Apparatus and method for quiescent current measurement of vehicle sensor

Abstract

The application relates to a device (10) for measuring a quiescent current of a vehicle sensor (12), in particular via a peripheral sensor interface 5, PSI5, comprising:-a voltage source (14) and a shunt resistor (16) arranged between the voltage source (14) and a reference node, the shunt resistor (16) having a first terminal and a second terminal; -a comparator (22),-an evaluation unit (26) for evaluating the comparator output signal and outputting an evaluation unit output signal; -a control unit (30) configured to receive the evaluation unit output signal and to output a control unit output signal based on the received evaluation unit output signal; and-a digital-to-analog conversion unit (28) configured to convert the control unit output signal into an offset signal and feed the offset signal to the input path of the comparator (22).

Description

TECHNICAL FIELD

[0001] The present application relates to a device for measuring the quiescent current of a vehicle sensor, in particular via a peripheral sensor interface 5 (PSI5), and a corresponding measuring method. BACKGROUND

[0002] Knowledge of the quiescent current of a vehicle sensor is crucial for the reliable operation of the vehicle sensor. Knowledge of the quiescent current of a vehicle sensor is particularly important for the control unit and the vehicle sensor to communicate via a communication interface, for example, PSI5. Only with knowledge of the quiescent current, the signals received by the vehicle sensor can be evaluated correctly, since it is possible to distinguish between the quiescent current component and signal pulses superimposed on the quiescent current signal. For example, the quiescent current can be 35 mA, while the amplitude of the current pulses for communication with the control unit is 25 mA.

[0003] In addition, the quiescent current is an important indicator of the proper functioning of a vehicle sensor. For example, if the quiescent current of a vehicle sensor deviates significantly from the typical quiescent current of this sensor, this can be interpreted as an indication that this vehicle sensor is malfunctioning.

[0004] Various devices for measuring the quiescent current are known from the prior art. However, the methods used to date exhibit strong, sometimes systematic, susceptibility to disturbances, for example, EMC.

[0005] DE 102007003542 A1 describes a method of controlling a personal protection system, which method provides a sensor signal and controls the personal protection system in dependence on the sensor signal. To provide the sensor signal, the sensor signal is processed by first and second signal processing units to generate first and second comparison signals. The first and second comparison signals are compared with one another to generate an input signal for a decoder, wherein the decoder provides a decoded input signal for controlling the personal protection system.

[0006] DE 102016116059 A1 describes a method for detecting whether a data bus capacitor of a data bus interface is present and functioning properly. In this method, first, a first voltage level having a predetermined or predeterminable voltage value is provided relative to a reference potential. Then, a second voltage level is determined, the voltage value of which relative to the reference potential depends on the voltage value of the data bus terminal relative to the reference potential. A power supply line is connected to the data bus terminal. Furthermore, a data bus current value of a data bus current flowing from the PSI5 data bus connection is also determined. The determined data bus current value of the data bus current is compared with a first threshold value, wherein a comparison result is generated. Finally, it is determined from the comparison result whether the data bus capacitor is functioning properly and / or whether the data bus capacitor is present. SUMMARY

[0007] Based on the above problems, the object of the present invention is to provide a device for measuring the quiescent current of a vehicle sensor, which provides reliable measurement results even in the presence of disturbances.

[0008] To achieve the above object, the present invention proposes a device for measuring the quiescent current of a vehicle sensor, in particular via a peripheral sensor interface 5 (i.e. PSI5), comprising:

[0009] - a voltage source and a shunt resistor arranged between the voltage source and a reference node, the shunt resistor having a first terminal and a second terminal;

[0010] - a comparator configured to: - receive at its first input a voltage value dependent on the voltage at the first terminal of the shunt resistor; - receive at its second input a voltage value dependent on the voltage at the second terminal of the shunt resistor; and - provide at its output a comparator output signal dependent on these two input values; the comparator output signal having a bandwidth f1 ;

[0011] - an evaluation unit for evaluating the comparator output signal and outputting an evaluation unit output signal;

[0012] - a control unit configured to receive the evaluation unit output signal and output a control unit output signal in dependence on the received evaluation unit output signal; and

[0013] - an offset generator configured to convert the control unit output signal into an offset signal and to feed the offset signal to the comparator or to an input path of the comparator; wherein,

[0014] - the evaluation unit is configured to oversample the comparator output signal with a frequency f2, wherein f2≥ 2•f1.

[0015] The device according to the present invention enables a robust measurement of the quiescent current, providing reliable measurement results even in the presence of disturbances. In particular, the oversampling of the comparator output signal with a frequency f2 enables a reliable measurement of the quiescent current, which is not significantly affected by noise at the frequency f1.

[0016] In previously known measuring devices, in particular in devices used in conjunction with PSI5, the measurement data is evaluated at a first frequency of f1 = 1 MHz. In practice, problems are often observed when there are interference signals of a frequency which also has f ~ 1 MHz. According to the device according to the application, on the one hand, by selectively oversampling the comparator output signal, reliable measurement results can be obtained even in the presence of interference signals of a frequency of approximately 1 MHz. On the other hand, the device according to the application can retain the components and evaluation frequencies in the previously employed measuring devices.

[0017] The vehicle sensor can be connected to the reference node to measure a static current.

[0018] The shunt resistor, often referred to as shunt or measurement resistor, has a low resistance.

[0019] The input of the comparator is connected, at least indirectly, to the terminals of the shunt resistor. Thereby, the comparator can compare the voltage values applied across the two terminals of the shunt resistor. To this end, the comparator can be directly resting on the terminals of the shunt resistor. Alternatively, a separate element can also be provided between the terminals of the shunt resistor and the input of the comparator to, for example, adjust the voltage values to a range which can be evaluated by the comparator.

[0020] The comparator is configured to output a "high" signal in the event that the voltage at the positive input is greater than the voltage at the negative input. In the event that the voltage at the positive input is not greater than the voltage at the negative input, the comparator outputs a "low" signal.

[0021] The comparator can be configured to receive and evaluate an offset signal at one of its inputs. Furthermore, an adjustable offset can be generated in the comparator. Thus, the present application is not limited to a specific way of providing an offset signal to the comparator.

[0022] In the device according to the application, the evaluation unit can be configured to determine whether the sampled comparator output signal is set to "high" at least n times within a measurement period T = 1 / f1, wherein, preferably, n = 1 / 2 x f2 / f1. For example, f1 = 1 MHz and f2 = 12 MHz, wherein the evaluation unit is configured to determine whether the sampled comparator output signal is set to "high" at least six times within a measurement period T = 1 µs. In this respect, the evaluation unit can be configured to majority-decide the received values and to provide an output signal which depends on whether the received values are set to "high" at least n = 1 / 2 x f2 / f1 times. Alternatively, n can be any value between 1 and f2 / f1.

[0023] Furthermore, the evaluation unit can be configured to generate the evaluation unit output signal depending on whether at least a first predetermined proportion of the values received within the measurement period T = 1 / f1 is set to "high" or depending on whether at least a first predetermined proportion of the values received within the measurement period T = 1 / f1 is set to "low".

[0024] According to a preferred embodiment of the device according to the application, the evaluation unit can be configured to output "1" if at least a first predetermined proportion (for example, half) of the values of the comparator output signal received within the measurement period T = 1 / f1 is set to "high" and to output "0" if at least a second predetermined proportion (for example, half) of the values of the comparator output signal received within the measurement period T = 1 / f1 is set to "low". This will implement a majority decision in the evaluation unit, according to which it is determined whether the limit value is exceeded or undershot in the average sense. For example, the majority decision can be used to determine whether the static current determined in the last measurement period is too high or too low compared to the actual static current. Then, for example, the meter reading of the control unit can be reduced or increased depending on the majority decision. For example, the first frequency can be f1 = 1 MHz and the second frequency can be f2 = 12 MHz, wherein the output signal of the evaluation unit is determined as follows:

[0025]

[0026] Furthermore, in the device according to the application, the control unit can be configured to increase the current meter reading by one value when the value received from the evaluation unit is set to "1" and to reduce the current meter reading by one value when the value received from the evaluation unit is set to "0". In this way, a digital control unit is provided which can iteratively determine the static current, wherein the control unit exhibits an integral characteristic. Furthermore, the control unit can be operated at the frequency f1, but preferably uses a different temporal, linear or non-linear evaluation method to decide on the adjustment of the offset signal.

[0027] Furthermore, according to the application, preferably, an additional low-pass filter circuit is arranged at the input of the comparator. This low-pass circuit can suppress high-frequency interference signals that can occur during the measurement. This increases the robustness of the measurement device to high-frequency interference signals. The combination of oversampling and low-pass circuit can also provide the advantage that a low-pass filter with a higher cut-off frequency can be provided without the occurrence of aliasing effects (Nyquist-Shannon sampling theorem). The desired low-pass function can also be achieved by the inherent properties of the comparator.

[0028] Furthermore, in the device according to the application, the low-pass filter circuit can comprise a capacitor arranged between the two inputs of the comparator and two resistors each arranged in series with the two inputs of the comparator. This arrangement is effective in filtering out differential high-frequency interference signals, which, if not low-pass filtered, can have an adverse effect on the measurement result. This further improves the interference immunity and robustness of the device according to the application. Furthermore, this arrangement is simple and can be implemented in a cost-effective manner.

[0029] Furthermore, in the device according to the application, the cut-off frequency f c of the low-pass filter circuit can satisfy f1≤f c ≤f2 / 2, wherein preferably f1≤f c ≤1.4xf1, particularly preferably f1≤f c ≤1.3xf1or f1≤f c ≤1.2xf1, and particularly f1≤f c ≤1.1xf1. Thus, interference signals can be suppressed which would actually have a great influence on the measurement result, thereby further improving the robustness of the device according to the application. The first frequency preferably satisfies f1=1 MHz.

[0030] Furthermore, in the device according to the application, the second frequency satisfies f2≥6xf1, preferably f2≥12xf1, and particularly preferably f2≥24xf1. In particular, the first frequency can be 1 MHz and the second frequency can be 6 MHz, 12 MHz or 24 MHz. Preliminary studies have shown that by oversampling using the above-mentioned sampling frequency (f2), an extremely robust and noise- immune static current measurement can be achieved.

[0031] Furthermore, in order to achieve the above-mentioned object, a method for measuring the static current of a vehicle sensor, in particular via a peripheral sensor interface 5 (i.e. PSI 5), is proposed, the method comprising the following steps:

[0032] - receiving a first voltage value and a second voltage value at the input of the comparator and outputting a comparator output signal dependent on the two input values, wherein - the first voltage value is dependent on the voltage at the first terminal of the shunt resistor; - the second voltage value is dependent on the voltage at the second terminal of the shunt resistor; - the comparator output signal has a bandwidth f1;

[0033] - sampling the comparator output signal by means of the evaluation unit;

[0034] - evaluating the sampled comparator output signal by means of the evaluation unit and outputting an evaluation unit output signal;

[0035] - generating a control unit output signal by the control unit depending on the evaluation unit output signal and outputting the control unit output signal;

[0036] - converting the control unit output signal into an offset signal using an offset generator and feeding the offset signal to the comparator or to an input path of the comparator; wherein,

[0037] - the evaluation unit is configured to sample the comparator output signal with a frequency f2, wherein f2≥ 2 • fi.

[0038] Compared to methods known in the prior art, the method according to the present application can measure the static current of a vehicle sensor more robustly, wherein the measurement result remains unaffected even in the presence of interference signals, in particular interference signals with a frequency of fi.

[0039] Furthermore, in the method according to the present application, the evaluation unit can output an evaluation unit output signal which depends on whether at least a first predetermined proportion of the values received within a measurement period T = 1 / fi is set to "high" or output an evaluation unit output signal which depends on whether at least a second predetermined proportion of the values received within a measurement period T = 1 / fi is set to "low".

[0040] In the method according to the present application, the following method steps can preferably be provided:

[0041] - outputting "1" at the output of the evaluation unit if at least a first predeterminable proportion of the values received within a measurement period T = 1 / fi is set to "high"; and

[0042] - outputting "0" at the output of the evaluation unit if at least a second predeterminable proportion of the values received within a measurement period T = 1 / fi is set to "low".

[0043] In the method according to the present application, the following method steps can also be provided:

[0044] - increasing the current instrument reading of the control unit by one value if the value received from the evaluation unit is set to "1"; and

[0045] - decreasing the current instrument reading of the control unit by one value if the value received from the evaluation unit is set to "0".

[0046] Preferably, the method according to the present application can also comprise the following method steps:

[0047] - low-pass filtering the input signal of the comparator by using a low-pass filter circuit which is preferably arranged at the input of the comparator.

[0048] Alternatively, the low-pass filter function can also be provided by the inherent properties of the comparator and the comparator can be selected such that its manufacturing-related processing or delay properties provide the desired low-pass filter characteristics.

[0049] Furthermore, in the method according to the application, the input signal of the comparator can be low-pass filtered by using a low-pass filter circuit which comprises a capacitor arranged between the two inputs of the comparator and two resistors each arranged in series with the two inputs of the comparator.

[0050] Furthermore, the cut-off frequency of the low-pass filter circuit can satisfy f1≤f c ≤f2 / 2, wherein preferably f1≤f c ≤1.4xf1, particularly preferably f1≤f c ≤1.3xf1or f1≤f c ≤1.2xf1, and in particular f1≤f c ≤1.1xf1. According to a preferred embodiment, f1=1 MHz. As mentioned above, the desired low-pass function can be provided by a separate circuit at the inputs of the comparator or can be provided by the inherent properties of the comparator.

[0051] Finally, the second frequency f2may satisfy f2≥6xf1, preferably f2≥12xf1, particularly preferably f2≥24xf1. BRIEF DESCRIPTION OF DRAWINGS

[0052] The application will be explained in more detail below with reference to the drawings.

[0053] Figure 1 a measuring device according to the prior art is shown,

[0054] Figure 2 an embodiment of a measuring device according to the application is shown, and

[0055] Figure 3 an embodiment of a measuring method according to the application is shown. DETAILED DESCRIPTION

[0056] Figure 1A device 10 for measuring the quiescent current of a vehicle sensor 12 is shown schematically. The device 10 comprises a voltage source 14 and a shunt resistor 16. The shunt resistor 16 is arranged between the voltage source 14 and a reference node to which the vehicle sensor 12 can be connected. Furthermore, the device 10 comprises a comparator 22, wherein the inputs of the comparator 22 are connected to the two terminals of the shunt resistor 16 via a second resistor 18 and a third resistor 20. The first resistor 18 and the second resistor 20 can serve to convert the voltage values present at the terminals of the shunt resistor 16 into a range that can be processed by the comparator 22. The comparator 22 is configured to output a comparator output signal at its output, which comparator output signal depends on the values received by the comparator at its inputs. The output signal of the comparator 22 can also depend on an adjustable internal offset of the comparator 22. The comparator output signal has a bandwidth f1.

[0057] The comparator output signal is received and processed by a control unit 30. The control unit 30 samples the comparator output signal at a frequency f1, evaluates the sampled comparator output signal and determines a control variable from the evaluation signal. For example, an average sensor current can be estimated, which estimate is based on the last m values. For example, m can be 4, 6 or 8. Thus, an integral control unit can be provided. However, the invention is not limited to an integral control unit. Rather, the above-described control unit serves merely as an exemplary example of a measurement principle according to the prior art.

[0058] Thus, an estimated control variable (for example, an estimated average quiescent current) can be set in dependence on the values received from the control unit 30. This control variable can be updated, for example, once per microsecond. The control unit 30 then generates a control unit output signal and transmits it to an offset generator 28. The offset generator generates an offset signal, which offset signal can be fed, for example, to the input path of the comparator 28. Alternatively, the offset signal can also be fed directly to the comparator 22. The comparator 22, the control unit 30 and the offset generator 28 together form a control loop, which control loop is configured to adjust the control variable of the control loop until the control variable (for example, the estimated average current of the vehicle sensor) adjusts to the actual value.

[0059] As mentioned above, the system frequency in the shown measurement device can be 1 MHz. In this case, when an interference signal with a frequency of f ~ 1 MHz occurs, a significantly distorted measurement result is actually observed, whereas the present invention can eliminate these distortions.

[0060] Figure 2 An embodiment of a device 10 according to the invention is shown schematically. The device 10 comprises a voltage source 14 and a shunt resistor 16. The shunt resistor 16 is arranged between the voltage source 14 and a reference node to which the vehicle sensor 12 can be connected. Furthermore, the device 10 comprises a comparator 22, wherein the inputs of the comparator 22 are connected to the two terminals of the shunt resistor 16 via a second resistor 18 and a third resistor 20. The first resistor 18 and the second resistor 20 can serve to convert the voltage values present at the terminals of the shunt resistor 16 into a range that can be processed by the comparator 22. The comparator 22 is configured to output a comparator output signal at its output, which comparator output signal depends on the values received by the comparator at its inputs. The output signal of the comparator 22 can also depend on an adjustable internal offset of the comparator 22. The comparator output signal has a bandwidth f1. Figure 1The shown device is similar, the device according to the application also has a voltage source 14 and a shunt resistor 16, which is arranged between the voltage source 14 and a reference node, which can be connected to a vehicle sensor 12. In addition, the device 10 also has a comparator 22, which is configured to receive a voltage value at its first input, which depends on the voltage value at the first terminal of the shunt resistor 16, and to receive a voltage value at its second input, which depends on the voltage value at the second terminal of the shunt resistor. Between the shunt resistor 16 and the input of the comparator 22, a first resistor 18 and a second resistor 20 are arranged. These resistors serve to convert the voltage values on the terminals of the shunt resistor 16 into a value range that can be evaluated by the comparator 22. In addition, the device 10 also has a third resistor 32, a fourth resistor 34 and a capacitor 36, which together form a low-pass filter circuit 38. The low-pass filter circuit 38 can suppress high-frequency interference signals that can have a negative effect on the measurement result. The device 10 is therefore very robust to high-frequency interference.

[0061] In addition, the device 10 also has an evaluation unit 26, which is configured to sample the comparator output signal at a frequency f2 (where f2≥ 2 fi) and then evaluate it. For example, it can be assumed that the first frequency f1 = 1 MHz and the second frequency f2 = 12 MHz. The evaluation unit can receive and evaluate 12 values within a measurement period of 1 μβ, for example. The evaluation unit can be configured to make a majority decision (Mehrheitsentscheidung) and to generate an evaluation unit output signal, which is set to "high" depending on a certain proportion (for example, at least 50%) of the received values. The evaluation unit output signal is then output to the control unit 30. The control unit 30 can then set a control variable (for example, an estimated average current of the vehicle sensor) depending on the received values and generate a control unit output signal. The control unit output signal is then transmitted to the offset generator 28, which is configured to generate an offset signal. As described above, there are different ways of using the offset signal. For example, the offset signal can be fed to the input path of the comparator 22. Alternatively, the offset signal can also be fed directly to the comparator itself.

[0062] The evaluation unit 26 and the control unit 30 can be configured to generate an output signal having a first frequency f1, wherein f1 is preferably 1 MHz. The bandwidth of the comparator output signal is f1. In contrast, the comparator output signal is sampled at a second frequency f2, wherein the second frequency f2 is at least twice the first frequency f1, preferably six, twelve or twenty-four times the first frequency f1. In particular, the evaluation unit 26 can be configured to generate an evaluation unit output signal indicating whether the current average value currently flowing through the shunt resistor 16 is higher or lower than the current value determined during the previous measurement period. This is preferably achieved by a majority decision in which the sampled values are evaluated over one measurement period. For example, if the first frequency is 1 MHz and the second frequency is 12 MHz, a total of twelve comparator output values are evaluated over a measurement period having a measurement duration of 1 microsecond. In this case, the evaluation unit 26 can be configured to determine whether at least six of the twelve output values are greater than the current value determined during the previous measurement period. Thus, a majority decision can be made and an evaluation unit output signal updated at a frequency of 1 MHz can be generated on the basis of the majority decision.

[0063] The device according to the application allows a robust measurement of the static current of a vehicle sensor, wherein in particular the oversampling provides a higher robustness with respect to interference signals having a frequency of f ~ f1. Furthermore, the evaluation unit configured to perform a majority decision and to generate an output signal having a frequency of f = f1 allows using the same components as previously available measurement devices, thereby ensuring a high compatibility with previously available measurement systems.

[0064] Figure 3An embodiment of the method 100 according to the application is schematically illustrated. In a first method step 110, a first voltage value and a second voltage value are received at the input of a comparator, and a comparator output signal is generated depending on the received voltage values. The first voltage value depends on the voltage at a first terminal of a shunt resistor, and the second voltage value depends on the voltage at a second terminal of the shunt resistor. In a second method step 120, the generated comparator output signal is sampled by an evaluation unit which is configured to sample and evaluate the comparator output signal. In a third method step 130, the sampled comparator output signal is evaluated by the evaluation unit, and a corresponding evaluation unit output signal is generated. In a fourth method step 140, depending on the output signal of the evaluation unit, a meter reading of a control unit is adjusted, wherein a control unit output signal is generated. In a fifth method step 150, the control unit output signal is converted into an offset signal using an offset generator, wherein the analog offset signal is fed to the comparator or to an input path of the comparator. In the method 100 according to the application, the control unit output signal and the evaluation unit output signal can each have a first frequency f1, while the evaluation unit is configured to sample the comparator output signal with a second frequency f2, wherein the second frequency f2 is at least twice the first frequency f1.

[0065] The sequence of the above-described method embodiment of the application is only for reference. The method of the application is not limited to carrying out the method steps in the above-described sequence.

[0066] List of reference signs

[0067] 10 device

[0068] 12 vehicle sensor

[0069] 14 voltage source

[0070] 16 shunt resistor

[0071] 18 first resistor

[0072] 20 second resistor

[0073] 22 comparator

[0074] 26 evaluation unit

[0075] 28 offset generator

[0076] 30 control unit

[0077] 32 third resistor

[0078] 34 fourth resistor

[0079] 36 capacitor

[0080] 38 low pass filter circuit

[0081] 100 method

[0082] 110 first method step

[0083] 120 second method step

[0084] 130 third method step

[0085] 140 fourth method step

[0086] 150 fifth method step

Claims

1. A device (10) for measuring the quiescent current of a vehicle sensor (12), in particular via a peripheral sensor interface 5, namely a PSI5, comprising: - a voltage source (14) and a shunt resistor (16) arranged between the voltage source (14) and a reference node, the shunt resistor (16) having a first terminal and a second terminal; - a comparator (22) configured to receive at its first input a voltage value that depends on the voltage at the first terminal of the shunt resistor (16); - receiving at its second input a voltage value that depends on the voltage at the second terminal of the shunt resistor (16); and - providing at its output a comparator output signal which depends on the two input values; said comparator output signal having a bandwidth f1; - an evaluation unit (26) for evaluating the comparator output signal and outputting an evaluation unit output signal; - a control unit (30) configured to receive the evaluation unit output signal and output a control unit output signal according to the received evaluation unit output signal; as well as - an offset generator (28) configured to convert the control unit output signal into an offset signal and to feed the offset signal to the comparator or to an input path of the comparator (22); wherein, - The evaluation unit (26) is configured to sample the comparator output signal at a frequency f2, wherein f2 ≥ 2·f1.

2. The device (10) according to claim 1, characterized in that The evaluation unit (26) is configured to output "1" if at least a first predetermined proportion of the values ​​received within the measurement period T=1 / f1 is set to "high", and to output "0" if at least a second predetermined proportion of the values ​​received within the measurement period T=1 / f1 is set to "low".

3. The device (10) according to any one of claims 1 or 2, characterized in that The control unit (30) is configured to increase a current meter reading by a value if the value received from the evaluation unit (26) is set to "1"; and to decrease the current meter reading by a value if the value received from the evaluation unit (26) is set to "0".

4. The device (10) according to any one of claims 1 to 3, characterized in that An additional low-pass filter circuit (38) is arranged at the input of the comparator (22).

5. The device (10) according to claim 4, characterized in that The low-pass filter circuit (38) includes a capacitor (36) arranged between the two input terminals of the comparator (22) and two resistors (32, 34) respectively arranged in series with the two input terminals of the comparator (22).

6. The device (10) according to any one of claims 4 or 5, characterized in that The cut-off frequency f of the low-pass filter circuit (38) c satisfy f1≤f c ≤f2 / 2, where, preferably, f1≤f c ≤1.4×f1, particularly preferably, f1≤f c ≤1.3×f1 or f1≤f c ≤1.2×f1, and in particular, f1≤f c ≤1.1×f1.

7. The device (10) according to any one of claims 1 to 6, characterized in that The second frequency f2 satisfies f2≥6•f1, preferably f2≥12•f1, and particularly preferably f2≥24•f1.

8. A method for measuring the quiescent current of a vehicle sensor (12), in particular via a peripheral sensor interface 5, namely a PSI 5, comprising the following steps: - receiving (110) a first voltage value and a second voltage value at input terminals of a comparator (22) and outputting a comparator output signal that depends on the two input values, wherein: - the first voltage value depends on the voltage at the first terminal of the shunt resistor (16); - the second voltage value depends on the voltage at the second terminal of the shunt resistor (16); - the comparator output signal has a bandwidth f1; - sampling (120) the comparator output signal by means of an evaluation unit (26); - evaluating (130) the sampled comparator output signal by means of the evaluation unit (26) and outputting an evaluation unit output signal; - generating (140) a control unit output signal by means of a control unit (30) based on the evaluation unit output signal, and outputting the control unit output signal; - converting (150) the control unit output signal into an offset signal using an offset generator (28) and feeding the offset signal to the comparator or to an input path of the comparator (22); wherein, - The evaluation unit (26) is configured to sample the comparator output signal at a frequency f2, wherein f2 ≥ 2·f1.

9. The method according to claim 8, characterized in that The method comprises the following steps: - outputting a "1" at the output of the evaluation unit (26) if at least a first predefinable proportion of the values ​​received within the measuring period T=1 / f1 is set to "high"; and - outputting a "0" at the output of the evaluation unit (26) if at least a second predefinable proportion of the values ​​received within the measuring period T=1 / f1 is set to "low".

10. The method according to claim 8 or 9, characterized in that The method comprises the following steps: - if the value received from the evaluation unit (26) is set to "1", the current meter reading of the control unit (30) is increased by one value; and - if the value received from the evaluation unit (26) is set to "0", the current meter reading of the control unit (30) is reduced by one value.

11. The method according to any one of claims 8 to 10, characterized in that The method comprises the following steps: - low-pass filtering the input signal of the comparator (22) by using a low-pass filter circuit (38) arranged at the input of the comparator (22).

12. The method according to claim 11, characterized in that The input signal of the comparator (22) is low-pass filtered by using a low-pass filter circuit, wherein the low-pass filter circuit includes a capacitor (36) arranged between the two input terminals of the comparator (22) and two resistors (32, 34) respectively arranged in series with the two input terminals of the comparator (22).

13. The method according to any one of claims 11 or 12, characterized in that The cut-off frequency f of the low-pass filter circuit (38) c satisfy f1≤f c ≤f2 / 2, where, preferably, f1≤f c ≤1.4×f1, particularly preferably, f1≤f c ≤1.3×f1 or f1≤f c ≤1.2×f1, and in particular, f1≤f c ≤1.1×f1.

14. The method according to any one of claims 8 to 13, characterized in that The second frequency f2 satisfies f2≥6•f1, preferably f2≥12•f1, and particularly preferably f2≥24•f1.

Images