Sensor system with a MEMS gyroscope and method for operating a sensor system with a MEMS gyroscope

Abstract

A sensor system and a method for its operation, incorporating a MEMS gyroscope, are proposed, comprising at least [number] components. --- a drive circuit configured to generate an analog drive signal to drive a vibrating seismic element of the MEMS gyroscope and comprising a first interface amplifier of a drive detection circuit, wherein the drive detection circuit is configured such that, as a result of a movement of the vibrating seismic element in a drive direction, a first analog signal is detected and fed to an input of the first interface amplifier; --- a detection circuit coupled to the drive circuit and the oscillating seismic element, comprising a second interface amplifier, wherein the detection circuit is configured such that, due to a movement of the oscillating seismic element in a detection direction substantially perpendicular to the drive direction, a second analog signal is detected and fed to an input of the second interface amplifier, wherein the second analog signal comprises an analog rotation rate signal component and an analog quadrature signal component.

Description

State of the art

[0001] The invention relates to a sensor system with a MEMS gyroscope according to the preamble of the main claim.

[0002] Sensor systems with a MEMS gyroscope are typically operated using a drive circuit to generate the vibration of a seismic element and a detection circuit to read or detect the vibration perpendicular to the drive direction. Often, in addition to the drive circuit, a separate detection circuit is also present to detect the vibration in the drive direction. Due to various elements within the signal processing chain, a phase shift usually occurs in both the first analog signal from the drive detection circuit and the second analog signal from the detection circuit. This phase shift can be attributed to two main sources of error: defects within the MEMS structure itself and defects within an ASIC structure connected to the MEMS.

[0003] Current technology does not allow for the direct measurement of such phase shifts or phase differences, but rather compensates for them using an estimated offset value. This, for example, does not permit an accurate prediction of the temperature operating range of a sensor system using a MEMS gyroscope. Consequently, this methodology also precludes quality assurance of the sensor system's functionality, both during production and operation.

[0004] Furthermore, compensating for unwanted signal components of the first analog signal and / or second analog signal presents a further challenge.

[0005] MEMS gyroscope sensors typically consist of a drive unit that generates a vibration (drive movement) of a test mass, and a sensing unit that detects the movement of the test mass based on the angular velocity.

[0006] An extremely important parameter of the system is the phase delay of the drive and measurement signal paths, as they create an offset on the output signal in the case of a disturbing quadrature signal.

[0007] The phase delays are partly due to the MEMS and partly due to the ASIC subcomponent.

[0008] Normally, such phases are not measured directly in gyroscopes; only the resulting offset is compensated. This method does not allow for accurate prediction of the device's performance across a wide temperature range. Furthermore, this method does not permit the rejection of parts with anomalous values, which lowers the quality level in production. Disclosure of the invention

[0009] It is an object of the present invention to provide a sensor system with a MEMS gyroscope which has a structure for the efficient and effective detection and evaluation of phase differences of signals to be processed within the sensor system and additionally compensates for components to be compensated within the signals to be processed.

[0010] The purpose of this invention is to provide a function that makes it possible to measure the phase delays of driver and readout channels on the ASIC signal paths.

[0011] Such phase delays are important factors for the device's performance. The ability to measure them allows their effects on the output signal to be compensated for, thus improving the device's performance.

[0012] Furthermore, their measurement offers a method to identify and eliminate anomalous parts during testing in the manufacturing of the sensor system components, thus improving the overall quality of the components.

[0013] The sensor system according to the main claim has the advantage over the prior art that the digital test signal is provided to detect or measure the phase difference at the first interface amplifier and / or at the second interface amplifier. This (initial) digital test signal is converted into the analog test signal via a digital-to-analog converter and fed into the detection device and the drive detection device by means of the first switch-capacitance structure and the second switch-capacitance structure, respectively.

[0014] Specifically, different phases can be measured at the output of the first interface amplifier (with respect to the first analog test signal) and at the output of the second interface amplifier (with respect to the second analog test signal), thus enabling the detection of phase differences resulting from the respective signal paths. Such phase differences can provide information about the function or introduced noise signal components of elements within the signal processing chain and / or the MEMS structure and / or an associated ASIC structure. At least one of the first or second analog test signals used, or those applied to the signal paths, can exhibit different amplitudes (or different amplitudes depending on the application) and can be used for different configurations of the MEMS and ASIC structures or for different operating states of the signal paths used.According to the invention, such detection of the resulting or introduced different phase differences via the signal paths can be carried out at various times: On the one hand, this is possible during the manufacture of the sensor system or its components; on the other hand, this is possible during a test operating mode during the (operational) operation of the sensor or during a startup or settling-in process of the sensor system, also during the (operational) operation of the sensor; furthermore, it is also possible to perform this as needed, due to the occurrence of a condition, or continuously.

[0015] Furthermore, the quadrature compensation circuit connected to the drive detection circuit and the detection circuit allows for highly efficient compensation of the quadrature signal component within the second analog signal by applying a compensation signal. This also ensures suitable operation within the respective temperature range.

[0016] In particular, according to the invention, a circuit is provided for the generation and injection of the same analog test signal (or identical first and second analog test signals) into both the input of the drive channel (or drive signal path) and the readout channel (or readout signal path). Such a test signal is processed by the signal paths and generates a signal component at their output that can be used to obtain information about the phase delay of the drive and readout channels.

[0017] Such a signal can be activated with different amplitudes and with different configurations of the signal chains in order to also measure the phase delay of sub-blocks of the system.

[0018] The proposed measurement of the phase delay can be performed during testing and / or commissioning and / or as needed and / or depending on a condition and / or continuously.

[0019] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0020] According to an advantageous embodiment of the invention, the first switch-capacitance structure comprises a first variable capacitance for adjusting the application of the first analog test signal, and the second switch-capacitance structure comprises a second variable capacitance for adjusting the application of the second analog test signal. This advantageously allows for the input of specially generated test signals for the detection circuit and / or the drive circuit into the first and / or second interface amplifier. Consequently, a much more detailed analysis of the respective circuit structure is possible.

[0021] According to an advantageous embodiment of the invention, the first switch-capacitance structure comprises a first switch for interrupting the application of the first analog test signal, and the second switch-capacitance structure comprises a second switch for interrupting the application of the second analog test signal. Advantageously, this results in targeted and therefore efficient application of the first or second analog test signal to either the first or the second interface amplifier. In particular, the first and / or second switch makes it possible to selectively use either the first analog test signal or the second analog test signal at the input of the respective interface amplifier.

[0022] According to an advantageous embodiment of the invention, the analog test signal is a periodic signal, particularly preferably a sine wave signal. This makes it advantageously possible to compare the phases of two signals or test signals in a particularly efficient and effective manner by means of a phase difference.

[0023] According to an advantageous embodiment of the invention, the digital test generator circuit is configured such that the digital test signal is generated by means of a generation element, in particular comprising a second-order Butterworth filter, and / or derived from the drive detection circuit by means of a suitable structure, in particular derived from an internal time signal which is regulated to the output of the drive detection circuit. Thus, it is advantageously possible to ensure, on the one hand, the most effective possible provision of a usable test signal by means of derivation from the drive detection circuit and, on the other hand, the most efficient possible digital generation of the test signal by means of the generation element, in particular by means of a second-order Butterworth filter.

[0024] Another object of the invention is a method for operating a sensor system with a MEMS gyroscope according to the dependent method claim.

[0025] The inventive method for operating a sensor system with a MEMS gyroscope is advantageous compared to the prior art in that the quadrature signal component of the second analog signal is efficiently and effectively compensated in the first method step by means of the compensation signal generated by the quadrature compensation circuit. In the second method step, the first and second test signals are generated by means of the digital test signal and the application of the converted analog test signal to the first and second switch-capacitance structures. Thus, the detection circuit and the drive detection circuit are supplied with the first and second test signals extremely effectively and efficiently.In detail, the input of the first interface amplifier is supplied with the first analog test signal, and the input of the second interface amplifier is supplied with the second analog test signal. The effects of the first and / or the second test signal can be effectively evaluated at the output of the first and second interface amplifiers. This also allows for a correlation to be established with the phase delay or phase shift within the quadrature compensation circuit. Therefore, information about the phase delay within the acquisition circuit and within the drive acquisition circuit can be effectively obtained. Furthermore, the signal processing structures within the MEMS structure and within the ASIC structure can also be examined with regard to the phase delays occurring there.The recording of the different phases can be carried out continuously during operation as well as on demand for testing purposes and also provides information about the operation of the sensor system in different temperature ranges.

[0026] The proposed invention uses a circuit for generating and feeding the same signal into the input of drive and read channels. This signal is processed by the signal paths and generates an output that can be used to obtain information about the phase delay of the drive and read channels.

[0027] Such a signal can be activated with different amplitudes and with different configurations of the signal chains in order to also measure the phase delay of sub-blocks of the system.

[0028] The proposed measurement of the phase delay can be performed during testing and / or commissioning and / or as needed and / or depending on a condition and / or continuously.

[0029] The advantages and features described in connection with the embodiments of the sensor system according to the invention with a MEMS gyroscope can be applied to the method for operating a sensor system with a MEMS gyroscope.

[0030] Exemplary embodiments of the present invention are shown in the drawings and explained in more detail in the following description. Brief description of the drawings: Fig. Figure 1 shows a schematic diagram of a basic circuit diagram of a sensor system with a MEMS gyroscope, in which two signal paths can be supplied with a test signal. Fig. Figure 2 shows a schematic diagram of the basic circuit of the sensor system with a MEMS gyroscope and a quadrature compensation circuit. Fig. Figure 3 schematically shows a circuit diagram of the sensor system with a MEMS gyroscope with the quadrature compensation circuit according to the present invention. Fig. Figure 4 schematically shows a block diagram of the generation steps within a digital test generator circuit according to the present invention. Embodiments of the invention:

[0031] Fig. Figure 1 shows, in a very schematic representation – solely for the purpose of illustrating the basic principle – a schematic diagram of a sensor system 100 with a MEMS gyroscope 101 without a quadrature compensation circuit 320. Two signals are generated from the MEMS gyroscope 101: a first analog signal to a drive detection circuit 300 (which is configured such that the first analog signal is detected due to a movement of the oscillating seismic element of the MEMS gyroscope 101 in a drive direction) and a second analog signal to a detection circuit 310 (which is configured such that the second analog signal is detected due to a movement of the oscillating seismic element of the MEMS gyroscope 101 in a detection direction that is essentially perpendicular to the drive direction).The output of the drive detection circuit 300 is designated with the reference numeral 700, and the output of the detection circuit 310 is designated with the reference numeral 710. Specifically, the first analog signal is supplied to the drive detection circuit 300, and the second analog signal is supplied to the detection circuit 310; this is shown in [reference number]. Fig. 1 (as well as in the Fig. 2) schematically represented by dotted arrows. Furthermore, two test signals, a first analog test signal 600 and a second analog test signal 610, are fed to the drive detection circuit 300 and the detection circuit 310, respectively, which in Fig. 1 (as well as in Fig. 2) is schematically represented by means of dashed arrows. The first and second analog test signals 600, 610 are generated according to the invention such that within a digital test generator circuit 330' they are first generated as a digital test signal 520 and then, by means of a suitable structure (in Fig. 1 not explicitly shown, but comprising a digital-to-analog converter 510, a first switch-capacitance structure 400 and a second switch-capacitance structure 410, cf. Fig. 3 and Fig. 4) are converted into analog test signals. Specifically, the drive detection circuit 300 is supplied with the first analog test signal 600 and the detection circuit 310 with the second analog test signal 610. Within or at the outputs 700 and 710 of the detection circuit 310 and the drive detection circuit 300, a phase difference can be detected or determined based on or by means of the first analog test signal 600 and the second analog test signal 610, and this difference can be related to each other and to the phase of the analog test signal 500 within the test generator circuit 330'.

[0032] As a further and / or additional embodiment, the analog test signal 500 (here, however, not derived from the test generator circuit 330') can also be derived from the drive detection circuit 300 by means of a suitable structure.

[0033] The test generator circuit 330' is implemented in particular as a block that generates a test signal (in the form of the first and second analog test signals 600, 610) which is fed to the inputs of the ASIC signal chain. The drive detection circuit 300 or the detection circuit 310 can be operated with the first and / or second analog test signal 600, 610 applied, both with the MEMS gyroscope 101 connected and – at least during the manufacture of the sensor system, but possibly also afterwards, for example during a calibration mode in the operational mode of the sensor system – if the MEMS gyroscope 101 is electrically disconnectable from the ASIC signal chain.

[0034] Fig. Figure 2 shows a schematic diagram of the basic circuit of the sensor system 100 with a MEMS gyroscope 101 and a schematically represented quadrature compensation circuit 320. The representation is the same as in Fig. 1, however, with the quadrature compensation circuit 320, which is coupled to the drive detection circuit 300 and the detection circuit 310 (in particular, the output of the quadrature compensation circuit 320 acts on the input of the detection circuit 310). The quadrature compensation circuit 320 compensates for the quadrature signal component in the second analog signal and improves the signal quality of the second analog signal, which is supplied to the detection circuit 310. The output of the drive detection circuit 300 is designated with the reference numeral 700 and the output of the detection circuit 310 is designated with the reference numeral 710. Furthermore, within such an arrangement, a phase difference with respect to the first analog test signal 600 and the second analog test signal 610 can also be detected and compared with respect to the phase of the analog test signal 500 and a phase or...The phase delay within the quadrature compensation circuit 320 (due to the application of an analog compensation signal) is related; in particular, if the first analog test signal 600 is present at the drive detection circuit 300, this also affects the signal supplied by the quadrature compensation circuit 320 (at the input of the detection circuit 310) and thereby also the signal detectable at the output 710 of the detection circuit 310.

[0035] Since the origin (i.e., the analog test signal 500) of the first and second test signals 600 and 610 (i.e., which are present or can be applied to the drive circuit 300 and the sense circuit 310) is the same, the phase difference between the drive and sense signal paths can be measured by evaluating the two output signals. According to the Fig. In the arrangement shown in Figure 2, the quadrature is compensated by a special block (quadrature compensation circuit 320) which generates a compensation signal that is fed into the sensor input (input of Sense) from a signal generated by the drive signal path (Drive). According to the invention, the measurement of the phase (or a phase difference) of such a quadrature compensation circuit is thus also made possible.

[0036] Fig. Figure 3 schematically shows a circuit diagram of the sensor system 100 with the MEMS gyroscope 101 and with the quadrature compensation circuit 320 according to the present invention. As in Fig. 1 and Fig. As already shown in Figure 2, the MEMS gyroscope 101 supplies the first analog signal and the second analog signal to the drive detection circuit 300 and the detection circuit 310, respectively. The output of the drive detection circuit 300 is designated 700 and the output of the detection circuit 310 is designated 710. Specifically, the input of the first interface amplifier 200 receives the first analog signal and the input of the second interface amplifier 210 receives the second analog signal.A signal derived from the output of the first interface amplifier 200 is forwarded to the quadrature compensation circuit 320. Within the quadrature compensation circuit 320, a compensation signal is generated using the derived signal. This compensation signal is forwarded to the input of the second interface amplifier 210 within the detection circuit 310 to compensate for the quadrature component within the second analog signal. Furthermore, the test generator circuit 330' (not explicitly shown here) generates the analog test signal 500. The analog test signal 500 is fed into the first switch-capacitor circuit 400 to generate the first analog test signal 600, and is also fed into the second switch-capacitor circuit 410 to generate the second analog test signal 610. The first switch-capacitance circuit 400 is connected on the output side to the input of the first interface amplifier 200 (orThe first analog test signal 600 is present or can be present at the input of the drive detection circuit 300. Furthermore, the second switch-capacitor circuit 410 is also connected on its output side to the second interface amplifier 210 (or to the input of the detection circuit 310), so that the second analog test signal 610 is present or can be present there. If the first analog test signal 600 is present at the input of the first interface amplifier 200 or at the input of the drive detection circuit 300, or if the second analog test signal 610 is present at the input of the second interface amplifier 210 or at the input of the detection circuit 310, this results in a corresponding signal, or at least a corresponding signal component, at the output of the first and / or second interface amplifier 200, 210. The phases or phase differences of such signals are...Signal components can be detected and correlated with the phase of the analog test signal 500. Furthermore, a correlation with the phase within the quadrature compensation circuit 320 can also be determined. Thus, in addition to the information obtained from the detected phase differences, information about a phase delay within the quadrature compensation circuit 320 (due to the application of the analog compensation signal) can also be determined. Furthermore, it is also possible to obtain information about the phase delay within selected sub-circuits of the detection and / or drive detection circuit 310, 300. It is also possible to obtain information about the respective temperature range for optimal operation.

[0037] Thus, the test signal (first or second analog test signal 600, 610) or the test signals (first and second analog test signal 600, 610) are generated from a common source (analog test signal 500) to ensure the same phase between the test signal injection at drive and sense.

[0038] Such a test signal(s) are then coupled to both the Drive input and the Sense input via special configurable capacitors (first and second switch-capacitor circuits 400 and 410). These capacitors can be configured independently for the Drive input and the Sense input to allow the amount of charge injected at the input nodes to be selected independently.

[0039] Since the charge injected at the drive and sense inputs has the same phase, the difference in phase delay at the sense output compared to the drive output corresponds to the difference φCVsns- φCVrd, i.e., the difference in phase delays or phase differences due to the sensing circuit (φCVsns) and due to the drive sensing circuit (φCVrd).

[0040] Another phase measurement can be performed by using the additional quadrature compensation circuit with charge injection at the Sense input deactivated and charge injection activated by the configurable capacitor connecting the DriveCV output (i.e., output 700 of the drive sensing circuit 300) to the SenseCV input (i.e., the input of the sensing circuit 310). In this case, the difference in phase delay at the Sense output (i.e., output 710 of the sensing circuit 310) compared to the Drive output (i.e., output 700 of the drive sensing circuit 300) corresponds to φCVsns + φqc, i.e., the sum of the phase differences due to the sensing circuit (φCVsns) and due to quadrature compensation (φqc).

[0041] The test signals (i.e. the first and / or second analog test signal 600, 610) can also be provided according to the invention without a connected MEMS gyroscope 101, e.g. in ASIC wafer-level testing, for example to reject parts with anomalous behavior.

[0042] Such test signals can also be added to the signals coming from the MEMS gyroscope 101 to obtain information about the ASIC phase delays and compensate for them accordingly. This method can also be used for monitoring to ensure the correct functioning of the ASIC.

[0043] The test signal can be, in particular, a sine wave or another signal suitable for measuring the phase delay of the respective signal paths under investigation.

[0044] Such a signal can be generated by a dedicated block or taken directly from the forcing section of the gyroscope system (i.e., from the drive circuit for the oscillating seismic element of the MEMS gyroscope). In the latter case, the phase delay of the drive circuit and its proper functioning can also be measured.

[0045] In gyroscope architectures where the drive output cannot be measured directly, the difference between drive and sense output can be determined by closing the phase control loop of the drive section and measuring only the sampling output, which in such a case already corresponds to the difference between drive and sampling.

[0046] Fig. Figure 4 shows a block diagram of the generation steps within the digital test generator circuit 330' according to the present invention. The digital test signal 520 is generated and converted into an analog test signal 500 by means of the digital-to-analog converter 510, in particular a second-order Butterworth filter. The preferred embodiment using the second-order Butterworth filter allows the generation of a phase shift, due to its low-pass filter properties, to which the drive detection circuit 300 can be adjusted. Furthermore, it is preferably provided that the analog test signal 500 is a periodic signal, particularly preferably a sine wave signal.

[0047] Another and / or additional embodiment for the generation is a suitable (not explicitly shown here) structure for deriving a suitable test signal from the drive detection circuit 300.

[0048] A circuit for generating the test signal for a closed-loop system at the ASIC level (without a connected MEMS) is described in Fig. Figure 4 illustrates this. The signal at the filter input is generated by a clock controlled by the phase-locked loop. The filter (e.g., a second-order Butterworth filter) allows for the generation of a phase shift to which the control loop can adjust. In one implementation, the filter input can be generated by a digital signal.

Claims

[1] Sensor system (100) with a MEMS gyroscope (101), at least comprising: --- a drive circuit configured to generate an analog drive signal for driving an oscillatory seismic element of the MEMS gyroscope and comprising a first interface amplifier (200) of a drive detection circuit (300), wherein the drive detection circuit (300) is configured such that, due to a movement of the oscillatory seismic element in a drive direction, a first analog signal is detected and supplied to an input of the first interface amplifier (200); --- a detection circuit (310) coupled to the drive circuit and the vibratory seismic element and comprising a second interface amplifier (210), wherein the detection circuit (310) is configured such that, due to a movement of the oscillatable seismic element in a detection direction substantially perpendicular to the drive direction, a second analog signal is detected and fed to an input of the second interface amplifier (210), wherein the second analog signal comprises an analog yaw rate signal component and an analog quadrature signal component; characterized by that the sensor system (100) additionally comprises: --- a quadrature compensation circuit (320) configured with the drive detection circuit (300) such that the input of the second interface amplifier (210) is supplied with an analog compensation signal of the quadrature compensation circuit (320) for compensating the analog quadrature signal component, --- a digital test signal generator circuit (330') configured to apply a digital test signal (520) to a digital-to-analog converter (510) for conversion into an analog test signal (500), wherein the output of the digital-to-analog converter (510) is connected to the input of the first interface amplifier (200) via a first switch-capacitance structure (400) and to the input of the second interface amplifier (210) via a second switch-capacitance structure (410), wherein the first interface amplifier (200) can be supplied with the analog test signal (500) by means of the first switch-capacitance structure (400) and / or the second interface amplifier (210) can be supplied with the analog test signal (500) by means of the second switch-capacitance structure (410), wherein a first analog test signal (600) can be provided by means of the analog test signal (500) through the first switch-capacitance structure (400), wherein a second analog test signal (610) can be provided by means of the analog test signal (500) through the second switch-capacitance structure (410), wherein a phase difference can be detected by selectively applying the first analog test signal (600) to the input of the first interface amplifier (200) and / or by selectively applying the second analog test signal (610) to the input of the second interface amplifier (210). [2] Sensor system (100) according to claim 1 characterized by that the first switch-capacitance structure (400) has a first variable capacitance for adjusting the application of the first analog test signal (600) and the second switch-capacitance structure (410) has a second variable capacitance for adjusting the application of the second analog test signal (610). [3] Sensor system (100) according to one of the preceding claims characterized bythat the first switch-capacitance structure (400) has a first switch for interrupting the application of the first analog test signal (600) and the second switch-capacitance structure (410) has a second switch for interrupting the application of the second analog test signal (610). [4] Sensor system (100) according to one of the preceding claims characterized by that the analog test signal (500) is a periodic signal, particularly preferably a sine signal. [5] Sensor system (100) according to one of the preceding claims characterized bythat the digital test generator circuit (330') is configured such that the digital test signal (520) is generated by means of a generation element, in particular comprising a second-order Butterworth filter, and / or is derived from the drive detection circuit (300) by means of a suitable structure, in particular derived from an internal time signal which is regulated to the output of the drive detection circuit. [6] Method for operating a sensor system (100) with a MEMS gyroscope (101), at least comprising: --- a drive circuit configured to generate an analog drive signal for driving an oscillatory seismic element of the MEMS gyroscope and comprising a first interface amplifier (200) of a drive detection circuit (300), wherein the drive detection circuit (300) detects a first analog signal based on a movement of the oscillatory seismic element in a drive direction and is supplied to an input of the first interface amplifier (200); --- a detection circuit (310) coupled to the drive circuit and the vibratory seismic element and comprising a second interface amplifier (210), wherein the detection circuit (310) detects a second analog signal due to a movement of the oscillatable seismic element in a detection direction substantially perpendicular to the drive direction and feeds it to an input of the second interface amplifier (210), wherein the second analog signal comprises an analog yaw rate signal component and an analog quadrature signal component; characterized by that the sensor system (100) additionally comprises a quadrature compensation circuit (320), a digital test signal generator circuit (330') and a digital-to-analog converter (510), wherein the output of the digital-to-analog converter (510) is connected via a first switch-capacitance structure (400) to the input of the first interface amplifier (200) and via a second switch-capacitance structure (410) to the input of the second interface amplifier (210), wherein: --- in a first method step, the quadrature compensation circuit (320) with the drive detection circuit (300) applies an analog compensation signal of the quadrature compensation circuit (320) to the input of the second interface amplifier (210) for compensating the analog quadrature signal component, --- in a second method step, the digital test signal generator circuit (330') applies a digital test signal (520) to the digital-to-analog converter (510) for conversion into an analog test signal (500), wherein the first interface amplifier (200) is supplied with the analog test signal (500) by means of the first switch-capacitance structure (400) and / or the second interface amplifier (210) is supplied with the analog test signal (500) by means of the second switch-capacitance structure (410), wherein a first analog test signal (600) is provided by means of the analog test signal (500) through the first switch-capacitance structure (400), wherein a second analog test signal (610) is provided by means of the analog test signal (500) through the second switch-capacitance structure (410), wherein a phase difference is detected by selectively applying the first analog test signal (600) and / or by selectively applying the second analog test signal (610) to one input of the first interface amplifier (200) and / or the second interface amplifier (210).

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