field sensor element. The orientation is selected with respect to the magnetic field-sensitive resistors R of the magnetic field sensor elements of the bridge circuit such that, in the presence of an existing (arbitrary) external magnetic field MF, no bridge output signal is generated at the signal output C, D of the bridge circuit, provided the orientation of the pinning layer has not changed due to external influences (e.g., high temperature, high magnetic field / magnetic shock).

[0078] It is assumed that the external magnetic field MF in the embodiments shown in Fig. 4a and Fig. 4c has the same field strength and orientation for all magnetic field sensor elements with the resistors R. The full-bridge circuit 4 according to Fig. 4a and the half-bridge circuit 5 according to Fig. 4c are implemented locally.

[0079] In Fig. 4b, the full-bridge circuit 4 is implemented with two spatially separated partial paths. It is assumed that the external magnetic field MF1 in the first half-bridge circuit 5-1, which comprises the resistors R1 and R3, and the external magnetic field MF2 in the second half-bridge circuit 5-2, which comprises the resistors R2 and R4, have the same field strength and orientation for both resistors contained in the respective half-bridge 5-1, 5-2, whereas the partial paths or half-bridges 5-1, 5-2 can be exposed to different field strengths and orientations of the external magnetic field. In other words, the resistors R1, R3 of the first half-bridge circuit 5-1 are exposed to a first magnetic field MF1 and the resistors R1, R3 of the second half-bridge circuit 5-2 are exposed to a second magnetic field MF2, which can differ in field strength and orientation from the first magnetic field MF1.

[0080] Other connections for the magnetic-field-sensitive resistors are also conceivable, e.g., crosswise (two half-bridges) or via operational amplifiers, etc. - not shown. The pinning orientation is chosen to be the same for all magnetic field sensor elements R1-R4 in Figs. 4a, 4b, and 4c ("Variant A"), as indicated by an arrow pointing to the right. However, this orientation can be implemented in any direction - in the same way for all R1-R4.

[0081] In particular, a random reorientation of the pinning layer due to an external influence (e.g. at high temperature and an external magnetic field MF which is on average "0" - i.e. with high dynamics of the external alternating field to be detected by the sensor element) generates a bridge output signal different from zero within the detection circuit 3A of the monitoring circuit 3 in the embodiments of the bridge circuits shown in Fig.4a, 4b, 4c.

[0082] Variant A according to the embodiment of Fig. 4a, 4b, 4c thus relates to the application case of a change in the pinning orientation independent of the originally preset pinning orientation.

[0083] In a further possible embodiment of the detection circuit 3A of the monitoring circuit 3, the pinning layers of the two magnetic field sensor elements connected in series within the half-bridge circuits 5-1, 5-2 of a full bridge 4 have an opposite magnetic orientation, as shown schematically in Figs. 5a, 5b.

[0084] Fig. 5a, 5b are analogous to Fig. 4a, 4b, although in Fig. 5a, 5b, in contrast to Fig. 4a, 4b, the pinning orientation is selected differently for the magnetic field sensor elements R1 -R4 ("variant B"). Here, the upper magnetic field sensor elements R1, R2 and the lower magnetic field sensor elements R3, R4 have the same pinning orientation in order to achieve a bridge output signal "0" for (arbitrary) external magnetic fields MF and unchanged pinning orientation.

[0085] Resistors R1-R4 can generally (i.e., in all embodiments) be geometrically very small and located very close to each other per half-bridge path, for example, in the range 10 μm x 10 μm ... 100 μm x 100 μm. This assumes that the external magnetic field is, on average, homogeneous in the range of a half-bridge—i.e., both resistors see the same magnetic field (magnitude and direction).

[0086] In particular, a directional reorientation of the pinning layer due to an external influence (e.g., a magnetic shock) can be detected by the full-bridge circuits 4 shown in Fig. 5a, 5b. In addition, a change in the pinning orientation, which occurs depending on the originally preset pinning orientation, can be detected.

[0087] In the initial state, the resistances R of the magnetic field sensor elements of the full-bridge circuit 4 are defined such that the bridge output signal at the signal output of the full-bridge circuit 4 between the output signal terminals C, D is zero volts (Vout=0V). A voltage other than zero volts is also possible—this is then used as a reference. The four magnetic field sensor elements of the full-bridge circuit 4 with the resistors R1, R2, R3, R4 can all be set to the same reference value, or each pair can be set to the same reference value (R1 = R2, R3 = R4) so ​​that the bridge output voltage Vout of the full-bridge circuit 4 is zero volts (Vout = 0V).

[0088] The monitoring circuit 3 thus enables the detection of pinning disturbances in "random" reorientation ("variant A") and in rotation of the orientation ("variant B"), depending on the design. Furthermore, a combination of both variants is advantageously possible.

[0089] In a further possible embodiment of the detection circuit 3A of the monitoring circuit 3, the two half-bridge circuits 5-1, 5-2 of the full-bridge circuit 4 implemented in the detection circuit 3A each have an at least partially shielded magnetic field sensor element and an unshielded magnetic field sensor element connected in series therewith, as shown in Fig.6.

[0090] Fig. 6 shows an embodiment using magnetic shielding for individual bridge resistors. For example, the two magnetic field sensor elements shown at the top of Fig. 6 are shielded from an external magnetic field MF by resistors R1s and R2s. The TMR / GMR effect is not sensitive to an external magnetic field MF in the shielded magnetic field sensor elements R1s and R2s. The shielding can completely or at least partially (attenuate the field) shield the magnetic field sensor element from the external magnetic field MF.

[0091] Possible shielding arrangements and pinning orientations are shown in Fig. 6 via arrows, so that the (unshielded) sensitive magnetic field sensor elements (resistors R3, R4) change similarly in an external magnetic field MF. In the presence of an intact pinning layer and an external magnetic field MF, the bridge output voltage Vout at the signal output C,D of the full-bridge circuit 4 shown in Fig. 6 is thus zero volts (Vout=0V). However, if the pinning layer of one of the magnetic field sensor elements is disturbed, the bridge output voltage Vout at the signal output C,D of the full-bridge circuit 4 shown in Fig. 6 is not equal to zero volts. The shielding of one or more magnetic field sensor elements can be achieved in the manufacturing process for producing the magnetic field sensor 1 by means of additional layers or by further packaging of the respective magnetic field sensor elements.

[0092] In a further possible embodiment of the detection circuit 3A of the monitoring circuit 3, the two half-bridge circuits 5-1, 5-2 of the full-bridge circuit 4 implemented in the detection circuit 3A each have a fixed ohmic resistor Rf and an unshielded magnetic field sensor element connected in series therewith, as shown in Fig. 7. Fig. 7 shows an implementation analogous to the embodiment shown in Fig. 6a, but instead of shielding, fixed resistors Rf are used, e.g., ohmic resistors. The fixed resistors shown in Fig. 7 can be implemented as GMR / TMR elements, although the free layer is removed or modified, for example, in order to be insensitive to an external magnetic field MF. Alternatively, they can be implemented as conventional resistors within a CMOS process. The position in the bridge circuit has an advantageous effect, for example,to compensate for temperature-related resistance changes.

[0093] The various embodiments described above can be combined as desired. Furthermore, several of these elements can be provided on one sensor chip.

[0094] The GMR / TMR sensor (resistance) can be integrated on an evaluation ASIC or implemented as a 2-chip solution (sensor chip and ASIC chip).

[0095] The use of other magnetic field sensor elements is possible, for example the use of anisotropic magnetoresistive sensors (AMR) or Hall sensors.

[0096] Furthermore, the monitoring circuit 3 can also monitor several magnetic field sensor circuits 2, which are redundantly integrated on the chip of the magnetic field sensor 1. If a magnetic field sensor circuit 2 malfunctions, it can automatically switch to another, still functional magnetic field sensor circuit 2' (not shown).

[0097] The arrangement and number of variable resistors and pinning orientations in the bridge circuits 4, 5 may differ from the number shown in Figures 3 to 7.

[0098] The magnetic field sensor 1 with its integrated monitoring circuit 3 is particularly suitable for applications requiring reliable, stable long-term operation. The magnetic field sensor 1 can be used for automotive applications, particularly for wheel speed sensors, but also for position, angle, or current sensors. The magnetic field sensor 1 can be used for other applications (e.g., in consumer electronics applications such as "eCompass").

[0099] The method according to the invention can be extended to multidimensional magnetic field sensors (e.g., 2-axis, 3-axis sensors). Although the present invention has been fully described above with reference to the preferred embodiments, it is not limited thereto, but can be modified in a variety of ways.

Claims

Patent claims:

1. Monitoring circuit (3) for monitoring the functionality of a magnetic field sensor circuit (2) which contains magnetic field sensor elements which each have a pinning layer with a predetermined magnetic orientation, wherein the monitoring circuit (3) contains correspondingly designed magnetic field sensor elements which at least partially have a pinning layer with a magnetic orientation which corresponds to the predetermined magnetic orientation of the pinning layer of the associated magnetic field sensor element within the monitored magnetic field sensor circuit (2).

2. Monitoring circuit according to claim 1, wherein the magnetic field sensor elements of the monitoring circuit (3) are designed such that the monitoring circuit (3) has no or negligible sensitivity to an external magnetic field.

3. Monitoring circuit according to claim 1 or 2, wherein the magnetic field sensor elements comprise GMR sensor elements or TMR sensor elements.

4. Monitoring circuit according to one of the preceding claims, wherein the magnetic field sensor elements of the monitoring circuit (3) are connected in a detection circuit (3A).

5. Monitoring circuit according to claim 4, wherein the detection circuit (3A) comprises a full bridge circuit (4) comprising two half-bridge circuits (5-1, 5-2).

6. Monitoring circuit according to claim 5, wherein the two half-bridge circuits (5-1, 5-2) of the full-bridge circuit (4) are spatially separated from one another and are exposed to different external magnetic fields or are not spatially separated from one another and are exposed to the same external magnetic field.

7. Monitoring circuit according to claim 4, wherein the detection circuit (3A) comprises a half-bridge circuit (5).

8. Monitoring circuit according to claim 5 to 7, wherein the half-bridge circuits (5-1, 5-2, 5) each have two magnetic field sensor elements connected in series between supply voltage terminals (A, B).

9. Monitoring circuit according to claim 8, wherein the pinning layers of the two magnetic field sensor elements connected in series within a half-bridge circuit (5-1, 5-2, 5) have an identical magnetic orientation or an opposite magnetic orientation.

10. Monitoring circuit according to claim 5, wherein the two half-bridge circuits (5-1, 5-2) of the full-bridge circuit (4) each have an at least partially shielded magnetic field sensor element and an unshielded magnetic field sensor element connected in series therewith.

11. Monitoring circuit according to claim 5, wherein the two half-bridge circuits (5-, 5-2) of the full-bridge circuit (4) each have an ohmic resistor and an unshielded magnetic field sensor element connected in series therewith.

12. Monitoring circuit according to one of the preceding claims 5 to 11, wherein the detection circuit (3A) of the monitoring circuit (3) has a signal output (C,D) which is connected to a signal input of a signal evaluation circuit (3B) of the monitoring circuit (3).

13. Monitoring circuit according to one of the preceding claims 5 to 12, wherein the magnetic field sensor elements connected in the detection circuit (3A) are designed such that the detection circuit (3A) does not generate an output signal or a reference output signal at its signal output (C, D) when an external magnetic field is applied and the magnetic alignment of the pinning layers of the magnetic field sensor elements contained therein remains unchanged. 14.Monitoring circuit according to one of the preceding claims, wherein the monitoring circuit (3) and the associated monitored magnetic field sensor circuit (2) are integrated on a chip of a magnetic field sensor (1).

15. Method for monitoring the functionality of a magnetic field sensor circuit (2) which contains magnetic field sensor elements which at least partially have a pinning layer with a predetermined magnetic orientation, wherein a monitoring circuit (3) automatically generates an error message as soon as the magnetic orientation of a pinning layer of at least one magnetic field sensor element within the magnetic field sensor circuit (2) changes.

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