Sensor system with a readout circuit and method for operating a sensor system with a readout circuit

Abstract

A sensor system and a method for its operation are proposed, comprising a readout circuit for a capacitive differential sensor output for detecting an analog sensor output signal, wherein the readout circuit comprises at least --- a capacitance-voltage converter and --- a compensation device for compensating at least one parasitic impedance includes, wherein the capacitance-to-voltage converter has a converter input and wherein the capacitance-to-voltage converter detects the sensor output signal at its converter input under the influence of both the at least one parasitic impedance and the compensation device as an analog sensor output signal, wherein the compensation device provides a further impedance component at the converter input which at least partially compensates for the influence of the parasitic impedance

Description

State of the art

[0001] The invention is based on a sensor system with a readout circuit according to the preamble of the main claim.

[0002] Sensor systems with seismic elements excited to oscillate, particularly resonant sensor systems with MEMS gyroscopes, place high demands on the interface amplifiers or capacitance-to-voltage converters used in the readout circuit. On the one hand, the interface amplifier or capacitance-to-voltage converter must ensure a stable phase and a stable gain factor under various operating conditions, and on the other hand, the interface amplifier or capacitance-to-voltage converter must be able to withstand a wide range of parasitic impedances at the converter input of the capacitance-to-voltage converter. Critical parameters such as noise behavior, linearity and the power consumption of the sensor system depend heavily on the performance of the interface amplifier.capacitance-voltage converter and the influence of parasitic impedances at the converter input.

[0003] Various circuit methods for compensating or reducing parasitic impedances (at the converter input) are known in the state of the art. However, since in practice different applications often require different power requirements for different operating modes, for example, for gyroscopes, optimal use of the sensor system in most cases represents a compromise between the required power and the gain values ​​or noise components required for the application. Therefore, matching the power requirements for the operation of the sensor system and the noise components associated with the gain values ​​is advantageous over a wide range and represents a challenge.

[0004] The option described in the prior art for achieving this is to readjust the power consumption of the interface amplifier or capacitance-to-voltage converter. However, this is an inadequate option due to the need to maintain stability and the impact on the parameters of the interface amplifier. The impact on the parameters of the interface amplifier must be compensated for by long test times and costs using readjustment procedures, or - alternatively - the operating ranges must be severely limited.

[0005] High-performance capacitive MEMS, such as gyroscopes and accelerometers, place stringent demands on their interface amplifiers (IAs). On the one hand, the amplifier must exhibit stable phase and gain under various operating conditions, while simultaneously being stable with a wide range of parasitic capacitances at its input nodes. On the other hand, the noise performance, linearity, and performance of the entire system depend heavily on the interface amplifier. Disclosure of the invention

[0006] It is an object of the present invention to provide a sensor system with a readout circuit which does not have the above-mentioned disadvantages.

[0007] The sensor system according to the invention according to the main claim has the advantage over the prior art that the configurable capacitance arrangement, on the one hand, provides the output signal of the compensation device corresponding to the further impedance component as the analog signal corresponding to a variable capacitance at the converter input and, on the other hand, is adjustable by means of a digital input. Furthermore, the compensation device has a control input (for selecting the respective operating and / or power mode; operating mode selection) for setting a respective operating and / or power mode to be used. Providing the analog signal corresponding to a variable capacitance at the converter input advantageously makes it possible to ensure efficient and effective operation of the sensor system, particularly with regard to performance requirements.The configurable capacitance arrangement can be efficiently adjusted using the digital input (hereinafter also referred to as “trim code X”).

[0008] Furthermore, the sensor system can also be operated effectively and efficiently using different gain values ​​and the associated different noise components. Furthermore, the use of different gain values ​​within certain operating modes (i.e., among other things, during operation of changing operating modes) can be advantageously optimized for specific uses (and this does not have to be readjusted for each application or operating mode). Furthermore, the influence of the parasitic impedance at the transducer input on the introduced phase difference and / or the gain factor and / or the stability can be advantageously reduced or significantly reduced. This allows the properties of the sensor system to be determined more specifically, and the effort required for testing and / orThis effectively reduces calibration times and additional space requirements (and thus additional costs). In addition to the aforementioned advantages, costs can also be saved, particularly in manufacturing.

[0009] The described invention enables a much wider range of power and performance modes than the prior art, while eliminating the impact on phase, gain, and stability of the IA (capacitance-to-voltage converter). This not only significantly simplifies the design of the interface amplifier but also reduces the test time and area required to enable mode changes.

[0010] The described invention enables: - Adjustment of the performance (power consumption and noise) of the frontend over a wide range. - Minimize the impact on other front-end operation parameters due to performance adjustment. - Due to the above-mentioned properties, the sensors can be optimized for a specific application and do not need to be readjusted for each operating mode, thus saving costs.

[0011] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0012] According to an advantageous embodiment of the invention, the compensation device comprises an auxiliary amplifier, wherein the auxiliary amplifier has an amplification factor greater than 2. Thus, it is advantageously possible for a simulation of the reference potential (virtual ground) of the capacitance-to-voltage converter to be amplified by an amplification factor typically greater than 2, but in particular less than 10. This forms the basis for the output signal of the compensation device, which corresponds to the analog signal corresponding to a variable capacitance.

[0013] According to an advantageous embodiment of the invention, the configurable capacitor array is designed as a digital-to-analog converter with a configurable capacitor array. This advantageously provides the possibility of adapting the configurable capacitor array to a wide range of different operating modes, particularly with regard to the use of different power requirements for operating the sensor system and / or the application of different gain values ​​and, consequently, different noise components.

[0014] According to an advantageous embodiment of the invention, the compensation device with the configurable capacitance arrangement and the auxiliary amplifier is capable of providing the additional impedance component in such a way that the additional impedance component corresponds to the negative of the impedance caused by the parasitic impedance and essentially compensates for it. This advantageously makes it possible to ensure effective and efficient operation.

[0015] According to an advantageous embodiment of the invention, it is provided that the operation of the compensation device and the compensation of the at least one parasitic impedance causes the capacitance-voltage converter to be operable in a wide range of different operating modes (according to the invention in particular such that the noise can be changed by a factor of 10 and therefore the current consumption by a factor of 100), in particular -- using different power requirements to operate the capacitance-to-voltage converter and / or -- by applying different gain values ​​and thus different noise components, or by changing the noise by changing the open-loop parameters of the auxiliary amplifier (such as current consumption or transconductance). This advantageously ensures effective and efficient operation.

[0016] According to an advantageous embodiment of the invention, it is provided that the operation of the compensation device causes the influence on the operation of the capacitance-voltage converter with regard to -- the introduced phase difference and / or -- the gain factor and / or -- the stability disappears or is at least significantly reduced or minimized over a wide operating range of the capacitance-to-voltage converter. This advantageously results in effective and efficient operation of the sensor system.

[0017] A further subject of the invention is a method for operating a sensor system with a readout circuit according to the independent method claim.

[0018] The method according to the invention for operating a sensor system with a readout circuit proves to be advantageous compared to the prior art in that the configurable capacitance arrangement -- on the one hand, provides the output signal of the compensation device corresponding to the further impedance component as well as the analogue signal corresponding to a variable capacitance at the converter input and -- on the other hand, has a digital input for setting the operating state of the configurable capacity arrangement.

[0019] Thus, by providing the analog signal corresponding to a variable capacitance, it is advantageously possible to ensure efficient and effective operation of the sensor system, in particular of the capacitance-to-voltage converter, while using different power requirements. The digital input (hereinafter also referred to as "trim code X") allows a compensation signal to be used effectively and efficiently to adjust an operating state of the configurable capacitance arrangement.

[0020] Furthermore, the method according to the invention allows the sensor system to be operated in a wide range of different operating modes. This particularly applies to the use of different power requirements for operating the sensor system and / or the application of different gain values ​​and the associated different noise components. Furthermore, the operation of the sensor system according to the invention results in efficient and effective compensation or a significant reduction of the influence (on the operation of the capacitance-to-voltage converter) with regard to the phase difference introduced by the parasitic impedance and / or the gain factor and / or the stability over a wide operating range. Furthermore, the design of the capacitance-to-voltage converter can be adapted effectively and efficiently, and the testing and calibration time and space requirements can be reduced effectively and efficiently.Furthermore, the advantages mentioned also allow costs to be saved, particularly in the production of the sensor system to be operated.

[0021] The described invention enables a much wider range of power and performance modes than previous architectures, while eliminating or at least greatly reducing the impact on phase, gain, and stability of the IA (capacitance-to-voltage converter). This not only significantly simplifies the design of the interface amplifier but also reduces test time and the area or wafer space required to enable mode changes.

[0022] The described invention enables: -- adjusting the performance (power consumption and noise) of the front end (readout circuit) over a wide range. -- minimizing the impact on other front-end operation parameters due to a performance adjustment. -- Due to the above-mentioned properties, the sensors can be optimized for a specific application and do not have to be readjusted for each operating mode, thus saving costs and, in particular, time required to carry out adjustment of components during their manufacture.

[0023] For the method for operating a sensor system with a readout circuit, the advantages and configurations described in connection with the embodiments of the sensor system with a readout circuit according to the invention can be applied.

[0024] Embodiments of the present invention are illustrated in the drawings and explained in more detail in the following description. Short description of the drawings: Fig. 1 shows a schematic representation of an equivalent circuit diagram of the sensor system with a readout circuit according to the prior art. Fig. 2 shows a schematic representation of an equivalent circuit diagram of the sensor system with a readout circuit to explain the procedure according to the invention. Fig. 3 shows a schematic diagram of the sensor system with a readout circuit according to the present invention. Fig. 4 shows a schematic diagram of the sensor system with a readout circuit or a part thereof according to the present invention. Embodiments of the invention:

[0025] Fig. Figure 1 shows a schematic representation of an equivalent circuit diagram of the sensor system with a readout circuit 100 according to the prior art. The micromechanical structure with a capacitive (in particular differential) sensor output, ie a capacitive sensor - in Fig. 1 and the following Fig. 2 and Fig. 3 schematically represented by a rectangle with a capacitance symbol - is excited to oscillate in a known manner, and typically via a capacitive differential sensor output, an analog sensor output signal is forwarded to a readout circuit 100, which is coupled to the capacitive sensor. In addition, the influence of one (or at least one) parasitic impedance 101 is schematically represented in the form of an equivalent circuit diagram. Furthermore, an interface amplifier or capacitance-to-voltage converter 120 with a converter input 121 of the interface amplifier or capacitance-to-voltage converter 120 is shown. The analog sensor output signal is present at the converter input 121 under the influence of the (at least one) parasitic impedance 101. Specifically, the interface amplifier or capacitance-to-voltage converter 120 detects the analog sensor output signal at its converter input 121 under the influence of the (at least one) parasitic impedance 101.Parasitic impedance 101 (or the majority of parasitic impedances) arises in particular from a combination of sensor, package, and circuit parasitics, whereby these are examples, and other environmentally dependent sources of parasitic impedances are possible or may occur. These affect the loop gain of the interface amplifier or capacitance-to-voltage converter 120 and thus several parameters of the sensor system, including the output noise of the interface amplifier or capacitance-to-voltage converter 120.

[0026] Fig. Figure 2 shows a schematic representation of an equivalent circuit diagram of the sensor system with a readout circuit 100 to explain the procedure according to the invention. The micromechanical structure of the capacitive sensor is excited to oscillate in a known manner, and the analog sensor output signal is forwarded to the readout circuit 100 via the capacitive differential sensor output. In addition, the (at least one) parasitic impedance 101 is shown as an equivalent circuit diagram, as are the interface amplifier or capacitance-to-voltage converter 120 and its converter input 121. To at least partially compensate for the effect of the parasitic impedance, a compensation device 140 is shown according to the invention, which causes the analog sensor output signal to be present at the converter input 121 under the influence of the (at least one) parasitic impedance 101 and under the influence of the compensation device 140.The influence of the compensation device 140 at the converter input 121 relates to a further impedance component which is provided by the output signal of the compensation device 140 and at least partially compensates for the influence of the parasitic impedance 101.

[0027] Fig. Figure 3 shows a schematic circuit diagram of the sensor system with a readout circuit 100 according to the present invention. The micromechanical structure of the capacitive sensor is excited to oscillate in a known manner, and the analog sensor output signal is forwarded to the readout circuit 100 via the capacitive differential sensor output. Also shown are the (at least one) parasitic impedance 101 in the form of an equivalent circuit diagram, the interface amplifier or capacitance-to-voltage converter 120, its converter input 121, and the compensation device 140. The analog sensor output signal is again applied to the converter input 121 under the influence of the (at least one) parasitic impedance 101 and the compensation device 140.

[0028] According to an exemplary embodiment of the invention, an auxiliary amplifier 150 is arranged within the compensation device 140, which has an amplification factor typically greater than 2. Furthermore, a configurable capacitor array 145 is shown, which has a digital input 146 for setting an operating state of the configurable capacitor array 145. In the exemplary embodiment, the configurable capacitor array is designed as a digital-to-analog converter with a configurable capacitor array.

[0029] The influence of the compensation device 140 at the converter input 121 relates to the additional impedance component, which is provided as the output signal of the compensation device 140. Within the compensation device 140, the output signal is provided at the output of the configurable capacitance arrangement 145 as an analog signal corresponding to a variable capacitance. Furthermore, the compensation device 140, by means of the configurable capacitance arrangement 145 and the auxiliary amplifier 150, is capable of providing the additional impedance component in such a way that the additional impedance component corresponds to the negative of the impedance caused by the parasitic impedance and essentially compensates for it.

[0030] Furthermore, a setting of the configurable capacitance arrangement 145 is fed in or performed via the digital input 146 using a compensation signal (hereinafter also referred to as "trim code X"). This advantageously results in an adjustment of the output signal of the compensation device 140 and can be adapted with respect to different operating modes, for example, using different power requirements for operating the interface amplifier or capacitance-to-voltage converter 120 and / or using different gain values ​​and, consequently, different noise components.

[0031] Fig. 3 thus represents an embodiment variant according to the invention, in which an implementation of the compensation device 140 is shown. The auxiliary amplifier 150 with a gain of +A and the digital-to-analog converter with a configurable capacitor array are used to realize the compensation device 140. The auxiliary amplifier 150 generates a simulation of the reference potential (virtual ground) of the interface amplifier or capacitance-to-voltage converter 120 with a gain of typically more than 2. The gain A can be selected to be larger if necessary in order to reduce the memory requirement of the digital-to-analog converter with a configurable capacitor array. If the capacitive influence at the reference potential (virtual ground) of the interface amplifier orSince the noise gain of the capacitance-to-voltage converter 120 dominates and is canceled out by the compensation device 140, the noise power is now dominated by the compensation device 140. More precisely, this would be the case in the implementation of . Fig. 3 the auxiliary amplifier 150 with the gain A.

[0032] The noise gain NG IA of the interface amplifier or capacitance-voltage converter 120 can be described as follows: NGIA=Cparasitic−Cpar−cancelCfb+1 while the noise NG assisting-amplifier of the auxiliary amplifier 150 is amplified as follows: NGassisting−amplifier=CNDACCfb∗A

[0033] Where C parasitic the (at least one) parasitic impedance 101 at the converter input 121 of the interface amplifier or capacitance-voltage converter 120, C par-cancelthe capacity of the compensation device 140, which is introduced to C parasitic (partially or completely) to cancel, C NDAC is the capacity of the digital-to-analog converter with configurable capacitor array and C fbis the capacitance of the feedback capacitor of the interface amplifier or capacitance-to-voltage converter 120. It should be noted that, according to the invention, the requirements for the auxiliary amplifier 150 are much lower than for the interface amplifier or capacitance-to-voltage converter 120. The auxiliary amplifier 150 only sees the very small virtual ground signals of the interface amplifier or capacitance-to-voltage converter 120 and requires only comparatively low closed-loop gain. Therefore, this amplifier 150 can be implemented with a much simpler architecture than the interface amplifier or capacitance-to-voltage converter 120 and can therefore be easily implemented with a wide range of power modes or operating modes.Due to the impedance cancellation by the auxiliary amplifier 150, the phase delay, the loop gain, and the stability of the interface amplifier or capacitance-to-voltage converter 120 depend, to a first order, only on the control loop characteristic of the auxiliary amplifier 150 and the digital-to-analog converter with a configurable capacitor array. The dependence of the parameters of the interface amplifier or capacitance-to-voltage converter 120 depends, to a first order, only on the closed-loop characteristic of the auxiliary amplifier 150, and the dependence of these parameters of the interface amplifier on the open-loop characteristic of the auxiliary amplifier 150 is low. According to the invention, it is advantageously preferably provided that the amplifier 150 (which has a much simpler architecture than the interface amplifier orCapacitance-to-voltage converter 120 can be implemented) in a wide range of power modes or operating modes; for this purpose, the invention particularly provides that the amplifier 150 is designed to operate in different operating modes and / or power modes and in particular has a control input for selecting the respective operating and / or power mode to be used (operating mode selection) (this control input, however, is in . Fig. 3 not shown for simplicity).

[0034] Fig. Figure 4 shows a schematic diagram of the sensor system with a readout circuit 100 or a part thereof according to the present invention. Shown are the interface amplifier or capacitance-to-voltage converter 120 and the compensation device 140, which in this embodiment comprises the configurable capacitance arrangement 145 as shown in Fig. 3. An adjustable voltage noise source 155, by which the auxiliary amplifier 150 can be modeled, is shown as an equivalent circuit. The auxiliary amplifier 150 can thus be modeled by the adjustable voltage noise source 155, so that at a converter output of the interface amplifier or capacitance-to-voltage converter 120, this adjustable voltage noise source is represented by the capacitance ratio C NDAC / C fbis amplified. According to the invention, the interface amplifier or capacitance-to-voltage converter 120 can thus be operated in different operating modes both during a switch-on process and during operation, or, among other things, a change between the different operating modes can take place during operation. For example, operating modes with a low power requirement and a high noise component, an average power requirement and an average noise component, and a high power requirement and a low noise component can be implemented, or the interface amplifier 120 can be operated in these operating modes. According to the invention, it is advantageously preferably provided that the adjustable voltage noise source 155 (and thus the auxiliary amplifier 150) can be used in a wide range of power modes oroperating modes; for this purpose, the invention provides in particular that the adjustable voltage noise source 155 is provided for operation in different operating modes and / or power modes and in particular has a control input for selecting the respective operating and / or power mode to be used (operating mode selection) (wherein the control input, however, is in . Fig.4 is also not shown for the sake of simplicity). Furthermore, here too, the compensation is carried out with the aid of the configurable capacitance arrangement 145, wherein the configurable capacitance arrangement 145 can be changed by means of the digital input 146 (trim code X), but both the compensation capacitance (of the configurable capacitance arrangement 145) and the feedback capacitance remain stable at their set value - even with different operating and / or power modes of the adjustable voltage noise source 155 to be used, which are selected via the control input.

Claims

[1] Sensor system with a readout circuit (100) for a capacitive sensor output for detecting an analog sensor output signal, wherein the readout circuit (100) has at least --- a capacitance-voltage converter (120) and --- a compensation device (140) for compensating at least one parasitic impedance (101) includes, wherein the capacitance-to-voltage converter (120) has a converter input (121) and wherein the capacitance-to-voltage converter (120) detects the analog sensor output signal at its converter input (121) under the influence of both the at least one parasitic impedance (101) and the compensation device (140), wherein the compensation device (140) provides a further impedance component at the converter input (121) which at least partially compensates for the influence of the parasitic impedance (101), characterized bythat the compensation device (140) has a configurable capacitance arrangement (145), wherein the configurable capacitance arrangement (145) is provided to provide at its output an output signal of the compensation device (140) corresponding to the further impedance component as an analog signal corresponding to a variable capacitance at the converter input (121), wherein the configurable capacitance arrangement (145) has a digital input (146) for setting the configurable capacitance arrangement (145). [2] Sensor system according to claim 1, characterized byin that the compensation device (140) has an auxiliary amplifier (150), wherein the auxiliary amplifier (150) has an amplification factor of greater than 2, wherein in particular the auxiliary amplifier (150) is implemented more simply than the capacitance-to-voltage converter (120) and can be operated in a wide range of different power and / or operating modes, so that due to the at least partial compensation of the parasitic impedance (101) by the compensation device (140), the phase delay, the loop gain and the stability of the capacitance-to-voltage converter (120) in the first order only depend on the control loop characteristic of the auxiliary amplifier 150 and the digital-to-analog converter with a configurable capacitance array. [3] Sensor system according to one of the preceding claims, characterized bythat the configurable capacitor arrangement (145) is designed as a digital-to-analog converter with a configurable capacitor array. [4] Sensor system according to one of the preceding claims, characterized by that the compensation device (140) with the configurable capacitance arrangement (145) and the auxiliary amplifier is capable of providing the further impedance component in such a way that the further impedance component corresponds to the negative of the impedance caused by the parasitic impedance and substantially compensates for it. [5] Sensor system according to one of the preceding claims, characterized by that the operation of the compensation device (140) and the compensation of the at least one parasitic impedance (101) causes the capacitance-voltage converter (120) to be operable in a wide range of different operating modes, in particular -- using different power requirements for operating the capacitance-to-voltage converter (120) and / or -- using different gain values ​​and thus different noise components. [6] Sensor system according to one of the preceding claims, characterized by that the operation of the compensation device (140) causes the influence on the operation of the capacitance-voltage converter (120) with respect to -- the introduced phase difference and / or -- the gain factor and / or -- the stability disappears or is at least greatly reduced or minimized over a wide operating range of the capacitance-voltage converter (120). [7] Method for operating a sensor system with a readout circuit (100) for a capacitive differential sensor output for detecting an analog sensor output signal, wherein the readout circuit (100) has at least --- a capacitance-voltage converter (120) and --- a compensation device (140) for compensating at least one parasitic impedance (101) includes, wherein the capacitance-to-voltage converter (120) has a converter input (121) and wherein the capacitance-to-voltage converter (120) detects the analog sensor output signal at its converter input (121) under the influence of both the at least one parasitic impedance (101) and the compensation device (140), wherein the compensation device (140) provides a further impedance component at the converter input (121) which at least partially compensates for the influence of the parasitic impedance (101), characterized byin that the compensation device (140) has a configurable capacitance arrangement (145), wherein the configurable capacitance arrangement (145) provides at its output an output signal of the compensation device (140) corresponding to the further impedance component and as an analog signal corresponding to a changeable capacitance at the converter input (121), wherein the configurable capacitance arrangement (145) has a digital input (146) for setting the configurable capacitance arrangement (145).

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