COIL SENSOR CIRCUIT AND METHOD FOR OPERATING A COIL SENSOR CIRCUIT

Abstract

The present disclosure proposes a coil sensor circuit (200) comprising a sensor coil (120) configured to provide an AC sensor signal, a forward feedback amplifier stage (130) configured to amplify the AC sensor signal to obtain an amplified sensor signal, a feedback amplifier stage (140) coupled between an output (133) and an input (131) of the forward feedback amplifier stage (130) and configured to provide a control signal to suppress a DC offset of the forward feedback amplifier stage (130), and a switching circuit (210).The switching circuit (210) is configured to couple the sensor coil (120) with the input (131) of the forward feedback amplifier stage (130) during a first operating mode of the coil sensor circuit, and to decouple the sensor coil (120) from the forward feedback amplifier stage (130) during a second operating mode of the coil sensor circuit and to increase the gain of the coil sensor circuit with respect to the first operating mode.

Description

Area

[0001] The present disclosure relates generally to devices and methods for detecting magnetic fields and / or electric currents, and in particular to inductive current sensors and detection methods. background

[0002] A coil sensor, also known as an inductive sensor, is a type of sensor that operates based on the principle of electromagnetic induction. Coil sensors can be used to measure electric current in an electrical circuit without being directly connected to the circuit itself. An inductive current sensor comprises a coil of wire, which may be wound around a magnetic core. This coil can be placed near a conductor through which the current to be measured flows. When an alternating current (AC) flows through the conductor (the one being measured), it creates a magnetic field around the conductor. This magnetic field also passes through the coil of the inductive sensor. According to Faraday's law of electromagnetic induction, a change in the magnetic flux through a coil induces a voltage in the coil.In the case of an inductive current sensor, the changing magnetic field resulting from the AC current in the primary conductor induces a voltage in the coil. The induced voltage in the current sensor's coil is proportional to the current flowing through the primary conductor. By measuring this induced voltage, the sensor can accurately determine the current magnitude.

[0003] A coil sensor circuit can include a pickup coil (sensor element), a preamplifier (feedback) stage with gain and anti-saturation functions for high frequencies (e.g., provided by a low-pass filter), and a DC servo loop for DC offset suppression of the preamplifier stage. Operational amplifiers (op-amps), commonly used in amplifier circuits, can exhibit input offset voltage characteristics. This means that there can be a small DC voltage difference between their inverting and non-inverting inputs. If this voltage is amplified, it can result in a DC offset at the amplifier's output.

[0004] A signal-to-offset ratio V coil / V offset,outThe performance of a coil sensor can degrade linearly as the input signal frequency decreases. To eliminate the DC offset components without excessively limiting the minimum useful signal bandwidth of the input signal and without using very large capacitors in series with the signal, a DC servo loop can be used with an open loop frequency as low as possible, ideally 0 dB. In other words, if the DC servo loop has an open loop frequency of 0 dB that is too high, the loop would begin to reject the useful signal.

[0005] In a DC servo loop, the term "0 dB open-loop frequency" typically refers to the frequency up to which the system's open-loop gain is 0 decibels (dB), which corresponds to a gain of 1 in linear terms (unit gain). The 0 dB open-loop frequency represents the point at which the system begins to attenuate signals above this frequency.

[0006] Since a desired application may be broadband, high-frequency inputs to the system should also be addressed, and rapid offset removal is necessary. This means that a slow settling time of the DC servo loop is problematic, as a user would be forced to wait for a very long startup time until the offset is completely removed. An alternative way to remove the DC offset could be to use a chopper technique, but this may not be feasible due to broadband application frequencies.

[0007] Therefore, there is a need for fast DC offset removal for broadband application coil sensor assemblies with a pickup coil, a preamplifier stage and a DC servo loop for offset suppression of the preamplifier stage. Summary

[0008] This need is addressed by devices and methods according to the attached claims.

[0009] According to a first aspect, the present disclosure proposes an (inductive) coil sensor circuit. The coil sensor circuit comprises a sensor coil configured to provide an AC sensor signal (e.g., voltage) responding to a varying magnetic field. Downstream of the sensor coil, the coil sensor circuit comprises a feedforward amplifier circuit configured to amplify the AC sensor signal and obtain an amplified sensor signal. The coil sensor circuit further comprises a feedback amplifier circuit coupled between an output and an input of the feedforward amplifier circuit. The feedback amplifier circuit is configured to provide a control signal for suppressing a DC offset of the feedforward amplifier circuit.The proposed coil sensor circuit also includes a switching circuit configured to couple the sensor coil to the input of the feedforward amplifier stage during a first operating mode of the coil sensor circuit, and to decouple the sensor coil from the feedforward amplifier stage during a second operating mode, thereby increasing the gain of the coil sensor circuit relative to the first operating mode. The first operating mode can also be referred to as the normal operating mode. The second operating mode can also be referred to as the start-up or auto-calibration mode. In the second operating mode, a useful signal from the coil can be discarded, and only a DC offset can be processed by the servo loop encompassing the feedforward and feedback amplifier circuits.

[0010] In some embodiments, the switching circuit comprises a plurality of switches, each with a parasitic resistance. The respective parasitic resistances can be (significantly) smaller than the resistance of the coil. The gain of the feedforward amplifier stage is essentially independent of the parasitic resistances in the first operating mode (normal operating mode). For example, the switches may be positioned such that their parasitic resistances do not contribute to the gain of the feedforward amplifier.

[0011] In some embodiments, the switching circuit comprises at least a first switch coupled between the sensor coil and an input of the feedforward amplifier stage, at least a second switch coupled between an output and the input of the feedforward amplifier stage, and at least a third switch coupled between a DC voltage source and the input of the feedforward amplifier stage. The switching circuit can be configured to close the first switch and open the second and third switches during the first operating mode, and to close the second and third switches and open the first switch during the second operating mode.

[0012] In some embodiments, the switching circuit is designed to increase the gain of the feedforward amplifier stage during the second operating mode (start-up mode). For example, the switching circuit can be designed to change a resistance ratio between resistors at the input and in a feedback path of the feedforward amplifier stage.

[0013] In some embodiments, the switching circuit is designed to increase the gain of the coil sensor circuit during the second operating mode (start-up mode) by switching between a first and a second circuit configuration between the output and the input of the forward feedback amplifier stage. For example, the first circuit configuration may include the coil coupled to the input of the forward feedback amplifier stage and an RC low-pass filter coupled between the input and output of the forward feedback amplifier stage. The second circuit configuration may include the coil decoupled from the input of the forward feedback amplifier stage and a (high-impedance) resistor coupled between the input and output of the forward feedback amplifier stage.

[0014] In some embodiments, the switching circuit is configured to couple an RC low-pass filter between the input and output of the forward feedback amplifier stage during the first operating mode and to replace the RC low-pass filter with a feedback resistor during the second operating mode. The switching circuit can also be configured to decouple the feedback resistor from the input of the forward feedback amplifier stage during the first operating mode and to decouple the RC low-pass filter from the input of the forward feedback amplifier stage during the second operating mode.

[0015] In some embodiments, the switching circuit is designed to replace the sensor coil with a DC voltage source at the input of the forward feedback amplifier stage during the second operating mode and to replace the DC voltage source with the sensor coil at the input of the forward feedback amplifier stage during the first operating mode.

[0016] In some embodiments, a DC voltage from the DC voltage source essentially corresponds to a common-mode voltage of the sensor coil in the first operating mode.

[0017] In some embodiments, the feedback amplifier stage is designed as an integrator. A capacitor can be coupled between an output and an input of the feedback amplifier stage.

[0018] In some embodiments, one or more resistors can be coupled between an output of the feedback amplifier stage and the input of the forward feedback amplifier stage.

[0019] In some embodiments, one or more resistors can be coupled between the output of the forward feedback amplifier stage and an input of the feedback amplifier stage.

[0020] In some embodiments, the forward feedback amplifier stage and the feedback amplifier stage are each designed as differential amplifier stages.

[0021] According to another aspect, the present disclosure proposes a method for operating a coil sensor circuit. The method comprises, during a first operating mode of the coil sensor circuit: - Providing an AC sensor signal from a sensor coil to a feedforward amplifier stage of the coil sensor circuit to obtain an amplified sensor signal, - Providing the amplified sensor signal from an output of the forward feedback amplifier stage to an input of a feedback amplifier stage of the coil sensor circuit to obtain a control signal to suppress a DC offset of the forward feedback amplifier stage, - Providing the control signal from an output of the feedback amplifier stage to an input of the forward feedback amplifier stage.

[0022] During a second operating mode of the coil sensor circuit, the procedure includes: - Decoupling the sensor coil from the input of the forward feedback amplifier stage, and - Increasing the gain of the coil sensor circuit with respect to the first operating mode.

[0023] The gain can be increased by replacing the sensor coil at the input of the forward feedback amplifier stage with a (common-mode) DC voltage source. Furthermore, an RC low-pass filter between the input and output of the forward feedback amplifier stage can be replaced by a feedback resistor.

[0024] According to another aspect, the present disclosure proposes an (inductive) coil sensor circuit. The coil sensor circuit comprises a sensor coil configured to provide an AC sensor signal (e.g., voltage) responding to a varying magnetic field. Downstream of the sensor coil, the coil sensor circuit comprises a feedforward amplifier circuit configured to amplify the AC sensor signal and obtain an amplified sensor signal. The coil sensor circuit further comprises a feedback amplifier circuit coupled between an output and an input of the feedforward amplifier circuit. The feedback amplifier circuit is configured to provide a control signal for suppressing a DC offset of the feedforward amplifier circuit.The proposed coil sensor circuit also includes a switching circuit configured to couple the sensor coil to the input of the forward-feedback amplifier stage during a first operating mode of the coil sensor circuit, and to replace the sensor coil with a DC voltage source at the input of the forward-feedback amplifier stage during a second operating mode. The DC voltage of the DC voltage source can correspond to a common-mode voltage of the sensor coil in the first operating mode. Furthermore, the switching circuit can be configured to replace an RC low-pass filter between the input and output of the forward-feedback amplifier stage with a feedback resistor during the second operating mode.

[0025] Exemplary embodiments of the present disclosure can enable the isolation of an unwanted amplified offset from a useful coil signal during startup (application of a supply or calibration mode). For rapid settling to a system operating point, the input of the feedforward amplifier stage can be multiplexed from a coil input signal to a common-mode signal (= differential short circuit), and low-impedance feedback circuits can be switched on during a calibration phase. This isolation can guarantee rapid offset suppression during an auto-calibration mode. Brief description of the characters

[0026] Some examples of devices and / or methods are described below only by way of example and with reference to the accompanying figures, in which Fig. 1 shows a conventional inductive current sensor arrangement; Fig. 2 shows a coil sensor arrangement according to embodiments of the present disclosure; and Fig. Figure 3 shows a flowchart of a method for operating a coil sensor arrangement according to embodiments of the present disclosure. Detailed description

[0027] Some examples are now described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these detailed embodiments. Other examples may exhibit modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe certain examples should not be considered restrictive for other possible examples.

[0028] Identical or similar reference symbols throughout the description of the figures refer to identical or similar elements and / or features, which may be implemented identically or in a modified form, while providing the same or a similar function. Furthermore, the thickness of lines, layers, and / or areas in the figures may be exaggerated for clarity.

[0029] When two elements A and B are combined using "or," this is to be understood as revealing all possible combinations, i.e., only A, only B, and A and B, unless explicitly defined otherwise in a specific case. As an alternative formulation for the same combinations, "at least one of A and B" or "A and / or B" can be used. This applies accordingly to combinations of more than two elements.

[0030] When a singular form, e.g., "ein, eine" and "der, die, das", is used, and the use of only a single element is neither explicitly nor implicitly defined as mandatory, subsequent examples may also use multiple elements to implement the same function. If a function is subsequently described as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity.It is further understood that the terms "include", "comprehensive", "exhibit" and / or "exhibit" when used describe the presence of the specified features, integers, steps, operations, processes, elements, components and / or a group thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or a group thereof.

[0031] Fig. Figure 1 shows an example of an inductive current sensor arrangement 100.

[0032] The inductive current sensor arrangement 100 comprises a primary conductor 110 through which an alternating current (AC) to be measured can flow. The primary conductor 110 can be a busbar, a conductor path of an IC, or another electrical conductor, such as a wire. The electric current causes a changing magnetic field around the primary conductor 110.

[0033] The inductive current sensor arrangement 100 comprises one or more sensor coils 120 positioned near the primary conductor 110. The one or more coils 120 are not directly connected to the primary conductor 110, but are located in sufficient proximity to it. One sensor coil may be sufficient for single-ended measurement concepts. One or two sensor coils may be used for differential measurement concepts. The person skilled in the art, taking advantage of the present disclosure, recognizes that the concepts proposed herein can be used for both single-ended and differential measurement concepts.

[0034] The in Fig. The illustrated sensor coil 120 comprises a first coil section (coil1) and a second coil section (coil2). Each coil section (coil1, coil2) includes a respective inductance L1, L2 and a respective resistance R1, R2. The total resistance of coil 120 can be R1 + R2 = R coilThe resistance of the inductance is 3.5 kΩ. A first terminal 122-1 of the coil 120 is coupled to an inverting input terminal 131-1 of a feedforward amplifier stage 130 of the inductive current sensor arrangement 100. A second terminal 122-2 of the coil 120 is coupled to a non-inverting input terminal 131-2 of the feedforward amplifier stage 130. The changing magnetic field induced by the primary conductor 110 causes a voltage to be induced in the coil 120 by electromagnetic induction. The induced voltage in the coil 120 is proportional to the current flowing through the primary conductor 110. This induced voltage is then used as the input signal of the feedforward amplifier stage 130 connected downstream of the coils 120.

[0035] The forward feedback amplifier stage 130, which is coupled to the coil 120, has a transfer function with one pole at a frequency f p (e.g. f p= 200 kHz). A pole of the transfer function denotes a root of the denominator polynomial of the transfer function. A pole frequency corresponds to a corner frequency at which the slope of the transfer function's amplitude curve decreases by 20 dB / decade. The pole of the transfer function at frequency f p can limit an overload effect on the coil 120 caused by high-frequency (AC) magnetic fields (currents). The feedforward amplifier stage 130 includes an RC filter 132 coupled between the input 131 and an output 133 of an operational amplifier 134. The RC filter 132 causes the pole at the frequency f p and can therefore be considered a low-pass filter.

[0036] The RC filter 132 in this differential circuit example comprises an inverting filter branch coupled between the inverting input terminal 131-1 and the output terminal 133-1 of the operational amplifier 134. The inverting filter branch includes a resistor R1 in parallel with an adjustable capacitor C1. The RC filter 132 in this differential circuit example also comprises a non-inverting branch, comprising a resistor R1 in parallel with a capacitor C1, coupled between the non-inverting input 131-2 and the output 133-2 of the operational amplifier 134. A person skilled in the art, benefiting from the present disclosure, will recognize that in the case of a non-differential setup, only one filter branch may be required. The RC filter 132, comprising the resistor R1 in parallel with the capacitor C1, causes the pole at the frequency f pThe resistance value of resistor R1 can be, for example, 14.8 kΩ. The capacitance of capacitor C1 can be, for example, 53.1 pF.

[0037] The inductive current sensor arrangement 100 further comprises a feedback amplifier stage 140, which is coupled between the output 133 and the input 131 of the forward feedback amplifier stage 130 and is configured to provide a control signal for suppressing a DC offset of the forward feedback amplifier stage 130. The forward feedback amplifier stage 130 and the feedback amplifier stage 140 between the output 133 and the input 131 of the forward feedback amplifier stage 130 together form a so-called DC servo loop.

[0038] The feedback amplifier stage 140 comprises an operational amplifier 144. A non-inverting input 141-1 of the operational amplifier 144 is connected via an optional resistor R. DSL1coupled to the inverting output 133-1 of the feedforward amplifier stage 130. An inverting input 141-2 of the operational amplifier 144 is connected via an optional resistor R. DSL1 coupled to the non-inverting output 133-2 of the forward feedback amplifier stage 130. The feedback amplifier stage 140 includes a capacitor 142, which is coupled between the input 141 and an output 143 of the operational amplifier 144. In this differential circuit example, the capacitor 142 includes a second capacitor branch C DSL , which is coupled between the non-inverting input 141-1 and the inverting output 143-1 of the operational amplifier 144. The person skilled in the art, taking advantage of the present disclosure, recognizes that in the case of a non-differential setup, perhaps only one capacitor branch is required.

[0039] The feedback amplifier stage 140 further comprises one or more feedback resistors R DSL_FB , which are coupled between the output 143 of the operational amplifier 144 and the input 131 of the feedforward feedback amplifier stage 130 (or the operational amplifier 134). In the illustrated differential circuit example, the feedback amplifier stage 140 includes a first feedback resistor R DSL_FB , which is coupled between the non-inverting output 143-2 of the operational amplifier 144 and the non-inverting input 131-2 of the forward feedback amplifier stage 130, and a second feedback resistor R DSL_FB , which is coupled between the inverting output 143-1 of the operational amplifier 144 and the inverting input 131-1 of the forward feedback amplifier stage 130.

[0040] The feedback amplifier stage 140 acts as an integrator. The DC offset (the error signal) at the output 133 of the forward feedback amplifier stage 130 is passed through the integrator 140, which continuously sums the DC offset over time. AC components of the output signal of the forward feedback amplifier stage 130 cannot pass through the feedback amplifier stage 140. This process accumulates the DC offset and produces an output signal that increases or decreases over time based on the cumulative error. The output of the feedback amplifier stage 140 is the control signal that is sent to the forward feedback amplifier stage 130. The output of the integrator acts as a correction signal that can help eliminate steady-state errors.

[0041] In some embodiments, the sensor coil 120, the feedforward amplifier stage 130, and the feedback amplifier stage 140 can be integrated in a single integrated circuit (IC). The primary conductor 110 can be located outside the IC.

[0042] A voltage coil signal at the forward feedback amplifier output 133 for frequencies lower than the low-pass filter pole (i.e., f < f p ), is: Vcoil=2πf∗nA∗B∗R1Rcoil [coil = coil]

[0043] A DC offset of the forward feedback amplifier stage 130 at its output 133 is amplified as follows: Voffset,out=Voffset,in∗(1+R1Rcoil) [offset = offset; out = output; in = input]

[0044] The signal-to-offset ratio V coil / V offset,outThe signal deteriorates linearly as the input signal frequency is reduced. To eliminate the DC offset components without excessively limiting the minimum useful signal bandwidth of the input signal at input 131 and without using very large capacitors in series with the signal, the DC servo loop 130, 140 is used with a 0 dB open-loop frequency as low as possible.

[0045] If a desired application is broadband, high-frequency inputs should also be addressed to the system, and rapid removal of the DC offset is necessary. This means that the slow settling time of the DC servo loop is a problem (a user would be forced to wait for a very long start-up time until the DC offset is completely removed).

[0046] The present disclosure proposes an arrangement of circuits that can separate the unwanted amplified DC offset from the useful coil signal during startup. For rapid settling to a system operating point, the present disclosure proposes multiplexing the input 131 of the forward feedback amplifier stage 130 from an inductor input signal to a common-mode signal (= differential short circuit) and activating lower-impedance feedback circuits during the startup / calibration phase. This separation can assist offset suppression in a rapid manner during an auto-calibration mode.

[0047] Fig. Figure 2 shows an inductive current sensor arrangement 200 according to an embodiment of the present disclosure.

[0048] In addition to the one in Fig. The inductive current sensor arrangement 100 shown in Figure 1 includes the inductive current sensor arrangement 200. Fig. 2 A switching circuit 210 is configured to switch between two operating modes of the inductive current sensor arrangement 200. During a first operating mode (normal operation), the sensor coil 120 is coupled to the input 131 of the feedforward amplifier stage 130. During a second operating mode (start-up / calibration mode), the sensor coil 120 is decoupled from the feedforward amplifier stage 130, and the gain of the amplifier circuit 130, 140 is increased with respect to the first operating mode.

[0049] In the illustrated example, the switching circuit 210 comprises three (pairs of) switches S1, S2, and S3, arranged such that the respective parasitic resistances of switches S1, S2, and S3 do not contribute substantially to the gain of the feedforward amplifier stage 130. In other words, the feedforward amplifier gain in the first operating mode does not depend on (is independent of) the respective parasitic resistances of switches S1, S2, and S3.

[0050] The switch S1 is connected between a DC voltage source 220 and the input 131 of the forward-feedback amplifier stage 130 and is configured to couple or decouple the DC voltage source 220 from the forward-feedback amplifier stage 130. A DC voltage from the DC voltage source 220 can essentially be a common-mode voltage V. cmThe sensor coil 120 corresponds to the first operating mode. In the illustrated differential circuit example, a first switch S1 is coupled between the DC voltage source 220 and the inverting input 131-1 of the feedforward amplifier stage 130, and a second switch S1 is coupled between the DC voltage source 220 and the non-inverting input 131-2 of the feedforward amplifier stage 130. Each of the switches S1 has a low-value parasitic resistance R. S1 (R S1 < R coil ) on.

[0051] Switch S2 is coupled between output 133 and input 131 of the forward feedback amplifier stage 130 and is designed to increase the gain of the forward feedback amplifier stage 130 during the second operating mode by switching between a first and a second circuit configuration between output 133 and input 131 of the forward feedback amplifier stage 130. The forward feedback amplifier stage 130 of the in Fig. The exemplary implementation shown in section 2 additionally includes a feedback resistor R1. cal , which is coupled between output 133 and input 131 of the forward feedback amplifier stage 130. Switch S2 is connected between the feedback resistor R1. caland the input 131 of the forward feedback amplifier stage 130. In the illustrated differential circuit example, a first switch S2 in the feedback branch is coupled between the inverting output 133-1 and the inverting input 131-1 of the operational amplifier 134. The first switch S2 is connected between the feedback resistor R1 cal and the inverting input 131-1 of the operational amplifier 134. In the illustrated differential circuit example, a second switch S2 in the feedback branch is coupled between the non-inverting output 133-2 and the non-inverting input 131-2 of the operational amplifier 134. The second switch S2 is connected between the feedback resistor R1 cal and coupled to the non-inverting input 131-1 of the operational amplifier 134. Each of the switches S2 has a low-impedance parasitic resistance R. S2 (R S2 < R coil and R S2< R1 cal ) on.

[0052] Switch S3 is coupled between sensor coil 120 and input 131 of the feedforward amplifier stage 130 and is configured to couple or decouple sensor coil 120 from the feedforward amplifier stage 130. In the illustrated differential circuit example, a first switch S3 is coupled between the first terminal 122-1 of coil 120 and the inverting input 131-1 of operational amplifier 134. In the illustrated differential circuit example, a second switch S3 is coupled between the second terminal 122-2 of coil 120 and the non-inverting input 131-2 of operational amplifier 134. Each of the switches S3 can have a low-value parasitic resistance R. S3 (R S3 < R coil exhibit.

[0053] The switching circuit 210 is configured to close switches S3 and open switches S1 and S2 during the first operating mode (normal operation). Thus, closing switch(es) S3 couples the coil 120 to the input 131 of the forward feedback amplifier stage 130. Opening switch(es) S1 decouples the DC voltage source 220 from the input 131 of the forward feedback amplifier stage 130. Opening switch(es) S2 couples the RC low-pass filter 132 between the output 133 and the input 131 of the operational amplifier 134 and the feedback resistor R1. cal is decoupled from the input 131 of the operational amplifier 134.

[0054] The switching circuit 210 is configured to open switches S3 and close switches S1 and S2 during the second operating mode (start / calibration mode). Opening switch(es) S3 decouples the coil 120 from the input 131 of the forward feedback amplifier stage 130. Closing switch(es) S1 couples the DC voltage source 220 to the input 131 of the forward feedback amplifier stage 130. Closing switch(es) S2 decouples the RC low-pass filter 132 from the input 131 of the operational amplifier 134, and instead, the feedback resistor R1 is connected. cal coupled between the output 133 and the input 131 of the operational amplifier 134. With a high-impedance R1 cal and low-impedance parasitic resistance R S1By switching S1, the gain of the forward feedback amplifier stage 130 can be increased during the second operating mode (auto-calibration) compared to the first operating mode.

[0055] The proposed arrangement for isolating the forward feedback amplifier offset from the useful signal comprises a double pair of switches S1 and S2, a pair of simulation resistors R1 cal and a pair of S3 switches. A person skilled in the art who benefits from the present disclosure recognizes that other circuit arrangements may also be possible to achieve the same or a similar result. For example, adjustments could also be made to the feedback amplifier stage 140.

[0056] When fast DC offset compensation is enabled, i.e., during the second operating mode (auto-calibration), S1 and S2 are closed, while S3 is open. In this phase, the useful signal from sensor coil 120 is discarded, and only the DC offset is processed by servo loops 130 and 140. The total amplified offset at the output is: Voffset,out=Voffset,in1∗(1+R1_calRS1)

[0057] The forward feedback amplifier 130 is used in the illustrative example of Fig. 2 with a dual input gm = ΔI out / ΔV in (Transconductance) stage 134 is built and the entire DC offset input, which is designated at the second (here: upper) input, is: Voffset,in2=Voffset,in1(gm1gm2), where gm2< <gm1

[0058] The servo loop transfer function, which detects the DC offset at the output of the forward feedback amplifier 130 and feeds it back to a second (here: upper) input of the forward feedback amplifier 130, is: Voffset,in2=Voffset,out(12πfRDSL1CDSL)∗12A

[0059] During the second operating mode (auto-calibration), the open-loop offset transfer function obtained by opening the DC servo loop can be calculated from equations (1), (2) and (3): Hautocal(f)=(1+R1_calRS1)(gm2gm1)(12πfRDSL1CDSL)∗12A

[0060] Similarly, the open-loop offset transfer function can be calculated when the system transitions to the first operating mode (normal operating mode). In this case, the DC offset and the useful signal are processed as soon as S3 is closed and S1 and S2 are open. The entire system now evolves from the DC offset integrated during the second operating mode (auto-calibration phase) and present at the second feedforward amplifier input. The system now rejects the remaining DC offset much more slowly, and the rate can be evaluated by combining equations (0), (2), and (3): Hnorm(f)=(1+R1Rcoil)(gm2gm1)(12πfRDSL1CDSL)∗12A

[0061] The significant increase in the speed of the servo loop 130, 140 during auto-calibration is explained by comparing f 0DB determined by H(s) during auto-calibration and during normal application mode.

[0062] The acceleration factor is given by: (1+R1_calRS1)(1+R1Rcoil)

[0063] The more R1cal has a high resistance and the parasitic impedance of the switch(es) S1 compared to R1 and R respectively coil The lower the resistance, the faster the offset suppression will be during autocalibration. This means there is more freedom to accelerate the autocalibration phase to remove as much offset as possible before the remaining offset error is removed at a much slower rate during normal operation.

[0064] It can be observed that the way in which the signal from the input coil is discarded during auto-calibration does not affect the signal transfer function at all, since switches S1 and S2 are never in series with R1 or R2. coilare and the only switch (the only switches) S3, which are closed during normal operation, connect high-impedance nodes (no current flow).

[0065] Fig. Figure 3 shows a flowchart of a procedure 300 for operating the coil sensor circuit 200.

[0066] The exemplary procedure 300 of Fig. 3 includes: During the first operating mode of the coil sensor circuit: - Providing 310 an AC sensor signal from the sensor coil 120 to the forward feedback amplifier stage 130 of the coil sensor circuit 200 to obtain an amplified sensor signal, - Providing 320 of the amplified sensor signal from an output of the forward feedback amplifier stage 130 to an input of the feedback amplifier stage 140 of the coil sensor circuit 200, in order to obtain a control signal to suppress the DC offset of the forward feedback amplifier stage 130, - Providing 330 of the control signal from an output of the feedback amplifier stage 140 to an input of the forward feedback amplifier stage 130.

[0067] During a second operating mode of the coil sensor circuit, the gain of the coil sensor circuit is increased by 200 relative to the first operating mode by: - Replace 340 of the sensor coil 120 at the input of the forward feedback amplifier stage 130 with a (common-mode) DC voltage source 220.

[0068] Furthermore, the method 300 can additionally involve replacing 350 the RC low-pass filter 132 between the input 131 and the output 133 of the forward feedback amplifier stage 130 with the feedback resistor R1. cal include.

[0069] Users can experience a fast start (for coil or hybrid sensors) regardless of the input frequency speed, i.e., start time of DC-DC converters or current measurement.

[0070] The aspects and characteristics described in connection with one of the previous examples can also be combined with one or more of the further examples to replace an identical or similar characteristic of that further example or to additionally introduce the characteristic into the further example.

[0071] It is further understood that the disclosure of several steps, processes, operations, or functions in the description or claims should not be interpreted as necessarily occurring in the described sequence, unless explicitly stated in a specific case or required for technical reasons. Therefore, the preceding description does not restrict the execution of several steps or functions to a specific sequence. Furthermore, in other examples, a single step, function, process, or operation may comprise and / or be broken down into several sub-steps, functions, processes, or operations.

[0072] When certain aspects related to a device or system are described, these aspects should also be understood as a description of the corresponding procedure. For example, a block, device, or functional aspect of the device or system may correspond to a feature, such as a process step, of the corresponding procedure. Similarly, aspects described in connection with a procedure should also be understood as a description of a corresponding block, element, property, or functional feature of that device or system.

[0073] The following claims are hereby included in the detailed description, each claim being a separate example. It should also be noted that, although a dependent claim may refer to a specific combination with one or more other claims, other examples may include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly proposed unless it is stated in a specific case that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be included, even if that claim is not directly defined as dependent on that other independent claim.

Claims

[1] A coil sensor circuit (200) comprising: a sensor coil (120) configured to provide an AC sensor signal; a feedforward amplifier stage (130) configured to amplify the AC sensor signal to obtain an amplified sensor signal; a feedback amplifier stage (140) coupled between an output (133) and an input (131) of the feedforward amplifier stage (130) and configured to provide a control signal for suppressing a DC offset of the feedforward amplifier stage (130); and a switching circuit (210) which is designed to during a first operating mode of the coil sensor circuit, to couple the sensor coil (120) to the input (131) of the feedforward amplifier stage (130), and during a second operating mode of the coil sensor circuit, to decouple the sensor coil (120) from the feedforward amplifier stage (130), and to increase a gain of the coil sensor circuit with respect to the first operating mode. [2] The coil sensor circuit (200) according to claim 1, wherein the switching circuit (210) is configured to increase a gain of the feedforward amplifier stage (130) during the second operating mode. [3] The coil sensor circuit (200) according to claim 1 or 2, wherein the switching circuit (210) is configured to increase the gain of the feedforward amplifier stage (130) during the second operating mode by switching between a first and a second circuit configuration between the output (133) and the input (131) of the feedforward amplifier stage (130). [4] The coil sensor circuit (200) according to any one of the preceding claims, wherein the switching circuit (210) is configured to during the first operating mode, to couple an RC low-pass (132) filter between the input (131) and the output (133) of the feedforward amplifier stage (130), and to replace the RC low-pass filter (132) with a feedback resistor during the second operating mode. [5] The coil sensor circuit (200) according to claim 4, wherein the switching circuit (210) is configured to to decouple the feedback resistor from the input (131) of the feedforward amplifier stage (130) during the first operating mode, and to decouple the RC low-pass filter (132) from the input (131) of the feedforward amplifier stage (130) during the second operating mode. [6] The coil sensor circuit (200) according to any one of the preceding claims, wherein the switching circuit (210) comprises: a first switch (S3) coupled between the sensor coil (120) and an input (131) of the feedforward amplifier stage (130); a second switch (S2) coupled between the output (133) and the input (131) of the feedforward amplifier stage (130); and a third switch (S1) coupled between a DC voltage source (220) and the input (131) of the feedforward amplifier stage (130). [7] The coil sensor circuit (200) according to claim 6, wherein the switching circuit (210) is configured to during the first operating mode, to close the first switch (S3) and to open the second and third switches (S2; S1), and during the second operating mode, to close the second and third switches (S2; S1) and to open the first switch (S3). [8] The coil sensor circuit (200) according to any one of the preceding claims, wherein the switching circuit (210) is configured to during the second operating mode, to replace the sensor coil (120) by a DC voltage source (220) at the input (131) of the feedforward amplifier stage (133), and during the first operating mode, to replace the DC voltage source (220) by the sensor coil (120) at the input (131) of the feedforward amplifier stage (130). [9] The coil sensor circuit (200) according to any one of claims 6 to 8, wherein a DC voltage of the DC voltage source (220) substantially corresponds to a common mode voltage of the sensor coil (120) in the first operating mode. [10] The coil sensor circuit (200) according to any one of the preceding claims, wherein the feedback amplifier stage (140) is designed as an integrator. [11] The coil sensor circuit (200) according to claim 10, wherein a capacitor is coupled between an output (143) and an input (141) of the feedback amplifier stage (140). [12] The coil sensor circuit (200) according to any one of the preceding claims, wherein at least one resistor is coupled between an output (143) of the feedback amplifier stage (140) and the input (131) of the feedforward amplifier stage (130). [13] The coil sensor circuit (200) according to any one of the preceding claims, wherein at least one resistor is coupled between the output (133) of the feedforward amplifier stage (130) and an input (141) of the feedback amplifier stage (140). [14] The coil sensor circuit (200) according to any one of the preceding claims, wherein the feedforward amplifier stage (130) and the feedback amplifier stage (140) are each designed as differential amplifier stages. [15] A method (300) for operating a coil sensor circuit, the method comprising: during a first operating mode of the coil sensor circuit, Providing (310) an AC sensor signal from a sensor coil (120) to a feedforward amplifier stage (130) of the coil sensor circuit to obtain an amplified sensor signal; Providing (320) the amplified sensor signal from an output of the feedforward amplifier stage (130) to an input of a feedback amplifier stage (140) of the coil sensor circuit to obtain a control signal for suppressing a DC offset of the feedforward amplifier stage; Providing (330) the control signal from an output of the feedback amplifier stage (140) to an input of the feedforward amplifier stage (130); and during a second operating mode of the coil sensor circuit, Replacing (340) the sensor coil (120) at the input of the feedforward amplifier stage (130) with a DC voltage source (220). [16] The method according to claim 15, further comprising during the second operating mode, Replacing (350) an RC low-pass filter (132) between the input (131) and the output (133) of the feedforward amplifier stage (130) by a feedback resistor.

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