Voltage measurement via reference circuit-based impedance detection

Abstract

Circuit (100) for measuring a voltage, wherein the circuit (100) comprises: a passive detection element (110) designed to be coupled between a measuring point (101) and a reference point (102), wherein the passive The detection element (110) has a voltage-dependent impedance; a reference circuit (150) designed to provide a reference response; an impedance detector (120) configured to detect the voltage-dependent impedance of the passive sensing element (110) by supplying a test signal to the passive sensing element (110) and evaluating a response to the test signal from the passive sensing element (110) and the reference response provided by the reference circuit (150); and a converter circuit (140) designed to convert a result of evaluating the response and the reference response into voltage level information.

Description

TECHNICAL FIELD

[0001] The present application relates to a circuit for measuring a voltage and a method for measuring a voltage. BACKGROUND

[0002] In many applications, there is a need to measure or monitor a voltage. For this purpose, various types of measurement circuits can be used, e.g., based on an analog-to-digital (AD) converter, with or without input signal conditioning, filtering, offsets, resistive dividers, or the like. However, more complex measurement circuits may be necessary in scenarios where the voltage measurement must be performed in a first voltage domain, while the measurement result must be delivered to a second voltage domain that is separate from the first voltage domain. For example, the first voltage domain and the second voltage domain may use different reference potentials. For example, the first voltage domain may be a high-voltage domain, and the second voltage domain may be a low-voltage domain, e.g.,for safety reasons, or because circuit components in the low-voltage domain are not compatible with voltages in the high-voltage domain, must be isolated from the first voltage domain.

[0003] For example, WO 2018 / 005631 A1 describes a wireless sensing system for a battery system in which a cell measurement circuit measures a voltage at terminals of a battery module. A wireless communication transceiver is used to transmit the voltage measurement information from the cell measurement circuit to a battery controller.

[0004] US 2014 / 0300374 A1 describes a device for measuring a DC voltage from a DC voltage source. An electrode forms a capacitive connection with the DC voltage source. A nonlinear capacitor has a first node connected to the electrode. An initial voltage source is arranged to generate an initial voltage. A switch is arranged to selectively apply the initial voltage to a second node of the nonlinear capacitor. A voltage sensor is arranged to measure the voltage of the second node of the nonlinear capacitor, and a processor is programmed to derive the DC voltage from the DC voltage source by analyzing the decay rate of the measured voltage.

[0005] US 2014 / 0159735 A1 describes the indirect monitoring of voltage outputs from cells of an electrochemical generator using a reactive passive component whose impedance varies depending on the voltage to be monitored. The passive reactive component is part of a resonant circuit, and the voltage is monitored indirectly by detecting a variation in the resonant frequency of the resonant circuit.

[0006] However, the above-mentioned technologies using wireless transmission of measurement information or detection of variations of a resonance frequency lead to a high complexity of the measurement circuit.

[0007] Accordingly, there is a need for techniques that enable efficient measurement of a voltage in a separate voltage domain. SUMMARY

[0008] According to embodiments disclosed herein, a circuit according to claim 1 and a method according to claim 13 are provided. The dependent claims define further embodiments.

[0009] According to one embodiment, a circuit for measuring a voltage is provided. The circuit comprises a passive sensing element configured to be coupled between a measuring point and a reference point. The passive sensing element has a voltage-dependent impedance. For example, the passive sensing element may comprise a varactor, a varicap diode, and / or a field-effect transistor. The circuit further comprises an impedance detector and a reference circuit. The impedance detector is configured to detect the voltage-dependent impedance of the passive sensing element by supplying a test signal to the passive sensing element and evaluating a response to the test signal from the passive sensing element with respect to a reference response from the reference circuit.Furthermore, the circuit comprises a converter circuit configured to convert a result of evaluating the response and the reference response into voltage level information.

[0010] According to one embodiment of the circuit, the impedance detector also supplies the test signal to the reference circuit. The reference response can then be a further response to the test signal from one or more circuit elements of the reference circuit. The further response can be measured during regular operation of the circuit, e.g., at substantially the same time as the response from the passive sensing element.

[0011] According to another embodiment of the circuit, the reference response can be based on a previous measurement and stored in the reference circuit. For example, the reference response can be measured and stored during a calibration phase in which one or more known voltages are applied to the passive sensing elements and one or more corresponding responses to the test signal are measured and then stored to be used as reference responses.

[0012] According to one embodiment of the circuit, the test signal has a constant frequency. The frequency of the test signal can be selected from several frequencies.

[0013] According to one embodiment of the circuit, the test signal is a pulse signal.

[0014] According to one embodiment of the circuit, the impedance detector is configured to evaluate the response and the reference response by determining a difference between the response and the reference response.

[0015] According to one embodiment of the circuit, the converter circuit is configured to determine the voltage level information by associating the determined difference between the response and the reference response with corresponding voltage level information.

[0016] According to one embodiment of the circuit, the difference between the response and the reference response comprises a phase difference.

[0017] According to one embodiment of the circuit, the circuit comprises a coupling circuit configured to allow passage of the test signal from the impedance detector to the passive sensing element and to provide DC decoupling between the passive sensing element and the impedance detector.

[0018] According to one embodiment of the circuit, the coupling circuit is configured to capacitively couple the passive sensing element and the impedance detector. Additionally or alternatively, the coupling circuit may be configured to inductively couple the passive sensing element and the impedance detector.

[0019] According to one embodiment, the circuit may further comprise a voltage divider for coupling the passive sensing element between the measuring point and the reference point.

[0020] According to one embodiment of the circuit, the reference circuit is designed to replicate an impedance of the coupling circuit.

[0021] According to one embodiment, the reference circuit is configured to store a result of a previous measurement and to output the reference response based on the stored result of the previous measurement.

[0022] According to a further embodiment, a method for measuring a voltage is provided. The method comprises coupling a passive sensing element between a measurement point and a reference point. The passive sensing element has a voltage-dependent impedance. For example, the passive sensing element may comprise a varactor, a varicap diode, and / or a field-effect transistor. The method further comprises supplying a test signal to the passive sensing element. The method further comprises receiving a response to the test signal from the passive sensing element through the coupling circuit and receiving a reference response from a reference circuit. The method further comprises detecting the impedance of the passive sensing element by evaluating the response and the reference response.The method further comprises converting a result of the evaluation of the response and the reference response into voltage level information.

[0023] According to one embodiment of the method, the test signal has a constant frequency. The frequency of the test signal can be selected from several frequencies.

[0024] According to one embodiment of the method, the test signal is a pulse signal.

[0025] According to one embodiment, the method further comprises evaluating the response and the reference response by determining a difference between the response and the reference response.

[0026] According to one embodiment, the method further comprises determining the voltage level information by associating the determined difference between the response and the reference response with corresponding voltage level information.

[0027] According to one embodiment of the method, the difference between the response and the reference response comprises a phase difference.

[0028] According to one embodiment of the method, the coupling of the passive detection element between the measuring point and the reference point can be achieved by a voltage divider.

[0029] According to one embodiment of the method, the method further comprises supplying the test signal to the passive sensing element through a coupling circuit. In this case, the coupling circuit can provide DC decoupling with respect to the passive sensing element.

[0030] According to one embodiment of the method, the reference circuit replicates an impedance of the coupling circuit. The impedance detector can also supply the test signal to the reference circuit. The reference response can then be received as a further response to the test signal from one or more circuit elements of the reference circuit. The further response can be measured during regular operation of the circuit, e.g., at substantially the same time as the response from the passive sensing element.

[0031] According to one embodiment of the method, the reference response is based on a result of a previous measurement. The result of the previous measurement and / or the reference response can be stored in the reference circuit. For example, the reference response can be measured and stored during a calibration phase in which one or more known voltages are applied to the passive sensing elements and one or more corresponding responses to the test signal are measured and then stored to be used as reference responses.

[0032] The above summary is intended only to provide a brief overview of some embodiments and is not to be considered limiting, as other embodiments may employ other features. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a voltage measurement circuit according to one embodiment. Fig. 2 shows an embodiment of an impedance detection in the voltage measuring circuit. Fig. 3 shows another embodiment of an impedance detection in the voltage measuring circuit. Fig. 4 shows yet another embodiment of impedance detection in the voltage measuring circuit. Fig. 5 shows exemplary impedance characteristics of sensing elements that may be used according to one embodiment. Fig. 6 is a flowchart illustrating a method according to one embodiment. DETAILED DESCRIPTION

[0033] Various embodiments will be discussed below with reference to the accompanying drawings. It should be noted that these embodiments are given merely as illustrative examples and are not to be construed as limiting. For example, although embodiments may be described as including several features or elements, this should not be construed to indicate that all of these features or elements are necessary for implementation. Rather, some of these features or elements may be omitted from other embodiments and / or may be replaced by alternative features or elements. In addition to the features or elements explicitly shown in the drawings or described herein, other features or elements may be provided, for example, features or elements used in conventional power supply circuits.

[0034] Fig. 1 illustrates a measuring circuit 100 for measuring a voltage U between a measuring point 101 and a reference point 102. The measuring point 101 and the reference point 102 may correspond to terminals of a circuit or a circuit component, e.g. terminals of a battery, or various types of internal or external circuit nodes.

[0035] In the illustrated example, the measuring circuit 100 is provided with a passive detection element 110, an impedance detector 120, an AC coupling circuit 130, a converter 140, a reference circuit 150, and a DC coupling circuit 160. Although Fig. While Figure 1 illustrates the impedance detector 120, the AC coupling circuit 130, the converter 140, and the reference circuit 150 as separate components, it should be noted that functionalities of the illustrated components could also be combined. For example, the reference circuit 150 could be implemented as an additional functionality of the impedance detector 120.

[0036] The passive sensing element 110 has a voltage-dependent impedance Z. For example, the passive sensing element 110 may correspond to or include a varactor, a varicap diode, a high-voltage diode, or a field-effect transistor, e.g., a power MOS field-effect transistor (MOS: metal-oxide-semiconductor). In the latter case, a drain-source capacitance may vary depending on a voltage applied between the drain and source of the power MOS field-effect transistor. In some scenarios, the passive sensing element 110 may also include a combination of two or more of the aforementioned circuit elements.

[0037] By means of the DC coupling circuit 160, the passive sensing element 110 is coupled between the measuring point 101 and the reference point 102. As illustrated, the DC coupling circuit 160 includes a first resistor 161 and a second resistor 162. The first resistor 161, the passive sensing element 110, and the second resistor 162 are connected in series between the measuring point 101 and the reference point 102. In some examples, the DC coupling circuit 160 may further include a voltage divider configured to apply a certain portion of the voltage U between the measuring point 101 and the reference point 102 to the passive sensing element 110. The voltage divider may be implemented, for example, by an optional further resistor 163 coupled in parallel with the passive sensing element 110. The resistance values ​​of the resistors 161, 162 can be in the range from 50 kΩ to 500 kΩ, e.g. about 100 kΩ.Together with the capacitance of the passive sensing element 110, the resistors 161, 162 can form a low-pass filter. As a result, the current flowing through the measuring circuit 100 between the measuring point 101 and the reference point 102 can be minimized. It is noted that other implementations of the DC coupling circuit 160 could also be used. For example, at least one of the resistors 161, 162 could be omitted.

[0038] Due to the coupling of the passive sensing element 110 to the measuring point 101 and the reference point 102, the impedance Z of the passive sensing element 110 varies depending on the voltage U between the measuring point 101 and the reference point 102. The impedance detector 120 is designed to detect the variable impedance Z of the passive sensing element 110. For this purpose, the impedance detector 120 is coupled to the passive sensing element 110 via the AC coupling circuit 130. The AC coupling circuit 130 is designed to provide an AC coupling of the passive sensing element 110 and the impedance detector 120. At the same time, the AC coupling circuit 130 is designed to provide a DC decoupling of the passive sensing element 110 and the impedance detector 120. In the example from Fig. 1, the impedance detector 120 and the converter 140 are connected to a reference potential U Ref, e.g. a supply voltage chain, and the measuring point 101 and the reference point 102 and the passive detection element 110 have no DC coupling to this reference potential U Ref on.

[0039] Accordingly, the measuring point 101 and the reference point 102 can be arranged in a first voltage domain, while the impedance detector 120 is arranged in a second voltage domain that is separate from the first voltage domain, e.g., galvanically or otherwise isolated. For example, the first voltage domain could be a high-voltage domain, with the voltage U between the measuring point 101 and the reference point 102 being in the range of up to 400 V to 800 V. In comparison, the impedance detector 120 and the converter 140 are operated with lower voltages, e.g., in the range of 5 V to 50 V, such as 12 V. Since the measuring circuit 100 uses only passive components in the first voltage domain, no power supply is required in the first voltage domain.

[0040] In the illustrated example, the AC coupling circuit 130 includes a first capacitor 131 and a second capacitor 132. The first capacitor 131 connects a first terminal of the passive sensing element 110 to the impedance detector 120. The second capacitor 132 connects a second terminal of the passive sensing element 110 to the impedance detector 120. Accordingly, the AC coupling circuit 130 in the example of Fig. 1 on a capacitive coupling of the passive sensing element 110 to the impedance detector 120. However, it is noted that alternatively or additionally, an inductive coupling could be used. Fig. 4 shows an example of a configuration in which the AC coupling circuit 130 is based on inductive coupling.

[0041] In the illustrated example, the impedance detector 120 can be configured to detect the impedance Z of the passive sensing element 110 in the following manner: The impedance detector 120 supplies a test signal via the AC coupling circuit 130 to the passive sensing element 110 and the reference circuit 150. The test signal can be a pulse signal, in particular a rectangular pulse signal. The pulse signal can be formed from a sequence of pulses with a constant frequency. Alternatively, the pulse signal could also be formed from a single pulse. Furthermore, the impedance detector 120 receives a first response to the test signal from the passive sensing element 110 via the AC coupling circuit 130 and receives a second response to the test signal from the reference circuit 150. The second response is also referred to herein as a reference response.The impedance detector 120 can then determine the impedance Z by evaluating the first response and the second response. In particular, the impedance detector 120 can evaluate a difference between the first response and the second response.

[0042] In a modified example, the reference circuit 150 may provide the second response based on stored information from a previous measurement, e.g., during a calibration phase with known voltages applied to the passive sensing element 110 or to circuit elements of the reference circuit 150. The second response may then be based on information stored in a memory of the reference circuit 150.

[0043] As mentioned above, the impedance detector 120 can operate with a constant test signal frequency, meaning variations in the test signal frequency are not necessary to estimate the impedance. However, the constant test signal frequency could be selectable or adjustable in some scenarios, e.g., for the purpose of reducing the influence of different noise sources on the measurement process. Such noise sources could, for example, include other circuitry that generates noise in a certain frequency range. By appropriately selecting the test signal frequency, the measurement process can be performed with a test signal frequency that avoids interference from other circuits or other noise sources.

[0044] During a measurement of the voltage U by the measuring circuit 100, the test signal generates an AC signal at the passive sensing element 110, and the properties of this AC signal are determined by the impedance Z of the passive sensing element 110. For example, the impedance Z can determine a phase of the AC signal generated at the passive sensing element 110. Furthermore, the impedance Z can determine a frequency of the AC signal generated at the passive sensing element 110. In some scenarios, the passive sensing element 110 and parts of the AC coupling circuit 130 could form an oscillator, and the AC signal generated at the passive sensing element can correspond to an oscillator signal with a frequency determined by the impedance Z.

[0045] The characteristics of the AC signal generated at the passive sensing element 110 are represented by the first response received by the impedance detector. The first response may include properties of a transfer function H m of a circuit formed by the AC coupling circuit 130 and the passive sensing element 110. The second response may indicate properties of a transfer function H r of the reference circuit 150. The reference circuit 150 can replicate properties of the AC coupling circuit 130 and / or the passive sensing element 110 that do not depend on the voltage U between the measurement point 101 and the reference point 102.

[0046] By comparing the first response with the second response from the reference circuit, the impedance detector 120 can estimate the impedance Z. For example, a phase difference between the first response and the second response can be evaluated, and the impedance Z can be determined from the phase difference. Furthermore, a frequency difference between the first response and the second response can be evaluated, and the impedance Z can be determined from the frequency difference.

[0047] The converter 140 receives the impedance Z detected by the impedance detector 120 and determines voltage level information representing the voltage U between the measuring point 101 and the reference point 102 from the impedance Z. For this purpose, the converter 140 may use a stored mapping of impedance values ​​to corresponding voltage level information. In the illustrated example, the voltage level information is related to a measured voltage value U mwhich is represented, for example, by a digital value. However, it is noted that other ways of representing the voltage level information corresponding to the voltage U could be used as an alternative or in addition, e.g. an indicator that the voltage U is above a certain threshold, an indicator that the voltage U is below a certain threshold, or an indicator that the voltage U is within a certain voltage range. It is further noted that the voltage level information can be represented in the form of a digital signal or in the form of an analog signal.

[0048] Fig. Figure 2 illustrates an example of an implementation of the detection of the impedance Z by the impedance detector 120. In the example of Fig. 2, the AC coupling circuit 130 includes capacitors 131 and 132. The capacitor 132 couples a first terminal of the passive sensing element 110 to a test signal terminal P of the impedance detector 120. The capacitor 131 couples the passive sensing element to a measurement signal terminal M of the impedance detector 120. In the example of Fig. 2, the reference circuit 150 includes a capacitor 151.

[0049] The capacitor 151 couples the first terminal of the passive sensing element 110 to a reference terminal R of the impedance detector 120. The capacitor 151 can replicate properties of the capacitor 131, e.g., can have a similar capacitance. Optionally, the reference circuit 150 can also include a reference impedance Z Ref The reference impedance Z Refcan replicate the impedance of the passive sensing element 110 at a certain voltage U, but without depending on the voltage U between the measuring point 101 and the reference point 102.

[0050] In the example of Fig. 2, the impedance detector 120 can detect the impedance Z of the passive sensing element 110 in the following way: The impedance detector 120 outputs the test signal at the test signal terminal P. The test signal can be, for example, a rectangular pulse or a sequence of rectangular pulses. Furthermore, the impedance detector 120 receives a first response to the test signal at the measuring terminal M and a second response to the test signal at the reference terminal R. The first response reflects the transfer function of the circuit formed by the AC coupling circuit 130, i.e., the capacitors 131, 132, and the passive sensing element 110. The second response reflects the transfer function formed by the capacitor 132 and the capacitor 151, and optionally the reference impedance Z Ref, is formed. Since the capacitor 151 can replicate properties of the capacitor 131, the second response can reflect similar properties to a circuit formed from the AC coupling circuit 130 without the passive sensing element 110. Accordingly, the second response can also reflect, for example, effects of temperature change or aging in a similar manner to the first response. In the example of Fig. 2, the impedance detector 120 may detect the impedance Z by evaluating a phase difference of the first response received at the measurement terminal and the second response received at the reference terminal.

[0051] In a modified example, the test signal may include voltage pulses delivered by impedance detector 120 to terminal P, and the phase relationship between the voltage pulses and resulting currents at terminal M and optionally at terminal R is used to determine the impedance Z of passive sensing element 110. The first response and the second response may correspond to measured currents, respectively. In this modified example, the waveform of the voltage pulses may be a sine wave, triangular, or rectangular, or a combination of different waveforms.

[0052] Fig. Figure 3 illustrates another example of an implementation of the detection of the impedance Z by the impedance detector 120. In the example of Fig. 3, the impedance detector includes a measuring circuit 121, a reference measuring circuit 122, and an evaluation circuit 123. The AC coupling circuit 130 includes capacitors 131 and 132. The capacitor 132 couples a first terminal of the passive detection element 110 to a test signal terminal P of the measuring circuit 121. The capacitor 131 couples the passive detection element to a measurement signal terminal M of the measuring circuit 121. In the example from Fig. 3, the reference circuit 150 includes a first capacitor 152 and a second capacitor 153 and optionally a reference impedance Z Ref. The capacitors 152, 153 couple a test signal terminal P of the reference measurement circuit 122 to a reference terminal R of the reference measurement circuit 122. The capacitor 152 can replicate properties of the capacitor 131, e.g., can have a similar capacitance. The capacitor 153 can replicate properties of the capacitor 132, e.g., can have a similar capacitance. The optional reference impedance Z Ref can replicate the impedance of the passive sensing element 110 at a certain voltage U, but without depending on the voltage U between the measuring point 101 and the reference point 102. It is noted that the capacitors 152, 153 could also be replaced by a single capacitor replicating the combined properties of the capacitors 131, 132, e.g., by a single capacitor with a capacitance corresponding to a series connection of the capacitors 131 and 132.

[0053] In the example of Fig. 3, the impedance detector 120 can detect the impedance Z of the passive sensing element 110 in the following manner: The measuring circuit 121 outputs the test signal at the test signal terminal P of the measuring circuit 121. The test signal can be, for example, a rectangular pulse or a sequence of rectangular pulses. Furthermore, the measuring circuit 121 receives a first response to the test signal at the measuring terminal M of the measuring circuit 121. The reference measuring circuit 122 outputs the test signal at the test signal terminal P of the reference measuring circuit 122. Furthermore, the reference measuring circuit 122 receives a second response to the test signal at the reference terminal R of the reference measuring circuit 122. The first response reflects the transfer function H mthe circuit formed by the AC coupling circuit 130, i.e., the capacitors 131, 132, and the passive sensing element 110. The second response reflects the transfer function formed by the reference circuit 150, i.e., the capacitor 152 and the capacitor 153. Since the capacitors 152, 153 can replicate properties of the capacitors 131, 132, the second response can reflect similar properties to a circuit formed from the AC coupling circuit 130 without the passive sensing element 110. Accordingly, the second response can also reflect, for example, the effects of temperature change or aging in a similar manner to the first response.

[0054] In the example of Fig. 3, the measuring circuit 121 provides information about properties of the transfer function H mto the evaluation circuit 123. This information may, for example, include information about a phase shift, frequency shift, and / or amplitude variation of the first response with respect to the test signal. Similarly, the reference measurement circuit 122 provides information about properties of the transfer function H r to the evaluation circuit 123. This information may, for example, include information about a phase shift, frequency shift, and / or amplitude variation of the second response with respect to the test signal. Based on the received information, the evaluation circuit 123 determines the impedance Z of the passive sensing element 110. This may be based on determining a difference between the information received from the measuring circuit 121 and the information received from the reference measuring circuit 122, e.g., a phase difference, a frequency difference, and / or an amplitude difference.

[0055] Fig. Figure 4 illustrates another example of an implementation of the detection of the impedance Z by the impedance detector 120. In the example of Fig. 4, the impedance detector includes a measuring circuit 121, a reference measuring circuit 122, and an evaluation circuit 123. The AC coupling circuit 130 includes a first transformer 133, a second transformer 134, and a capacitor 135. A first side of the transformer 134 is coupled to a test signal terminal P of the measuring circuit 121, and a second side of the transformer 134 is connected to a first terminal of the passive sensing element 110. A first side of the transformer 133 is coupled to a measurement signal terminal M of the measuring circuit 121, and a second side of the transformer 133 is connected to a second terminal of the passive sensing element 110. The capacitor 135 is coupled between the second side of the transformer 133 and the second side of the transformer 134. In the example of Fig. 4, the reference circuit 150 includes a first transformer 154, a second transformer 155 and a capacitor 156 and optionally a reference impedance Z RefA first side of the transformer 155 is coupled to a test signal terminal P of the reference measurement circuit 122. A first side of the transformer 154 is coupled to a reference terminal R of the reference measurement circuit 122. On the one hand, a second side of the transformer 133 and a second side of the transformer 134 are directly coupled to each other. On the other hand, the capacitor 135 is coupled between the second side of the transformer 133 and the second side of the transformer 134. The transformers 154, 155 and the capacitor 156 accordingly couple the test signal terminal P of the reference measurement circuit 122 to the reference terminal R of the reference measurement circuit 122. The transformer 154 can replicate properties of the transformer 133, for example, can have a similar number of windings, similar inductance values, or the like. The transformer 155 can replicate properties of the transformer 134, for example,have a similar number of windings, similar inductance values, or the like. Capacitor 156 may replicate properties of capacitor 135, e.g., may have a similar capacitance. The optional reference impedance Z. Ref can replicate the impedance of the passive sensing element 110 at a certain voltage U, but without depending on the voltage U between the measuring point 101 and the reference point 102.

[0056] In the example from Fig. 4, the impedance detector 120 can detect the impedance Z of the passive sensing element 110 in the following manner: The measuring circuit 121 outputs the test signal at the test signal terminal P of the measuring circuit 121. The test signal can be, for example, a rectangular pulse or a sequence of rectangular pulses. Furthermore, the measuring circuit 121 receives a first response to the test signal at the measuring terminal M of the measuring circuit 121. The reference measuring circuit 122 outputs the test signal at the test signal terminal P of the reference measuring circuit 122. Furthermore, the reference measuring circuit 122 receives a second response to the test signal at the reference terminal R of the reference measuring circuit 122. The first response reflects the transfer function H mthe circuit formed by the AC coupling circuit 130, i.e., the transformers 133, 134 and the capacitor 135, and the passive sensing element 110. The second response reflects the transfer function formed by the reference circuit 150, i.e., the transformers 154, 155 and the capacitor 156. Since the transformers 154, 155 and the capacitor 156 can replicate properties of the transformers 133, 134 and the capacitor 135, the second response can reflect similar properties to a circuit formed from the AC coupling circuit 130 without the passive sensing element 110. Accordingly, the second response can also reflect, for example, effects of temperature change or aging in a similar manner to the first response.

[0057] In the example of Fig. 4, the measuring circuit 121 provides information about properties of the transfer function H mto the evaluation circuit 123. This information may, for example, include information about a phase shift, frequency shift, and / or amplitude variation of the first response with respect to the test signal. Similarly, the reference measurement circuit 122 provides information about properties of the transfer function H r to the evaluation circuit 123. This information may, for example, include information about a phase shift, frequency shift, and / or amplitude variation of the second response with respect to the test signal. Based on the received information, the evaluation circuit 123 determines the impedance Z of the passive sensing element 110. This may be based on determining a difference between the information received from the measuring circuit 121 and the information received from the reference measuring circuit 122, e.g., a phase difference, a frequency difference, and / or an amplitude difference.

[0058] In some scenarios, for example if a change in the properties of the coupling elements 131, 132 or 133, 134, e.g. due to aging, process variation, temperature or the like, can be neglected compared to effects of the voltage applied to the passive sensing element, the reference measuring circuit 122 can be made of Fig. 3 or Fig. 4 can be omitted. In this case, the reference circuit 150 may provide a previously stored reference response, e.g., during a calibration phase with known voltages applied to the passive sensing element 110.

[0059] Fig. Figure 5 illustrates exemplary impedance characteristics of passive sensing elements that can be used in the measurement circuit. In particular, Fig. 5 a dependence of the detected impedance Z and the voltage U between the measuring point 101 and the reference point 102. In Fig. 5, filled circles and filled squares show linear dependencies that can be achieved, for example, by using a varactor as the passive sensing element 110. The different slopes of the linear dependence can be due to a different structure or doping profile of the varactors. Furthermore, Fig. 5, filled triangles represent a nonlinear, saturating dependence, which can be achieved, for example, by using a MOS field-effect transistor or a diode as the passive sensing element 110. The measuring circuit 100 may include a memory, e.g., a non-volatile memory such as a flash memory, an EEPROM (electrically erasable programmable read-only memory), or an OTP (one-time programmable) memory, that stores information representing the characteristics of the passive sensing element 110. For example, the information representing the characteristics of the passive sensing element 110 may be stored in a table relating values ​​of the voltage U to values ​​of the impedance. In some scenarios, the measuring circuit 100 may also interpolate between the stored values.The stored information representing the characteristics of the passive sensing element 110 can be measured during the manufacture of the measuring circuit 100, e.g., during a production test phase. Alternatively or additionally, the stored information representing the characteristics of the passive sensing element 110 could also be measured in a calibration mode of the measuring circuit 100.

[0060] In some scenarios, instead of using the impedance Z, other values ​​can be used in the impedance evaluation. For example, the phase shift, frequency, attenuation, or the like can be stored as reference information for known voltages U at the passive sensing element 110. In some scenarios, these values ​​can be used directly to determine the applied voltage U, instead of determining an impedance value as an intermediate result.

[0061] The measuring circuit 100 of the illustrated examples can be applied in various scenarios. For example, the measuring circuit 100 could be used to measure an output voltage of a high-voltage battery, e.g., a battery with an output voltage in the range of 400 V to 800 V, such as is used in hybrid or electric vehicles. The measuring point 101 and the reference point 102 could then correspond to the terminals of the battery. The impedance detector 120, the converter 140, and typically one or more further control devices that measure the measured value U m The batteries receiving the voltage U can then be located in a low-voltage domain, which is defined, for example, with reference to the vehicle's chassis ground. The battery can be isolated from the low-voltage domain, for example, from the vehicle's chassis ground.

[0062] In some applications, e.g., in DC / DC converters, motor drives, or the like, it may not be necessary to measure the voltage U with high accuracy. For example, it might be sufficient to obtain an indication of a voltage range in which the voltage U currently lies, or an indication of a trend of the voltage U, e.g., whether the voltage is increasing or decreasing. The latter could, for example, indicate whether a switch is fully closed or open, whether a fuse is blown, whether a capacitor is discharged, whether insulation is intact or leaking, or the like. In such scenarios, the measuring circuit 100 can provide an efficient solution because it can be implemented with low complexity and low manufacturing costs. The elements of the AC coupling circuit 130, the impedance detector 120, and the converter 140 can be formed in a single integrated circuit.In this case, the capacitors of the AC coupling circuit can be insulated, for example, by oxide layers. The ones used in the example from . Fig. 4 transformers can be efficiently implemented in the integrated circuit by using coreless transformer (CT) technology.

[0063] Fig. Figure 6 shows a flowchart illustrating a method for measuring a voltage. The method can be used to implement the concepts described above. The method can be implemented, for example, in the measurement circuit 100 described above.

[0064] At 610, a passive sensing element is coupled between a measurement point and a reference point. The passive sensing element has a voltage-dependent impedance. The passive sensing element may, for example, correspond to the above-mentioned passive sensing element 110. The measurement point may correspond to the above-mentioned measurement point 101. The reference point may correspond to the above-mentioned reference point 102. The passive sensing element may, for example, correspond to or include a varactor, a varicap diode, and / or a field-effect transistor.

[0065] At 620, a test signal is delivered to the passive sensing element through a coupling circuit. Furthermore, the test signal may be delivered to a reference circuit. The test signal may be a pulse signal, e.g., with a substantially rectangular waveform. The test signal may have a constant frequency. In some scenarios, the frequency of the test signal may be selectable from multiple frequencies.

[0066] The reference circuit may, for example, correspond to the reference circuit 150, as in the examples from Fig. 1, Fig. 2, Fig. 3 or Fig. 4. The coupling circuit provides DC decoupling with respect to the passive sensing element. The coupling circuit may, for example, correspond to the AC coupling circuit 130, as in the examples of Fig. 1, Fig. 2, Fig. 3 or Fig. 4. The coupling circuit can be based on capacitive coupling, as in the examples from Fig. 1, Fig. 2 and Fig. 3, or on inductive coupling, as in the examples from Fig. 4. Furthermore, the coupling circuit could also be based on a combination of capacitive coupling and inductive coupling. The reference circuit can be configured to replicate an impedance of the coupling circuit.

[0067] At 630, a response to the test signal is received from the passive sensing element via the coupling circuit. At 640, a reference response to the test signal is received from a reference circuit. The reference response may be received from a reference circuit that has been stimulated similarly to the passive sensing element to which, for example, the test signal was applied at 620. Accordingly, in some scenarios, the test signal may be delivered to the reference circuit and the reference response may be received as a further response to the test signal from one or more circuit elements, such as elements 151, 152, 153, 154, 155, 156, Z Ref , the reference circuit. Furthermore, the reference response can be defined by information previously stored, e.g., during a calibration phase. The reference response can therefore be based on a previous measurement and stored in the reference circuit.

[0068] At 650, the impedance of the passive sensing element is detected by evaluating the response and the reference response. In some scenarios, the response and the reference response can be evaluated by determining a difference between the response and the reference response, e.g., a phase difference, a frequency difference, and / or an amplitude difference.

[0069] At 660, the result of evaluating the response and the reference response, e.g., an impedance value or a difference between the response and the reference response, is converted into voltage level information. In some scenarios, this may include determining the voltage level information based on a mapping of differences between the response and the reference response to corresponding voltage level information. Such a mapping may, for example, be based on a characteristic of the passive sensing element, as in Fig.5. The voltage level information determined at 660 may represent a value of the voltage between the measurement point and the reference point. Additionally or as an alternative, the voltage level information may represent the voltage in the form of an indicator that the voltage between the measurement point and the reference point is above a certain threshold, an indicator that the voltage between the measurement point and the reference point is below a certain threshold, or an indicator that the voltage between the measurement point and the reference point is within a certain voltage range. In some examples, the voltage level information may be represented in the form of an analog signal, e.g., a voltage signal or a current signal. In other examples, the voltage level information may be represented in the form of a digital signal, e.g.,represented in a binary coded data word that encodes a numerical value and / or a logical state.

[0070] It is understood that embodiments as explained above may be subject to various modifications. For example, the measurement circuit 100 may be used in various applications where a measurement of a voltage across an insulating barrier to a separate voltage domain is required. Furthermore, various types of coupling the impedance detector 120 to the passive sensing element 110 could be used. Furthermore, the measurement circuit 100 could be implemented based on various types of passive sensing elements with a voltage-dependent impedance. Various types of circuit technology may be used to implement the measurement circuit 100 or components thereof.

Claims

[1] Circuit (100) for measuring a voltage, the circuit (100) comprising: a passive detection element (110) designed to be coupled between a measuring point (101) and a reference point (102), wherein the passive Sensing element (110) has a voltage-dependent impedance; a reference circuit (150) configured to provide a reference response; an impedance detector (120) configured to detect the voltage-dependent impedance of the passive sensing element (110) by supplying a test signal to the passive sensing element (110) and evaluating a response to the test signal from the passive sensing element (110) and the reference response provided by the reference circuit (150); and a converter circuit (140) configured to convert a result of evaluating the response and the reference response into voltage level information. [2] The circuit (100) of claim 1, wherein the test signal has a constant frequency. [3] The circuit (100) of claim 1 or 2, wherein the test signal is a pulse signal. [4] The circuit (100) of any preceding claim, wherein the impedance detector (120) is configured to evaluate the response and the reference response by determining a difference between the response and the reference response. [5] The circuit (100) of claim 4, wherein the converter circuit (140) is configured to determine the voltage level information by associating the determined difference between the response and the reference response with corresponding voltage level information. [6] The circuit (100) of claim 4 or 5, wherein the difference between the response and the reference response comprises a phase difference. [7] Circuit (100) according to one of the preceding claims, further comprising: a coupling circuit (130) configured to to allow passage of the test signal from the impedance detector (120) to the passive sensing element (110) and to provide DC decoupling between the passive sensing element (110) and the impedance detector (120). [8] The circuit (100) of claim 7, wherein the coupling circuit (130) is configured to capacitively couple the passive sensing element (110) and the impedance detector (120). [9] The circuit (100) of claim 7 or 8, wherein the coupling circuit (130) is configured to inductively couple the passive sensing element (110) and the impedance detector (120). [10] The circuit (100) of any one of claims 7 to 9, wherein the reference circuit (150) is configured to replicate an impedance of the coupling circuit (130). [11] Circuit (100) according to one of the preceding claims, wherein the impedance detector (120) is further configured to supply the test signal to the reference circuit (150), and wherein the reference response comprises a further response to the test signal from one or more circuit elements (151, 152, 153, 154, 155, 156, Z Ref ) of the reference circuit (150). [12] The circuit (100) of any preceding claim, wherein the reference circuit (150) is configured to store a result of a previous measurement and to output the reference response based on the stored result of the previous measurement. [13] A method for measuring a voltage, the method comprising: - coupling a passive sensing element (110) between a measuring point (101) and a reference point (102), wherein the passive sensing element (110) has a voltage-dependent impedance; - supplying a test signal to the passive sensing element (110); - receiving a response to the test signal from the passive sensing element (110) via the coupling circuit (130); - receiving a reference response from a reference circuit (150); - detecting the voltage-dependent impedance of the passive sensing element (110) by evaluating the response and the reference response; and - Converting a result of the evaluation of the response and the reference response into voltage level information. [14] The method of claim 13, wherein the test signal has a constant frequency. [15] A method according to claim 13 or 14, wherein the test signal is a pulse signal. [16] The method of any one of claims 13 to 15, wherein evaluating the response and the reference response comprises determining a difference between the response and the reference response. [17] The method of claim 16, wherein the voltage level information is determined by associating the difference between the response and the reference response with corresponding voltage level information. [18] A method according to claim 16 or 17, wherein the difference between the response and the reference response comprises a phase difference. [19] A method according to any one of claims 13 to 18, further comprising: Supplying the test signal to the reference circuit (150) and receiving the reference response as a further response to the test signal from one or more circuit elements (151, 152, 153, 154, 155, 156, Z Ref ) of the reference circuit (150). [20] A method according to any one of claims 13 to 19, wherein the reference response is based on a result of a previous measurement and is stored in the reference circuit (150). [21] A method according to any one of claims 13 to 20, further comprising: Providing the test signal through a coupling circuit (130) to the passive sensing element (110), wherein the coupling circuit (130) provides DC decoupling with respect to the passive sensing element (110).

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