Method for iso 26262 compliance evaluation of pressure sensor signals

Abstract

The invention relates to a device and a method for evaluating signals from one or more Wheatstone bridges. Here, the requirements of ISO 26262 are taken into account by mixing a test signal with the measurement signal before amplification and before analog-digital conversion. After amplification and analog-digital conversion, the measurement signal is again unmixed from the test signal. If the test signal does not correspond to the expected value, the amplifier and / or the analog-digital converter is faulty. The process has the advantage that it can be used during regular operation without being disturbed.

Description

TECHNICAL FIELD

[0001] The present invention discloses a method for monitoring a sensor system in operation with a sensor element (WB), in particular with a piezoresistive Wheatstone bridge (WB) of a pressure sensor, and related apparatus and method variants. BACKGROUND

[0002] Automotive applications often employ a large number of safety-relevant sensors, the operation of which the vehicle control system must monitor during operation to ensure their correct functioning. These sensors include, for example, pressure measuring devices in brake systems.

[0003] PRIOR ART

[0004] Various chopper methods for improving the signal-to-noise ratio in an amplifier are known from the prior art. Here, a multiplier upstream of the amplifier multiplies the signal with a chopper signal having a chopper frequency, which is then amplified and then multiplied again with the chopper signal. In this process, the multiplication both up- and down-mixes the amplified signal. Since only the down-mixed portion is of interest, a low-pass filter suppresses signal components having the chopper frequency and all higher frequencies. This generally suppresses the 1 / f noise of the amplifier stage.

[0005] The combination of this method with a sensor element results in a low-noise sensor system.

[0006] The sensor system thus implements a method for operating a sensor system, wherein the sensor system has a sensor element providing an input signal, the input signal having a time course of its input signal values. The sensor system comprises a signal path. At a first location in the signal path, the signal path comprises an amplifier having an input and an output. The signal path starts with the input signal from the sensor element and ends with a first output signal of the sensor system. The value of the first output signal or of a signal derived from the first output signal represents a measurement value. In a first step of the prior art method, at a second location in the signal path, the signal in the signal path is first mixed with a chopper signal. Here, the second location in the signal path is between the input signal from the sensor element at the start of the signal path and the input of the amplifier at the first location of the signal path. The chopper signal is usually single-frequency. As a next step, at a third location in the signal path, the signal is second mixed. The second mixing of the signal is usually a down-mixing of the signal with the chopper signal into a first demodulation signal. The third location in the signal path is between the output of the amplifier at the first location of the signal path and the first output signal of the sensor system at the end of the signal path. At a fourth location in the signal path, a first filtering of the first demodulation signal or of a signal derived from the first demodulation signal is carried out. The fourth location is between the third location of the signal path and the output signal of the sensor system at the end of the signal path. The first filtering is carried out by applying a first filter function to the first demodulation signal or to a signal derived from the first demodulation signal. The first filter function describes a relationship between the time course of the first demodulation signal or of a signal derived from the first demodulation signal and the time course of this signal immediately after the first filtering. The first output signal depends on the signal as a result of the first filtering or is the result of the first filtering.

[0007] The first filter function F1[] is chosen such that the filtering result of the chopper signal Cs with the first filter function F1[] is essentially zero, i.e. F1[Cs] = 0, and the filtering of a constant results in F1[1] = β1, where β1 is a real or complex value in the form of a constant.

[0008] The disadvantage is that the control system usually has to switch off these sensor systems during operation to check their function. SUMMARY

[0009] TASK

[0010] It is therefore the task of the present invention to create a solution which does not have this disadvantage of the prior art and has further advantages.

[0011] SOLUTION

[0012] To solve this problem, a method for monitoring a sensor system in operation is proposed herein, wherein the sensor system has a sensor element WB, which provides an input signal Si, which has a time course Si(t) of its input signal values. The sensor system has a signal path, in which various device elements modify and evaluate the signal in the signal path. At a first location of the signal path, the signal path comprises an amplifier DV with an input and an output. The signal path starts with the input signal Si, i.e. the output signal of the sensor element WB. The signal path ends at a first output signal out1 of the sensor system. The value of the first output signal out1 of the sensor system or of a signal derived from the first output signal, if necessary, for example by amplification, filtering or other further processing, typically represents a measurement value. As an exemplary first step, the proposed method comprises a first mixing of the signal in the signal path with a chopper signal Cs by a first mixer, for example a first multiplier M1, at a second location of the signal path, which is typically different from the first location at which the amplifier DV is located. Thus, preferably, the mixer or the first multiplier M1 is located at the second location of the signal path. Of course, it is also conceivable to carry out this mixing in the amplifier DV by suitably designing the amplifier DV, in which case, for example, the gain of the amplifier DV will depend on the chopper signal Cs. For this purpose, for example, the amplifier DV can comprise a Gilbert multiplier as an amplifier stage. Instead, it has proven useful to typically implement the signal path in differential fashion and to implement the first multiplier M1 as a switch that swaps the two signals of the differential signal in the signal path depending on the chopper signal Cs. It is particularly useful to use a Wheatstone bridge as the sensor element WB, as it already provides a differential signal. The second location for carrying out the first mixing, for example the location of the first multiplier, is typically located in the signal path between the input signal Si, i.e. the output signal of the sensor element, at the start of the signal path and the input of the amplifier DV at the first location of the signal path. In order to reliably suppress 1 / f noise, the chopper signal Cs is preferably band-limited or single-frequency. This measure raises the frequency of the chopper signal Cs in the frequency spectrum of the sensor output signal, i.e. of the time course Si(t) of the input signal Si, which is typically very low-frequency. The subsequent amplifier stages, analog-to-digital converter stages and filter stages thus only pollute the frequency range of the frequency-enhanced input signal Si with white noise and improve the signal-to-noise ratio. In order to be able to use the amplified, digitized sensor signal again, the sensor system must reverse this process. For this purpose, the signal is typically second-mixed with the chopper signal Cs by a second mixer, typically a second multiplier M2, at a third location of the signal path to form a first demodulation signal DM1.Preferably, the third position in the signal path is located between the output of the amplifier DV at the first position in the signal path and the first output signal outl of the sensor system at the end of the signal path. The first demodulation signal DM1 or a signal derived from the first demodulation signal is first filtered at a fourth position in the signal path, which is located between the third position of the signal path and the output signal outl of the sensor system at the end of the signal path. Typically, the first low-pass filter LP1 performs this first filtering with a first filter function F1 []. Thus, the first low-pass filter LP1 performs the first filtering by applying the first filter function F1 [] to the first demodulation signal DM1 or a signal derived from the first demodulation signal. In addition to low-pass filters, other filters can also be considered depending on the application. However, it is assumed here that the measured value to be determined varies only slowly, unpredictably periodically, and thus the DC component of the measured value represents the essential information. The first filter function F1 [] describes the relationship between the time course DM1 (t) of the first demodulation signal DM1 or a signal derived from the first demodulation signal and the time course of this signal immediately after the first filtering. The first output signal outl depends on the signal immediately after the first filtering with the first filter function F1 []. However, the first output signal outl can also be the result of this first filtering with the first filter function F1 [] directly. Now, in order to be able to monitor the signal processing means in the signal path at least to a large extent, contrary to the prior art, the sensor system feeds a test signal TSS into the signal path. After the modified test signal TSS has passed through the signal path, the sensor system extracts this test signal from the signal path again. The sensor system then evaluates this extracted test signal. The first filter function F1 [] and the test signal TSS are preferably designed such that the first output signal outl no longer contains any significant components of the test signal TSS. Thus, in the sensor system, the first low-pass filter LP1 for implementing the first filter function F1 [] blocks the transmission of signal components corresponding to the test signal TSS from its input to its output. In order to perform the injection and extraction of the test signal in the signal path, the proposed method comprises additional steps. In particular, this comprises adding the quadrature chopper signal Cs90 or a test signal TSS derived from the quadrature chopper signal to the signal in the signal path. This addition takes place at a fifth position in the signal path. Preferably, this fifth position is located between the input signal Si at the beginning of the signal path, i.e. the output signal of the sensor element WB, and the input of the amplifier DV at the first position of the signal path. The chopper signal Cs has a time course Cs(t) of the chopper signal Cs, and the quadrature chopper signal Cs90 likewise has a time course Cs90(t) of the quadrature chopper signal Cs90. The time course Cs(t) of the chopper signal Cs must satisfy certain conditions which will be given in the following.As long as these conditions are met, the time course of the chopper signal Cs can be chosen relatively freely. However, it is suggested herein that the frequency bandwidth of the chopper signal should not be too wide, otherwise the response time of the sensor system can be affected. The time course Cs90(t) of the quadrature chopper signal Cs90 must also meet certain, but more narrow conditions which will also be given in the following. As long as these conditions are met, the time course of the quadrature chopper signal Cs90 can be chosen relatively freely. However, it is suggested herein that the frequency bandwidth of the quadrature chopper signal Cs90 should also not be too wide, otherwise the response time of the sensor system can also be affected in certain cases. With respect to the first filter function F1[], the time course Cs90(t) of the quadrature chopper signal Cs90 has at least at times substantially the property F1[Cs90(t) x Cs(t)] = 0 in addition to noise and similar signal errors. This means that the quadrature chopper signal Cs90 is orthogonal to the chopper signal Cs at times which are usually predetermined.

[0013] For the sake of explanation, let us assume that X(t) is the time course of an arbitrary, not further defined signal. Let us assume as an example that the first filter function F1[X] is the time indefinite integral of the time course of the exemplary signal X(t) over time. Thus, let us assume that the following equation holds:

[0014] F1[X] = ∫ X dt

[0015] Under this condition, the following equation holds:

[0016] F1[Cs90(t) x Cs(t)] = ∫ Cs90(t) x Cs(t) dt

[0017] In this example, the first filter function F1[] is the L2 product of the chopper signal Cs and the quadrature chopper signal Cs90. With respect to the L2 product, reference can be made, for example, to https: / / de.wikipedia.org / wiki / Lp-Raum#Der_Hilbertraum_L2, and here to the section "Der Hilbertraum L 2 ". The L2 product is an L 2the scalar product on R3. Another article is for example the lecture notes "Introduction to Differential Geometry" by Christopher R. Nerz, S198, definition X.1.5, which the reader can find at the time of submission of this text at the following address https: / / www.math.uni-tuebingen.de / de / forschung / gadr / lehre / sose2015 / diffgeo.pdf. It is for example conceivable that the chopper signal Cs follows a time sinus function and the orthogonal chopper signal Cs90 follows a time cosine function. In this case it is clear that the condition F1 [Cs90(t) x Cs(t)] = 0 is not always fulfilled but only at certain times. If the first low pass filter LP1 performs a first filter function F1 [], it is useful that the sensor system is designed such that a holding circuit is provided at the output of the first low pass filter LP1. As long as the condition F1 [Cs90(t) x Cs(t)] = 0 is fulfilled, the holding circuit samples the current value of the first filter function F1 [] of the first low pass filter LP1. Then the holding circuit freezes this current value at its output until the condition F1 [Cs90(t) x Cs(t)] = 0 is fulfilled again. This sampling by the holding circuit transforms the indefinite integral of the example into a definite integral.

[0018]

[0019] Here, it is assumed that the chopper signal Cs and the orthogonal chopper signal Cs90 are periodic signals with respect to a common signal period T p The periodic signals in the sense of the present application. This sampling of the filter output signal of the filter also applies to the filter and its filtering described below, if the orthogonality is actually present, i.e. if the boundary conditions are fulfilled.

[0020] As a next step, a third mixing is performed. The third mixing mixes the first demodulation signal DM1 or a signal derived from the first demodulation signal with the orthogonal chopper signal Cs90 or a signal derived from the orthogonal chopper signal Cs90. The third mixing generates a second demodulation signal DM2. In this third step, a second filter function F2 [] usually also filters the second demodulation signal DM2 or a signal derived from the second demodulation signal as a second filtering to obtain a second output signal out2.

[0021] In general, the second filter function F2[] is chosen such that the conditions F2[Cs(t)] = 0, F2[Cs90(t)] = 0 and F2[Cs(t) x Cs90(t)] = 0 and F2[1] = β2 essentially hold, where β2 is a real or complex value. Furthermore, in general, the first filter function F1[] is chosen such that the conditions F1[Cs90(t)] = 0, F1[Cs(t)] = 0, F1[Cs(t) x Cs90(t)] = 0 and F1[1] = β1 essentially hold, where β1 is a real or complex value. Here, preferably, the filter output signal of the second low pass filter LP2 using the second filter function F2[] is sampled always when the conditions of the second filter function F2[] are fulfilled. Here, similarly, the filter output signal of the first low pass filter LP1 using the first filter function F1[] is sampled always when the conditions of the first filter function F1[] are fulfilled. Thus, preferably, the second output signal out2 consists of the sampled values of the output values of the second filter function F2[DM2] of the second low pass filter LP2 sampled by the sensor system when the conditions of the second filter function F2[] are fulfilled. Thus, preferably, the first output signal out1 consists of the sampled values of the output values of the first filter function F1[DM1] of the first low pass filter LP1 sampled by the sensor system when the conditions of the first filter function F1[] are fulfilled.

[0022] For inferring a correct functioning of the device components in the signal path, the value of the second output signal out2 or of a signal derived from the second output signal is compared to an expected value interval in a first comparison. Furthermore, if the value of the second output signal out2 or of a signal derived from the second output signal is outside the expected value interval, it is inferred that a device component in the signal path is faulty.

[0023] It is obvious to the person skilled in the art that components of the signal path can be implemented in a signal processor and related signal processor programs if necessary. When here the signal path is talked about, the spatial positioning becomes a temporal positioning in case of implementation as a program in a signal processor. Thus, the positions in the signal path are converted into processing times in the order of the signal processing steps. Thus, even if the subject matter claimed by the present invention suggests a spatial positioning and arrangement from the wording, these subject matters also include a temporal positioning and order.

[0024] The Dicke method for reducing white noise can complement the presented method if necessary. The basic idea of the Dicke receiver is to compare the DUT placed in a noisy environment with an equivalent noise source.

[0025] Therefore, as a reference noise source, the example of the Wheatstone bridge WB here uses a second Wheatstone bridge (reference Wheatstone bridge RW), the sensor system preferably being designed such that this reference Wheatstone bridge is identical and therefore its manufacturing method is generally identical. The reference Wheatstone bridge RW can generally but preferably not give a measurement signal. For example, if the sensor element is a piezoresistive micromechanical pressure sensor and a Wheatstone bridge with piezoresistive resistors is arranged on a membrane above a cavity, the reference element RW can be a second pressure sensor with a second Wheatstone bridge which has the same structure and is preferably implemented on the same silicon crystal. In the subsequent solution, the sensor system generates a second output signal out2 which represents the difference between the output signal of the reference element (in the following called reference signal Rs) and the output signal of the sensor element (here the input signal Si). In the case of identical sensor element WB and reference element RW, this second output signal out2 should be zero. However, due to manufacturing tolerances and slightly different operating parameters (e.g. temperature etc.) despite close proximity and unavoidable system noise, this second output signal out2 is in fact never completely zero. Rather, its value must be within a desired value interval which the sensor system is able to check. This is also the case in the event that the reference element is not able to provide a measurement value. In the case of an exemplary micromechanical pressure sensor as a sensor element, for example, the reference element RW can also only comprise a reference Wheatstone bridge which has no membrane and no cavity, so that the influence of pressure is significantly less. In this example, the reference Wheatstone bridge is identical (matched) to the Wheatstone bridge. In this example of a piezoresistive pressure sensor, the Wheatstone bridge of the pressure sensor with its membrane and cavity and the reference Wheatstone bridge are together housed on a common silicon crystal. In this exemplary case, the reference Wheatstone bridge and the Wheatstone bridge produce noise in the same way, which enables the noise to be eliminated.

[0026] The proposed noise reduction method thus comprises, as a first step, providing a reference element RW which provides a reference signal Rs. For example, the reference element RW can be the reference Wheatstone bridge mentioned by way of example. In analogy to the processing of the input signal Si in the signal path, a corresponding processing of the reference signal Rs is carried out in the reference signal path. It is particularly important that the reference signal path is designed identically to the signal path for processing the input signal Si. This means that the reference signal processing locations in the reference signal path directly correspond to the respective signal processing locations in the signal path. If a device in the reference signal path carries out a processing at a certain location in the reference signal path, the corresponding device with the same design in the signal path carries out the same processing of the signal in the signal path in the same way. The signal processing of the reference signal Rs in the reference signal path is thus initially a spatially parallel processing with the signal processing of the input signal Si in the signal path, wherein the signal processing of the reference signal Rs in the reference signal path is carried out in as identical a manner as possible to the signal processing of the input signal Si in the signal path.

[0027] Now, as an alternative design, time multiplexing can be used instead of this spatial multiplexing in certain sections of the signal path if necessary, with the advantage that the sensor system not only uses similar device components and processing steps, but identical device components and processing steps. This increases the equality of the noise in the reference signal path and the signal path compared to the spatial multiplexing.

[0028] Here, spatial multiplexing is understood to mean a parallel processing of the signals in time in a plurality of identical or similar devices. In contrast, time multiplexing is understood here to mean a serial processing of the signals in one device. In the case of time multiplexing, the processing is carried out in signal packets which are processed in time one after the other by the device.

[0029] The reference signal path starts with the reference element RW with the reference signal Rs. The reference signal path ends with the second output signal out2.

[0030] However, in order to use the reference element RW, the reference signal path at the start of the reference signal path (at the reference signal Rs) must be different from the signal path at the start of the signal path (at the input signal Si). In the proposed solution, at least the amplifier DV should be common for the reference signal path and the signal path. Thus, at the first position of the reference signal path, the reference signal path comprises the amplifier DV with an input and an output. Thus, the first position of the reference signal path comprising the amplifier DV with an input and an output is also the first position of the signal path comprising the amplifier DV with an input and an output. Thus, the amplifier DV is part of the reference signal path at the first position of the reference signal path, while it is also part of the signal path at the first position of the signal path. The reference signal Rs is at the start of the reference signal path. The reference signal path has a sixth position in the reference signal path, which sixth position is between the reference signal Rs and the input of the amplifier DV at the first position of the reference signal path. The signal path has a corresponding sixth position of the signal path, which sixth position is between the input signal Si at the start of the signal path and the input of the amplifier DV (which is common for the signal path and the reference signal path) at the first position of the signal path. In the reference signal path as well as in the signal path, at the sixth position which is common for the reference signal path and the signal path, there is a switch DS which is common for the signal path and the reference signal path and which has a first input and a second input. Thus, in the reference signal path, the common switch DS is at the sixth position of the reference signal path. Thus, in the signal path, the common switch DS is at the corresponding sixth position of the signal path, which is also the common sixth position in the reference signal path and the signal path.

[0031] The common switch DS selects between its first input and its second input as its active input according to the second chopping signal Cs2.

[0032] The signal path comprises the first input of the switch DS, while the reference signal path comprises the second input of the switch DS. Correspondingly, the signal path does not comprise the second input of the switch DS, and the reference signal path does not comprise the first input of the switch DS.

[0033] The common switch DS selects its active input according to the second chopping signal Cs2, and accordingly switches the current value at this active input of the common switch DS to the output of the common switch DS.

[0034] Thus, in the part from the output of the common switch DS at the sixth position of the reference signal path and the signal path to the input of the amplifier DV at the first position of the reference signal path and the signal path, the reference signal path and the signal path are identical.

[0035] However, the first filtering using the first filter function F1 [] is excluded here and explicitly, the first filtering is not part of the reference signal path. Typically, the exemplary first low pass filter TP1 is not part of the reference signal path.

[0036] A fourth mixing of the first demodulation signal DM1 or a signal derived from the first demodulation signal with the second chopper signal Cs2 results in a third demodulation signal DM3. This third mixing can be performed in a third mixer, e.g. a third multiplier M3.

[0037] Here, a step of third filtering of the third demodulation signal DM3 or a signal derived from the third demodulation signal with a third filter function F3 [] to form a third output signal out3 ends the signal processing first. For example, this third filtering can be performed in a third low pass filter LP3 implementing the third filter function F3 [].

[0038] The sensor system has to ensure that i) the measurement signal component of the sensor element, ii) the differential signal component resulting from the difference between the measurement signal component of the sensor element WB and the reference signal component of the reference element RW and iii) the test signal component are clearly separated. To this end, a) the first filter function F1 [] of the exemplary first low pass filter LP1, b) the second filter function F2 [] of the exemplary second low pass filter LP2 and c) the third filter function F3 [] of the exemplary third low pass filter LP3 have to fulfill certain conditions.

[0039] Thus, the sensor system is designed to select the first filter function F1 [] such that the following conditions are substantially fulfilled:

[0040] F1 [Cs(t)] = 0 and

[0041] F1 [Cs2(t)] = 0

[0042] F1 [Cs90(t)] = 0

[0043] F1 [Cs(t) x Cs2(t)] = 0

[0044] F1 [Cs(t) x Cs90(t)] = 0

[0045] F1 [Cs2(t) x Cs90(t)] = 0

[0046] F1 [Cs(t) x Cs2(t) x Cs90(t)] = 0

[0047] F1 [1] = β1

[0048] Here, β1 is a real or complex value. As mentioned before, the device of the sensor system preferably samples the output of the exemplary first low-pass filter LP1 exactly when these conditions are met, neglecting inevitable slight deviations caused by noise and manufacturing errors, etc. Likewise, the sensor system is designed to select the second filter function F2[] such that the following conditions are substantially met:

[0049] F2[Cs(t)] = 0

[0050] F2[Cs2(t)] = 0

[0051] F2[Cs90(t)] = 0

[0052] F2[Cs(t) x Cs2(t)] = 0

[0053] F2[Cs(t) x Cs90(t)] = 0

[0054] F2[Cs2(t) x Cs90(t)] = 0

[0055] F2[Cs(t) x Cs2(t) x Cs90(t)] = 0

[0056] F2[1] = β2

[0057] Here, β2 is a real or complex value. As mentioned before, the device of the sensor system preferably samples the output of the exemplary second low-pass filter LP2 exactly when these conditions are met, neglecting inevitable slight deviations caused by noise and manufacturing errors, etc. In this regard, the technical teaching herein neglects inevitable slight deviations caused by noise and manufacturing errors, etc. Similarly, the sensor system is designed to select the third filter function F3[] such that the following conditions are substantially met:

[0058] F3[Cs(t)] = 0

[0059] F3[Cs2(t)] = 0

[0060] F3[Cs90(t)] = 0

[0061] F3[Cs(t) x Cs2(t)] = 0

[0062] F3[Cs(t) x Cs90(t)] = 0

[0063] F3[Cs2(t) x Cs90(t)] = 0

[0064] F3[Cs(t) x Cs2(t) x Cs90(t)] = 0

[0065] F3[1] = β3

[0066] Here, β3 is a real or complex value. Preferably, the holding circuit of the sensor system samples the output of the exemplary third low-pass filter LP3 at sampling times. These sampling times are thus exactly the times at which the above-mentioned condition is met. In this case, the technical teaching herein disregards unavoidable slight deviations caused by noise and manufacturing errors, etc. In order to detect a defect of the reference element or of the sensor element, the value of the third output signal out3 or of a signal derived from the third output signal is preferably compared to a third expected value interval in a second comparison. Furthermore, if the value of the third output signal out3 or of a signal derived from the third output signal is outside the third expected value interval, a conclusion is drawn that an error is present. This comparison can be carried out, for example, by means of a third comparator and a fourth comparator or by means of a signal processor, etc. The third comparator thus compares the value of the third output signal out3 to a third threshold value, if necessary. The fourth comparator compares the value of the third output signal out3 to a fourth threshold value, if necessary.

[0067] The above-mentioned method has the disadvantage that the sensor element, here the exemplary Wheatstone bridge WB, is not part of the signal path portion that is tested using the test signal TSS. The proposed method variant now remedies this.

[0068] The technical teaching herein thus proposes an improved method for monitoring a sensor system in operation, wherein, as before, the sensor system comprises a sensor element WB that provides an input signal Si having an input signal value in dependence on a test signal TSS.

[0069] As before, the sensor system has a signal path that likewise comprises an amplifier DV having an input and an output at a first location in the signal path.

[0070] As before, the signal path begins with the input signal Si from the sensor element WB and ends with a first output signal out1.

[0071] Here, the value of the output signal out1 likewise represents a measurement value.

[0072] Likewise, a first mixing of the signal in the signal path with a chopper signal Cs takes place at a second location in the signal path. This second location in the signal path is located between the input signal Si from the sensor element at the beginning of the signal path and the input of the amplifier DV at the first location in the signal path.

[0073] Likewise, the chopper signal Cs is bandwidth-limited or single-frequency.

[0074] Likewise, a mixing of the signal with the chopper signal Cs is performed at a third position of the signal path to form a first demodulation signal DM1. The third position of the signal path is located between an output of the amplifier DV at the first position of the signal path and the first output signal out1 of the sensor system at the end of the signal path.

[0075] As previously described, a first filtering of the first demodulation signal DM1 or a signal derived from the first demodulation signal is performed at a fourth position of the signal path, which is located between the third position of the signal path and the first output signal out1 at the end of the signal path. This first filtering is performed by applying a first filter function F1 [] to the first demodulation signal DM1 or a signal derived from the first demodulation signal. The first filter function F1 [] describes a relationship between a time course DM1 (t) of the first demodulation signal DM1 or a signal derived from the first demodulation signal and a time course of the signal. This signal course is the course following the first filtering, i.e. usually the course of the filter output signal. Likewise, the first output signal out1 depends on this signal following the first filtering or is itself a result of the first filtering.

[0076] However, in contrast to the prior art, a test signal TSS is now also generated from the quadrature chopper signal Cs90. The chopper signal Cs has a time course Cs(t) of the chopper signal Cs. The quadrature chopper signal Cs90 thus has a time course Cs90(t) of the quadrature chopper signal Cs90. In relation to the first filter function F1 [], the time course Cs90(t) of the quadrature chopper signal Cs90 thus has at least at times substantially the property F1 [Cs90(t) x Cs(t)] = 0, in addition to noise and similar signal errors. At least the time course Cs90(t) of the quadrature chopper signal Cs90 has these properties at the times already discussed.

[0077] In contrast to the prior art, a third mixing of the first demodulation signal DM1 or a signal derived from the first demodulation signal with the quadrature chopper signal Cs90 or a signal derived from the quadrature chopper signal is also performed, and a second demodulation signal DM2 is further generated.

[0078] A second filtering of the second demodulation signal DM2 or a signal derived from the second demodulation signal with a second filter function F2 [] results in the second output signal out2.

[0079] A second filter function F2[] is chosen such that F2[Cs(t)] = 0, F2[Cs90(t)] = 0, F2[Cs(t) x Cs90(t)] = 0 and F2[1] = β2 essentially hold, where β2 is a real or complex value. As already mentioned before, in case these conditions are met, a second holding circuit (Sample & Hold) samples the output value of a preferred exemplary second low pass filter LP2 implementing the second filter function F2[DM2].

[0080] A first filter function F1[] is chosen such that F1[Cs(t)] = 0, F1[Cs90(t)] = 0, F1[Cs(t) x Cs90(t)] = 0 and F1[1] = β1 essentially hold, where β1 is a real or complex value. As already mentioned before, in case these conditions are met, a first holding circuit (Sample & Hold) samples the output value of a preferred exemplary first low pass filter LP1 implementing the first filter function F1[DM1].

[0081] If necessary, the sensor device can comprise a first trigger circuit. The first trigger circuit signals to the first holding circuit to sample the result of the first filter function F1[] in case the conditions F1[Cs(t)] = 0, F1[Cs90(t)] = 0, F1[Cs(t) x Cs90(t)] = 0 and F1[1] = β1 are met. Here, β1 is a real or complex value. The first holding circuit samples the first demodulation signal DM1. The first holding circuit forms a first output signal out1 by this sampling.

[0082] If necessary, the sensor device can comprise a second trigger circuit. The second trigger circuit signals to the second holding circuit to sample the result of the second filter function F2[] in case the conditions F2[Cs(t)] = 0, F2[Cs90(t)] = 0, F2[Cs(t) x Cs90(t)] = 0 and F2[1] = β2 are met. Here, β2 is a real or complex value. The second holding circuit samples the second demodulation signal DM2. The second holding circuit forms a second output signal out2 by this sampling.

[0083] Finally, the value of the second output signal out2 or of a signal derived from the second output signal is also compared to the expected value interval and a false conclusion is drawn if the value of the second output signal out2 or of the signal derived from the second output signal is outside the expected value interval. Here, reference is made to the explanations of the previous sections.

[0084] Likewise, it is meaningful to include a sensor element and a reference element in the signal path to be tested. In this case, a reference element RW is also provided here which provides a reference signal Rs. The sensor system processes the reference signal Rs in the reference signal path. Again, the reference signal path is designed to be identical to the signal path for processing the input signal Si. At this point, reference is made to the already explained procedure. The reference signal path likewise starts with the reference signal Rs and likewise ends with the second output signal out2.

[0085] As already mentioned, the reference signal path at the start of the reference signal path (at the reference signal Rs) is different from the signal path at the start of the signal path (at the input signal Si).

[0086] As already mentioned, the reference signal path at the first position of the reference signal path comprises an amplifier DV having an input and an output. Thus, as already mentioned, the amplifier DV is also part of the reference signal path at the first position of the reference signal path and at the same time part of the signal path at the first position of the signal path.

[0087] As already mentioned, the reference signal path has a sixth position in the reference signal path which is located between the reference signal Rs at the start of the reference signal path and the input of the amplifier DV at the first position of the reference signal path. Likewise, the signal path has a sixth position in the signal path which is located between the input signal Si at the start of the signal path and the input of the amplifier DV (which is common to the signal path and the reference signal path) at the first position of the signal path. Again, at this common sixth position of the reference signal path and the signal path, the signal path and the reference signal path comprise a changeover switch DS having a first input and a second input and which is common to the signal path and the reference signal path.

[0088] As already mentioned, the changeover switch DS which is common to the signal path and the reference signal path selects its active input between its first input and its second input in dependence on the second chopping signal Cs2.

[0089] Again, the signal path comprises the first input of the changeover switch DS and does not comprise the second input of the changeover switch DS. Correspondingly, the reference signal path comprises the second input of the changeover switch DS and does not comprise the first input of the changeover switch DS.

[0090] The common changeover switch DS selects the active input in dependence on the second chopping signal Cs2 and passes on the value at this active input of the common changeover switch DS to the output of the common changeover switch DS.

[0091] In the part of the reference signal path and the signal path from the output of the common switch DS at the sixth position of the reference signal path and the signal path to the input of the amplifier DV at the first position of the reference signal path and the signal path, the reference signal path and the signal path are identical.

[0092] The first filtering using the first filter function F1 [] (e.g. the first low-pass filter LP1) is not part of the reference signal path.

[0093] The third filtering of the third demodulation signal DM3 or a signal derived from the third demodulation signal by a third filter function F3 [] (e.g. in the third low-pass filter LP3) generates the third output signal out3.

[0094] The sensor system must ensure that i) the measurement signal component of the sensor element, ii) the differential signal component resulting from the difference between the measurement signal component of the sensor element WB and the reference signal component of the reference element RW and iii) the test signal component are clearly separated. For this purpose, the first filter function F1 [] of the exemplary first low-pass filter LP1, the second filter function F2 [] of the exemplary second low-pass filter LP2 and the third filter function F3 [] of the exemplary third low-pass filter LP3 must likewise satisfy certain conditions.

[0095] The sensor system is therefore designed to select the first filter function F1 [] such that the following conditions are substantially satisfied:

[0096] F1 [Cs (t)] = 0

[0097] F1 [Cs2 (t)] = 0

[0098] F1 [Cs90 (t)] = 0

[0099] F1 [Cs (t) x Cs2 (t)] = 0

[0100] F1 [Cs (t) x Cs90 (t)] = 0

[0101] F1 [Cs2 (t) x Cs90 (t)] = 0

[0102] F1 [Cs (t) x Cs2 (t) x Cs90 (t)] = 0

[0103] F1 [1] = β1

[0104] Here, β1 is a real or complex value. As mentioned before, the sample & hold circuit preferably samples the output of the exemplary first low pass filter LP1 just when these conditions are met. In this case, the technical teaching herein ignores inevitable slight deviations caused by noise and manufacturing errors etc. Likewise, the sensor system is designed to select the second filter function F2[] such that the following conditions are substantially met:

[0105] F2[Cs(t)] = 0

[0106] F2[Cs2(t)] = 0

[0107] F2[Cs90(t)] = 0

[0108] F2[Cs(t) x Cs2(t)] = 0

[0109] F2[Cs(t) x Cs90(t)] = 0

[0110] F2[Cs2(t) x Cs90(t)] = 0

[0111] F2[Cs(t) x Cs2(t) x Cs90(t)] = 0

[0112] F2[1] = β2

[0113] Here, β2 is a real or complex value. As mentioned before, the sample & hold circuit preferably samples the output of the exemplary second low pass filter LP2 just when these conditions are met. Here, the technical teaching herein ignores inevitable slight deviations caused by noise and manufacturing errors etc. In the same way, the sensor system is designed to select the third filter function F3[] such that the following conditions are substantially met:

[0114] F3[Cs(t)] = 0

[0115] F3[Cs2(t)] = 0

[0116] F3[Cs90(t)] = 0

[0117] F3[Cs(t) x Cs2(t)] = 0

[0118] F3[Cs(t) x Cs90(t)] = 0

[0119] F3[Cs2(t) x Cs90(t)] = 0

[0120] F3[Cs(t) x Cs2(t) x Cs90(t)] = 0

[0121] F3[1] = β3

[0122] Here, β3 is a real or complex value. As already mentioned, a sample & hold preferably samples the output of the exemplary third low-pass filter LP3 exactly when these conditions are met. The technical teaching herein neglects inevitable slight deviations caused by noise and manufacturing errors etc. Now, in order to detect a defect of the reference element or sensor element, the value of the third output signal out3 or a signal derived from the third output signal is preferably next compared to a third expected value interval. Furthermore, if the value of the third output signal out3 or a signal derived from the third output signal is outside the third expected value interval, it is next preferred to conclude that there is an error. For example, a third comparator can compare the value of the third output signal out3 to a third threshold value. For example, a fourth comparator can compare the value of the third output signal out3 to a fourth threshold value. For example, the second comparison can be made by the third and fourth comparator or by a signal processor etc.

[0123] In order to be able to perform this procedure, a dedicated pressure sensor or sensor is advantageous.

[0124] Therefore, a pressure sensor for use in a method according to one or more of the preceding methods is proposed. The proposed pressure sensor comprises a Wheatstone bridge with four piezo-resistive resistors R1, R2, R3, R4 and a reference Wheatstone bridge with four reference piezo-resistive resistors R5, R6, R7, R8. Preferably, the reference resistors R5, R6, R7, R8 of the reference Wheatstone bridge RW are arranged in the same way as the resistors R1, R2, R3, R4 of the Wheatstone bridge WB. In order to achieve a good thermal coupling and thus a better noise uniformity, the pressure sensor with the Wheatstone bridge WB as sensor element and the reference Wheatstone bridge RW as reference element are arranged together on a single piece of crystal. This means that they are subjected to approximately the same influences during manufacturing and operation. The same orientation of the components and the same arrangement of the components relative to each other maximizes this equality.

[0125] The pressure sensor comprises at least one first cavity which is closed on at least one side by a first diaphragm and is surrounded by a continuous wall. The cavity surface of the first cavity opposite the first diaphragm can be completely or partially open to allow the ingress of a medium in the case of a differential pressure sensor or is closed in the case of an absolute pressure sensor. Preferably, the piezo-resistive resistors R1, R2, R3, R4 of the Wheatstone bridge WB are arranged at least partially on the first diaphragm. In this case, reference is made herein, for example, to the industrial property rights EP 2 524 389 B1, EP 2 524 390 B1, EP 2 524 198 B1, EP 2 523 896 B1 and EP 2 523 895 B1.

[0126] Now, the following options exist for the reference sensor element:

[0127] A) The reference sensor element can be designed to provide a reference signal Rs, which should equal the input signal Si. In this case, the reference signal Rs and the input signal Si equally depend on the value of the physical quantity, which influences the respective output signal of the sensor element and the output signal of the reference element. Thus, a change of the value of this physical quantity then leads to a change of the same value of the input signal Si and the reference signal Rs. In the example of a pressure sensor discussed here, this exemplary physical quantity is the pressure.

[0128] B) The reference sensor element can be designed to provide a reference signal Rs. This reference signal should differ from the input signal Si in a predetermined manner. In this case, the input signal Si is provided by the sensor element. In this case, the reference signal Rs and the input signal Si non-equally depend on the value of the physical quantity, which influences the respective output signal of the sensor element and the output signal of the reference element. Thus, a change of the value of this physical quantity leads to a non-equally value change of the input signal Si and a non-zero change of the reference signal Rs. In the example of a pressure sensor discussed here, this exemplary physical quantity is typically the pressure.

[0129] C) The reference sensor element can be designed to provide a reference signal Rs, which should differ from the input signal Si in a pre-known manner (i.e. essentially constant). Thus, now preferably, the reference signal Rs essentially does not depend on the value of the physical quantity, which influences the respective output signal of the sensor element. In contrast, the input signal Si continues to depend on the value of the physical quantity, which influences the respective output signal of the sensor element, so that a change of the value of this physical quantity leads to a change of the input signal Si, while the reference signal Rs has no or only negligible change. In the example of a pressure sensor discussed here, this exemplary physical quantity is the pressure.

[0130] Case A): The reference element and the sensor element have the same design.

[0131] In the pressure sensor example of case A, the pressure sensor comprises a reference cavity which is closed on at least one side by a second diaphragm and is surrounded by a continuous wall. Preferably, the second diaphragm is of the same construction as the first diaphragm. Preferably, the first diaphragm is of the same size and shape as the second diaphragm. Preferably, the reference cavity is of the same construction as the first cavity. The cavity surface of the reference cavity opposite the second diaphragm can be completely or partially open to allow the ingress of medium, it can also be closed. Preferably, the cavity surface of the reference cavity is closed when the corresponding cavity surface of the first cavity is closed. Preferably, the cavity surface of the reference cavity is open when the corresponding cavity surface of the first cavity is open, in which case the openings of the corresponding cavity surfaces are made in the same way. In the case of a closed cavity, the first cavity and the reference cavity are preferably filled with the same gas at the same pressure or preferably at the same vacuum. Preferably, the piezoresistive reference resistors R5, R6, R7, R8 of the exemplary reference Wheatstone bridge RW are arranged at least partially on the second diaphragm above the reference cavity. In the best case, the behavior of the first Wheatstone bridge WB interacting with the first diaphragm and the first cavity and the behavior of the reference Wheatstone bridge RW interacting with the second diaphragm and the reference cavity are identical, so that on the third output signal out3 a non-zero signal other than noise can essentially not be measured. If a non-zero signal can be measured on the third output out3 outside the third desired value interval, an error exists.

[0132] Case B): the reference element and the sensor element are not designed identically and the reference element has a different sensitivity to the physical quantity than the sensor element.

[0133] In this pressure sensor example of case B, the pressure sensor comprises a reference cavity which is closed on at least one side by a second diaphragm and which is surrounded by a continuous wall. In this case, it is preferred that the mechanical structure realized by the reference cavity and the second diaphragm is different from the mechanical structure realized by the first cavity and the first diaphragm. For example, the second diaphragm can be designed differently from the first diaphragm. For example, it can be thicker, thinner, larger, smaller, differently shaped or differently structured. The shape of the reference cavity is different from the first cavity. For example, the reference cavity can be smaller or larger, deeper or shallower, or differently shaped or differently filled. The shape of the cavity surface of the reference cavity facing the second diaphragm can be different from the shape of the cavity surface of the first cavity facing the first diaphragm. One of these cavity surfaces can be closed, while the other can be open; or one can be open, while the other can be closed. If both are open, the shape, position and size of the openings within the respective cavities can be different. In the case of closed cavities, they can be filled with different gases and / or filled at different pressures, a low pressure is also understood herein to include a vacuum. Of course, it is also conceivable that the design of the piezoresistors R1, R2, R3, R4 of the Wheatstone bridge WB can be different from the design of the reference piezoresistors R5, R6, R7, R8 of the reference Wheatstone bridge RW. This different design can involve the resistance values, the dimensions, the size, the design, the orientation, the dopants, etc. In this case, the third output signal out3 and the first output signal out1 together form an output signal vector, the output signal vector value of which can only be within a predetermined range. Thus, it can be checked whether the two-dimensional output signal vector value of this two-dimensional vector is consistent with a two-dimensional expected value range, or two values of two different physical parameters that have a different influence on the sensor element and the reference element can be extracted from the two-dimensional output signal vector value. If the two-dimensional value of the two-dimensional output vector leaves the two-dimensional expected value range, the sensor system or the superior computer system can conclude that an error has occurred.

[0134] Case C) : Reference element and sensor element are not identical and the reference element is not sensitive to the physical quantity.

[0135] In case C, the pressure sensor preferably does not comprise a reference cavity. Thus, the mechanical structure of the reference element in the form of a reference Wheatstone bridge RW deviates significantly from the mechanical structure of the sensor element in the form of a Wheatstone bridge WB. Ideally, case C is an extreme case of case B. In this extreme case, the reference element then typically has no sensitivity to the physical quantity at all. In this case, the reference element has the form of a reference Wheatstone bridge RW. Here, the physical quantity is the physical quantity that the sensor system is to detect by means of the sensor element, in this case in the form of a Wheatstone bridge WB. The reference sensor element RW then typically detects a parasitic parameter such as pressure or humidity. The evaluation is similar to the evaluation in case B.

[0136] Preferably, in the exemplary case of a micromechanical pressure sensor, the piezoresistive reference resistors R5, R6, R7, R8 are arranged in such a way that the deflection of the first diaphragm does not affect the reference resistors R5, R6, R7, R8 of the reference Wheatstone bridge RW. Preferably, for this purpose, the reference resistors R5, R6, R7, R8 are not located on the first diaphragm.

[0137] The first resistor R1 of the Wheatstone bridge WB is identical to the fifth resistor R5 of the reference Wheatstone bridge RW in that they are constructed in the same way.

[0138] The second resistor R2 of the Wheatstone bridge WB is identical to the sixth resistor R6 of the reference Wheatstone bridge RW in that they are constructed in the same way.

[0139] The third resistor R3 of the Wheatstone bridge WB is identical to the seventh resistor R7 of the reference Wheatstone bridge RW in that they are constructed in the same way.

[0140] The fourth resistor R4 of the Wheatstone bridge WB is identical to the eighth resistor R8 of the reference Wheatstone bridge RW in that they are constructed in the same way.

[0141] The sensor system then, in this example, preferably uses this reference element in the form of the reference Wheatstone bridge RW as a reference noise source for the subsequent signal processing of the input signal Si from the sensor element, in this case the Wheatstone bridge WB.

[0142] A sensor for one of the above-mentioned methods is therefore proposed. In particular, the sensor can be a pressure sensor. The proposed sensor comprises a first resistor R1 having a first terminal and a second terminal. The proposed sensor comprises a second resistor R2 having a first terminal and a second terminal. The proposed sensor comprises a third resistor R3 having a first terminal and a second terminal. The proposed sensor comprises a fourth resistor R4 having a first terminal and a second terminal. Now, in order to be able to generate a first differential modulation voltage V mod1The sensor in this embodiment comprises a first voltage source VI with a first terminal and a second terminal and a second voltage source V2 with a first terminal and a second terminal. The first terminal of the first voltage source VI is connected to the first supply voltage line VDD. The second terminal of the first voltage source VI is connected to the first terminal of the first resistor R1. The second terminal of the first resistor R1 is connected to the first terminal of the second resistor R2. The second terminal of the second resistor R2 is connected to the second supply voltage line GND. The first terminal of the second voltage source V2 is connected to the first supply voltage line VDD. The second terminal of the second voltage source V2 is connected to the first terminal of the third resistor R3. The second terminal of the third resistor R3 is connected to the first terminal of the fourth resistor R4. The second terminal of the fourth resistor R4 is connected to the second supply voltage line GND. The first voltage of the first voltage source VI depends on the test signal TSS. The second voltage of the second voltage source V2 depends on the test signal TSS in an opposite manner to the first voltage of the first voltage source VI.

[0143] As an alternative to feeding the test signal through the voltage sources VI, V2, VIb, V2b, it is also possible to feed this signal through a respective pair of current sources, in which case the sensor system must not excite the Wheatstone bridge WB and the reference Wheatstone bridge RW through the voltage source pairs [VI, V2], [VIb, V2b], but through the current source pairs. Thus, the Wheatstone bridge WS is assigned a first pair of current sources. The reference Wheatstone bridge RW is assigned a second pair of current sources. Each of these pairs of current sources then consists of two current sources, respectively. According to the assignment, a first current source of the pair of current sources feeds a first current from the current source of the pair of current sources to the first branch of the Wheatstone bridge WB or the reference Wheatstone bridge RW. According to the assignment, a second current source of the pair of current sources feeds a second current from the current source of the pair of current sources to the second branch of the Wheatstone bridge WB or the reference Wheatstone bridge RW. The first current and the second current depend on the test signal TSS in different signs. The sensor system thus requires a total of four current sources, which the sensor system is preferably designed to be identical (matched) to each other as well. Since this possibility is obvious to the person skilled in the art, no drawing is made for this.

[0144] As an alternative to feeding the test signal component to the input signal Si by means of a voltage or current source, it is also possible to modulate the values of the resistors R1, R2, R3, R4 of the Wheatstone bridge WB and the values of the reference resistors R5, R6, R7, R8 of the reference Wheatstone bridge RW. For this purpose, as a further embodiment, a sensor, in particular a pressure sensor, is proposed herein which is generally used in a method according to one or more of the methods described above. The sensor then comprises a first resistor R1 having a first terminal and a second terminal, a second resistor R2 having a first terminal and a second terminal, a third resistor R3 having a first terminal and a second terminal, and a fourth resistor R4 having a first terminal and a second terminal. Furthermore, the sensor comprises a first variable resistor RV1 having a first terminal and a second terminal and a second variable resistor RV2 having a first terminal and a second terminal.

[0145] The first terminal of the first variable resistor RV1 is connected to a first supply voltage line VDD. The second terminal of the first variable resistor RV1 is connected to the first terminal of the first resistor R1. The second terminal of the first resistor R1 is connected to the first terminal of the second resistor R2. The second terminal of the second resistor R2 is connected to a second supply voltage line GND. The first terminal of the second variable resistor RV2 is connected to the first supply voltage line VDD. The second terminal of the second variable resistor RV2 is connected to the first terminal of the third resistor R3. The second terminal of the third resistor R3 is connected to the first terminal of the fourth resistor R4. The second terminal of the fourth resistor R4 is connected to the second supply voltage line GND. The resistance value of the first variable resistor RV1 depends on the test signal TSS, and the resistance value of the second variable resistor RV2 depends on the test signal TSS in an opposite manner to the resistance value of the first variable resistor RV1. Preferably, the sensor system is designed to implement the first variable resistor RV1 and the second variable resistor RV2 in the same (matched) manner.

[0146] Advantages

[0147] At least in some embodiments, the methods and exemplary devices in the following figures allow for a signal path to be able to be verified during operation. However, the advantages are not limited thereto. BRIEF DESCRIPTION OF DRAWINGS

[0148] The figures represent exemplary designs proposed herein. They are schematic and simplified.

[0149] Figure 1 A simple exemplary embodiment of the invention is shown.

[0150] Figure 2 Exemplary waveforms showing the operation of a device according to Figure 1

[0151] ​Figure 3 diagram corresponding to Figure 1 is shown, where the first adder and the first multiplier are interchanged.

[0152] Figure 4 diagrams corresponding to Figure 2 are shown, but now apply to Figure 3 exemplary signals.

[0153] Figure 5 diagrams based on Figure 3 are shown.

[0154] Figure 6 diagrams corresponding to Figure 5 are shown, but differ in that, Figure 6 the excitation voltages of the Wheatstone bridge and the reference Wheatstone half-bridge are modulated.

[0155] Figure 7 diagrams corresponding to Figure 6 are shown, but differ in that, Figure 7 the resistors of the Wheatstone bridge and the reference Wheatstone half-bridge are modulated. DETAILED DESCRIPTION

[0156] Figure 1

[0157] Figure 1 A simple exemplary embodiment of the present application is shown. A Wheatstone bridge WB is chosen as an exemplary sensor having differential outputs. The exemplary Wheatstone bridge WB comprises a first resistor Rl, a second resistor R2, a third resistor R3 and a fourth resistor R4. For example, when used in a piezoresistive pressure sensor, the first resistor Rl is a piezoresistive first resistor Rl, the second resistor R2 is a piezoresistive second resistor R2, the third resistor R3 is a piezoresistive third resistor R3 and the fourth resistor R4 is a piezoresistive fourth resistor R4. The first resistor Rl and the second resistor R2 are connected in series between a first supply voltage line VDD and a second supply voltage line GND. The third resistor R3 and the fourth resistor R4 are also connected in series between the first supply voltage line VDD and the second supply voltage line GND. For example, the sensor system operates the Wheatstone bridge WB with a supply voltage between the first supply voltage line VDD and the second supply voltage line GND. Thus, the Wheatstone bridge WB has a first terminal connected to the supply voltage line VDD and a second terminal connected to the second supply voltage line GND. For example, a node between the first resistor Rl and the second resistor R2 forms a negative input signal Sin of a differential input signal Si. For example, a node between the third resistor R3 and the fourth resistor R4 forms a positive input signal Sip of the differential input signal Si.

[0158] It is known that in many sensor systems a Wheatstone bridge is used to convert a physical parameter of interest into a differential voltage signal between a positive input signal Sip and a negative input signal Sin. For example, the Wheatstone bridge WB can be such a bridge of piezo-resistive resistors R1, R2, R3, R4 of a sensor element of a piezo-resistive micro-machined pressure sensor or the like.

[0159] The signal pair consisting of the positive input signal Sip and the negative input signal Sin forms a differential input signal Si. In the example of Fig. 1, the differential input signal Si is a differential voltage signal. Figure 1 In the example of Fig. 1, a first adder A1 adds a differential test signal TSS to the differential input signal Si to form a differential input signal SiT with a test signal component.

[0160] A first multiplier M1 multiplies the differential input signal SiT with a test signal component with a chopping signal Cs, thereby forming a differential product input signal MSiT with a test signal component. Preferably, the chopping signal Cs is a digital signal with two logic values, here exemplarily 0 and 1. For example, the first multiplier M1 can be implemented as a switching device. Then, the design forms the functionality of the switching device, for example, in the following way:

[0161] A) if the value of the chopping signal Cs is logic 0, the differential product input signal MSiT with a test signal component corresponds to the differential input signal SiT with a test signal component,

[0162] B) if the value of the chopping signal Cs is logic 1, the differential product input signal MSiT with a test signal component corresponds to the differential input signal SiT with a test signal component in case of a cross-over line.

[0163] A differential amplifier DV amplifies the differential product input signal MSiT with a test signal component into an amplifier output signal VO.

[0164] An analog-to-digital converter ADC converts the amplifier output signal VO into an input signal DFI of a digital filter DF. The input signal DFI of the digital filter DF is from the analog-to-digital converter ADC and is typically a digital signal of a sampled value of the amplifier output signal VO.

[0165] The digital filter DF filters the input signal DFI of the digital filter DF into an output signal DFO of the digital filter DF. In this case, the digital filter suppresses any signal components that can exist at interference frequencies. Typically, the digital filter is a decimation filter that is used for conversion artifacts added by the sampling with the analog-to-digital converter ADC.

[0166] An exemplary phase compensator PC corrects the resulting phase error and forms a phase compensator output signal PCO.

[0167] After amplification and digitization, the second multiplier M2 multiplies the phase compensator output signal PCO with the chopper signal Cs to form the first demodulated signal DM1.

[0168] The first low-pass filter LP1 suppresses frequencies in the first demodulated signal DM1 that correspond to frequencies in the signal spectrum of the chopped signal Cs. The first low-pass filter LP1 also suppresses frequencies in the signal spectrum of the quadrature chopped signal Cs90. Furthermore, the first low-pass filter LP1 suppresses mixing frequencies that may be generated by multiplying the chopped signal Cs and the quadrature chopped signal Cs90. The first low-pass filter LP1 suppresses these signal components in the first demodulated signal DM1, except for the DC component. Therefore, the first low-pass filter LP1 forms the first output signal out1, the value of which corresponds to the value of the differential input signal Si.

[0169] The third multiplier M3 mixes the first demodulated signal DM1 with the quadrature chopper signal Cs90 to form the second demodulated signal DM2. The second low-pass filter LP2 suppresses frequencies in the second demodulated signal DM2 that correspond to frequencies in the signal spectrum of the chopper signal Cs. The second low-pass filter LP2 also suppresses frequencies in the signal spectrum of the quadrature chopper signal Cs90. The second low-pass filter LP2 further suppresses mixing frequencies that may result from the multiplication of the chopper signal Cs and the quadrature chopper signal Cs90. The second low-pass filter LP2 suppresses these frequencies in the second demodulated signal DM2, except for the DC component. Therefore, the second low-pass filter LP2 forms the second output signal out2.

[0170] exist Figure 1 In the example, signal generator G1 generates a chopped signal Cs and a quadrature chopped signal Cs90. Preferably, the chopped signal Cs is bandwidth-limited or single-frequency. Preferably, the quadrature chopped signal Cs90 is also bandwidth-limited or single-frequency. Preferably, the quadrature chopped signal Cs90 is different from the chopped signal Cs. The first low-pass filter LP1 has a first filter characteristic of the form of a first filter function F1[], such that: out1 = F1[DM1]. The second low-pass filter LP2 has a filter characteristic of the form of a second filter function F2[], such that: out2 = F2[DM2]. Generally, and very preferably, the first low-pass filter LP1 and the second low-pass filter LP2 have the same filter characteristics and the same filter function F[] = F1[] = F2[].

[0171] The chopping signal Cs and the quadrature chopping signal Cs90 should be orthogonal to each other, relative to the first filter LP1 and relative to the second filter LP2. That is, at least at the preferred time, the following should hold true:

[0172] a) F1 [Cs(t) x Cs90(t)] = 0

[0173] b) F2 [Cs(t) x Cs90(t)] = 0

[0174] Here, Cs(t) shall denote the time course of the values of the chopper signal Cs, and Cs90(t) shall denote the time course of the values of the quadrature chopper signal Cs90.

[0175] Furthermore, the first filter function F1 [] shall preferably be a substantially linear filter function. That is, for the signal sum of any first example signal X1(t) and any second example signal X2(t), and for a real value a, it shall hold that:

[0176] A) F1 [X1(t) + X2(t)] = F1 [X1(t)] + F1 [X2(t)]

[0177] B) F1 [a x X1(t)] = a x F1 [X1]

[0178] Furthermore, the second filter function F2 [] shall preferably be a substantially linear filter function. That is, for the signal sum of any first example signal X1(t) and any second example signal X2(t), and for a real value a, it shall hold that:

[0179] C) F2 [X1(t) + X2(t)] = F2 [X1(t)] + F2 [X2(t)]

[0180] D) F2 [a x X1(t)] = a x F2 [X1]

[0181] Finally, both the first filter function F1 [] and the second filter function F2 [] shall have low-pass characteristics. That is, it shall hold that:

[0182] F1 [1] = β1 and F2 [1] = β2, where β1 is a non-zero real constant and β2 is a non-zero real constant.

[0183] For example, the chopper signal Cs can be a single-frequency PWM signal with values of -1 and 1, a duty cycle of 50% and a chopper signal frequency. Then, the quadrature chopper signal Cs90may be a + / - 90° phase-shifted signal with values of -1 and 1 and a duty cycle of 50%, for example. Alternatively, the quadrature chopper signal Cs90may be a single-frequency PWM signal with values of -1 and 1 and a duty cycle of 50% and a signal frequency that is an integer multiple of the chopper signal frequency, for example. The chopper signal Cs can also be a bandwidth-limited non-single-frequency signal. The only important thing is to satisfy the quadrature condition. Typically, the chopper signal Cs is periodic and the quadrature chopper signal Cs90is periodic. If necessary, it is useful that the first low-pass filter LP1 and the second low-pass filter LP2 can be provided with a sample & hold at their respective outputs. In this case, it is useful that the output of the first low-pass filter LP1 is sampled with a first one of these sample & hold circuits when the quadrature conditions a) and b) are satisfied. The first sample & hold circuit outputs the sampled first value as the value of the first output signal out1 until the next time the quadrature conditions a) and b) are satisfied. In the described case, it is useful that the output of the second low-pass filter LP2 is sampled with a second one of these sample & hold circuits when the quadrature conditions a) and b) are satisfied. Then, the second sample & hold circuit outputs the sampled second value as the value of the second output signal out2 until the next time the quadrature conditions a) and b) are satisfied.

[0184] In Figure 1 In the example, a test signal generator TSG (which can also be part of the signal generator G1) generates a test signal TSS from the quadrature chopper signal Cs90. The test signal generator TSG typically sets the amplitude according to a preset value.

[0185] The design can also be implemented digitally, for example by means of a digital circuit or by means of a signal processor system with appropriate programming, of the digital filter DF, the phase compensator PC, the signal generator G1, the test signal generator TSG, the second multiplier M2, the third multiplier M3, the first low-pass filter LP1 and the second low-pass filter LP2.

[0186] Preferably, the comparison means (for example, a first and a second comparator in cooperation or the signal processor) compare the value of the second output signal with a range of desired values defined by a first desired value and a second desired value. If the value of the second output signal is between the first desired value and the second desired value (i.e. within the range of desired values), it is concluded that the input stage comprising the first multiplier M1, the differential amplifier DV1, the analog-to-digital converter ADC, the digital filter DF, the phase compensator PC and the second multiplier M2 is operating correctly. The sensor system is thus able to draw conclusions in this way about the presumed correct functioning of the input stage.

[0187] Figure 2 Exemplary waveforms showing the operation of the apparatus according to Figure 1 The levels are arbitrarily chosen. The short dashed lines represent the respective zero lines. The long dashed lines shall represent the respective average value lines.

[0188] Figure 3 In the case of a sensor system corresponding substantially to Figure 1 but now the first adder Al and the first multiplier Ml are interchanged in the signal path from the sensor to the first output signal outl. This has the advantage that the sensor system is designed such that it is easy to integrate the first adder Al into the input stage of the differential amplifier DV. However, this has the disadvantage that the test signal TSS no longer tests the first multiplier Ml jointly. Furthermore, a further multiplier is required in the test signal generator TSG for multiplying the quadrature chopper signal Cs90 with the chopper signal Cs and processing it into the test signal TSS.

[0189] Figure 4 Exemplary waveforms showing the operation of the apparatus according to Figure 2 but now applied to Figure 3 Exemplary signals.

[0190] Figure 5 based on Figure 3 In the exemplary case of Figure 5 a reference Wheatstone bridge RW is also provided.

[0191] Again, a Wheatstone bridge WB is chosen as an exemplary sensor having differential outputs. The Wheatstone bridge WB comprises a first piezoresistive resistor Rl, a second piezoresistive resistor R2, a third piezoresistive resistor R3 and a fourth piezoresistive resistor R4. The first resistor Rl and the second resistor R2 are connected in series between a first supply voltage line VDD and a second supply voltage line GND. The third resistor R3 and the fourth resistor R4 are also connected in series between the first supply voltage line VDD and the second supply voltage line GND. For example, the sensor system operates the Wheatstone bridge WB with supply voltages. Thus, the Wheatstone bridge WB has a first terminal connected to the first supply voltage line VDD and a second terminal connected to the second supply voltage line GND. For example, the node between the first resistor Rl and the second resistor R2 forms a negative input signal Sin of a differential input signal Si. For example, the node between the third resistor R3 and the fourth resistor R4 forms a positive input signal Sip of the differential input signal Si.

[0192] In many sensor systems, a Wheatstone bridge is used to convert a relevant physical parameter into a differential voltage signal between a positive input signal Sip and a negative input signal Sin. For example, the Wheatstone bridge WB can be such a bridge of piezoresistive resistors of a sensor element of a piezoresistive micromechanical pressure sensor or the like. In this regard, for example, reference is made to the following industrial property rights as examples of such pressure sensors: EP 2 524 389 B1, EP 2 524 390 B1, EP 2 524 198 B1, EP 2 523 896 B1 and EP 2 523 895 B1.

[0193] For example, reference is made to a Wheatstone bridge RW comprising a fifth piezoresistive resistor R5, a sixth piezoresistive resistor R6, a seventh piezoresistive resistor R7 and an eighth piezoresistive resistor R8. The fifth resistor R5 is connected in series with the sixth resistor R6 between a first supply voltage line VDD and a second supply voltage line GND. The seventh resistor R7 is also connected in series with the eighth resistor R8 between the first supply voltage line VDD and the second supply voltage line GND. For example, the sensor system operates with a supply voltage with reference to the Wheatstone bridge RW. Thus, the reference Wheatstone bridge RW has a first terminal connected to the first supply voltage line VDD. The reference Wheatstone bridge RW has a second terminal connected to the second supply voltage line GND. Exemplarily, a node between the fifth resistor R5 and the sixth resistor R6 forms a negative reference signal Rin of a differential reference signal Rs. Exemplarily, a node between the seventh resistor R7 and the eighth resistor R8 forms a positive reference signal Rip of the differential reference signal Rs. The fifth resistor R5, the sixth resistor R6, the seventh resistor R7 and the eighth resistor R8 represent resistors of the reference Wheatstone bridge RW. The first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 represent resistors of the Wheatstone bridge WB. Preferably, the resistors of the reference Wheatstone bridge RW and the resistors of the Wheatstone bridge WB are manufactured simultaneously in the same step by a manufacturing process. For example, the Wheatstone bridge WB can be a sensing bridge of a piezoresistive micromechanical pressure sensor on a silicon single wafer or the like. In this example, the manufacturing method according to the design preferably manufactures the reference Wheatstone bridge RW together with the Wheatstone bridge WB on the same silicon single wafer. In this example, the manufacturing method according to the design preferably also manufactures in the same orientation of the respective resistors. The technical term for this is “matching”. For example, the reference Wheatstone bridge RW can be part of a second pressure sensor which is similar to the pressure sensor of the Wheatstone bridge WB and is manufactured in the same substrate (e.g. in the same semiconductor crystal). In this case, a third output signal out3 representing a difference between the differential value of the reference signal Rs and the differential value of the differential input signal Si should be close to zero.

[0194] When the reference Wheatstone bridge RW is the same as the Wheatstone bridge WB, the deviation between the differential value of the reference signal Rs, represented by the value of the third output signal out3, and the differential value of the differential input signal Si should disappear. When the reference Wheatstone bridge is designed to be the same as the Wheatstone bridge WB, a value of the third output signal out3 outside the allowable expected value range near this zero value indicates an error. Furthermore, in this case, the value of the first output signal only represents the average of the signal component based on the value of the input signal Si and the signal component based on the value of the reference signal. In this respect, Figure 5 The drawback of this system is that the sensitivity is typically halved. Only when the reference Wheatstone bridge RW and WB are affected by the same physical parameter in the same way that the Wheatstone bridge WB changes its reference signal Rs according to the value of that physical parameter. Only then will the value of the first output signal out1 at maximum sensitivity correspond to the value of that physical parameter. For example, in the case of a pressure sensor, the physical parameter could be pressure.

[0195] However, when the reference Wheatstone bridge RW differs from the Wheatstone bridge WB, the deviation between the differential value of the reference signal Rs, represented by the value of the third output signal out3, and the differential value of the differential input signal Si no longer disappears. If the reference Wheatstone bridge is substantially insensitive to the physical parameter sensed by the Wheatstone bridge WB, the value of the third output signal out3 typically reflects the value of that physical parameter, and this value is generally adjusted for such influencing factors that affect both the reference Wheatstone bridge RW and the Wheatstone bridge in the same way.

[0196] However, it is also conceivable that, in the example of the micromechanical pressure sensor, the reference Wheatstone bridge RW is not located on the diaphragm. Therefore, in this case, the reference Wheatstone bridge RW should essentially provide a signal independent of pressure. Thus, the measured value... Figure 5 In the example, it appears as the value of the third output signal out3.

[0197] Figure 5 The advantage of this arrangement is that, with good thermal coupling between the reference Wheatstone bridge RW and the Wheatstone bridge WB, the reference Wheatstone bridge RW will generate noise in the same way as the Wheatstone bridge WB itself. This allows the sensor system to reliably suppress 1 / f of the noise of the Wheatstone bridge WB itself, which is... Figure 1 It is impossible in the middle.

[0198] A signal pair consisting of a positive input signal Sip and a negative input signal Sin forms a differential input signal Si. A signal pair consisting of a positive reference signal Rip and a negative reference signal Rin forms a differential reference signal Rs.

[0199] According to the second chopping signal Cs2, the Dicke-Schalter DS switches between the differential input signal S1 and the differential reference signal Rs.

[0200] exist Figure 5 In the example, the first multiplier M1 multiplies the resulting mixed signal of differential input signal Si and differential reference signal Rs by chopping signal Cs to form product input signal MSi.

[0201] like Figure 5 As shown, the first adder A1 adds the differential test signal TSS to the product input signal MSi, forming a differential product input signal MSiT with the test signal component. Preferably, as previously mentioned, the chopping signal Cs is a digital signal with two logic values ​​(exemplarily 0 and 1 in this case).

[0202] The differential amplifier DV amplifies the differential product input signal MSiT, which contains the test signal component, into the amplifier output signal VO.

[0203] The analog-to-digital converter (ADC) converts the amplifier output signal VO into the input signal DFI of the digital filter DF. This input signal DFI of the digital filter DF comes from the ADC and is typically a digital signal of the sampled value of the amplifier output signal VO.

[0204] The digital filter DF filters the input signal DFI to the output signal DFO. In this process, the digital filter DF suppresses any signal components present at interference frequencies. Typically, the digital filter is a decimation filter used to eliminate conversion artifacts added by sampling using an analog-to-digital converter (ADC).

[0205] The phase error obtained by the phase compensator PC is corrected and the phase compensator output signal PCO is generated.

[0206] After amplification and digitization, the second multiplier M2 multiplies the phase compensator output signal PCO with the chopper signal Cs to form the first demodulated signal DM1.

[0207] The first low pass filter LP1 suppresses frequencies in the first demodulation signal DM1 that correspond to frequencies in the signal spectrum of the chopper signal Cs. The first low pass filter LP1 suppresses frequencies that correspond to frequencies in the signal spectrum of the quadrature chopper signal Cs90. The first low pass filter LP1 suppresses frequencies that correspond to frequencies in the signal spectrum of the second chopper signal Cs2. The first low pass filter LP1 suppresses mixing frequencies that can result from the multiplication of the chopper signal Cs with the quadrature chopper signal Cs90 and the second chopper signal Cs2. The first low pass filter LP1 suppresses these frequencies in the first demodulation signal DM1 except for the DC component. Thus, the first low pass filter LP1 forms the first output signal outl. If the sensors of the reference Wheatstone bridge RW are identical to the sensors of the Wheatstone bridge WB, the value of the first output signal outl corresponds to the value of the differential input signal Si.

[0208] The third multiplier M3 mixes the first demodulation signal DM1 with the quadrature chopper signal Cs90 to form a second demodulation signal DM2. The second low pass filter LP2 suppresses frequencies in the second demodulation signal DM2 that correspond to frequencies in the signal spectrum of the chopper signal Cs. The second low pass filter LP2 suppresses frequencies that correspond to frequencies in the signal spectrum of the quadrature chopper signal Cs90. The second low pass filter LP2 suppresses frequencies that correspond to frequencies in the signal spectrum of the second chopper signal Cs2. The second low pass filter LP2 suppresses mixing frequencies that can result from the multiplication of the chopper signal Cs with the quadrature chopper signal Cs90 and the second chopper signal Cs2. The second low pass filter LP2 suppresses these frequencies in the second demodulation signal DM2 except for the DC component. Thus, the second low pass filter LP2 forms the second output signal out2. As mentioned before, the value of the second output signal out2 is a measure for the correct functioning of the input stage.

[0209] A fourth multiplier M4 mixes the first demodulation signal DM1 with the second chopping signal Cs2 to form a third demodulation signal DM3. A third low pass filter LP3 suppresses frequencies in the third demodulation signal DM3 that correspond to frequencies in the signal spectrum of the chopping signal Cs. The third low pass filter LP3 suppresses frequencies that correspond to frequencies in the signal spectrum of the quadrature chopping signal Cs90. The third low pass filter LP3 suppresses frequencies that correspond to frequencies in the signal spectrum of the second chopping signal Cs2. The third low pass filter LP3 suppresses mixing frequencies that can result from the multiplication of the chopping signal Cs with the quadrature chopping signal Cs90 and the second chopping signal Cs2. The third low pass filter LP3 suppresses these frequencies in the third demodulation signal DM3 except for the DC component. Thus, the third low pass filter LP3 forms a third output signal out3. If the sensors of the reference Wheatstone bridge RW are identical to the sensors of the Wheatstone bridge WB, the user, the superior computer system or another superior system can use the value of this third output signal out3 as a measure for the correct operation of the Wheatstone bridge WB.

[0210] In Figure 5 In the example of Fig. 1, the signal generator G1 generates the chopping signal Cs, the quadrature chopping signal Cs90 and the second chopping signal Cs2. Preferably, the chopping signal Cs is bandwidth limited or single frequency. Preferably, the second chopping signal Cs2 is bandwidth limited or single frequency. Preferably, the quadrature chopping signal Cs90 is bandwidth limited or single frequency. Preferably, the quadrature chopping signal Cs90 is different from the chopping signal Cs. Preferably, the second chopping signal Cs2 is different from the quadrature chopping signal Cs90 and from the chopping signal Cs. The first low pass filter LP1 has a filter characteristic in the form of a first filter function F1 [] such that out1 = F1 [DM1 (t)]. The second low pass filter LP2 has a filter characteristic in the form of a second filter function F2 [] such that out2 = F2 [DM2 (t)]. The third low pass filter LP3 has a filter characteristic in the form of a third filter function F3 [] such that out3 = F3 [DM3 (t)]. Typically, the first low pass filter LP1, the second low pass filter LP2 and the third low pass filter LP3 have preferably identical filter characteristics and identical filter functions F [] = F1 [] = F2 [] = F3 [].

[0211] The chopping signal Cs, the second chopping signal Cs2 and the quadrature chopping signal Cs90 shall be orthogonal to each other with respect to the first filter LP1, with respect to the second filter LP2 and with respect to the third filter LP3, respectively. That is, it shall hold that:

[0212] i) F1 [Cs (t)] = 0

[0213] ii) F1 [Cs90 (t)] = 0

[0214] iii) F1 [Cs2(t)] = 0

[0215] iv) F1 [Cs(t) x Cs90(t)] = 0

[0216] v) F1 [Cs(t) x Cs2(t)] = 0

[0217] vi) F1 [Cs90(t) x Cs2(t)] = 0

[0218] vii) F2 [Cs(t)] = 0

[0219] viii) F2 [Cs90(t)] = 0

[0220] ix) F2 [Cs2(t)] = 0

[0221] x) F2 [Cs(t) x Cs90(t)] = 0

[0222] xi) F2 [Cs(t) x Cs2(t)] = 0

[0223] xii) F2 [Cs90(t) x Cs2(t)] = 0

[0224] xiii) F3 [Cs(t)] = 0

[0225] xiv) F3 [Cs90(t)] = 0

[0226] xv) F3 [Cs2(t)] = 0

[0227] xvi) F3 [Cs(t) x Cs90(t)] = 0

[0228] xvii) F3 [Cs(t) x Cs2(t)] = 0

[0229] xviii) F3 [Cs90(t) x Cs2(t)] = 0

[0230] Here, Cs(t) shall denote the time course of the values of the chopper signal Cs, Cs90(t) shall denote the time course of the values of the orthogonal chopper signal Cs90, and Cs2(t) shall denote the time course of the values of the second chopper signal Cs2.

[0231] Furthermore, the first filter function F1 [] shall preferably be a substantially linear filter function. That is, for the signal sum of the first example signal X1 (t) and the second example signal X2(t), and for a real value a, it shall hold that:

[0232] A) F1 [X1 (t) + X2(t)] = F1 [X1 (t)] + F1 [X2(t)]

[0233] B) F1 [a x X1 (t)] = a x F1 [X1 ]

[0234] Furthermore, the second filter function F2 [] shall preferably be a substantially linear filter function. That is, for the signal sum of the first example signal X1 (t) and the second example signal X2 (t), and for a real value a, it shall hold that:

[0235] C) F2 [X1 (t) + X2 (t)] = F2 [X1 (t)] + F2 [X2 (t)]

[0236] D) F2 [a x X1 (t)] = a x F2 [X1 ]

[0237] Finally, the third filter function F3 [] shall preferably be a substantially linear filter function. That is, for the signal sum of the first example signal X1 (t) and the second example signal X2 (t), and for a real value a, it shall hold that:

[0238] E) F3 [X1 (t) + X2 (t)] = F3 [X1 (t)] + F3 [X2 (t)]

[0239] F) F3 [a x X1 (t)] = a x F3 [X1 ]

[0240] Finally, the first filter function F1 [], the second filter function F2 [] and the third filter function F3 [] shall each have a low-pass characteristic. That is, it shall hold that:

[0241] F1 [1] = β1, F2 [1] = β2 and F3 [1] = β3, wherein β1 is a non-zero real constant, β2 is a non-zero real constant and β3 is a non-zero real constant.

[0242] For example, the chopper signal Cs can be a single-frequency PWM signal with values of -1 and 1, a duty cycle of 50% and a chopper signal frequency. Then, the quadrature chopper signal Cs90may be a + / - 90° phase-shifted signal with values of -1 and 1, a duty cycle of 50% and a chopper signal frequency, for example. Alternatively, the quadrature chopper signal Cs90may be a single-frequency PWM signal with values of -1 and 1 and a duty cycle of 50% and a signal frequency which is an integer multiple of the chopper signal frequency, for example. The chopper signal Cs can also be a bandwidth-limited non-single-frequency signal. The quadrature chopper signal Cs90may also be a bandwidth-limited non-single-frequency signal. Similarly, the second chopper signal Cs2may be a bandwidth-limited non-single-frequency signal. The only important thing is to satisfy the quadrature conditions i) to xviii). In other respects, the choice of the signals is free. Typically, the chopper signal Cs is periodic and the second chopper signal Cs2and the quadrature chopper signal Cs90are periodic. If necessary, it is useful for the first low-pass filter LP1, the second low-pass filter LP2and the third low-pass filter LP3to be provided with a sample & hold, respectively. In this case, it is useful for the output of the first low-pass filter LP1to be sampled with a first one of these sample & holds when the quadrature conditions i) to xviii) are satisfied. The first sample & hold then outputs the first value thus sampled as the value of the first output signal out1until the next time the quadrature conditions i) to xviii) are satisfied. Furthermore, it is useful for the output of the second low-pass filter LP2to be sampled with a second one of these sample & holds when the quadrature conditions i) to xviii) are satisfied. The second sample & hold then outputs the second value thus sampled as the value of the second output signal out2until the next time the quadrature conditions i) to xviii) are satisfied. Finally, it is useful for the output of the third low-pass filter LP3to be sampled with a third one of these sample & holds when the quadrature conditions i) to xviii) are satisfied. The third sample & hold then outputs the third value thus sampled as the value of the third output signal out3until the next time the quadrature conditions i) to xviii) are satisfied.

[0243] In Figure 5 the example, the test signal generator TSG, which can be part of the signal generator G1, generates the test signal TSS from the quadrature chopper signal Cs90. The test signal generator TSG sets the amplitude in accordance with a preset value.

[0244] The sensor system is designed in such a way that some of the circuit components can also be implemented by digital circuits or by a signal processor system with appropriate programming. These circuit components in particular relate to the digital filter DF, the phase compensator PC, the signal generator G1, the test signal generator TSG, the second multiplier M2, the third multiplier M3, the fourth multiplier M4, the first low-pass filter LP1, the second low-pass filter LP2 and the third low-pass filter LP3.

[0245] Preferably, the comparison means, for example the cooperating first and second comparators or the signal processor, compare the value of the second output signal with a range of expected values defined by a first expected value and a second expected value. If the value of the second output signal is between the first expected value and the second expected value, i.e. within the range of expected values, the input stage comprising the first multiplier M1, the differential amplifier (DV1 ), the analog-to-digital converter ADC, the digital filter DF, the phase compensator PC and the input of the second multiplier M2 is operating correctly. The sensor system, the superior computer system or another superior device can thus draw the conclusion in this way that the input stage is functioning correctly.

[0246] Preferably, the second comparison means, for example the cooperating third and fourth comparators or the signal processor, compare the value of the third output signal out3 with a second range of expected values defined by a third expected value and a fourth expected value. If the value of the third output signal out3 is between the third expected value and the fourth expected value, i.e. within the range of expected values, the Wheatstone bridge WB is operating correctly with respect to the reference Wheatstone bridge RW. The sensor system, the superior computer system or another superior device can thus draw the conclusion in this way that the Wheatstone bridge WB is functioning correctly.

[0247] Thus, the six main operating options are as follows:

[0248]

[0249] Figure 6 corresponds largely to Figure 5 but differs in that a first differential modulation voltage V mod1 The excitation voltage of the Wheatstone bridge WB is modulated. The voltages of the first voltage source V1 and the second voltage source V2 are each dependent on the test signal TSS in such a way that they are opposite to each other. Figure 6 and Figure 5 a second differential modulation voltage V mod2The excitation voltage of the reference Wheatstone bridge RW is modulated. The voltage of the third voltage source V1 b and the fourth voltage source V2b each preferably depends on the test signal TSS in an opposite manner to each other.

[0250] This modulation of the differential input signal Si and the differential reference signal Rs is proportional to the test signal TSS. Figure 6 The system of Fig. 1 has the advantage that the test signal path comprises the Wheatstone bridge WB and the reference Wheatstone bridge RW. The disadvantage is that the excitation voltage is effectively reduced and thus the useful signal swing of the input signal Si is effectively reduced. The first adder is then omitted. The signal processing is performed in an analogous manner to the preceding figures.

[0251] For example, the first differential modulated voltage V mod1 The differential voltage source of Fig. 2 consists of a first voltage source V1 and a second voltage source V2. The first voltage source V1 is connected between the first resistor R1 and the first supply voltage line VDD. The voltage of the first voltage source V1 depends on the test signal TSS. The second voltage source V2 is connected between the third resistor R3 and the first supply voltage line VDD. The voltage of the second voltage source V2 depends on the test signal TSS. The voltage of the first voltage source V1 and the voltage of the second voltage source V2 depend on the test signal TSS in an opposite manner. Apart from this sign difference in the dependence on the test signal TSS, the first voltage source V1 and the second voltage source V2 are preferably designed identically. They are preferably thermally coupled such that their behavior is essentially the same. Therefore, they are preferably manufactured on the same semiconductor substrate.

[0252] For example, the second differential modulated voltage V mod2 The differential voltage source of Fig. 3 consists of a third voltage source V1 b and a fourth voltage source V2b. The third voltage source V1 b is connected between the fifth resistor R5 and the first supply voltage line VDD. The voltage of the third voltage source V1 b depends on the test signal TSS. The fourth voltage source V2b is connected between the seventh resistor R7 and the first supply voltage line VDD. The voltage of the fourth voltage source V2b depends on the test signal TSS. Here, the voltage of the third voltage source V1 b and the voltage of the fourth voltage source V2b depend on the test signal TSS in an opposite manner. Apart from this sign difference in the dependence on the test signal TSS, the third voltage source V1 b and the fourth voltage source V2b are preferably designed identically. They are preferably thermally coupled such that their behavior is essentially the same. Therefore, they are preferably manufactured on the same semiconductor substrate.

[0253] The voltage of the first voltage source V1 and the voltage of the third voltage source V1b depend in the same way on the test signal TSS. The voltage of the second voltage source V2 and the voltage of the fourth voltage source V2b depend in the same way on the test signal TSS. The first voltage source V1 and the third voltage source V1b are preferably designed identically. The second voltage source V2 and the fourth voltage source V2b are preferably designed identically. Preferably, all four voltage sources are thermally coupled, so that their behavior is essentially identical, except for the mentioned signs. Thus, preferably, they are manufactured identically on the same semiconductor substrate.

[0254] Figure 7 corresponds largely to Figure 6 but differs in that a first differential modulation voltage V mod1 The excitation voltage of the Wheatstone bridge WB is not modulated. Here, a first differential modulation voltage V mod1 is the differential voltage between the output potential of the first voltage source V1 and the output potential of the second voltage source V2. Preferably, the voltage of the first voltage source V1 and the voltage of the second voltage source V2 each depend in opposite ways on the test signal TSS. In contrast to Figure 6 a second differential modulation voltage V mod2 The excitation voltage of the reference Wheatstone bridge RW is not modulated. The second differential modulation voltage V mod2 is the differential voltage between the output potential of the third voltage source V1b and the output potential of the fourth voltage source V2b. Preferably, the voltage of the third voltage source V1b and the voltage of the fourth voltage source V2b each depend in opposite ways on the test signal TSS.

[0255] In contrast, the sensor system modulates the value of the first resistor R1 and the value of the third resistor R3 in the Wheatstone bridge WB and the value of the fifth resistor R5 and the value of the seventh resistor R7 in the reference Wheatstone bridge RW.

[0256] In Figure 7 , the sensor system modulates the effective value of the first resistor R1. For this purpose, the first terminal of the first resistor R1 is connected to the second terminal of the first variable resistor RV1. Furthermore, for this purpose, the first terminal of the first variable resistor RV1, but not the first terminal of the first resistor R1, is connected to the first supply voltage line VDD. Here, the resistance value of the first variable resistor RV1 depends on the value of the test signal TSS. In Figure 7 the example, the test signal TSS switches a transistor which is connected in parallel to the resistance value of the first variable resistor RV1. For the purposes of this text, this transistor and the resistance value connected in parallel to this transistor form the first variable resistor RV1. The transistor of the first variable resistor RV1 is controlled by the test signal TSS which is inverted by the first inverting amplifier INV1.

[0257] In the Figure 7 , the sensor system modulates the effective value of the third resistor R3. For this purpose, the first terminal of the third resistor R3 is connected to the second terminal of the second variable resistor RV2. Furthermore, for this purpose, the first terminal of the second variable resistor RV2, but not the first terminal of the third resistor R3, is connected to the first supply voltage line VDD. Here, the resistance value of the second variable resistor RV2 depends on the value of the test signal TSS. In the Figure 7 example, the test signal TSS switches a transistor which is connected in parallel to the resistance value of the second variable resistor RV2. For the present text, this transistor and the resistance value connected in parallel to this transistor form the second variable resistor RV2. Thus, the test signal TSS controls the transistor of the second variable resistor RV2.

[0258] In the Figure 7 , the sensor system modulates the effective value of the fifth resistor R5. For this purpose, the first terminal of the fifth resistor R5 is connected to the second terminal of the third variable resistor RV3. Furthermore, for this purpose, the first terminal of the third variable resistor RV3, but not the first terminal of the fifth resistor R5, is connected to the first supply voltage line VDD. Here, the resistance value of the third variable resistor RV3 depends on the value of the test signal TSS. In the Figure 7 example, the test signal TSS switches a transistor which is connected in parallel to the resistance value of the third variable resistor RV3. For the present text, this transistor and the resistance value connected in parallel to this transistor form the third variable resistor RV3. The transistor of the third variable resistor RV3 is controlled by the test signal TSS which is inverted by the second inverting amplifier INV2.

[0259] In the Figure 7 , the sensor system modulates the effective value of the seventh resistor R7. For this purpose, the first terminal of the seventh resistor R7 is connected to the second terminal of the fourth variable resistor RV4. Furthermore, for this purpose, the first terminal of the fourth variable resistor RV4, but not the first terminal of the seventh resistor R7, is connected to the first supply voltage line VDD. Here, the resistance value of the fourth variable resistor RV4 depends on the value of the test signal TSS. In the Figure 7 example, the test signal TSS switches a transistor which is connected in parallel to the resistance value of the fourth variable resistor RV4. For the present text, this transistor and the resistance value connected in parallel to this transistor form the fourth variable resistor RV4. Thus, the test signal TSS controls the transistor of the fourth variable resistor RV4.

[0260] By this exemplary configuration, the test signal TSS modulates the differential input signal Si and the differential reference signal Rs proportionally. Figure 7The system of the first aspect has the advantage that the test signal path comprises a Wheatstone bridge WB and a reference Wheatstone bridge RW. The disadvantage is that the excitation voltage is effectively reduced and thus the stroke is effectively reduced. The first adder is then omitted. The signal processing is performed in a similar way as the preceding figures.

[0261] Preferably, the resistance values of the first and third variable resistors RV1, RV3 depend in the same way on the test signal TSS.

[0262] Preferably, the resistance values of the second and fourth variable resistors RV2, RV4 depend in the same way on the test signal TSS.

[0263] Preferably, the resistance values of the first and second variable resistors RV1, RV2 depend in opposite but otherwise identical ways on the test signal TSS.

[0264] Preferably, the resistance values of the third and fourth variable resistors RV3, RV4 depend in opposite but otherwise identical ways on the test signal TSS.

[0265] Preferably, the first variable resistor RV1 is designed identically (matched) to the second variable resistor RV2.

[0266] Preferably, the third variable resistor RV3 is designed identically (matched) to the fourth variable resistor RV4.

[0267] Preferably, the first variable resistor RV1 is designed identically (matched) to the third variable resistor RV3.

[0268] Preferably, the second variable resistor RV2 is designed identically (matched) to the fourth variable resistor RV4.

[0269] List of reference signs

[0270] A1 first adder

[0271] ADC analog-digital converter

[0272] Cs chopper signal

[0273] Cs2 second chopper signal

[0274] Cs90 quadrature chopper signal

[0275] DF digital filter

[0276] DFI input signal of the digital filter DF

[0277] DFO output signal of the digital filter DF

[0278] DM1 first demodulation signal

[0279] DM2 second demodulation signal

[0280] DM3 third demodulation signal

[0281] DS Diode switch

[0282] DV Differential amplifier

[0283] G1 Signal generator

[0284] GND Second supply voltage line

[0285] INV1 First inverting amplifier or inverter

[0286] INV2 Second inverting amplifier or inverter

[0287] LP1 First low pass filter

[0288] LP2 Second low pass filter

[0289] LP3 Third low pass filter

[0290] M1 First multiplier

[0291] M2 Second multiplier

[0292] M3 Third multiplier

[0293] M4 Fourth multiplier

[0294] MSi Multiplied input signal

[0295] MSiT Differential multiplied input signal with test signal component

[0296] out1 First output signal

[0297] out2 Second output signal

[0298] out3 Third output signal

[0299] PC Phase compensator

[0300] PCO Phase compensator output signal

[0301] R1 First resistor

[0302] R2 Second resistor

[0303] R3 Third resistor

[0304] R4 Fourth resistor

[0305] R5 Fifth resistor

[0306] R6 sixth resistor

[0307] R7 seventh resistor

[0308] R8 eighth resistor

[0309] Rin negative reference signal

[0310] Rip positive reference signal

[0311] Rs reference signal

[0312] RV1 first variable resistor

[0313] RV2 second variable resistor

[0314] RV3 third variable resistor

[0315] RV4 fourth variable resistor

[0316] RW reference Wheatstone bridge

[0317] Si differential input signal

[0318] Sin negative input signal

[0319] Sip positive input signal

[0320] SiT differential input signal with test signal component

[0321] t time

[0322] TSG test signal generator

[0323] TSS test signal

[0324] WB Wheatstone bridge consisting of a first resistor R1, a second resistor R2, a third resistor R3 and a fourth resistor R4

[0325] V1 first voltage source

[0326] V1b third voltage source

[0327] V2 second voltage source

[0328] V2b fourth voltage source

[0329] V mod1 first differential modulation voltage

[0330] V mod2 second differential modulation voltage

[0331] VO amplifier output signal

[0332] VDD first supply voltage line

[0333] List of cited documents

[0334] EP 2 524 389 B1,

[0335] EP 2 524 390 B1,

[0336] EP 2 524 198 B1,

[0337] EP 2 523 896 B1,

[0338] EP 2523895 B1.

[0339] Non-patent literature

[0340] Christopher R. Nerz's lecture "Introduction to Differential Geometry".

[0341] Link

[0342] https: / / de.wikipedia.org / wiki / Lp-Raum#Der_Hilbertraum_L2

[0343] https: / / www.math.uni-tuebingen.de / de / forschung / gadr / lehre / sose2015 / diffgeo.pdf

Claims

1. A method for monitoring a sensor system in operation, wherein the sensor system comprising a sensor element (WB) providing an input signal (Si) having a time course (Si(t)) of input signal values of the input signal (Si), and wherein the sensor system comprises a signal path, and wherein at a first location of the signal path, the signal path comprises an amplifier (DV) having an input and an output, and wherein the signal path starts with the input signal (Si) from the sensor element (WB), and wherein the signal path ends with a first output signal (outl) of the sensor system, and wherein a value of the first output signal (outl) or a value of a signal derived from the first output signal represents a measurement value, the method comprising the following steps: a) first mixing the input signal (Si) in the signal path with a chopper signal (Cs) at a second location of the signal path, - wherein the second location is located in the signal path between the sensor element (WB) and the input of the amplifier (DV), and - wherein the chopper signal (Cs) is band-limited or single-frequency; b) second mixing the input signal (Si) with the chopper signal (Cs) at a third location of the signal path to form a first demodulation signal (DM1), - wherein the third location of the signal path is located between the output of the amplifier (DV) at the first location of the signal path and the first output signal (outl) of the sensor system at the end of the signal path; c) first filtering the first demodulation signal (DM1) or a signal derived from the first demodulation signal at a fourth location of the signal path, the fourth location being located between the third location of the signal path and the first output signal (outl) of the sensor system at the end of the signal path, - wherein the first filtering is performed by applying a first filter function F1[] to the first demodulation signal (DM1) or the signal derived from the first demodulation signal, and - wherein the first filter function F1[] describes a relationship between a time course (DM1(t)) of the first demodulation signal (DM1) or the signal derived from the first demodulation signal and a time course of this signal immediately after the first filtering, and - wherein the first output signal (outl) depends on or is a result of the first demodulation signal (DM1) immediately after the first filtering, characterized in that it further comprises the additional step d) adding a quadrature chopper signal (Cs90) to the input signal (Si) in the signal path at a fifth location of the signal path, the fifth location being located between the sensor element (WB) and the amplifier (DV). - wherein the chopper signal (Cs) has a time course (Cs(t)) of the chopper signal (Cs), and - wherein the quadrature chopper signal (Cs90) has a time course (Cs90(t)) of the quadrature chopper signal (Cs90), and - wherein the time course (Cs90(t)) of the quadrature chopper signal (Cs90) has at least at times, apart from noise and signal errors, substantially the property F1 [Cs90(t) x Cs(t)] = 0 with respect to the first filter function F1 [], wherein Cs(t) denotes the time course (Cs(t)) of the chopper signal (Cs) and Cs90(t) denotes the time course (Cs90(t)) of the quadrature chopper signal (Cs90); e) third mixing of the first demodulation signal (DM1) or a signal derived from the first demodulation signal with the quadrature chopper signal (Cs90) or a signal derived from the quadrature chopper signal and generating a second demodulation signal (DM2); f) second filtering of the second demodulation signal (DM2) or a signal derived from the second demodulation signal by a second filter function F2 [] to form a second output signal (out2), wherein - the second filter function F2 [] is selected such that the following equations substantially hold: F2 [Cs(t)] = 0 and F2 [Cs90(t)] = 0 and F2 [Cs(t) x Cs90(t)] = 0 and F2 [1] = β2, wherein β2 is a real or complex value, and - the first filter function F1 [] is selected such that the following equations substantially hold: F1 [Cs(t)] = 0 and F1 [Cs90(t)] = 0 and F1 [Cs(t) x Cs90(t)] = 0 and F1 [1] = β1, wherein β1 is a real or complex value; g) first comparison of a value of the second output signal (out2) or a value of a signal derived from the second output signal with an expected value interval and, if the value of the second output signal (out2) or of the signal derived from the second output signal is outside the expected value interval, a conclusion is drawn that an error is present.

2. The method according to claim 1, comprising the following additional steps: h) providing a reference element (RW) for providing a reference signal (Rs), i) processing the reference signal (Rs) in a reference signal path, - wherein, the reference signal path being designed identically to the signal path for processing the input signal (Si), and - wherein the reference signal path starts at the reference signal (Rs), and - wherein the reference signal path ends at the second output signal (out2), and - wherein the reference signal path at the start at the reference signal (Rs) of the reference signal path is different from the signal path at the start at the input signal (Si) of the signal path, and - wherein, at a first position of the reference signal path, the reference signal path comprises the amplifier (DV) having the input and the output, and - wherein the amplifier (DV) is thus a part of the reference signal path at the first position of the reference signal path, and a part of the signal path at the first position of the signal path, and - wherein, at a sixth position of the reference signal path, the reference signal path comprises a switch (DS) having a first input and a second input, the sixth position of the reference signal path being between the reference element (RW) and the input of the amplifier (DV), the sixth position of the reference signal path corresponding to a sixth position of the signal path, so that the switch (DS) is also arranged at the sixth position of the signal path between the sensor element (WB) and the input of the amplifier (DV), the switch (DS) thus being a common switch (DS), and - wherein, in dependence of a second chopper signal (Cs2), the common switch (DS) selects an active input between its first input and its second input, and - wherein the signal path comprises the first input of the switch (DS), and - wherein the reference signal path comprises the second input of the switch (DS), and - wherein the signal path does not comprise the second input of the switch (DS), and - wherein the reference signal path does not comprise the first input of the switch (DS), and - wherein the common switch (DS) selects its active input which is selected in dependence of the second chopper signal (Cs2), and connects a respective current value at the selected active input of the common switch (DS) to an output of the common switch (DS), and - wherein, in the part from the output of the common switch (DS) at the sixth position of the reference signal path and the sixth position of the signal path to the input of the amplifier (DV) at the first position of the reference signal path and the signal path, the reference signal path and the signal path are identical, and - wherein the first filtering using the first filter function F1[] is only a part of the signal path, but not of the reference signal path; j) fourth mixing the first demodulation signal (DM1) or a signal derived from the first demodulation signal with the second chopper signal (Cs2) to form a third demodulation signal (DM3); k) third filtering the third demodulation signal (DM3) or a signal derived from the third demodulation signal by a third filter function F3[] to form a third output signal (out3), - wherein the first filter function F1 [] is chosen such that the following equations essentially hold: F1 [Cs (t)] = 0 and F1 [Cs2 (t)] = 0 and F1 [Cs90 (t)] = 0 and F1 [Cs (t) x Cs2 (t)] = 0 and F1 [Cs (t) x Cs90 (t)] = 0 and F1 [Cs2 (t) x Cs90 (t)] = 0 and F1 [Cs (t) x Cs2 (t) x Cs90 (t)] = 0 and F1 [1] = β1, where β1 is a real or complex value, wherein Cs2 (t) denotes the time course of the second chopper signal (Cs2), and - wherein the second filter function F2 [] is chosen such that the following equations essentially hold: F2 [Cs (t)] = 0, F2 [Cs2 (t)] = 0, F2 [Cs90 (t)] = 0, F2 [Cs (t) x Cs2 (t)] = 0, F2 [Cs (t) x Cs90 (t)] = 0, F2 [Cs2 (t) x Cs90 (t)] = 0, F2 [Cs (t) x Cs2 (t) x Cs90 (t)] = 0, and F2 [1] = β2, where β2 is a real or complex value, and - wherein the third filter function F3 [] is chosen such that the following equations essentially hold: F3 [Cs (t)] = 0, F3 [Cs2 (t)] = 0, F3 [Cs90 (t)] = 0, F3 [Cs (t) x Cs2 (t)] = 0, F3 [Cs (t) x Cs90 (t)] = 0, F3 [Cs2 (t) x Cs90 (t)] = 0, F3 [Cs (t) x Cs2 (t) x Cs90 (t)] = 0, and F3 [1] = β3, where β3 is a real or complex value; l) a second comparison of the value of the third output signal (out3) or of a signal derived from the third output signal with a third desired value interval, and a conclusion that an error is present if the value of the third output signal (out3) or of the signal derived from the third output signal is outside the third desired value interval.

3. A method for monitoring a sensor system in operation, wherein the sensor system comprising a sensor element (WB) for providing an input signal (Si) having an input signal value which depends on a test signal (TSS), and wherein the sensor system comprises a signal path, and wherein at a first location of the signal path, the signal path comprises an amplifier (DV) having an input and an output; and wherein the signal path starts with the input signal (Si) from the sensor element (WB), and wherein the signal path ends with a first output signal (out1), and wherein the value of the output signal (out1) represents a measurement value, the method comprising the following steps: a) a first mixing of the input signal (Si) with a chopper signal (Cs) at a second location of the signal path, - wherein the second position is located in the signal path between the sensor element (WB) and the input of the amplifier (DV), and - wherein the chopper signal (Cs) is bandwidth-limited or single-frequency; b) second mixing the input signal with the chopper signal (Cs) at a third position of the signal path to form a first demodulation signal (DM1), - wherein the third position is located in the signal path between the output of the amplifier (DV) and the first output signal (out1) of the sensor system; c) first filtering the first demodulation signal (DM1) or a signal derived from the first demodulation signal at a fourth position of the signal path, the fourth position being located between the third position of the signal path and the output signal (out1) at the end of the signal path, - wherein the first filtering is performed by applying a first filter function F1[] to the first demodulation signal (DM1) or the signal derived from the first demodulation signal, and - wherein the first filter function F1[] describes a relationship between a time course (DM1(t)) of the first demodulation signal (DM1) or the signal derived from the first demodulation signal and a time course of the input signal (Si), the relationship between the time course (DM1(t)) of the first demodulation signal (DM1) or the signal derived from the first demodulation signal and the time course of the input signal (Si) being a result of filtering the first demodulation signal (DM1) with the first filter function F1[], and - wherein the first output signal (out1) depends on the first demodulation signal (DM1) or is a result of the first filtering, The method is characterized in that it comprises the following steps: d) generating the test signal (TSS) from a quadrature chopper signal (Cs90); - wherein the chopper signal (Cs) has a time course (Cs(t)) of the chopper signal (Cs), and - wherein the quadrature chopper signal (Cs90) has a time course (Cs90(t)) of the quadrature chopper signal (Cs90), and - wherein the time course (Cs90(t)) of the quadrature chopper signal (Cs90) has at least at times substantially the property F1[Cs90(t) x Cs(t)] = 0 with respect to the first filter function F1[], in addition to noise and signal errors, wherein Cs(t) denotes the time course (Cs(t)) of the chopper signal (Cs) and Cs90(t) denotes the time course (Cs90(t)) of the quadrature chopper signal (Cs90); e) third mixing the first demodulation signal (DM1) or a signal derived from the first demodulation signal with the quadrature chopper signal (Cs90) or a signal derived from the quadrature chopper signal and generating a second demodulation signal (DM2); f) second filtering of the second demodulation signal (DM2) or a signal derived from the second demodulation signal by a second filter function F2[], to form a second output signal (out2), - wherein the second filter function F2[] is chosen such that the following equations substantially hold: F2[Cs(t)] = 0 and F2[Cs90(t)] = 0 and F2[Cs(t) x Cs90(t)] = 0 and F2[1] = β2, where β2 is a real or complex value, and - wherein the first filter function F1[] is chosen such that the following equations substantially hold: F1[Cs(t)] = 0 and F1[Cs90(t)] = 0 and F1[Cs(t) x Cs90(t)] = 0 and F1[1] = β1, where β1 is a real or complex value; g) first comparing a value of the second output signal (out2) or a signal derived from the second output signal with a desired value interval, and concluding that there is an error if the value of the second output signal (out2) or the value of the signal derived from the second output signal is outside the desired value interval.

4. The method according to claim 3, comprising the following additional steps: h) providing a reference element (RW) for providing a reference signal (Rs), i) processing the reference signal (Rs) in a reference signal path, - wherein, the reference signal path being designed to be identical to the signal path for processing the input signal (Si), - wherein the reference signal path starts at the reference signal (Rs), and - wherein the reference signal path ends at the second output signal (out2), and - wherein the reference signal path at the start at the reference signal (Rs) in the reference signal path is different from the signal path at the start at the input signal (Si) in the signal path, and - wherein at a first position in the reference signal path, the reference signal path comprises the amplifier (DV) having the input terminal and the output terminal, and - wherein the amplifier (DV) is thus part of the reference signal path at the first position in the reference signal path, and part of the signal path at the first position in the signal path, and - wherein at a sixth position in the reference signal path between the reference element (RW) and the input terminal of the amplifier (DV), a switching device (DS) is inserted which is common to the signal path and the reference signal path and has a first input terminal and a second input terminal, the sixth position in the reference signal path corresponding to a sixth position in the signal path between the sensor element (WB) and the input terminal of the amplifier (DV), so that the switching device (DS) is a common switching device (DS), and - wherein, in dependence on the second chopper signal (Cs2), the common transfer switch (DS) selects as active input, respectively, the first input or the second input thereof, and - wherein the signal path comprises the first input of the transfer switch (DS), and - wherein the reference signal path comprises the second input of the transfer switch (DS), and - wherein the signal path does not comprise the second input of the transfer switch (DS), and - wherein the reference signal path does not comprise the first input of the transfer switch (DS), and - wherein the common transfer switch (DS) selects the active input thereof selected in dependence on the second chopper signal (Cs2) and passes the value at the active input of the common transfer switch (DS) to the output of the common transfer switch (DS), the value corresponding to the input signal (Si) or the reference signal (Rs), and - wherein, in the part between the output of the common transfer switch (DS) and the input of the amplifier (DV), the reference signal path and the signal path are identical, and - wherein the first filtering using the first filter function F1[] is not part of the reference signal path; j) fourth mixing of the first demodulation signal (DM1) or a signal derived from the first demodulation signal with the second chopper signal (Cs2) to form a third demodulation signal (DM3), k) third filtering of the third demodulation signal (DM3) or a signal derived from the third demodulation signal by a third filter function F3[] to form a third output signal (out3), - wherein the first filter function F1[] is selected such that the following equations substantially hold: F1 [Cs(t)] = 0 and F1 [Cs2(t)] = 0 and F1 [Cs90(t)] = 0 and F1 [Cs(t) x Cs2(t)] = 0 and F1 [Cs(t) x Cs90(t)] = 0 and F1 [Cs2(t) x Cs90(t)] = 0 and F1 [Cs(t) x Cs2(t) x Cs90(t)] = 0 and F1 [1] = β1, where β1 is a real or complex value, where Cs2(t) denotes the time course of the second chopper signal (Cs2), and - wherein the second filter function F2[] is selected such that the following equations substantially hold: F2 [Cs(t)] = 0 and F2 [Cs2(t)] = 0 and F2 [Cs90(t)] = 0 and F2 [Cs(t) x Cs2(t)] = 0 and F2 [Cs(t) x Cs90(t)] = 0 and F2 [Cs2(t) x Cs90(t)] = 0 and F2 [Cs(t) x Cs2(t) x Cs90(t)] = 0 and F2 [1] = β2, where β2 is a real or complex value, and - wherein the third filter function F3[] is chosen such that the following equations essentially hold: F3[Cs(t)] = 0, and F3[Cs2(t)] = 0, and F3[Cs90(t)] = 0, and F3[Cs(t) x Cs2(t)] = 0, and F3[Cs(t) x Cs90(t)] = 0, and F3[Cs2(t) x Cs90(t)] = 0, and F3[Cs(t) x Cs2(t) x Cs90(t)] = 0, and F3[l] = β3, wherein β3 is a real or complex value; l) a second comparison of the value of the third output signal (out3) or of a signal derived from the third output signal with a third desired value interval, and a conclusion that an error is present if the value of the third output signal (out3) or of the signal derived from the third output signal is outside the third desired value interval.

5. Sensor system for use in a method according to claim 2 or 4, wherein the sensor system comprising a pressure sensor, which comprises a sensor element (WB) in the form of a Wheatstone bridge and having four piezoresistive resistors (R1, R2, R3, R4), and wherein the pressure sensor comprises a reference element (RW) in the form of a reference Wheatstone bridge and having four piezoresistive reference resistors (R5, R6, R7, R8), and wherein the reference resistors (R5, R6, R7, R8) of the reference Wheatstone bridge (RW) are arranged in the same way as the resistors (R1, R2, R3, R4) of the Wheatstone bridge (WB), and wherein the pressure sensor is arranged on a single crystal, and wherein the pressure sensor comprises a cavity which is closed on one side by a diaphragm, and wherein the resistors (R1, R2, R3, R4) of the Wheatstone bridge (WB) are arranged at least partially on the diaphragm, and wherein the reference resistors (R5, R6, R7, R8) of the reference Wheatstone bridge (RW) are not arranged on the diaphragm, and wherein a first resistor (R1) of the Wheatstone bridge (WB) and a fifth resistor (R5) of the reference Wheatstone bridge (RW) are identical in that they are constructed in the same way, and wherein a second resistor (R2) of the Wheatstone bridge (WB) and a sixth resistor (R6) of the reference Wheatstone bridge (RW) are identical in that they are constructed in the same way, and wherein a third resistor (R3) of the Wheatstone bridge (WB) and a seventh resistor (R7) of the reference Wheatstone bridge (RW) are identical in that they are constructed in the same way, and wherein a fourth resistor (R4) of the Wheatstone bridge (WB) and an eighth resistor (R8) of the reference Wheatstone bridge (RW) are identical in that they are constructed in the same way, and wherein the reference Wheatstone bridge (RW) serves as a reference noise source for subsequent signal processing.

6. Sensor system for use in a method according to claim 2 or 4, wherein the sensor system comprising a pressure sensor, the pressure sensor comprising a sensor element (WB) in the form of a Wheatstone bridge with four piezoresistive resistors (R1, R2, R3, R4), and wherein the pressure sensor comprises a reference element (RW) in the form of a reference Wheatstone bridge with four piezoresistive reference resistors (R5, R6, R7, R8), and wherein the reference resistors (R5, R6, R7, R8) of the reference Wheatstone bridge (RW) are arranged in the same way as the resistors (R1, R2, R3, R4) of the Wheatstone bridge (WB), and wherein the pressure sensor is arranged on a single crystal, and wherein the pressure sensor comprises a first cavity closed by a first diaphragm on a first side, and wherein the first cavity has a cavity surface of the first cavity opposite the first side of the first cavity, and wherein the pressure sensor comprises a reference cavity closed by a second diaphragm on a second side, and wherein the reference cavity has a cavity surface of the reference cavity opposite the second side of the reference cavity, and wherein the resistors (R1, R2, R3, R4) of the Wheatstone bridge (WB) are at least partially arranged on the first diaphragm, and wherein the reference resistors (R5, R6, R7, R8) of the reference Wheatstone bridge (RW) are at least partially arranged on the second diaphragm, and wherein a first resistor (R1) of the Wheatstone bridge (WB) is identical to a fifth resistor (R5) of the reference Wheatstone bridge (RW) in that they are constructed in the same way, and wherein a second resistor (R2) of the Wheatstone bridge (WB) is identical to a sixth resistor (R6) of the reference Wheatstone bridge (RW) in that they are constructed in the same way, and wherein a third resistor (R3) of the Wheatstone bridge (WB) is identical to a seventh resistor (R7) of the reference Wheatstone bridge (RW) in that they are constructed in the same way, and wherein a fourth resistor (R4) of the Wheatstone bridge (WB) is identical to an eighth resistor (R8) of the reference Wheatstone bridge (RW) in that they are constructed in the same way, and wherein the reference Wheatstone bridge (RW) serves as a reference noise source for subsequent signal processing, and wherein the first diaphragm is designed differently from the second diaphragm, and / or wherein the first cavity is designed differently from the reference cavity, and / or wherein the cavity surface of the first cavity opposite the first side of the first cavity is constructed differently from the cavity surface of the reference cavity opposite the second side of the reference cavity, and / or wherein the first cavity and the reference cavity are filled with a fluid, respectively, wherein the fluid in the first cavity is different from the fluid in the reference cavity, or the fluid in the first cavity is in a different state than the fluid in the reference cavity, wherein a vacuum is considered a fluid.

7. A sensor system for use in a method according to claim 3 or 4, wherein the sensor system comprises a sensor, the sensor comprises a first resistor (R1) having a first terminal and a second terminal, and wherein the sensor comprises a second resistor (R2) having a first terminal and a second terminal, and wherein the sensor comprises a third resistor (R3) having a first terminal and a second terminal, and wherein the sensor comprises a fourth resistor (R4) having a first terminal and a second terminal, and wherein the sensor comprises a first voltage source (V1) having a first terminal and a second terminal, and wherein the sensor comprises a second voltage source (V2) having a first terminal and a second terminal, and wherein the first terminal of the first voltage source (V1) is connected to a first supply voltage line (VDD), and wherein the second terminal of the first voltage source (V1) is connected to the first terminal of the first resistor (R1), wherein the second terminal of the first resistor (R1) is connected to the first terminal of the second resistor (R2), and wherein the second terminal of the second resistor is connected to a second supply voltage line (GND), and wherein the first terminal of the second voltage source (V2) is connected to the first supply voltage line (VDD), and wherein the second terminal of the second voltage source (V2) is connected to the first terminal of the third resistor (R3), wherein the second terminal of the third resistor (R3) is connected to the first terminal of the fourth resistor (R4), and wherein the second terminal of the fourth resistor (R4) is connected to the second supply voltage line (GND), and wherein a first voltage of the first voltage source (V1) depends on a test signal (TSS), and wherein a second voltage of the second voltage source (V2) depends on the test signal (TSS) in an opposite way than the first voltage of the first voltage source (V1).

8. The sensor system according to claim 7, wherein, the sensor is a pressure sensor.

9. A sensor system for use in a method according to claim 3 or 4, wherein, the sensor system comprises a sensor, the sensor comprises a first resistor (R1) having a first terminal and a second terminal, and wherein the sensor comprises a second resistor (R2) having a first terminal and a second terminal, and wherein the sensor comprises a third resistor (R3) having a first terminal and a second terminal, and wherein the sensor comprises a fourth resistor (R4) having a first terminal and a second terminal, and wherein the sensor comprises a first variable resistor (RV1) having a first terminal and a second terminal, and wherein the sensor comprises a second variable resistor (RV2) having a first terminal and a second terminal, and wherein the first terminal of the first variable resistor (RV1) is connected to a first supply voltage line (VDD), and wherein the second terminal of the first variable resistor (RV1) is connected to the first terminal of the first resistor (R1), wherein the second terminal of the first resistor (R1) is connected to the first terminal of the second resistor (R2), and wherein the second terminal of the second resistor is connected to a second supply voltage line (GND), and wherein the first terminal of the second variable resistor (RV2) is connected to the first supply voltage line (VDD), and wherein the second terminal of the second variable resistor (RV2) is connected to the first terminal of the third resistor (R3), wherein the second terminal of the third resistor (R3) is connected to the first terminal of the fourth resistor (R4), wherein the second terminal of the fourth resistor (R4) is connected to the second supply voltage line (GND), and wherein the resistance value of the first variable resistor (RV1) depends on a test signal (TSS), and wherein the resistance value of the second variable resistor (RV2) depends on the test signal (TSS) in an opposite manner to the resistance value of the first variable resistor (RV1).

10. The sensor system according to claim 9, wherein, the sensor is a pressure sensor.

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