Self-calibrating magnetoresistance-based magnetic field sensor

Abstract

The system, circuit, and method provide self-calibration for a magnetoresistive-based magnetic field sensor. Examples include the use of a closed loop acting as a feedback or calibration loop configured to process a reference signal applied to one or more magnetoresistive elements in an MR-based magnetic field sensor that also senses one or more external magnetic fields. The closed loop can adjust a bias voltage applied to the one or more magnetoresistive elements based on the reference signal. The calibration loop can thus provide automatic or self-calibration of the sensitivity of one or more magnetoresistive elements of the sensor to compensate for external factors that affect the sensitivity of the one or more magnetoresistive elements.

Description

[Background technology]

[0001]

[0001] Magnetic field sensors utilize magnetic field sensing elements to detect one or more magnetic fields for a variety of purposes. For example, magnetic field sensors are often used to detect electrical current flowing in a conductor. Magnetic field sensors can also be used to sense ferromagnetic or conductive targets and generally act to detect the movement or position of a target. Such sensors are found in many technological fields, including robotics, automotive, manufacturing, and the like. For example, a magnetic field sensor can be used to detect when a vehicle wheel jams (stops turning), triggering the vehicle's control processor to engage the anti-lock braking system. Magnetic field sensors can also detect the distance to an object. As an example, a magnetic field sensor can be used to detect the position of a hydraulic piston or the angular position of a steering column.

[0002]

[0002] A magnetoresistive element is a type of magnetic sensing element that has a variable resistance that changes in response to changes in an applied or sensed magnetic field. There are different types of magnetoresistive elements, such as semiconductor magnetoresistive elements, such as those containing indium antimonide (InSb), anisotropic magnetoresistive (AMR) elements, giant magnetoresistive (GMR) elements, and tunneling magnetoresistive (TMR) elements, also known as magnetic tunnel junction (MTJ) elements. Some magnetoresistive elements, such as GMR and TMR elements, may have a relatively small or limited linear output range, where changes in the sensed magnetic field strength are linear with the corresponding change in the element's resistance. When used in a magnetic closed-loop configuration, xMR-based sensors may offer a relatively limited dynamic range, which may be undesirable for certain sensor applications. Summary of the Invention

[0003] Aspects of the present disclosure include a self-calibrating magnetic field sensor. The self-calibrating magnetic field sensor may include a magnetoresistive (MR) circuit configured to receive an external magnetic field in a first frequency band and a reference magnetic field in a second frequency band, the magnetoresistive circuit configured to generate an MR output electrical signal including an external signal based on the external magnetic field and a reference signal based on the reference magnetic field. The sensor may include a coil driver circuit configured to generate and direct the reference magnetic field to the magnetoresistive circuit. The sensor may include a feedback loop configured to receive the MR output electrical signal from the magnetoresistive circuit, the feedback loop configured to block the external signal to extract the reference signal, the feedback loop further configured to adjust the sensitivity of the magnetoresistive circuit based on the reference signal. The sensor may include a main signal path configured to receive the MR output electrical signal and block the reference signal to extract the external signal, the main signal path configured to generate, based on the external signal, a main signal path output signal indicative of information encoded in the external magnetic field.

[0004]

[0004] Implementations may include one or more of the following features. The magnetoresistive circuit of the sensor may include multiple magnetoresistive elements configured in a bridge. The magnetoresistive circuit may include one or more giant magnetoresistive (GMR) elements. The magnetoresistive circuit may include one or more anisotropic magnetoresistive (AMR) elements. The magnetoresistive circuit of the sensor may include one or more tunneling magnetoresistive (TMR) elements. The feedback loop may include a demodulator configured to demodulate the MR output signal at a modulation frequency of the reference magnetic field to generate a corresponding demodulated signal. The feedback loop may include a first summation unit configured to subtract a nominal reference voltage from the demodulated signal to generate a feedback error signal. The feedback loop may further include a gain correction unit configured to receive the feedback error signal and adjust the sensitivity of the magnetoresistive circuit based on the feedback error signal. The feedback loop may further include a second summation unit configured to subtract the feedback error signal from a bias voltage supplied to an MR driver of the magnetoresistive circuit. The gain correction unit may include a third amplifier. The feedback loop may include a first amplifier configured to provide a desired gain to the demodulated signal. The feedback loop may include an analog-to-digital converter configured to convert the demodulated signal to a digital signal. The feedback path may further include a digital integrator configured to receive a digital (reference) signal and output an integral of the digital signal over time. The feedback loop may further include a low-pass filter configured to receive the demodulated signal and remove residual signal components of the external signal. The low-pass filter may include a digital filter. The digital filter may include a Cascaded Integrator-Comb (CIC) filter. The filter may include an analog filter. The analog filter may include a notch filter. The feedback path may include an analog integrator configured to receive the demodulated (reference) signal and output an integral of the demodulated signal over time. The main signal path output signal may include position information regarding the target. The main signal path output signal may include information regarding a current in a conductor.Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

[0005] A further aspect of the present disclosure includes a method for automatically adjusting the sensitivity of a magnetic field sensor. The method may include detecting an external magnetic field in a first frequency band (e.g., baseband) and providing a reference magnetic field in a second frequency band (e.g., modulation frequency band) for a magnetoresistive (MR) circuit configured to generate an MR output signal based on the sensed magnetic field. The method may further include providing a main signal path configured to receive the MR output signal and extract an external signal corresponding to the external magnetic field, the main signal path configured to generate, based on the external signal, a main signal path output signal indicative of information encoded in the external signal. The method may include providing a closed loop configured to extract a reference signal corresponding to the reference magnetic field from the MR output signal, the closed loop configured to adjust the sensitivity of the magnetoresistive circuit based on the reference signal. The method may include adjusting the sensitivity of the magnetoresistive circuit based on the reference signal using the closed loop. Embodiments of this aspect may include or be used in conjunction with corresponding computer systems, apparatus, and computer programs stored on one or more computer storage devices, each configured to perform the processing of the method.

[0006] Implementations may include one or more of the following features. Adjusting the sensitivity of the magnetoresistive circuit may include adjusting a bias voltage applied to one or more magnetoresistive elements of the magnetoresistive circuit. Adjusting the sensitivity of the magnetoresistive circuit may include adjusting a gain setting of an amplifier in the closed loop. Adjusting the sensitivity of the magnetoresistive circuit may include demodulating the MR output signal at a modulation frequency of the reference magnetic field. The method may further include applying a low-pass filter to the demodulated MR output signal. Applying a low-pass filter to the demodulated MR output signal may include applying a digital CIC filter. Applying a low-pass filter to the demodulated MR output signal may include applying an analog filter. The main signal path output signal may be indicative of a position of a target. The main signal path output signal may be indicative of a current in a conductor. Adjusting the sensitivity of the magnetoresistive (MR) circuit may include compensating for any ambient or environmental operating conditions that affect MR sensitivity, such as temperature changes, the presence of mechanical stress, the addition of stray magnetic fields, etc. Such conditions may even include nonlinearities in the MR element or transducer itself, such as nonlinear sensitivity changes as an input signal swings through the transfer function curve of the MR transducer / element. The magnetoresistive circuit may include one or more giant magnetoresistive (GMR) elements. The magnetoresistive circuit may include one or more anisotropic magnetoresistive (AMR) elements. The magnetoresistive circuit may include one or more tunneling magnetoresistive (TMR) elements. Implementations of the described techniques may include hardware, methods or processes, or computer software on a computer-accessible medium.

[0007] Other embodiments of the described aspects and examples may include corresponding computer systems, devices, and computer programs stored on one or more computer storage devices, each configured to perform the processes of the methods as described herein. One or more computer computer systems may be configured to perform particular operations or processes as described herein by having software, firmware, hardware, or a combination thereof installed on the system that, during operation, causes the system to perform the processes. One or more computer programs may be configured to perform particular operations or processes by including instructions that, when executed by a data processing device, cause the device to perform the processes.

[0008]

[0008] The features and advantages described herein are not all-inclusive, and many additional features and advantages will be apparent to those skilled in the art in view of the drawings, specification, and claims. Moreover, the language used herein has been chosen primarily for ease of reading and guidance, and does not in any way limit the scope of the present disclosure, which may accommodate many embodiments. What follows is intended to be illustrative, but not exhaustive, of the scope of the present disclosure.

[0009] The manner and process of making and using the disclosed embodiments can be understood by reference to the figures in the accompanying drawings. It should be understood that the components and structures illustrated in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the concepts described herein. Moreover, the embodiments are illustrated in the figures by way of example and not by way of limitation. [Brief explanation of the drawings]

[0010] [Figure 1A]

[0010] FIG. 1 illustrates an exemplary self-calibrating magnetic field sensor with digital components in the feedback loop according to the present disclosure. [Figure 1B]

[0011] 1B illustrates an example self-calibrating magnetic field sensor similar to the magnetic field sensor of FIG. 1A but with a different configuration for the feedback loop, in accordance with the present disclosure. [Figure 2A]

[0012] FIG. 1 illustrates an example self-calibrating magnetic field sensor with analog components in the feedback loop according to the present disclosure. [Figure 2B]

[0013] 2B illustrates an exemplary self-calibrating magnetic field sensor similar to the magnetic field sensor of FIG. 2A but with a different configuration for the feedback loop, in accordance with the present disclosure. [Figure 3]

[0014] FIG. 1 illustrates an exemplary method for providing self-calibration for a magnetoresistive-based magnetic field sensor according to the present disclosure. [Figure 4A]

[0015] FIG. 10 is a set of graphs illustrating the operating conditions of an exemplary self-calibrating magnetic field sensor having an MR bridge circuit and a calibration loop according to the present disclosure that generates an output sense field signal while the calibration loop is in an inactive state. [Figure 4B]

[0016] 4B is a set of graphs illustrating the operating conditions of the example self-calibrating magnetic field sensor of FIG. 4A with the calibration loop in an active state, calibrating the sensor in response to external conditions. [Figure 5]

[0017] 5A and 5B illustrate an example MR bridge according to the present disclosure having different sensitivity directions for some of its included MR elements, showing a first configuration in which the bridge MR elements share a common sensitivity direction, and a second configuration in which paired or re-pinned MR elements have opposite sensitivity directions. [Figure 6]

[0018] FIG. 1 is a block diagram of an exemplary computer system operable to perform processing according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011]

[0019] The features and advantages described herein are not all-inclusive, and many additional features and advantages will be apparent to those skilled in the art upon consideration of the drawings, specification, and claims. Moreover, the language used herein has been chosen primarily for purposes of readability and guidance and does not in any way limit the scope of the inventive subject matter. The subject technology is susceptible to many embodiments. What follows is intended to be illustrative, but not exhaustive, of the scope of the subject technology.

[0012]

[0020] Aspects of the present disclosure are directed to and include systems, circuits, and methods that provide self-calibration for magnetoresistive-based magnetic field sensors. Examples may include the use of a closed loop acting as a feedback or calibration loop configured to process a reference signal applied to one or more magnetoresistive elements in an MR-based magnetic field sensor that also detects one or more external magnetic fields. The closed loop may adjust a bias voltage applied to the one or more magnetoresistive elements based on the reference signal. The calibration loop may thus provide self-calibration (also known as auto-compensation) of the MR block (sensor or element) sensitivity (gain) to compensate for external factors affecting the sensitivity of the one or more magnetoresistive elements. Aspects, examples, and embodiments of the present disclosure may therefore provide continuous configuration of the sensitivity of an open-loop MR-based sensor by utilizing a closed loop operating on a reference magnetic field signal, achieving high bandwidth (typically required for many current sensor applications) while also calibrating the sensor sensitivity in a continuous manner. Aspects, examples, and embodiments of the present disclosure may therefore provide a high bandwidth suitable for processing signals on the open loop (main signal path) while providing the ability to compensate for sensitivity drift caused by temperature, mechanical stress, stray magnetic fields, or any other external factors.

[0013]

[0021] 1A is a diagram illustrating an example self-calibrating magnetic field sensor 100A with a digital component in the feedback loop in accordance with the present disclosure. As shown, the magnetic field sensor 100A detects one or more external magnetic fields (B SIG) and also a reference magnetic field generated by the sensor 100A itself. The xMR block 102 is configured to generate an output 103 with a corresponding signal component. The magnetic field sensor 100A may also include a closed loop 110 configured as a feedback loop, a main signal path 130 configured to process a signal derived from or corresponding to one or more external magnetic fields, and a reference magnetic field section 140 configured to provide a reference magnetic field to the xMR block 102 for calibration using the closed loop 110. The main signal path 130 is configured to process a signal derived from or corresponding to one or more external magnetic fields (B SIG ) which may be indicative of information encoded in the main signal (V SIG The output may be generated based on the

[0014]

[0022] The MR section 101 may include an xMR transducer or block 102 that may sense one or more magnetic fields (sensing fields) that may be outside and / or inside the sensor 100A and generate an output 103 having a corresponding signal component. When used in the term "xMR," the "x" indicates that the MR element may be of any suitable type, for example, an anisotropic magnetoresistance (AMR) element, a giant magnetoresistance (GMR) element, or a tunneling magnetoresistance (TMR) element. When multiple xMR elements are present for the xMR block 102, they may be configured in a bridge, for example, a half bridge, or a full bridge such as a Wheatstone bridge. The xMR driver 104 drives any sensing magnetic fields (B SIG 1. The xMR block 102 may provide a drive voltage for the xMR element of the xMR block 102, which generates an output signal that is indicative of the closed loop 110 and the main signal path 130. As shown, the xMR block 102 may be connected to the closed loop 110 and the main signal path 130.

[0015]

[0023] The reference magnetic field area 140 is a reference magnetic field (BREF ) to the xMR block 102. The reference magnetic field section 140 may include a coil 142, a coil driver 144, and a current source 146 configured to generate a current at a desired modulation frequency, indicated by modulation frequency f1. The coil 142 is shown with an exemplary coil strength of 800 Gauss / Amp, although other values ​​may of course be used within the scope of this disclosure. The coil driver 144 receives a current and provides it to the coil 142 to generate a reference magnetic field B for detection by the xMR 102. REF , which in turn causes the xMR 102 to provide the reference signal V REF The reference magnetic field 140 may be generated independently of changes in environmental conditions or variables, such as temperature and / or mechanical stress. In the reference magnetic field region 140, the use of resistors with a low thermal coefficient (TC) and / or high insensitivity to mechanical stress, such as highly doped poly resistors, may facilitate the generation of the reference magnetic field independently of external factors that affect the sensitivity of the xMR block 102, such as changes in temperature, the application of stray magnetic fields, or the introduction of mechanical stress.

[0016]

[0024] As mentioned above, the output signal 103 generated by the xMR block 102 is a function of one or more external magnetic fields (B SIG ) corresponding to the main signal component (V SIG ), and also the reference magnetic field B generated by the reference magnetic field area 140 REF The reference signal component (V REFand (denoted as ). An example of the main signal and reference signal component 103' of output 103 is shown at location 1 (circled) adjacent to the branch point in the signal path identified at the output of xMR block 102 and at tap point (T) with the branch leading to closed loop 110 and main signal path 130. As described in further detail below, closed loop 110 may operate to automatically calibrate or adjust the sensitivity of xMR block 102 as operating conditions that affect the sensitivity of xMR block 102 are changed, such as changes in ambient temperature, introduction of mechanical strain, introduction of stray magnetic fields, etc. Additionally, closed (feedback) loop 110 may operate to automatically calibrate or adjust the sensitivity of xMR block 102 to compensate for nonlinearities inherent in the included xMR transducers or xMR elements.

[0017]

[0025] The closed loop 110 receives the reference signal V as shown at location 3 (circled). REF While passing the external field signal V SIG The closed loop 110 may include a blocking capacitor 114 to facilitate blocking of low frequency components of the reference frequency V. The closed loop 110 may include a demodulator 112 configured to receive the output signal 103 from the xMR block 102 and demodulate the signal, for example, at a demodulation frequency denoted as f1. The demodulator 112 may thus demodulate the reference frequency V, as shown at location 4 (circled). REF is demodulated to baseband, and at the same time the main signal V SIG、 or main signal V SIG (after passing through a blocking capacitor) at the modulation frequency.

[0018]

[0026] The closed loop 110 may include an amplifier 116 having a desired gain (A), as shown. The closed loop 110 may also include an analog-to-digital converter (ADC) 118 and a digital filter 120, as shown, for example, by the cascaded-integrator comb (CIC) filter shown. The closed loop 110 receives a nominal reference (voltage) signal (e.g., V REFNOM) to adjust the reference signal at that point in the closed loop 110 to generate a feedback (error) signal 125. REFNOM ) may represent the voltage expected to be generated by the reference (internal) field passed through the XMR bridge. For the desired target sensitivity level, after amplification by A, it becomes V REFNOM A particular output voltage from the bridge is predicted, equal to V. If the actual voltage from the bridge (xMR block 102) deviates from this "ideal" value, the closed loop 110 corrects for such error. REFNOM The voltage may be, for example, a scaled replica or version of the voltage used to generate the current used to drive the integration coil to generate the reference field.

[0019]

[0027] The feedback error signal 125 can be used to adjust the bias voltage 105, resulting in an adjusted bias voltage 107 supplied to the xMR driver 104. The signal adjustment in the closed loop 110 is shown as the change between the signals shown at locations 5 (circled) and 6 (circled), i.e., before and after the summing unit 122. The nominal reference voltage (V REFNOM ) may be set or adjusted as desired, for example, in response to external or internal operating conditions, or to meet a desired target or range of operation, etc. Summation unit 122 may provide the resulting signal 123 as a feedback error signal to digital-to-analog converter (DAC) 124, which may include gain adjustment / correction functionality.

[0020]

[0028] The closed loop 110 may include an optional integrator 121, as shown. While not required, the integrator 121 may be advantageous because it can provide or promote higher loop gain and better stability conditions for the loop 110. Such an integrator 121 may be used for digital and / or analog cases / applications. The signal generated by the DAC 124 may be provided to a summing unit 126, which may be configured to subtract the feedback error signal 125 from the initial bias signal 105 and provide the resulting adjusted bias signal 107 to the xMR driver 104 for driving the xMR block 102 and adjusting its sensitivity.

[0021]

[0029] The main signal path 130 includes an amplifier 132 having the indicated gain (B) and a V REF As shown in the area 2 (circled) where there is no SIG To extract the reference signal component (V REF ) may include a filter 134, for example a low pass filter (LPF) or a notch filter, configured to block the main signal V SIG The main signal path 130 may then include one or more additional components, as indicated, for example, by amplifier 136, for additional processing and / or signal conditioning of the signal. The main signal path 130 then receives a sensed magnetic field (B SIG ) the main signal V REF The signal processor 100 may generate one or more output signals 138 based on the received signal.

[0022]

[0030] During operation of the magnetic field sensor 100A, a closed loop (feedback loop) 110 receives and amplifies a reference field signal while blocking low frequency external field signals. A blocking capacitor 114 in the loop 110 amplifies the reference signal V, possibly with some residual level of the (residual) external magnetic field signal (as shown at location 3). REFThis may help block low frequency components of the external field signal while passing the reference signal V. REF and the residual of the external magnetic field signal can be demodulated at the frequency (f1) of the reference signal. As a result, the reference signal V REF is converted back to baseband, while the external field signal V SIG The residue of V is shifted to a higher frequency (as shown at location 3). These two signals may be amplified by an amplifier 116 (with a gain A) and then digitized by an ADC 118, e.g., a sigma-delta (SD) converter, to produce a reference signal V REF , which provides an output containing a digital version of the recovered reference signal V. A digital low-pass filter (LPF) 120 may provide further low-pass filtering to facilitate complete rejection of residuals of the external field signal. The output of the digital LPF 120 is then purely the recovered reference signal V, as shown at location 5 (circled). REF In examples where the ADC 118 includes a sigma-delta (SD) converter, the LPF 120 may include a cascaded integrator-comb (CIC) filter, as shown.

[0023]

[0031] The summation unit 122 outputs the recovered reference signal V SIG from a nominal reference signal (e.g., V REFNOM ) may be subtracted from the output of the gain correction DAC 124. The difference between these two signals constitutes the feedback error signal as shown in position 6 (circled), which may then be fed to the gain correction DAC 124. When no changes occur over a sufficiently long time span (e.g., 2-3 time constants of the circuit, 2-3 seconds, etc.), the error feedback signal may be at or near zero (DC), as shown. Changes in external conditions may cause the output of the gain correction DAC 124 to change. SIG DAC 124 may, for example, vary the error feedback signal at Location 6 (which may be a nominal reference signal V REFNOMThe xMR block 102 may add or subtract an error voltage (or current) to the nominal value of the xMR element transducer 102 (which may correspond to a nominal voltage or current). Once the loop 110 is engaged (operating), any changes to the sensitivity of the MR element transducer 102 due to temperature, mechanical stress, aging, stray fields, etc. are compensated for by the feedback loop 110 by appropriately adjusting the MR bias voltage or current in the xMR driver 104. The sensitivity (e.g., volts / gauss sensitivity) provided by the xMR block 102 may therefore be essentially independent of external factors that would otherwise affect the sensitivity of the xMR element of the xMR block 102.

[0024]

[0032] The main signal path (channel) 130 then receives the xMR block output signal 103 and blocks the reference signal component at a selected modulation frequency (e.g., f1) to, for example, block the sensed magnetic field (B SIG ) to determine the information encoded in the main signal component V SIG Such information may correspond, for example, to the current in a conductor or the position of a target / object. The main signal component processed by main signal path 130 may therefore be essentially independent of externally induced changes or effects on the sensitivity of the MR element, such as temperature, stray fields, mechanical stress, etc., as well as any nonlinearities inherent in the xMR element / transducer.

[0025]

[0033] 1B illustrates an example self-calibrating magnetic field sensor 100B according to the present disclosure that is similar to the magnetic field sensor 100A of FIG. 1A but has a different configuration for the feedback loop 110. Within FIG. 1B, the same reference numbers are used to indicate features / components shared with the magnetic field sensor 100A. As shown, the magnetic field sensor 100B may include an xMR block 101, a closed loop 110 configured as a feedback loop to the xMR block 101, a main signal channel 130, and a reference magnetic field section 140. The blocking capacitor 114 may be omitted in some examples.

[0026]

[0034] In sensor 100B, closed (feedback) loop 110 is configured to provide a feedback signal to the amplifier 116 of the feedback loop (instead of xMR driver 104). Changes in the sensitivity of xMR block 102 are therefore used to adjust the gain (A) of amplifier 116. In some examples, main signal path 130 may include a (second) demodulator 112b that receives a signal from loop 110 at a tap point (T) located after amplifier 116. The signal on main signal channel or path 130 may therefore be provided from a location on loop 110 (e.g., tap point T) by connection 131, undergo demodulation by demodulator 112b (reverses the modulation applied by modulator 112a) to bring the signal back to baseband, and then may undergo further processing. Main signal path 130 receives main signal V REF and sensing magnetic fields (B SIG ) may generate one or more output signals 138, which may be indicative of the information encoded in the signal.

[0027]

[0035] Alternative examples and / or embodiments may include analog components in addition to or instead of digital components, and Figures 2A-2B show two examples.

[0028]

[0036] 2A is a diagram illustrating an example self-calibrating magnetic field sensor 200A with analog components in the feedback loop according to the present disclosure. The magnetic field sensor 200A is generally similar to the magnetic field sensor 100A of FIG. 1A, but may have some analog components instead of digital components. As shown, the magnetic field sensor 200A may include an xMR section 201, a feedback loop 210, a main signal path 230, and a reference magnetic field section 240.

[0029]

[0037] MR section 201 may include an xMR transducer or block 202 that may sense (detect) one or more magnetic fields (sensing fields) that may be outside and / or inside sensor 200A and generate an output 203 having corresponding signal components. Sensor 200A may include an xMR driver 204 that may be configured to provide a drive voltage for the xMR elements of xMR block 202. As shown, xMR block 202 may be connected to closed loop 210 and main signal path 230.

[0030]

[0038] The reference magnetic field area 240 is a reference magnetic field (B REF ) to the xMR block 202. The reference magnetic field section 240 may include a coil 242, a coil driver 244, and a current source 246 configured to generate a current at a desired modulation frequency indicated by modulation frequency f1. The coil driver 244 receives a current and provides it to the coil 242 to generate a reference magnetic field B for detection by the xMR block 202. REF , which results in the xMR 202 providing the reference signal V REF may be provided.

[0031]

[0039] The closed loop 210 may operate to automatically calibrate or adjust the sensitivity of the xMR block 202 (e.g., by adjusting the bias voltage supplied to the xMR driver 204) when operating conditions that affect the sensitivity of the xMR block 202 change, such as changes in ambient temperature, the introduction of mechanical strain, the introduction of stray magnetic fields, etc.

[0032]

[0040] The closed loop 210 may include a blocking capacitor 214 to facilitate blocking of low frequency components of the external field signal while passing the reference signal. The closed loop 210 may include a demodulator 212 configured to receive the output signal 203 from the xMR element of the xMR block 202 and demodulate the output signal 203, for example, with a demodulation frequency denoted as f1. The demodulator 212 thus demodulates the reference frequency VREF and simultaneously demodulates the main signal VREF after passing through the blocking capacitor. SIGAttenuated version of (B SIG The closed loop 210 may operate to place a modulated frequency (corresponding to ) at the modulation frequency. The closed loop 210 may include an amplifier 216 having a desired gain (A), as shown.

[0033]

[0041] The closed loop 210 may further include an analog filter 218, such as a notch filter. The filtering and demodulation may allow or promote noise aliasing. The closed loop 210 may include a summing unit 220 that outputs a reference signal V to generate a feedback (error) signal 210 used to adjust the bias voltage supplied to the xMR driver 204. REF To adjust the nominal reference signal (e.g., V REFNOM ) can be used to subtract the nominal reference voltage (V REFNOM ) may be set or adjusted as desired, for example, in response to external or internal operating conditions, or to meet a desired target or range of operation, etc. The summing unit 220 may provide a resulting signal 223 (feedback error signal) to a gain correction block 222, which may include a gain adjustment / correction function. The closed loop 210 may include an optional integrator 221 as shown. The integrator 221, while not required, may be advantageous because it can provide or promote higher loop gain and better stability conditions for the loop 210. Similar to that described above for the sensor 100A of FIG. 1A, the signal 225 generated by the gain correction block 222 may be provided to a summing unit 226, which may be configured to subtract the feedback signal 225 from the initial bias signal 205 and provide the resulting adjusted bias signal 207 to the xMR driver 204 for driving the xMR block 202 and adjusting its sensitivity.

[0034]

[0042] The main signal path 230 includes an amplifier 232 having the indicated gain (B), as well as a reference signal component (V REF ) and from the output 203 of the xMR block 202 to the main signal VSIG The main signal path 230 may optionally include a filter 234, for example a low pass filter (LPF) or a notch filter, configured to extract the main signal V SIG The main signal path 230 may include one or more additional components, represented by, for example, amplifier 236, for additional processing and / or signal conditioning of the main signal V. REF and sensing magnetic fields (B SIG ) may generate one or more output signals 238 that may be indicative of the information encoded in the signal.

[0035]

[0043] 2B is a diagram illustrating an example self-calibrating magnetic field sensor 200B according to the present disclosure that is similar to the magnetic field sensor 200A of FIG. 2A but has a different configuration for the feedback loop 210. Within FIG. 2B, the same reference numbers are used to indicate features / components shared with the magnetic field sensor 200A of FIG. 2A. As shown, the magnetic field sensor 200B may include an xMR block 201, a closed loop 210, a main signal channel 230, and a reference magnetic field section 240.

[0036]

[0044] 2A , except that within the feedback loop 210, the sensor 200B may include a general filter 218 to illustrate that any suitable filter (e.g., IIR or FIR), filter bank, or combination of filters with other elements (e.g., resistors, capacitors, and / or inductors) may be utilized. Similarly, instead of a gain correction unit, the closed loop 210 includes an amplifier 228 that may have any desired gain C.

[0037]

[0045] FIG. 3 illustrates an example method 300 for providing self-calibration for a magnetoresistive-based magnetic field sensor according to the present disclosure. Method 300 may include providing an external magnetic field in a first frequency band and a reference magnetic field in a second frequency band for a magnetoresistive circuit configured to generate an MR output signal based on a sensed magnetic field, as shown at 302. Method 300 may include providing a primary signal path configured to receive the MR output signal and extract an external signal corresponding to the external magnetic field, the primary signal path configured to generate an output indicative of information encoded in the external magnetic field. Method 300 may include providing a closed loop configured to extract a reference signal corresponding to the reference magnetic field from the MR output signal, as described at 306, the closed loop configured to adjust the sensitivity of the magnetoresistive circuit based on the reference signal. Method 300 may include adjusting the sensitivity of the magnetoresistive circuit based on the reference signal by using the closed loop, as described at 308. Method 300 may include other or alternative steps in other examples.

[0038]

[0046] FIG. 4A is a set 400A of graphs (i)-(iv) illustrating the operating conditions of an exemplary self-calibrating magnetic field sensor having an MR bridge circuit (e.g., similar to that shown in FIG. 1A) and calibration loop according to the present disclosure, which generates a sense field signal while the calibration loop is in an inactive state. Graph (i) shows a plot 410 of the ambient temperature around the MR bridge versus time, with a step change highlighted to further illustrate the effect on the MR sensor sensitivity and the resulting closed-loop compensation. Graph (ii) shows a plot 420 of the voltage output of the MR bridge versus time. Graph (iii) shows a plot 430 of the bias voltage applied to the MR bridge versus time. Graph (iv) shows a plot 440 of the sense field output signal generated by the sensor versus time. All four graphs extend over a common time span (t=4.0 seconds to 8.0 seconds). Over the time spans shown, the MR bridge circuit generates a sense field signal while the MR bridge circuit is in an inactive state, generating a sense field signal. SIG) The corresponding predicted output voltage from the bridge (10mv) is shown in (ii).

[0039]

[0047] As shown in graphs (i)-(ii), a sudden increase in ambient temperature, shown as a step change in temperature 412 to temperature 414, causes an increase in the sensitivity of the MR elements in the MR bridge circuit, which correspondingly increases the output voltage of the MR bridge circuit from the expected 10 mV (in this example) 422 to a higher value 424 (11 mV in this example). In addition, the signal associated with the internally generated field at f1 changes amplitude due to the XMR sensitivity change. With a constant bias voltage applied to the MR bridge and the calibration loop in an inactive or off state, as shown in graph (iii), even though the applied XMR bias voltage remains constant as shown in graph (iii), the sensor output signal (indicating the sensed field) exhibits a temperature-induced increase by changing from an initial value 442 (starting at 444) and increasing during a transition period 446 before reaching a higher value 448, as shown in graph (iv), where values ​​442 and 446 correspond to steady-state conditions before and after the change in temperature shown in graph (i).

[0040]

[0048] FIG. 4B is a set 400B of graphs (i)-(iv) illustrating the conditions of the example self-calibrating magnetic field sensor of FIG. 4A generating a sensed field signal with an active calibration loop that calibrates the sensor in response to external conditions. In FIG. 4B, graph (i) illustrates the ambient temperature around the MR bridge, graph (ii) illustrates the voltage output of the MR bridge, graph (iii) illustrates the bias voltage applied to the MR bridge, and graph (iv) illustrates the sensed field output signal generated by the sensor, each over a common time span (t=4.0 seconds to 8.0 seconds). Over the time span shown, the MR bridge circuit generates a constant applied (sensed) magnetic field (B SIG ) is subject to

[0041]

[0049] In FIG. 4B, graph (i) shows a sudden increase in ambient temperature from temperature 412 to temperature 424, as shown for FIG. 4B. Graph (ii) shows the output voltage (V) of the MR bridge circuit, similar to that shown in FIG. 4A. MAX Graph (ii) shows that the MR bridge output voltage 422 initially increases (denoted by V) resulting in a corresponding increase in MR sensitivity (of the MR elements in the sensor MR bridge circuit). However, as further shown in graph (ii), after a period of temperature change, the MR bridge output voltage 422 undergoes correction (calibration) and returns to its initial value 422b after a transition period 422a. With the sensor closed loop (e.g., the calibration or feedback loop 110 in FIG. 1A) in an active state, the loop operates to lower the bias voltage applied to the MR bridge, as shown in graph (iii). As a result, the applied bias voltage 430 is lowered from an initial higher value before the temperature change in (i) to a final lower value 434 after moving through transition 436. The adjustment of the bias voltage shown in graph (iii) compensates for the increase in temperature as shown in graph (iv), and the sensor output signal 440 (representing the sensed field) decreases from an initial value 442 (10 mV in this example) to a temperature-induced value V after the temperature change in graph (i). MAX to, but then adjusts (due to the sensor's self-calibration) to return to the initial output value 442' corresponding to a constant applied magnetic field after a transient period (t = 5.0 seconds to approximately 7.0 seconds). The initial portion of the transient period 446a resembles the temperature-induced change shown in graph (iv) of Figure 4A. The self-calibration function provided by the sensor closed loop is shown by the later portion 446b.

[0042]

[0050] In Figures 4A-4B, the horizontal (X) axis is shown in seconds (S), but this is not necessarily a reference to what may be typically implemented. Some realistic settling time examples for feedback (closed) loops according to the present disclosure may range (without limitation) from tens of microseconds to several milliseconds. Additionally, while temperature steps are shown for illustrative purposes, those skilled in the art will understand that delta temperatures typically occur over a (short) time span. The temperature step changes shown are for illustrative purposes to illustrate the loop correction process. Furthermore, it should be understood that if the step function shown represented the sudden application of a stray magnetic field, the Y axis would show field strength (e.g., Gauss) instead of temperature (degrees C).

[0043]

[0051] As explained above, in an exemplary embodiment, an external magnetic field (B SIG ) and an internally generated reference magnetic field (B REF ) simultaneously generate respective differential outputs in the MR bridge of the MR block / transducer, e.g., the MR block 102 in FIG. 1A. To accommodate this and to avoid mixing of the respective output signals generated by the MR bridge, an internally generated reference magnetic field (B REF ) is the external magnetic field (B SIG ) or are generated / modulated in a different frequency band.

[0044]

[0052] 5A-5B are diagrams illustrating MR bridge configurations 500A-B having different sensitivity directions for some of the included MR elements, according to the present disclosure. In each figure, the MR block 500 includes a bridge 510 of MR elements 512A-D having a drive input connection 502 for a drive signal applied by, for example, an xMR driver, and a ground connection 504. The external magnetic field (B SIG ) and an internally generated reference magnetic field (B REF) is shown. The larger arrow (spanning the bridge MR elements 512A-D) indicates the direction of sensitivity of the MR elements 512A-D. A differential output voltage (shown as V1 and V2) is generated at locations 522, 524, and the external and internally generated magnetic fields are in their respective frequency bands.

[0045]

[0053] 5A shows a first configuration 500A of the MR bridge 500 in which the bridge MR elements 512A-D share a common sensitivity direction (uniform direction of the large arrows), while FIG. 5B shows a second configuration in which a pair of repinned MR elements have opposite sensitivity directions (opposite large arrows shown for the MR elements 512A-B). In some applications, repinning two of the MR elements opposite to the MR elements of the other pair may enable or facilitate sensing a uniform external field. In such cases, the reference field is also preferably uniform (see FIG. 5B).

[0046]

[0054] 6 is a block diagram of an example computer system 600 operable to perform processing according to the present disclosure. The computer system 600 may perform all or at least a portion of the processing, e.g., steps, within the algorithms and methods described herein. The computer system 600 includes a processor 602, a volatile memory 604, a non-volatile memory 606 (e.g., a hard disk), an output device 608, and a user input or interface (UI) 610, such as a graphical user interface (GUI), a mouse, a keyboard, a display, and / or any common user interface. The non-volatile memory (non-transitory storage medium) 606 stores computer instructions 612 (also known as machine-readable instructions or computer-readable instructions), such as software (also known as a computer program product), an operating system 614, and data 616. In some examples / embodiments, the computer instructions 612 may be executed by the processor 602 from outside of the volatile memory 604. In some examples / embodiments, an article 618 (e.g., a storage device or medium such as a hard disk, optical disk, magnetic storage tape, optical storage tape, flash drive, etc.) includes or stores non-transitory computer-readable instructions. A bus 620 is also shown.

[0047]

[0055] The processing may be implemented in hardware, software, or a combination of the two. The processing may be implemented in a computer program (e.g., a software application) running on a programmable computer / machine, each of which includes a processor, a storage medium, or other article of manufacture (volatile and non-volatile memory and / or storage elements) readable by the processor, and optionally at least one input device and one or more output devices. The program code may be applied to data entered using an input device or input connection (e.g., a port or bus) to perform processing and to generate output information.

[0048]

[0056] System 600 may implement processes by a computer program product or software application (e.g., in a machine-readable storage device) for execution by or to control the operation of a data processing device (e.g., a programmable processor, computer, or multiple computers). Each such program may be implemented in a high-level procedural or object-oriented programming language for communicating with a computer system. The program may be implemented in assembly or machine language. The language may be a compiled or interpreted language, and it may be deployed in any form, such as as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. The computer program may be deployed to run on one computer or on multiple computers, either at one location or distributed across multiple locations and interconnected by a communications network. The computer program may be stored on a storage medium or device (e.g., a CD-ROM, hard disk, or magnetic diskette) readable by a general-purpose or special-purpose programmable computer for configuring and operating the computer when the storage medium or device is read by the computer. The processes may also be implemented as a machine-readable storage medium configured with a computer program, the instructions in the computer program, when executed, causing a computer to operate. Furthermore, the terms "computer" or "computer system" may include references to multiple similar terms unless expressly stated otherwise.

[0049]

[0057] Processing may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or portions of the system may be implemented as special purpose logic circuitry, e.g., FPGAs (field programmable gate arrays) and / or ASICs (application-specific integrated circuits). In some examples, digital logic circuitry, e.g., one or more FPGAs, may be operable as a processor as described herein.

[0050]

[0058] Accordingly, embodiments of the present subject matter may provide various advantages over the prior art. For example, embodiments and examples of the present disclosure may enable or facilitate systems and components to achieve or attain an Application Safety Integration Level (ASIL) in accordance with safety standards such as ISO 26262.

[0051]

[0059] Various embodiments of the concepts, systems, devices, structures, and techniques sought to be protected are described above with reference to the associated drawings. Alternative embodiments may be devised without departing from the scope of the described concepts, systems, devices, structures, and techniques.

[0052]

[0060] It should be noted that various connections and relationships (e.g., above, below, adjacent, etc.) may be used to describe elements and components in the description and drawings. These connections and / or relationships may be direct or indirect unless otherwise stated, and the described concepts, systems, devices, structures, and techniques are not intended to be limiting in this respect. Thus, coupling of entities may refer to either a direct coupling or an indirect coupling, and the relationship between entities may be a direct or indirect relationship.

[0053]

[0061] As an example of an indirect positional relationship, positioning element "A" above element "B" may include a situation where one or more intermediate elements (e.g., element "C") are between element "A" and element "B" as long as the relevant features and functions of elements "A" and "B" are not substantially changed by the intermediate elements.

[0054]

[0062] In addition, the following definitions and abbreviations shall be used for interpreting the claims and the specification. The terms "comprise," "comprises," "comprising," "include," "includes," "including," "has," "having," "contains," or "containing," or any other variation, are intended to cover a non-exclusive inclusion. For example, a device, method, composition, mixture, or article that includes a list of elements is not necessarily limited to only those elements and may include other elements not expressly listed or inherent in such device, method, composition, mixture, or article.

[0055]

[0063] Additionally, the term "exemplary" means serving as an example, instance, or illustration. Any embodiment or design described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "one or more" and "at least one" refer to any integer greater than one, i.e., 1, 2, 3, 4, etc. The term "plurality" refers to any integer greater than one. The term "connected" can include indirect and direct "connections."

[0056]

[0064] References herein to "an embodiment," "one embodiment," "an embodiment," "exemplary embodiment," "example," "case," "aspect," etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but that all embodiments may or may not include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or feature is described in connection with one embodiment, it may affect such feature, structure, or characteristic in other embodiments, whether or not explicitly described.

[0057]

[0065] Relative or positional terms, including but not limited to "above," "below," "right," "left," "vertical," "horizontal," "on," "below," and derivatives thereof, refer to the described structures and methods as oriented in the drawings. The terms "overlying," "atop," "on top," "positioned on," and "positioned atop" mean that a first element, such as a first structure, is above a second element, such as a second structure, and intervening elements, such as interfacial structures, may be present between the first and second elements. The term "direct contact" means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediate elements.

[0058]

[0066] The use of ordinal terms such as "first," "second," "third," etc. in the claims to modify claim elements does not, by itself, imply any priority, precedence, or order of one claim element over another, or any chronological order in which the actions of a method are performed, but is merely used as a label to distinguish one claim element having a particular name from another element having the same name (through the use of ordinal terms) to distinguish the claim elements.

[0059]

[0067] The terms "approximately" and "about" can be used in some embodiments to mean within ±20% of a target (or nominal) value, in some embodiments within plus or minus (±) 10% of a target value, in some embodiments within ±5% of a target value, and even in some embodiments within ±2% of a target value. The terms "approximately" and "about" can include the target value. The term "substantially equal" can be used to refer to values ​​that are within ±20% of each other in some embodiments, within ±10% of each other in some embodiments, within ±5% of each other, and even in some embodiments within ±2% of each other.

[0060]

[0068] The term "substantially" may be used to refer to values ​​that are within ±20% of a comparative measurement in some embodiments, within ±10%, within ±5%, and even within ±2% in some embodiments. For example, a first direction that is "substantially" perpendicular to a second direction may refer to a first direction that is within ±20% of making a 90° angle with the second direction in some embodiments, within ±10% of making a 90° angle with the second direction in some embodiments, within ±5% of making a 90° angle with the second direction in some embodiments, and even within ±2% of making a 90° angle with the second direction in some embodiments.

[0061]

[0069] The disclosed subject matter is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings The disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways.

[0062]

[0070] Also, the phraseology and terminology used in this patent is for the purpose of description and should not be regarded as limiting. As such, the conception upon which this disclosure is based may readily be utilized as a basis for the design of other structures, methods and systems for carrying out some of the purposes of the disclosed subject matter. The claims should therefore be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the disclosed subject matter.

[0063]

[0071] While the disclosed subject matter has been described and illustrated in the foregoing exemplary embodiments, the present disclosure is made by way of example only. Thus, numerous changes in the details of the implementation of the disclosed subject matter may be made without departing from the spirit and scope of the disclosed subject matter.

[0064]

[0072] Accordingly, the scope of this patent should not be limited to the described implementations, but rather should be limited only by the spirit and scope of the appended claims.

[0065]

[0073] All publications and references cited in this patent are expressly incorporated by reference in their entirety.

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