Sensor system having readout circuit and method for operating sensor system having readout circuit

Abstract

The invention relates to a sensor system and to a method for operating the sensor system, comprising a readout circuit for a capacitive differential sensor output for detecting an analog sensor output signal, the readout circuit comprising at least a capacitance-to-voltage converter and a compensation device for compensating for at least one parasitic impedance, 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 as an analog sensor output signal not only under the influence of the at least one parasitic impedance but also under the influence of the compensation device, the compensation device provides a further impedance component at the converter input, which further impedance component at least partially compensates for the influence of the parasitic impedance.

Description

Technical Field

[0001] The present invention proceeds from a sensor system having a readout circuit. Background Art

[0002] Sensor systems with vibrating elements excited to oscillate, in particular resonant sensor systems with MEMS gyroscopes, place high demands on the interface amplifiers or capacitance-to-voltage converters used in the readout circuits. On the one hand, they must ensure a stable phase and gain factor under varying operating conditions. On the other hand, they must be functional with respect to a wide range of parasitic impedances at the converter inputs of the capacitance-to-voltage converter. Critical parameters such as the noise behavior, linearity, and power requirements of the sensor system are strongly dependent on the operating capacity of the interface amplifier or capacitance-to-voltage converter and the influence of parasitic impedances at the converter inputs.

[0003] Various circuit approaches are known in the prior art for compensating for or reducing parasitic impedances (at the converter input). However, since different applications often have different power requirements for different operating modes, such as for gyroscopes, optimal use of the sensor system often results in a compromise between the required power and the gain or noise component required by the application. Therefore, adapting the power requirement for operating the sensor system and the associated noise component gain to a wide range is both advantageous and challenging.

[0004] One possibility described in the prior art for achieving this is to readjust the current consumption of the interface amplifier or the capacitor-to-voltage converter. However, due to the need to ensure stability and the influence on the parameters of the interface amplifier, this is only an insufficient option, as the influence on the parameters of the interface amplifier must be compensated again with high testing time and effort using readjustment methods, or alternatively, the operating range must be severely restricted.

[0005] Capacitive high-power MEMS, such as gyroscopes and accelerometers, place stringent demands on their interface amplifiers (IAs). On the one hand, the amplifier must maintain stable phase and gain across a wide range of operating conditions and be robust to a wide spectrum of parasitic capacitances at its input nodes. On the other hand, the noise performance, linearity, and power of the overall system are strongly dependent on the interface amplifier. Summary of the Invention

[0006] The object of the present invention is to provide a sensor system having a readout circuit which does not have the aforementioned disadvantages.

[0007] A subject of the present invention is a sensor system having a readout circuit for a capacitive sensor output for detecting an analog sensor output signal, wherein the readout circuit comprises at least

[0008] Capacitor-to-voltage converters and

[0009] compensation means for compensating at least one parasitic impedance,

[0010] wherein the capacitance-to-voltage converter has a converter input, and wherein the capacitance-to-voltage converter detects the analog sensor output signal at its converter input under the influence of the at least one parasitic impedance as well as the compensation device,

[0011] wherein the compensation device provides a further impedance component at the converter input, the further impedance component at least partially compensating for the influence of the parasitic impedance,

[0012] wherein the compensation device comprises a configurable capacitance component, wherein the configurable capacitance component is configured to provide an output signal of the compensation device at its output as a function of the further impedance component as an analog signal corresponding to a variable capacitance at the converter input,

[0013] The configurable capacitor component has a digital input terminal for adjusting the configurable capacitor component.

[0014] Compared to the prior art, the sensor system according to the present invention has the following advantages: the configurable capacitance component, on the one hand, provides the output signal of the compensation device as an analog signal corresponding to the variable capacitance at the converter input as a function of the additional impedance component, and on the other hand, is adjustable via a digital input. Furthermore, the compensation device has a control input (for selecting the operating mode and / or power mode to be used, respectively; operating mode selection) for adjusting the operating mode and / or power mode to be used. Advantageously, providing the analog signal corresponding to the variable capacitance at the converter input makes it possible to ensure efficient and effective operation of the sensor system, particularly with regard to power requirements. The configurable capacitance component can be efficiently adjusted via a digital input (hereinafter also referred to as "trim code X").

[0015] Furthermore, the sensor system can operate effectively and efficiently even when using different gain values and the different noise components associated therewith. Furthermore, advantageously, the use of different gain values can be optimized for specific applications within specific operating modes (i.e., primarily during operation of alternating operating modes) (without the need to re-adapt this for each application or each operating mode using readjustment methods). Furthermore, advantageously, the influence of parasitic impedances at the converter input can be mitigated or significantly reduced in terms of introduced phase differences and / or gain factors and / or stability during the operation of the sensor system. This allows for more specific determination of the performance of the sensor system, and effectively reduces the expenditure on test or calibration time, as well as the additional space required (and thus the additional costs). In addition to the aforementioned advantages, costs, particularly in manufacturing, can also be saved.

[0016] Compared to the prior art, the present invention enables a wider range of power modes and performance modes while offsetting the impact on the phase, gain, and stability of the IA (capacitor-to-voltage converter). This not only significantly simplifies the design of the interface amplifier, but also reduces test time and area consumption, making it possible to implement operational type changes.

[0017] The present invention can achieve:

[0018] - Adapt the power of the front end (power consumption and noise) within a wide range.

[0019] - Based on power adaptation, the impact on other parameters of front-end operation is minimized.

[0020] Due to the aforementioned properties, the sensor can be optimized for a specific application and does not have to be re-adjusted for each operating mode, thus saving costs.

[0021] Advantageous embodiments and developments of the invention can be gathered from the following description with reference to the accompanying drawings.

[0022] According to an advantageous embodiment of the invention, the compensation device has an auxiliary amplifier, wherein the auxiliary amplifier has a gain factor greater than 2. This advantageously allows a replica of the reference potential of the capacitance-to-voltage converter (virtual ground) to be amplified with a gain 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 an analog signal corresponding to the variable capacitance.

[0023] According to an advantageous embodiment of the invention, the configurable capacitor component is designed as a digital-to-analog converter having a configurable capacitor array. This advantageously allows for adapting the configurable capacitor component to a wide range of different operating modes, in particular with regard to operating the sensor system with different power requirements and / or using different gain values and the attendant different noise components.

[0024] According to an advantageous embodiment of the present invention, the compensation device, including the configurable capacitive component and the auxiliary amplifier, can provide a further impedance component such that it corresponds to the negative value of the impedance caused by the parasitic impedance and substantially compensates for this impedance. This advantageously ensures effective and efficient operation.

[0025] According to an advantageous embodiment of the invention, the operation of the compensation device and the compensation of at least one parasitic impedance result in the capacitor-to-voltage converter being able to be operated in a wide range of different operating modes (according to the invention, in particular such that the noise can be varied by a factor of 10 and thus the current consumption can be varied by a factor of 100), in particular,

[0026] - in the case of different power requirements for operating the capacitor-to-voltage converter, and / or

[0027] By using different gain values and thus different noise components, or by varying the noise by changing the open-loop parameters of the auxiliary amplifier (eg current consumption or transconductance), it is advantageously possible to ensure effective and efficient operation.

[0028] According to an advantageous embodiment of the invention, the operation of the compensation device results in the following effects on the operation of the capacitor-to-voltage converter being eliminated or at least greatly reduced or minimized over a wide operating range of the capacitor-to-voltage converter:

[0029] -Introduced phase difference and / or

[0030] - Gain factor and / or

[0031] -stability.

[0032] Advantageously, this results in an effective and efficient operation of the sensor system.

[0033] Another subject matter of the present invention is a method for operating a sensor system having a readout circuit for a capacitive differential sensor output for detecting an analog sensor output signal, wherein the readout circuit comprises at least

[0034] Capacitor-to-voltage converters and

[0035] compensation means for compensating at least one parasitic impedance,

[0036] wherein the capacitance-to-voltage converter has a converter input, and wherein the capacitance-to-voltage converter detects the analog sensor output signal at its converter input under the influence of the at least one parasitic impedance as well as the compensation device,

[0037] wherein a further impedance component is provided at the converter input by the compensation device, said further impedance component at least partially compensating for the influence of the parasitic impedance,

[0038] wherein the compensation device comprises a configurable capacitance component, wherein the configurable capacitance component provides an output signal of the compensation device at its output as a function of the further impedance component and as an analog signal corresponding to the variable capacitance at the converter input,

[0039] The configurable capacitor component has a digital input terminal for adjusting the configurable capacitor component.

[0040] Compared to the prior art, the method according to the invention for operating a sensor system having a readout circuit has proven to be advantageous because the configurable capacitive components

[0041] providing the output signal of the compensation device as a function of the further impedance component and as an analog signal at the converter input corresponding to the variable capacitance,

[0042] On the other hand, it has a digital input for setting the operating state of the configurable capacitive component.

[0043] Advantageously, by providing an analog signal corresponding to a variable capacitance, it is thus possible to ensure efficient and effective operation of the sensor system, in particular of the capacitance-to-voltage converter, even with varying power requirements. The compensation signal can be used to adjust the operating state of the configurable capacitance component in an effective and efficient manner via a digital input (hereinafter also referred to as "trim code X").

[0044] Furthermore, the method according to the invention enables the sensor system to be operated in a wide range of different operating modes. This relates in particular to operating the sensor system with different power requirements and / or using different gain values and the different noise components associated therewith. Furthermore, due to the operation of the sensor system according to the invention, the effects of phase differences and / or gain factors and / or stability introduced by parasitic impedances on the operation of the capacitor-to-voltage converter are efficiently and effectively compensated or significantly reduced over a wide operating range. Furthermore, not only can the design of the capacitor-to-voltage converter be effectively and efficiently adapted, but also the inspection time or alignment time and space requirements can be effectively and efficiently reduced. Furthermore, the aforementioned advantages also enable cost savings, particularly in manufacturing the sensor system to be operated.

[0045] Compared to previous architectures, the present invention enables a wider range of power and performance modes, while the impact on the phase, gain, and stability of the IA (capacitor-to-voltage converter) is offset or at least significantly reduced. This not only significantly simplifies the design of the interface amplifier, but also reduces test time and area consumption, or (chip) area requirements, to enable operational mode switching.

[0046] The present invention can achieve:

[0047] -Adapt the power (power consumption and noise) of the front end (readout circuit) within a wide range.

[0048] - Power-based adaptation minimizes the impact on other parameters of front-end operation.

[0049] Due to the aforementioned properties, the sensor can be optimized for a specific application and does not have to be readjusted for each operating mode, thereby saving costs and, in particular, also time expenditure for aligning the component during its production.

[0050] The advantages and embodiments described in the context of the specific embodiments of the sensor system according to the invention having a readout circuit can be used in a method for operating a sensor system having a readout circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

[0052] Figure 1 The schematic diagram shows an equivalent circuit diagram of a sensor system with a readout circuit according to the prior art.

[0053] Figure 2 In the schematic diagram, an equivalent circuit diagram of a sensor system with a readout circuit is shown to illustrate the procedure according to the present invention.

[0054] Figure 3 A sensor system according to the invention with a readout circuit is shown in a schematic diagram.

[0055] Figure 4 The schematic diagram shows a circuit diagram of a sensor system according to the invention or a part of the sensor system with a readout circuit. DETAILED DESCRIPTION

[0056] Figure 1 The schematic diagram shows an equivalent circuit diagram of a sensor system according to the prior art with a readout circuit 100. A micromechanical structure with a capacitive (especially differential) sensor output, i.e. a capacitive sensor (English: capacitive sensor) - in Figure 1 and subsequently Figure 2 and Figure 3 100 , which is schematically shown by a rectangle with a capacitor symbol, is excited into oscillation in a known manner and typically forwards an analog sensor output signal via a capacitive differential sensor output to a readout circuit 100 coupled to the capacitive sensor. Furthermore, the influence of one (or at least one) parasitic impedance 101 is schematically shown in the form of an equivalent circuit diagram. Furthermore, an interface amplifier or capacitance-to-voltage converter 120 is shown, which has a converter input 121 of the interface amplifier or of the capacitance-to-voltage converter 120. Under the influence of the (at least one) parasitic impedance 101, the analog sensor output signal is applied to the converter input 121. Specifically, under the influence of the (at least one) parasitic impedance 101, the interface amplifier or capacitance-to-voltage converter 120 detects the analog sensor output signal at its converter input 121. Parasitic impedance 101 (or multiple parasitic impedances) is generated, in particular, by a combination of sensor parasitics, housing parasitics, and circuit parasitics, which are examples, and further environment-dependent sources of parasitic impedance are possible or occur. These influence the loop gain of the interface amplifier or capacitance-to-voltage converter 120 and thus several parameters of the sensor system, and therefore also the output noise of the interface amplifier or capacitance-to-voltage converter 120.

[0057] Figure 2 The schematic diagram shows an equivalent circuit diagram of a sensor system with a readout circuit 100 to illustrate the process according to the present invention. The micromechanical structure of the capacitive sensor is excited into oscillation in a known manner, and an analog sensor output signal is forwarded to the readout circuit 100 via a capacitive differential sensor output. Furthermore, an equivalent circuit diagram of (at least one) parasitic impedance 101 is shown, as well as an interface amplifier or capacitance-to-voltage converter 120 and its converter input 121. To at least partially compensate for the effects of the parasitic impedance, a compensation device 140 is shown according to the present invention. This compensation device causes the analog sensor output signal to be applied to 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 on the converter input 121 involves an additional impedance component, which is provided by the output signal of the compensation device 140 and at least partially compensates for the effects of the parasitic impedance 101.

[0058] Figure 3 The schematic diagram shows a circuit diagram of a sensor system according to the present invention with a readout circuit 100. The micromechanical structure of the capacitive sensor is excited into oscillation in a known manner and forwards an analog sensor output signal to the readout circuit 100 via a capacitive differential sensor output. Furthermore, the (at least one) parasitic impedance 101 is shown in the form of an equivalent circuit diagram, showing an interface amplifier or capacitance-to-voltage converter 120, its converter input 121, and a compensation device 140. Under the influence of the (at least one) parasitic impedance 101 and the compensation device 140, the analog sensor output signal is again present at the converter input 121.

[0059] According to the exemplary embodiment of the present invention, an auxiliary amplifier 150 is arranged within the compensation device 140, which has a gain factor typically greater than 2. Furthermore, a configurable capacitor component 145 is shown, which has a digital input 146 for adjusting the operating state of the configurable capacitor component 145. In the exemplary embodiment shown, the configurable capacitor component is designed as a digital-to-analog converter having a configurable capacitor array.

[0060] The effect of compensation device 140 on converter input 121 involves an additional impedance component, which is provided as an output signal of compensation device 140. Within compensation device 140, the output signal at the output of configurable capacitance component 145 is provided as an analog signal corresponding to the variable capacitance. Furthermore, compensation device 140 can provide the additional impedance component using configurable capacitance component 145 and auxiliary amplifier 150 in such a way that it corresponds to the negative value of the impedance caused by the parasitic impedance and substantially compensates for this impedance.

[0061] Furthermore, an adjustment of the configurable capacitive component 145 is fed in or carried out via a compensation signal (hereinafter also referred to as "trimcode X") via a digital input 146. Advantageously, this results in an adaptation of the output signal of the compensation device 140 and can be adapted to different operating modes, for example, when operating the interface amplifier or the capacitor-to-voltage converter 120 with different power requirements and / or when using different gain values and, consequently, different noise components.

[0062] therefore, Figure 3 An embodiment variant according to the invention is shown, in which an embodiment of the compensation device 140 is shown. An auxiliary amplifier 150 with a gain of +A and a digital-to-analog converter with a configurable capacitor array are used to realize the compensation device 140. The auxiliary amplifier 150 generates a replica of the reference potential (virtual ground) of the interface amplifier or of the capacitor-to-voltage converter 120, which has a gain that is typically greater than 2. If necessary, the gain A can be selected to be larger in order to reduce the storage space requirement of the digital-to-analog converter with the configurable capacitor array. If the capacitance at the reference potential (virtual ground) of the interface amplifier or of the capacitor-to-voltage converter 120 influences the dominant noise gain and this noise gain is offset by the compensation device 140, the noise power is now dominated by the compensation device 140. More precisely, in Figure 3 In the embodiment of FIG. , this is an auxiliary amplifier 150 with a gain of A.

[0063] The noise gain NG of the interface amplifier or capacitor-to-voltage converter 120 IA It can be described as follows:

[0064]

[0065] The noise NG of the auxiliary amplifier 150 assisting-amplifier is amplified as follows:

[0066]

[0067] Here, C parasitic is the (at least one) parasitic impedance 101 at the converter input 121 of the interface amplifier or the capacitor-to-voltage converter 120, C par-cancel is the capacitance of the compensation device 140, which is introduced to (partially or completely) cancel out C parasitic , C NDAC is the capacitance of a digital-to-analog converter with a configurable capacitor array, and C fb is the capacitance of the feedback capacitor of the interface amplifier or the capacitance-to-voltage converter 120 .

[0068] It should be noted that, according to the present invention, the requirements placed on the auxiliary amplifier 150 are much lower than those placed on the interface amplifier or the capacitor-to-voltage converter 120. The auxiliary amplifier 150 only sees very small signals from the virtual ground of the interface amplifier or the capacitor-to-voltage converter 120 and requires only a relatively small gain in the closed control loop. Consequently, the amplifier 150 can be implemented with a much simpler architecture than the interface amplifier or the capacitor-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 provided by the auxiliary amplifier 150, the phase lag, loop gain, and stability of the interface amplifier or the capacitor-to-voltage converter 120 are primarily dependent on the control loop characteristic curve of the auxiliary amplifier 150 and the digital-to-analog converter with the configurable capacitor array. The parameters of the interface amplifier or of the capacitor-to-voltage converter 120 are primarily dependent on the closed-loop characteristic of the auxiliary amplifier 150, and these parameters of the interface amplifier have a low dependence on the open-loop characteristic of the auxiliary amplifier 150. According to the present invention, it is advantageously preferred to operate the amplifier 150 (which can be implemented with a much simpler architecture than the interface amplifier or the capacitor-to-voltage converter 120) in a wide range of power modes or operating modes; for this purpose, according to the present invention, it is particularly provided that the amplifier 150 is configured for operation in different operating modes and / or power modes and in particular has a control input for selecting the operating mode and / or power mode to be used (for simplicity, however, the operating mode selection is omitted). Figure 3 The control input is not shown in FIG.

[0069] Figure 4 The schematic diagram shows a circuit diagram of a sensor system or part of a sensor system according to the invention with a readout circuit 100. An interface amplifier or capacitance-to-voltage converter 120 and a compensation device 140 are shown, which in this embodiment comprises a sensor system according to Figure 3145. An adjustable voltage noise source 155 is shown as an equivalent circuit diagram, by which the auxiliary amplifier 150 can be modeled.

[0070] The auxiliary amplifier 150 can thus be modeled by an adjustable voltage noise source, so that at the converter output of the interface amplifier or of the capacitor-to-voltage converter 12 , the capacitor ratio C NDAC / C fb The adjustable voltage noise source is amplified. Thus, according to the invention, the interface amplifier or the capacitor-to-voltage converter 120 can be operated not only during the switch-on process but also during operation in different operating modes, or a change between different operating modes can be performed primarily during operation. For example, operating modes with a low power requirement and a high noise component, a medium power requirement and a medium noise component, and a high power requirement and a low noise component can be realized, 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 therefore the auxiliary amplifier 150) is operated in a wide range of power modes or operating modes; for this purpose, according to the invention, it is particularly provided 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 operating mode and / or power mode to be used (however, also for the sake of simplicity, the operating mode selection is not provided in the operating mode selection). Figure 4 ). Compensation is also performed here with the aid of configurable capacitance component 145, wherein configurable capacitance component 145 can be varied by means of digital input 146 (trim code X). However, both the compensation capacitance (of configurable capacitance component 145) and the feedback capacitance—even in the case of different adjustable voltage noise sources 155, for selecting the respective operating mode and / or power mode to be used by means of the control input—are kept stable at their set values.

Claims

1. A sensor system comprising a readout circuit (100) for a capacitive sensor output for detecting an analog sensor output signal, wherein: The readout circuit (100) comprises at least Capacitor-to-voltage converter (120) and a compensation device (140) for compensating at least one parasitic impedance (101), 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) not only under the influence of the at least one parasitic impedance (101) but also under the influence of the compensation device (140), wherein the compensation device (140) provides an additional impedance component at the converter input (121), the additional impedance component at least partially compensating for the influence of the parasitic impedance (101), The compensation device (140) is characterized in that the compensation device (140) has a configurable capacitance component (145), wherein the configurable capacitance component (145) is configured to provide an output signal of the compensation device (140) at its output as an analog signal corresponding to a variable capacitance at the converter input (121) as a function of the further impedance component. The configurable capacitor component (145) has a digital input terminal (146) for adjusting the configurable capacitor component (145).

2. The sensor system according to claim 1, characterized in that The compensation device (140) has an auxiliary amplifier (150), wherein the auxiliary amplifier (150) has a gain factor greater than 2, wherein in particular the auxiliary amplifier (150) is simpler to implement than the capacitor-to-voltage converter (120) and can be operated in a wide range of different power modes 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 lag, loop gain and stability of the capacitor-to-voltage converter (120) are mainly dependent only on the control loop characteristic curve of the auxiliary amplifier 150 and the digital-to-analog converter with the configurable capacitor array.

3. The sensor system according to any one of the preceding claims, characterized in that The configurable capacitor component (145) is constructed as a digital-to-analog converter having a configurable capacitor array.

4. The sensor system according to any one of the preceding claims, characterized in that The compensation device (140) having the configurable capacitive component (145) and the auxiliary amplifier can provide a further impedance component in such a way that the further impedance component corresponds to the negative value of the impedance caused by the parasitic impedance and substantially compensates for the impedance.

5. The sensor system according to any one of the preceding claims, characterized in that The operation of the compensation device (140) and the compensation of the at least one parasitic impedance (101) results in the ability to operate the capacitor-to-voltage converter (120) in a wide range of different operating modes, in particular: In case of using different power requirements for operating the capacitor-to-voltage converter (120), and / or In the case of using different gain values and accompanying different noise components.

6. The sensor system according to any one of the preceding claims, characterized in that The operation of the compensation device (140) results in the following aspects of the operation of the capacitor-voltage converter (120) being eliminated or at least significantly reduced or minimized over a wide operating range of the capacitor-voltage converter (120): The phase difference introduced and / or Gain factor and / or stability.

7. Method for operating a sensor system having a readout circuit (100) for a capacitive differential sensor output for detecting an analog sensor output signal, wherein: The readout circuit (100) comprises at least Capacitor-to-voltage converter (120) and a compensation device (140) for compensating at least one parasitic impedance (101), 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) not only under the influence of the at least one parasitic impedance (101) but also under the influence of the compensation device (140), wherein a further impedance component is provided at the converter input (121) by the compensation device (140), said further impedance component at least partially compensating for the influence of the parasitic impedance (101), The compensation device (140) comprises a configurable capacitance component (145), wherein the configurable capacitance component (145) provides an output signal of the compensation device (140) at its output as a function of the further impedance component and as an analog signal corresponding to the variable capacitance at the converter input (121). The configurable capacitor component (145) has a digital input terminal (146) for adjusting the configurable capacitor component (145).

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