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 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).The switching circuit (210) is designed to couple the sensor coil (120) to the input (131) of the feedforward amplifier stage (130) during a first operating mode of the coil sensor circuit, and to decouple the sensor coil (120) from the feedforward amplifier stage (130) during a second operating mode of the coil sensor circuit and to increase a 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 sensing magnetic fields and / or electrical currents, and more particularly to inductive current sensors and sensing methods. background

[0002] DE 10 2023 108 740 A1 describes magnetic field and current sensors that detect low- and high-frequency components in hybrid architectures. Hall or coil sensors are combined to cover different frequency ranges. A DC suppression path is implemented partly analog and partly digitally, for example, using sigma-delta converters or integrators. The device dispenses with external bypass capacitors and integrates pre- and output amplifiers on a single chip. DE 10 2023 108 740 A1 also addresses quantization noise and various variants for canceling DC offsets. The sensor signal remains continuously active.

[0003] 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 electrical current in an electrical circuit without being directly connected to the circuit itself. An inductive current sensor includes a coil of wire that 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 to be 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.

[0004] A coil sensor circuit may include a pickup coil (sensing element), a preamplifier (feedforward) stage with high-frequency amplification and anti-saturation functions (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, may exhibit input offset voltage characteristics. This means that there may be a small DC voltage difference between their inverting and non-inverting inputs. When this voltage is amplified, it can result in a DC offset at the amplifier's output.

[0005] A signal-to-offset ratio V coil / V offset,outThe performance of a coil sensor can degrade linearly by lowering the input signal frequency. To remove the DC offset components without overly 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 with an open loop frequency of 0 dB as low as possible can be used. In other words, if the DC servo loop has an open loop frequency 0 dB too high, the loop would begin to reject the useful signal.

[0006] 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 equal to 0 decibels (dB), which corresponds to a gain of 1 in linear terms (unity gain). The 0 dB open-loop frequency represents the point at which the system begins to attenuate signals above this frequency.

[0007] Since a desired application may be broadband, high-frequency inputs should also be addressed to the system, and rapid offset removal is necessary. This means that slow settling of the DC servo loop is a problem, as a user would be forced to wait for a very long start-up time until the offset is completely removed. An alternative way to remove the DC offset could be to use a chopping technique, but due to broadband application frequencies, this may not be feasible.

[0008] Therefore, there is a need for fast DC offset removal for broadband application coil sensor arrays comprising a pickup coil, a preamplifier stage, and a DC servo loop for offset cancellation of the preamplifier stage. Summary

[0009] This need is addressed by devices and methods according to the appended claims.

[0010] 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) in response 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 to 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 and increase the gain of the coil sensor circuit relative to the first operating mode during a second operating mode of the coil sensor circuit. The first operating mode may also be referred to as the normal operating mode. The second operating mode may also be referred to as the start-up or auto-calibration mode. In the second operating mode, a useful signal from the coil may be discarded, and only a DC offset may be processed by the servo loop comprising the feedforward and feedback amplifier circuit.

[0011] In some embodiments, the switching circuit comprises a plurality of switches, each switch having a parasitic resistance. The respective parasitic resistances may be (significantly) smaller than a resistance of the coil. A gain of the feedforward amplifier stage is substantially independent of the parasitic resistances in the first operating mode (normal operating mode). For example, a position / location of the switches is such that the parasitic resistances of the switches do not contribute to the gain of the feedforward amplifier.

[0012] 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 may be configured to close the at least one first switch and open the at least one second and one third switch during the first operating mode, and to close the second and third switches and open the first switch during the second operating mode.

[0013] In some embodiments, the switching circuit is configured to increase the gain of the feedforward amplifier stage during the second operating mode (start-up mode). For example, the switching circuit may be configured to change a resistance ratio between resistors at the input and in a feedback path of the feedforward amplifier stage.

[0014] In some embodiments, the switching circuit is configured 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 feedforward amplifier stage. For example, the first circuit configuration may include the coil coupled to the input of the feedforward amplifier stage and an RC low-pass filter coupled between the input and the output of the feedforward amplifier stage. The second circuit configuration may include the coil decoupled from the input of the feedforward amplifier stage and a (high-value) resistor coupled between the input and the output of the feedforward amplifier stage.

[0015] In some embodiments, the switching circuit is configured to couple an RC low-pass filter between the input and output of the feedforward 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 may be configured to decouple the feedback resistor from the input of the feedforward amplifier stage during the first operating mode and to decouple the RC low-pass filter from the input of the feedforward amplifier stage during the second operating mode.

[0016] In some embodiments, the switching circuit is configured to replace the sensor coil with a DC voltage source at the input of the feedforward amplifier stage during the second mode of operation and to replace the DC voltage source with the sensor coil at the input of the feedforward amplifier stage during the first mode of operation.

[0017] In some embodiments, a DC voltage of the DC voltage source substantially corresponds to a common mode voltage of the sensor coil in the first operating mode.

[0018] In some embodiments, the feedback amplifier stage is configured as an integrator. A capacitor may be coupled between an output and an input of the feedback amplifier stage.

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

[0020] In some embodiments, one or more resistors may be coupled between the output of the feedforward amplifier stage and an input of the feedback amplifier stage.

[0021] In some embodiments, the feedforward amplifier stage and the feedback amplifier stage are each designed as differential amplifier stages.

[0022] 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 feedforward amplifier stage to an input of a feedback amplifier stage of the coil sensor circuit in order to obtain a control signal for suppressing a DC offset of the feedforward amplifier stage, - Providing the control signal from an output of the feedback amplifier stage to an input of the feedforward amplifier stage.

[0023] During a second operating mode of the coil sensor circuit, the method comprises: - Decoupling the sensor coil from the input of the feedforward amplifier stage, and - Increasing a gain of the coil sensor circuit with respect to the first operating mode.

[0024] The gain can be increased by replacing the sensor coil at the input of the feedforward amplifier stage with a (common-mode) DC voltage source. Furthermore, an RC low-pass filter between the input and output of the feedforward amplifier stage can be replaced with a feedback resistor.

[0025] According to a further 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) in response 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 to 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 replace the sensor coil with a DC voltage source at the input of the feedforward amplifier stage during a second operating mode of the coil sensor circuit. A DC voltage of the DC voltage source may correspond to a common-mode voltage of the sensor coil in the first operating mode. Furthermore, the switching circuit may be configured to replace an RC low-pass filter between the input and output of the feedforward amplifier stage with a feedback resistor during the second operating mode.

[0026] Embodiments of the present disclosure may enable the separation of an unwanted amplified offset from a useful coil signal during startup (applying a supply or calibration mode). For a fast settling of a system operating point, multiplexing the input of the feedforward amplifier stage from a coil input signal to a common-mode signal (= differential short circuit) and switching on low-impedance feedback circuits during a calibration phase may be performed. This separation can guarantee offset suppression in a fast manner during an auto-calibration mode. Short description of the characters

[0027] Some examples of devices and / or methods are described below by way of example only and with reference to the accompanying figures, in which Fig. Figure 1 shows a conventional inductive current sensor arrangement; Fig. 2 shows a coil sensor arrangement according to embodiments of the present disclosure; and Fig. 3 shows a flowchart of a method for operating a coil sensor assembly according to embodiments of the present disclosure. Detailed description

[0028] Some examples will now be 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 include modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe particular examples is not intended to be limiting of other possible examples.

[0029] Throughout the description of the figures, the same or similar reference numerals refer to the same 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, in the figures, the thicknesses of lines, layers, and / or regions may be exaggerated for clarity.

[0030] When two elements A and B are combined using "or," this should be understood to mean that all possible combinations are disclosed, i.e., only A, only B, and A and B, unless explicitly defined otherwise in the individual case. Alternative wording for the same combinations may be "at least one of A and B" or "A and / or B." The same applies to combinations of more than two elements.

[0031] If a singular form is used, such as "a," "an," and "the," and the use of only a single element is neither explicitly nor implicitly defined as mandatory, further 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 "comprises", "comprising", "has" and / or "having" when used describe the presence of the specified features, integers, steps, operations, processes, elements, components and / or a group thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or a group thereof.

[0032] Fig. 1 shows an example of an inductive current sensor arrangement 100.

[0033] The inductive current sensor assembly 100 includes a primary conductor 110 through which an alternating current (AC) to be measured can flow. The primary conductor 110 can be a bus bar, a conductive path of an IC, or another electrical conductor, such as a wire. The electrical current causes a changing magnetic field around the primary conductor 110.

[0034] The inductive current sensor assembly 100 includes one or more sensor coils 120 placed 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. Those skilled in the art, having benefit from the present disclosure, will recognize that the proposed concepts described herein may be used for both single-ended and differential measurement concepts.

[0035] The Fig. The sensor coil 120 illustrated in Figure 1 comprises a first coil section (Coil1) and a second coil section (Coil2). The coil sections (Coil1, Coil2) each comprise a respective inductance L1, L2 and a respective resistor R1, R2. A total resistance of the coil 120 can be R1 + R2 = R coil= 3.5 kΩ. A first terminal 122-1 of coil 120 is coupled to an inverting input terminal 131-1 of a feedforward amplifier stage 130 of inductive current sensor assembly 100. A second terminal 122-2 of coil 120 is coupled to a non-inverting input terminal 131-2 of feedforward amplifier stage 130. The changing magnetic field induced by primary conductor 110 causes a voltage to be induced in coil 120 by electromagnetic induction. The induced voltage in coil 120 is proportional to the current flowing through primary conductor 110. This induced voltage is then used as the input signal to the feedforward amplifier stage 130 downstream of coils 120.

[0036] The feedforward 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 magnitude curve of the transfer function decreases by 20 dB / decade. The pole of the transfer function at the frequency f p can limit an overload effect from 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 as a low-pass filter.

[0037] The RC filter 132 in this differential circuit example includes 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 a variable capacitor C1. The RC filter 132 in this differential circuit example includes a further 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. Those skilled in the art having the benefit of the present disclosure will recognize that in the case of a non-differential design, only one filter branch may be required. The RC filter 132, which includes the resistor R1 in parallel with the capacitor C1, causes the pole at the frequency f pThe resistance of resistor R1 can be, for example, 14.8 kΩ. The capacitance of capacitor C1 can be, for example, 53.1 pF.

[0038] The inductive current sensor arrangement 100 further comprises a feedback amplifier stage 140 coupled between the output 133 and the 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. The feedforward amplifier stage 130 and the feedback amplifier stage 140 between the output 133 and the input 131 of the feedforward amplifier stage 130 together form a so-called DC servo loop.

[0039] The feedback amplifier stage 140 includes 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 feedforward amplifier stage 130. The feedback amplifier stage 140 includes a capacitor 142 coupled between the input 141 and an output 143 of the operational amplifier 144. The capacitor 142 in this differential circuit example 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. Those skilled in the art, having benefit from the present disclosure, will recognize that in the case of a non-differential design, only one capacitor branch may be required.

[0040] 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 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 feedforward 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 feedforward amplifier stage 130.

[0041] The feedback amplifier stage 140 acts as an integrator. The DC offset (the error signal) at the output 133 of the feedforward 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 feedforward 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 sent to the feedforward amplifier stage 130. The output of the integrator acts as a correction signal that can help eliminate steady-state errors.

[0042] In some embodiments, the sensor coil 120, the feedforward amplifier stage 130, and the feedback amplifier stage 140 may be integrated into a common integrated circuit (IC). The primary conductor 110 may be external to the IC.

[0043] A voltage coil signal at the feedforward 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]

[0044] A DC offset of the feedforward amplifier stage 130 at its output 133 is amplified as follows: Voffset,out=Voffset,in∗(1+R1Rcoil) [offset=offset;out=output;in=input]

[0045] The signal-to-offset ratio V coil / V offset,outdegrades linearly by lowering the input signal frequency. To remove 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.

[0046] If a desired application is broadband, high-frequency inputs should also be addressed to the system, and rapid DC offset removal is necessary. This means that the slow settling of the DC servo loop becomes a problem (a user would be forced to wait for a very long start-up time until the DC offset is completely removed).

[0047] The present disclosure proposes a circuit arrangement 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 feedforward amplifier stage 130 from a coil input signal to a common-mode signal (= differential short circuit) and engaging lower-impedance feedback circuits during the startup / calibration phase. This separation can support offset cancellation in a fast manner during an auto-calibration mode.

[0048] Fig. 2 shows an inductive current sensor assembly 200 according to an embodiment of the present disclosure.

[0049] In addition to the Fig. 1, the inductive current sensor arrangement 200 of Fig. 2 shows a switching circuit 210 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 / 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 relative to the first operating mode.

[0050] In the illustrated example, the switching circuit 210 includes three (pairs of) switches S1, S2, and S3 arranged such that respective parasitic resistances of the switches S1, S2, and S3 substantially do not contribute to the gain of the feedforward amplifier stage 130. In other words, the feedforward amplifier gain does not depend on (is independent of) the respective parasitic resistances of the switches S1, S2, and S3 in the first mode of operation.

[0051] The switch S1 is coupled between a DC voltage source 220 and the input 131 of the feedforward amplifier stage 130 and is configured to couple the DC voltage source 220 to or decouple it from the feedforward amplifier stage 130. A DC voltage of the DC voltage source 220 may substantially correspond to a common-mode voltage V cmof the sensor coil 120 in 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.

[0052] The switch S2 is coupled between the output 133 and the input 131 of the feedforward amplifier stage 130 and 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. The feedforward amplifier stage 130 of the Fig. 2 additionally includes a feedback resistor R1 cal , which is coupled between the output 133 and the input 131 of the feedforward amplifier stage 130. The switch S2 is connected between the feedback resistor R1 caland the input 131 of the feedforward 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 is coupled in the feedback branch 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 the non-inverting input 131-1 of the operational amplifier 134. Each of the switches S2 has a low-value parasitic resistance R S2 (R S2 < R coil and R S2< R1 cal ) on.

[0053] The switch S3 is coupled between the sensor coil 120 and the input 131 of the feedforward amplifier stage 130 and is configured to couple the sensor coil 120 to or decouple it 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 the coil 120 and the inverting input 131-1 of the operational amplifier 134. In the illustrated differential circuit example, a second switch S3 is coupled between the second terminal 122-2 of the coil 120 and the non-inverting input 131-2 of the operational amplifier 134. Each of the switches S3 can have a low-value parasitic resistor R S3 (R S3 < R coil ).

[0054] The switching circuit 210 is configured to close the switches S3 and open the switches S1 and S2 during the first operating mode (normal operation). Thus, by closing the switch(es) S3, the coil 120 is coupled to the input 131 of the feedforward amplifier stage 130. By opening the switch(es) S1, the DC voltage source 220 is decoupled from the input 131 of the feedforward amplifier stage 130. By opening the switch(es) S2, the RC low-pass filter 132 is coupled 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.

[0055] The switching circuit 210 is configured to open the switches S3 and close the switches S1 and S2 during the second operating mode (start / calibration mode). By opening the switch(es) S3, the coil 120 is decoupled from the input 131 of the feedforward amplifier stage 130. By closing the switch(es) S1, the DC voltage source 220 is coupled to the input 131 of the feedforward amplifier stage 130. By closing the switch(es) S2, the RC low-pass filter 132 is decoupled from the input 131 of the operational amplifier 134, and instead the feedback resistor R1 cal coupled between the output 133 and the input 131 of the operational amplifier 134. With a high-impedance R1 cal and low-ohm parasitic resistance R S1of the switch(es) S1, the gain of the feedforward amplifier stage 130 can be increased during the second operating mode (autocalibration) compared to the first operating mode.

[0056] The proposed arrangement for separating the feedforward amplifier offset from the useful signal comprises a double pair of switches S1 and S2, a pair of replica resistors R1 cal and a pair of S3 switches. Those skilled in the art, benefiting from the present disclosure, will recognize that other circuit arrangements may be possible to achieve the same or a similar result. For example, adjustments could also be made to the feedback amplifier stage 140.

[0057] When fast DC offset compensation is enabled, i.e., during the second operating mode (autocalibration), S1 and S2 are closed, whereas S3 is open. During this phase, the useful signal from the sensor coil 120 is discarded, and only the DC offset is processed by the servo loop 130, 140. The total amplified offset at the output is: Voffset,out=Voffset,in1∗(1+R1_calRS1)

[0058] The feedforward amplifier 130 is in the illustrative example of Fig. 2 with a double input gm = ΔI out / ΔV in (transconductance) stage 134 and the total DC offset input, which is designated at the second (here: upper) input, is: Voffset,in2=Voffset,in1(gm1gm2),where gm2< <gm1

[0059] The servo loop transfer function that detects the DC offset at the output of the feedforward amplifier 130 and feeds it back to a second (here: upper) input of the feedforward amplifier 130 is: Voffset,in2=Voffset,out(12πfRDSL1CDSL)∗12A

[0060] During the second operating mode (autocalibration), 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

[0061] Similarly, the open-loop offset transfer function can be calculated when the system enters the first operating mode (normal operating mode). In this case, the DC offset and the wanted signal are processed once S3 is closed and S1 and S2 are open. The entire system now evolves from the DC offset integrated during the second operating mode (autocalibration phase) and present at the second feedforward amplifier input. The system now rejects the residual DC offset much more slowly, and the speed can be evaluated by combining equations (0), (2), and (3): Hnorm(f)=(1+R1Rcoil)(gm2gm1)(12πfRDSL1CDSL)∗12A

[0062] The significant increase in the speed of the servo loop 130, 140 during autocalibration is determined by comparing f 0dB of H(s) during autocalibration and during normal application mode.

[0063] The acceleration factor is given by: (1+R1_calRS1)(1+R1Rcoil)

[0064] The more R1 cal is high-resistance and the parasitic impedance of the switch(es) S1 compared to R1 and R coil The lower the impedance, the faster the offset rejection will be during autocalibration. That is, the degree of freedom to accelerate the autocalibration phase to remove as much offset as possible before removing the remaining offset error at a much slower rate during normal operation.

[0065] It can be observed that the way the payload coil signal is discarded during autocalibration does not affect the signal transfer function at all, since the switches S1, S2 are never in series with R1 or R coiland the only switch(es) S3 that are closed during normal operation connect high-impedance nodes (no current flow).

[0066] Fig. 3 shows a flowchart of a method 300 for operating the coil sensor circuit 200.

[0067] The exemplary method 300 of Fig. 3 includes: During a first operating mode of the coil sensor circuit: - Providing 310 an AC sensor signal from the sensor coil 120 to the feedforward amplifier stage 130 of the coil sensor circuit 200 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 the feedback amplifier stage 140 of the coil sensor circuit 200 to obtain a control signal for suppressing the DC offset of the feedforward amplifier stage 130, - Providing 330 the control signal from an output of the feedback amplifier stage 140 to an input of the feedforward amplifier stage 130. During a second operating mode of the coil sensor circuit, increasing the gain of the coil sensor circuit 200 relative to the first operating mode by: - Replacing 340 the sensor coil 120 at the input of the feedforward amplifier stage 130 with a (common mode) DC voltage source 220.

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

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

[0070] The aspects and features described in connection with a particular one of the previous examples may also be combined with one or more of the further examples to replace an identical or similar feature of that further example or to additionally introduce the feature into the further example

[0071] It is further understood that the disclosure of multiple steps, processes, operations, or functions disclosed in the specification or claims should not be construed as necessarily being in the described order, unless explicitly stated in the individual case or required for technical reasons. Therefore, the foregoing description does not limit the performance of multiple steps or functions to any particular order. Furthermore, in further examples, a single step, function, process, or operation may include and / or be broken down into multiple sub-steps, functions, processes, or operations.

[0072] If some aspects have been described in the context of a device or system, these aspects are also to be understood as a description of the corresponding method. For example, a block, device, or functional aspect of the device or system may correspond to a feature, such as a method step, of the corresponding method. Accordingly, aspects described in the context of a method are also to be understood as a description of a corresponding block, element, property, or functional feature of a corresponding device or system.

[0073] The following claims are hereby incorporated into the Detailed Description, each claim being capable of standing on its own as a separate example. It should also be noted that although a dependent claim in the claims refers to a particular 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 contemplated unless it is specifically stated that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be encompassed, even if that claim is not directly defined as being 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 (200), 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 (200), to decouple the sensor coil (120) from the feedforward amplifier stage (130), and to increase a gain of the coil sensor circuit (200) 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 mode of operation 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 filter (132) 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 during the first operating mode, to decouple the feedback resistor from the input (131) of the feedforward amplifier stage (130), 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 (S 1) 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 (130), 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 one of the preceding claims, wherein the feedback amplifier stage (140) is designed as an integrator. [11] The coil sensor circuit (200) of 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 (200), the method comprising: during a first operating mode of the coil sensor circuit (200), Providing (310) an AC sensor signal from a sensor coil (120) to a feedforward amplifier stage (130) of the coil sensor circuit (200) to obtain an amplified sensor signal; Providing (320) the amplified sensor signal from an output (133) of the feedforward amplifier stage (130) to an input (141) of a feedback amplifier stage (140) of the coil sensor circuit (200) to obtain a control signal for suppressing a DC offset of the feedforward amplifier stage (130); Providing (330) the control signal from an output (143) of the feedback amplifier stage (140) to an input (131) of the feedforward amplifier stage (130); and during a second operating mode of the coil sensor circuit (200), Replacing (340) the sensor coil (120) at the input (131) of the feedforward amplifier stage (130) with a DC voltage source (220). [16] The method of 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) with a feedback resistor.

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