Coil sensor circuit and method for operating coil sensor circuit

Abstract

The invention relates to a coil sensor circuit and a method for operating a coil sensor circuit. The invention provides a coil sensor circuit. The sensor comprises a sensor coil configured to provide an AC sensor signal, a feed-forward amplifier stage configured to amplify the AC sensor signal to obtain an amplified sensor signal, a feedback amplifier stage coupled between the output and the input of the feed-forward amplifier stage and configured to provide a control signal for cancelling a DC offset of the feed-forward amplifier stage, and a switching circuit. The switching circuit is configured to couple the sensor coil to an input of the feed-forward amplifier stage during a first mode of operation of the coil sensor circuit, and to decouple the sensor coil from the feed-forward amplifier stage during a second mode of operation of the coil sensor circuit, and increase the gain of the coil sensor circuit with respect to the first mode of operation.

Description

Technical Field

[0001] The present disclosure generally relates to apparatus and methods for sensing magnetic fields and / or currents, and more particularly, to inductive current sensors and sensing methods. Background Art

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

[0003] The coil sensor circuit may include a pick-up coil (sensor element), a preamplifier (feed-forward) stage with amplification and anti-saturation functions for high frequencies (e.g. provided by a low-pass filter), and a DC servo loop for DC offset cancellation of the preamplifier stage. An operational amplifier (op-amp) is commonly used in amplifier circuits, which may have an input offset voltage characteristic. This means that there may be a small DC voltage difference between its inverting and non-inverting inputs. When this voltage is amplified, it may cause a DC offset at the output of the amplifier.

[0004] By reducing the input signal frequency, the coil sensor signal offset can be made smaller than V coil / V offset，out In order to remove the DC offset component without restricting the minimum useful signal bandwidth of the input signal too much and without using very large capacitors in series with the signal, a DC servo loop can be used that has a 0dB open-loop frequency as low as possible. In other words, if the DC servo loop has a 0dB open-loop frequency that is too high, the loop will begin to suppress the useful signal.

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

[0006] Since the application is expected to be broadband, high frequency inputs should also be addressed to the system and the offset must be removed quickly. This means that slow settling of the DC servo loop is a problem as the user will be forced to wait for a long start-up time until the offset is completely removed. An alternative method to remove the DC offset could be to use chopping techniques, but this may not be feasible due to the broadband application frequencies.

[0007] Therefore, there is a need for fast DC offset removal for a broadband application coil sensor device having a pick-up coil, a preamplifier stage, and a DC servo loop for offset cancellation of the preamplifier stage. Summary of the invention

[0008] This need is solved by an apparatus and a method according to the appended claims.

[0009] According to a first aspect, the present disclosure proposes a (inductive) coil sensor circuit. The coil sensor circuit comprises: a sensor coil, which is configured to provide an AC sensor signal (e.g., a voltage) in response to a changing magnetic field. Downstream of the sensor coil, the coil sensor circuit comprises a feedforward amplifier circuit, which is configured to amplify the AC sensor signal and acquire the amplified sensor signal. The coil sensor circuit also comprises a feedback amplifier circuit coupled between the output and the input of the feedforward amplifier circuit. The feedback amplifier circuit is configured to provide a control signal for counteracting a DC offset of the feedforward amplifier circuit. The proposed coil sensor circuit also comprises a switching circuit, which is configured to: during a first operating mode of the coil sensor circuit, couple the sensor coil to the input of the feedforward amplifier stage, and during a second operating mode of the coil sensor circuit, decouple the sensor coil from the feedforward amplifier stage, and increase the gain of the coil sensor circuit with respect to the first operating mode. The first operating mode may also be referred to as a normal operating mode. The second operating mode may also be referred to as a startup or auto-calibration mode. In the second operating mode, the useful signal from the coil may be discarded and only the DC offset may be processed by a servo loop comprising the feedforward amplifier circuit and the feedback amplifier circuit.

[0010] In some embodiments, the switching circuit includes a plurality of switches, each having a parasitic resistance. The corresponding parasitic resistance may be (substantially) smaller than the resistance of the coil. The gain of the feedforward amplifier stage is essentially independent of the parasitic resistance in the first operating mode (normal operating mode). For example, the position / orientation of the switch is such that the parasitic resistance of the switch does not contribute to the gain of the feedforward amplifier.

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

[0012] 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 can be configured to change the resistance ratio between the resistance at the input and the resistance in the feedback path of the feedforward amplifier stage.

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

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

[0015] 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 operating mode, and to replace the DC voltage source at the input of the feedforward amplifier stage during the first operating mode.

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

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

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

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

[0020] In some embodiments, the feedforward amplifier stage and the feedback amplifier stage are each configured as a differential amplifier stage.

[0021] According to another aspect, the present disclosure provides a method for operating a coil sensor circuit. The method includes during a first operating mode of the coil sensor circuit:

[0022] The AC sensor signal from the sensor coil is provided to the feed-forward amplifier stage of the coil sensor circuit to obtain an amplified sensor signal,

[0023] providing an amplified sensor signal from the output of the feedforward amplifier stage to the input of the feedback amplifier stage of the coil sensor circuit to obtain a control signal for canceling the DC offset of the feedforward amplifier stage,

[0024] A control signal from the output of the feedback amplifier stage is provided to the input of the feedforward amplifier stage.

[0025] During a second operating mode of the coil sensor circuit, the method comprises:

[0026] decoupling the sensor coil from the input of the feed-forward amplifier stage, and

[0027] The gain of the coil sensor circuit is increased with respect to the first operating mode.

[0028] The gain can be increased by replacing the sensor coil with a (common mode) DC voltage source at the input of the feed forward amplifier stage. Furthermore, the RC low pass filter between the input and output of the feed forward amplifier stage can be replaced by a feedback resistor.

[0029] According to another aspect, the present disclosure proposes a (inductive) coil sensor circuit. The coil sensor circuit includes a sensor coil, which is configured to provide an AC sensor signal (e.g., voltage) in response to a changing magnetic field. Downstream of the sensor coil, the coil sensor circuit includes a feedforward amplifier circuit, which is configured to amplify the AC sensor signal and obtain the amplified sensor signal. The coil sensor circuit also includes a feedback amplifier circuit coupled between the output and input of the feedforward amplifier circuit. The feedback amplifier circuit is configured to provide a control signal for offsetting the DC offset of the feedforward amplifier circuit. The proposed coil sensor circuit also includes a switching circuit, which is configured to: during a first operating mode of the coil sensor circuit, couple the sensor coil to the input of the feedforward amplifier stage, and during a second operating mode of the coil sensor circuit, replace the sensor coil with a DC voltage source at the input of the feedforward amplifier stage. The DC voltage of the DC voltage source may correspond to the common mode voltage of the sensor coil in the first operating mode. In addition, the switching circuit may be configured to: during the second operating mode, the RC low-pass filter between the input and output of the feedforward amplifier stage may be replaced with a feedback resistor.

[0030] Embodiments of the present disclosure may allow separation of the undesired amplified offset from the useful coil signal at start-up (application supply or calibration mode). In order to quickly stabilize the system operating point, during the calibration phase multiplexing of the input of the feedforward amplifier stage from the coil input signal to the common mode signal (= differential short circuit) may be done and the low impedance feedback circuit switched on. During the automatic calibration mode, this separation may ensure offset cancellation in a fast manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Some examples of apparatus and / or methods will be described below by way of example only and with reference to the accompanying drawings, in which:

[0032] Figure 1 A conventional inductive current sensor device is shown;

[0033] Figure 2 shows a coil sensor device according to an embodiment of the present disclosure; and

[0034] Figure 3 A flow chart of a method for operating a coil sensor device according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0035] Some examples are now described in more detail with reference to the accompanying drawings. However, other possible examples are not limited to the features of these embodiments described in detail. Other examples may include modifications to features and equivalents and substitutes of features. In addition, the terms used to describe some examples herein should not limit other possible examples.

[0036] Throughout the description of the drawings, the same or similar reference numerals refer to the same or similar elements and / or features, which may be equivalent or implemented in a modified form while providing the same or similar functions. For clarity, the thickness of the lines, layers and / or regions in the drawings may also be exaggerated.

[0037] When "or" is used to combine two elements A and B, this should be understood to disclose all possible combinations, i.e. only A, only B and A and B, unless otherwise clearly defined in individual cases. As alternative words for the same combination, "at least one of A and B" or "A and / or B" may be used. This applies equally to combinations of more than two elements.

[0038] If singular forms, such as "a", "an", and "the" are used, and the use of only a single element is not explicitly or implicitly defined as mandatory, other examples may also use several elements to implement the same functionality. If a functionality is described below as being implemented using multiple elements, other examples may use a single element or a single processing entity to implement the same functionality. It should also be understood that when the terms "include", "including", "comprise", and / or "comprising" are used, the presence of specified features, integers, steps, operations, processes, elements, components, and / or groups thereof is described, but the presence of one or more other features, integers, steps, operations, processes, elements, components, and / or groups thereof is not excluded.

[0039] Figure 1 An example of an inductive current sensor device 100 is shown.

[0040] The inductive current sensor device 100 comprises a primary conductor 110 through which an alternating current (AC) to be measured can flow. The primary conductor 110 may be a current rail, a conductor path of an IC, or another electrical conductor such as a wire. The current induces a changing magnetic field around the primary conductor 110 .

[0041] The inductive current sensor device 100 includes one or more sensor coils 120 located near the main conductor 110. The one or more coils 120 are not directly connected to the main conductor 110, but are close enough to it. One sensor coil may be sufficient for a single-ended measurement concept. One or two sensor coils may be used for a differential measurement concept. Those skilled in the art who benefit from this disclosure will recognize that the proposed concepts described herein may be used for both single-ended measurement concepts as well as differential measurement concepts.

[0042] Figure 1The sensor coil 120 shown in FIG. 1 includes a first coil portion (Coil1) and a second coil portion (Coil2). The coil portions (Coil1, Coil2) each include a corresponding inductance L1, L2 and a corresponding resistance R1, R2. The total resistance of the coil 120 may be R1+R2=R coil =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 device 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. The induced voltage is then used as an input signal to the feedforward amplifier stage 130 downstream of the coil 120.

[0043] The feedforward amplifier stage 130 coupled to the coil 120 has a transfer function with a pole at frequency f p (For example, f p =200kHz). The poles of the transfer function identify the roots of the denominator polynomial of the transfer function. The pole frequencies correspond to the angular frequencies where the slope of the transfer function amplitude curve drops by 20dB / dB. The transfer function at frequency f p The pole at can limit the overload effect of coil 120 caused by high frequency (AC) magnetic field (current). Feedforward amplifier stage 130 includes RC filter 132, which is coupled between input 131 and output 133 of operational amplifier 134. The RC filter causes p The pole at , and can therefore be considered as a low-pass filter.

[0044] 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 connected in parallel with an adjustable capacitor C1. The RC filter 132 in this differential circuit example includes another non-inverting branch including a resistor R1 connected in parallel with the capacitor C1, which is coupled between the non-inverting input 131-2 and the output 133-2 of the operational amplifier 134. A person skilled in the art who benefits from this disclosure will understand that only one filter branch may be required in the case of a non-differential arrangement. The RC filter 132 including the resistor R1 connected in parallel with the capacitor C1 causes a voltage drop at a frequency f p For example, the resistance of resistor R1 may be 14.8 kΩ. For example, the capacitance of capacitor C1 may be 53.1 pF.

[0045] The inductive current sensor device 100 further comprises a feedback amplifier stage 140, which is coupled between the output 133 and the input 131 of the feedforward amplifier stage 130 and is configured to provide a control signal for canceling the 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.

[0046] Feedback amplifier 140 includes an operational amplifier 144. The non-inverting input 141-1 of the operational amplifier is connected to the output of the amplifier via an optional resistor R DSL1 is coupled to the inverting output 133-1 of the feed-forward amplifier stage 130. The inverting input 141-2 of the operational amplifier 144 is coupled to the inverting output 133-1 of the feed-forward amplifier stage 130. DSL1 is 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 the 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. A skilled artisan having the benefit of this disclosure will appreciate that only one capacitor branch may be required in the case of a non-differential arrangement.

[0047] The feedback amplifier stage 140 also includes one or more feedback resistors R DSL_FB , which is 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 coupled between the non-inverting output 143-2 of the operational amplifier 144 and the non-inverting input 131-2 of the feedforward amplifier 130. DSL_FB , and a second feedback resistor R coupled between the inverting output 143 - 1 of the operational amplifier 144 and the inverting input 131 - 1 of the feedforward amplifier stage 130 DSL_FB .

[0048] The feedback amplifier stage 140 behaves as an integrator. The DC offset (error signal) at the output 133 of the feedforward amplifier stage 130 passes through the integrator 140, which continuously accumulates the DC offset over time. The AC component 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 generates an output signal that increases or decreases over time based on the accumulated error. The output of the feedback amplifier stage 140 is a control signal sent to the feedforward amplifier stage 130. The output of the integrator behaves as a correction signal, which can help eliminate steady-state errors.

[0049] In some embodiments, the sensor coil 120, the feed-forward 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.

[0050] The frequency is lower than the low-pass filter pole (i.e. f <f p ), the voltage coil signal at the output 133 of the feedforward amplifier is:

[0051]

[0052] The DC offset of the feedforward amplifier stage 130 at its output 133 is amplified as follows:

[0053]

[0054] By reducing the input signal frequency, the signal deviation is smaller than V coil / V offset，out In order to remove the DC offset component without too much restriction on the minimum useful signal bandwidth of the input signal at input 131 and without using very large capacitors in series to the signal, a DC servo loop 130, 140 with a 0 dB open loop frequency as low as possible is used.

[0055] If the desired application is broadband, handling high frequency inputs should also be addressed to the system and fast removal of DC offsets is necessary. This means that slow settling of the DC servo loop is a problem (the user will be forced to wait for a long start-up time until the DC offset is completely removed).

[0056] The present disclosure proposes a circuit arrangement that can separate the undesired amplified DC bias from the useful coil signal at startup. In order to quickly stabilize the system operating point, the present disclosure proposes to multiplex the input 131 of the feedforward amplifier stage 130 from the coil input signal to a common mode signal (= differential short circuit) and switch on a low impedance feedback circuit during the startup / calibration phase. During the auto-calibration mode, this separation can ensure offset cancellation in a fast manner.

[0057] Figure 2 An inductive current sensor device 200 according to an embodiment of the present disclosure is shown.

[0058] remove Figure 1 In addition to the inductive current sensor device 100 shown in FIG. Figure 2The inductive current sensor device 200 comprises a switching circuit 210 configured to switch between two operating modes of the inductive current sensor device 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 (startup / calibration mode), the sensor coil 120 is decoupled from the feedforward amplifier stage 130 and the gain of the amplifier circuits 130, 140 is increased with respect to the first operating mode.

[0059] In the illustrated example, the switching circuit 210 includes three (pairs of) switches S1, S2, and S3, which are placed so that the respective parasitic resistances of the switches S1, S2, and S3 do not substantially affect the gain of the feed-forward amplifier stage 130. In other words, the feed-forward amplifier gain in the first operating mode does not depend on (is independent of) the respective parasitic resistances of the switches S1, S2, and S3.

[0060] The switch S1 is coupled between the 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 the feedforward amplifier stage 130 or decouple it from the feedforward amplifier stage 130. The DC voltage of the DC voltage source 220 may substantially correspond to the common mode voltage V of the sensor coil 120 in the first operating mode. cm 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 and the non-inverting input 131-2 of the feedforward amplifier stage 130. Each switch S1 has a low ohmic parasitic resistance R S1 (R S1 < <R coil ).

[0061] Switch S2 is coupled between output 133 and input 131 of feedforward amplifier stage 130 and is configured to increase the gain of feedforward amplifier stage 130 by switching between a first circuit configuration and a second circuit configuration between output 133 and input 131 of feedforward amplifier stage 130 during a second operating mode. Figure 2 The feedforward amplifier stage 130 of the example implementation shown in FIG. 1 additionally includes a feedback resistor R1 cal , which is coupled between the output 133 and the input 131 of the feedforward amplifier stage 130. Switch S2 is coupled between the feedback resistor R1 cal and the input 131 of the feedforward amplifier stage 130. In the illustrated differential circuit example, the first switch S2 is coupled in the feedback branch between the inverting output 133-1 and the inverting input 131-1 of the operational amplifier 134. The first switch S2 is coupled to the feedback resistor R1cal and the inverting input 131-1 of the operational amplifier 134. In the illustrated differential circuit example, the 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 coupled to the feedback resistor R1 cal and the non-inverting input 131-1 of the operational amplifier 134. Each switch S2 has a low ohmic parasitic resistance R S2 (R S2 < <R coil And R S2 < <R1 cal ).

[0062] 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 the sensor coil 120 from the feedforward amplifier stage 130. In the illustrated differential circuit example, the 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, the 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 switch S3 may have a low ohmic parasitic resistance R S3 (R S3 < <R coil ).

[0063] The switching circuit 210 is configured to close the switch S3 and open the switches S1 and S2 during the first operation 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 is coupled between the output 133 and the input 131 of the operational amplifier 134, and the feedback resistor R1 cal Decoupled from input 131 of operational amplifier 134 .

[0064] The switching circuit 210 is configured to open switch S3 and close switch S1 and switch S2 during the second operating mode (startup / calibration mode). By opening switch(es) S3, the coil 120 is decoupled from the input 131 of the feedforward amplifier stage 130. By closing switch(es) S1, the DC voltage source 220 is coupled to the input 131 of the feedforward amplifier stage 130. By closing switch(es) S2, the RC low pass filter 132 is decoupled from the input 131 of the operational amplifier 134 and replaced by the feedback resistor R1. calis coupled between the output 133 and the input 131 of the operational amplifier 134. Due to the high resistance R1 of the switch S1 cal and low ohmic parasitic resistance R S1 , during the second operating mode (auto-calibration), the gain of the feed-forward amplifier stage 130 may be increased compared to the first operating mode.

[0065] The proposed device separates the feedforward amplifier offset from the useful signal and comprises two pairs of switches S1 and S2, a pair of replica resistors R1 cal and a pair of S3 switches. Those skilled in the art who have benefited from this disclosure will appreciate that other circuit arrangements may also achieve the same or similar results. For example, the feedback amplifier stage 140 may also be adjusted.

[0066] When setting fast DC offset compensation, i.e. during the second operating mode (autocalibration), S1 and S2 are closed and S3 is open. In 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 results in:

[0067]

[0068] The feed forward amplifier 130 is Figure 2 The illustrative example is constructed with a dual input gm = ΔI out / ΔV in (transconductance) stage 134, and the total DC offset input mentioned at the second (here: upper) input is:

[0069]

[0070] The servo transfer function senses the DC offset at the output of the feed-forward amplifier 130 and feeds it back to the second (here: upper) input of the feed-forward amplifier 130 and is:

[0071]

[0072] During the second operating mode (auto-calibration), the open-loop offset transfer function obtained by disconnecting the DC servo loop can be calculated by equations (1), (2) and (3):

[0073]

[0074] The open-loop offset transfer function can be calculated in a similar way when the system is running in the first operating mode (normal operating mode). In this case, once S3 is closed and S1 and S2 are open, the DC offset and the useful signal are processed. Now, the whole system evolves from the DC offset integrated during the second operating mode (autocalibration phase) and presented at the input of the second feedforward amplifier. Now, the system suppresses the residual DC offset more slowly, and this speed can be evaluated by combining equations (0), (2) and (3):

[0075]

[0076] By comparing the f of H(s) during auto calibration and during normal application mode 0dB A significant increase in the speed of the servo loops 130 , 140 during the autocalibration is determined.

[0077] The acceleration factor is given by:

[0078]

[0079] Compared with R1 and R coil , R1 cal The higher ohmic and the lower ohmic the parasitic impedance of the S1 switch(es), the faster the offset cancellation during autocalibration will be. That is, the degrees of freedom of the autocalibration phase are accelerated to remove as much offset as possible before the residual offset is removed much more slowly in normal operation.

[0080] It can be seen that the signal transfer function is not affected at all by the reduction of the useful coil signal during the automatic calibration, because switches S1 and S2 are never connected in series to R1 or R coil , and the only switch(es) S3 that is closed during normal operation connects the high-ohmic node (no current flows).

[0081] Figure 3 A flow chart of a method 300 for operating coil sensor circuit 200 is shown.

[0082] Figure 3 The example method 300 includes:

[0083] During the first operating mode of the coil sensor circuit:

[0084] The AC sensor signal from the sensor coil 120 is provided 310 to the feed-forward amplifier stage 130 of the coil sensor circuit 200 to obtain an amplified sensor signal,

[0085] providing 320 the amplified sensor signal from the output of the feedforward amplifier stage 130 to the input of the feedback amplifier stage 140 of the coil sensor circuit 200 to obtain a control signal for canceling the DC offset of the feedforward amplifier stage 130,

[0086] A control signal from the output of the feedback amplifier stage 140 is provided 330 to the input of the feedforward amplifier stage 130 .

[0087] During the second operating mode of the coil sensor circuit, the gain of the coil sensor circuit 200 is increased with respect to the first operating mode by:

[0088] The sensor coil 120 is replaced 340 with a (common mode) DC voltage source 220 at the input of the feed forward amplifier stage 130 .

[0089] Furthermore, the method 300 may additionally include: connecting 350 a feedback resistor R1 between the input 131 and the output 133 of the feed-forward amplifier stage 130. cal Replaces the RC low pass filter 132.

[0090] The user can experience a fast startup (of the coil or hybrid sensor) independent of the input frequency speed (i.e. the startup time of the DC-DC converter or the current measurement).

[0091] The aspects and features described in conjunction with a particular one of the foregoing examples may also be combined with one or more other examples to replace the same or similar features of the other examples, or to introduce additional features into further examples.

[0092] It is further understood that, unless otherwise explicitly stated in individual cases or necessary for technical reasons, the disclosure of several steps, processes, operations or functions disclosed in the specification and claims should not be interpreted as implying that these operations must depend on the described order. Therefore, the foregoing description does not limit the execution of several steps or functions to a certain order. In addition, in other examples, a single step, function, process or operation may include or be decomposed into several sub-steps, sub-functions, sub-processes or sub-operations.

[0093] If some aspects have been described with respect to a device or system, these aspects should also be understood as descriptions of corresponding methods. For example, a block, device, or functional aspect of a device or system may correspond to a feature (such as a method step) of a corresponding method. Therefore, aspects described with respect to a method should also be understood as descriptions of corresponding blocks, corresponding elements, attributes, or functional features of a corresponding device or corresponding system.

[0094] The following claims are hereby incorporated into the detailed description, where each claim may stand on its own as a separate example. It should also be noted that although in the claims, a dependent claim refers to a specific combination with one or more other claims, other examples may also include a combination of a dependent claim with the subject matter of any other dependent claim or independent claim. Unless it is stated in individual cases that a specific combination is not intended, such a combination is hereby explicitly proposed. In addition, features of a claim should also be included with respect to any other independent claim, even if the claim is not directly defined as dependent on the other 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 the output (133) and the input (131) of the feedforward amplifier stage (130) and configured to provide a control signal for canceling a DC offset of the feedforward amplifier stage (130); as well as The switching circuit (210) is configured to: During a first operating mode of the coil sensor circuit, coupling 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, decoupling the sensor coil (120) from the feedforward amplifier stage (130), and The gain of the coil sensor circuit is increased with respect to the first operating mode.

2. The coil sensor circuit (200) of claim 1, wherein the switching circuit (210) is configured to increase the gain of the feedforward amplifier stage (130) during the second operating mode.

3. The coil sensor circuit (200) of claim 1 or 2, wherein the switching circuit (210) is configured to increase the gain of the feedforward amplifier stage (130) by switching between a first circuit configuration and a second circuit configuration between the output (133) and the input (131) of the feedforward amplifier stage (130) during the second operating mode.

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 mode of operation, an RC low pass filter (132) is coupled between the input (131) and the output (133) of the feed forward amplifier stage (130), and During the second operating mode, the RC low pass filter (132) is replaced by a feedback resistor.

5. The coil sensor circuit (200) according to claim 4, wherein the switching circuit (210) is configured to: decoupling the feedback resistor from the input (131) of the feedforward amplifier stage (130) during the first operating mode, and During the second mode of operation, the RC low pass filter (132) is decoupled from the input (131) of the feed forward amplifier stage (130).

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); as well as A third switch (S1) is 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, closing the first switch (S3) and opening the second switch (S2) and the third switch (S1), and, During the second operating mode, The second switch (S2) and the third switch (S1) are closed and the first switch (S3) is opened.

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 mode of operation, the sensor coil (120) is replaced by a DC voltage source (220) at the input (131) of the feedforward amplifier stage (133), and During the first mode of operation, the DC voltage source (220) is replaced 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 the DC voltage of the DC voltage source (220) essentially corresponds to the 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 configured 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) of any one of the preceding claims, wherein at least one resistor is coupled between the 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 of the preceding claims, wherein at least one resistor is coupled between the output (133) of the feedforward amplifier stage (130) and the 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 configured as a differential amplifier stage.

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 feed-forward amplifier stage (130) of the coil sensor circuit to obtain an amplified sensor signal; providing (320) the amplified sensor signal from the output of the feedforward amplifier stage (130) to the input of a feedback amplifier stage (140) of the coil sensor circuit to obtain a control signal for canceling a DC offset of the feedforward amplifier stage; providing (330) the control signal from the output of the feedback amplifier stage (140) to the input of the feedforward amplifier stage (130); as well as During a second operating mode of the coil sensor circuit, The sensor coil (120) is replaced (340) with a DC voltage source (220) at the input of the feedforward amplifier stage (130).

16. The method according to claim 15, further comprising: During the second operating mode, An RC low pass filter (132) is replaced (350) with a feedback resistor between the input (131) and the output (133) of the feed forward amplifier stage (130).

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