Detection circuit and method for detecting connection defects

Abstract

Detection circuit (1) and method for detecting connection defects of an electrical connection between capacitive sensor electrodes (7A, 7B) and a signal input (4A) of a charge amplifier (4), having a signal generator (2) for generating a signal which is applied via a common-mode controller (3) as a common-mode signal to the signal input (4A) of the differential charge amplifier (4), the analogue output signal from which is converted into a digital output signal by a differential analogue / digital converter (5); and having an evaluation unit (6) which is designed to evaluate the digital output signal from the analogue / digital converter (5) in order to detect connection defects of the electrical connection between the capacitive sensor electrodes (7A, 7B) and the signal input (4A) of the charge amplifier (4).

Description

[0001] Description

[0002] title

[0003] Detection circuit and method for detecting connection defects

[0004] The invention relates to a circuit and a method for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, and in particular a method for performing a built-in online self-test for detecting bond wire defects in MEMS gyroscopes with common-mode excitation and common-mode detection.

[0005] State of the art

[0006] Gyroscopes for measuring rotation rates are well-known and are used, for example, as microelectromechanical systems (MEMS) in a wide variety of devices and applications. MEMS gyroscope sensors are used to measure rotational motion. The gyroscope incorporates a so-called seismic mass, which is used to measure the corresponding rotational movement.

[0007] DE102020203036A1 describes a circuit for operating a capacitive sensor and an associated sensor device.

[0008] Analog front ends (FEs) in open-loop MEMS gyroscopes typically use baseband detection for reasons of compactness and low power consumption. In this case, no pulse or excitation signal is applied to the MEMS sensor electrodes.

[0009] Only when the MEMS gyroscope deflects due to external rotation is a small electrical delta charge, or differential charge, generated. This electrical charge can be captured and amplified by an integrated low-noise, charge-sensitive amplifier.

[0010] The gyroscope's MEMS sensor electrodes are typically connected to the FE-ASIC via two bond wires per detection channel. The analog front-end (FE) circuit is designed to detect only differential charges. Consequently, in the absence of a rate signal, the output of the charge-sensitive amplifier displays only the MEMS quadrature signal, or its residue if quadrature compensation is used.

[0011] If one or both bond wires are broken, this fault event is conventionally detected by monitoring the magnitude of the quadrature signal. However, the quadrature signal can be relatively small, and its fluctuation may even be below the FE detection threshold. Therefore, conventional online detection of a broken bond wire using quadrature monitoring is either not feasible or too complex in such cases.

[0012] Disclosure of the invention

[0013] According to a first aspect, the invention provides a detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, comprising: a signal generator for generating a signal which is applied as a common-mode signal to the signal input of the differential charge amplifier via a common-mode regulator, the analog output signal of which is converted into a digital output signal by a differential analog-to-digital converter; and an evaluation unit which is designed to evaluate the digital output signal of the analog-to-digital converter for the detection of connection defects in the electrical connection between the capacitive sensor electrodes and the signal input of the charge amplifier.The detection circuit is used to detect connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier. The detection circuit is particularly suitable for detecting bond wire defects.

[0014] The charge amplifier can be implemented with FET or CMOS operational amplifiers and preferably features capacitive feedback. The charge amplifier functions like a signal integrator. The charge amplifier offers a high input impedance.

[0015] A common-mode signal is a signal that is present at all inputs of a component relevant to its function, e.g., at the inputs of an operational amplifier or a charge amplifier, simultaneously and with the same phase.

[0016] The common-mode regulator, or common-mode feedback circuit (CMFB), ensures that the common-mode voltage at the input terminals of the charge amplifier remains within a specific range. This is preferably achieved by a feedback loop that adjusts the amplifier's bias or gain to compensate for changes in the common-mode voltage. By keeping the common-mode voltage stable, the CMFB circuit helps prevent distortion of the output signal and ensures accurate current measurement.

[0017] In one possible embodiment of the detection circuit according to the invention for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, the signal generated by the signal generator has a single tone, a multiple tone or a pseudorandom sequence.

[0018] In one possible embodiment of the detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, the capacitive sensor electrodes are MEMS sensor electrodes. In another possible embodiment of the detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, the MEMS sensor electrodes are contained within a gyroscope.

[0019] In one possible embodiment of the detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, the electrical connection between the capacitive sensor electrodes and the signal input of a charge amplifier has bond wires whose impairment is detectable by the evaluation unit.

[0020] The identified impairment of the bond wires consists in particular of an unintentional mechanical interruption of the bond wires, which leads to a complete failure of the gyroscope.

[0021] The rapid detection of mechanical breaks in the bond wires significantly increases the operational safety and reliability of the sensor, especially a gyroscope.

[0022] In one possible embodiment of the detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, the signal generator contained therein can be actuated via an interface.

[0023] This interface can be a user interface or a control interface to a control bus. In particular, it allows the selection and adjustment of the signal output by the detection circuit's signal generator, which is applied as a common-mode signal to the signal input of the differential charge amplifier via the common-mode controller. This increases the flexibility of the detection circuit for various applications.

[0024] In one possible embodiment of the detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, the charge amplifier has a differential operational amplifier whose differential signal output is connected to the differential signal input of the operational amplifier via feedback capacitors.

[0025] In one possible embodiment of the detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, an input common-mode controller is provided at the differential signal input of the operational amplifier of the charge amplifier for feeding in the signal generated by the signal generator.

[0026] The input common-mode feedback control (ICMFB) also improves the performance of the charge amplifier with regard to noise.

[0027] In one possible embodiment of the detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, an output common-mode controller is provided at the differential signal output of the operational amplifier of the charge amplifier.

[0028] According to a further aspect, the invention provides a front-end circuit for a MEMS gyroscope, wherein the front-end circuit has an integrated detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, which comprises: a signal generator for generating a signal that is applied as a common-mode signal to the signal input of the differential charge amplifier via a common-mode regulator, the analog output signal of which is converted into a digital output signal by a differential analog-to-digital converter, and an evaluation unit designed to evaluate the digital output signal of the analog-to-digital converter for the detection of connection defects in the electrical connection between the capacitive sensor electrodes and the signal input of the charge amplifier.Furthermore, according to another aspect, the invention provides a method for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, comprising the following steps:

[0029] Generating a signal that is applied as a common-mode signal to the signal input of the differential charge amplifier via a common-mode controller,

[0030] Converting the analog output signal of the differential charge amplifier into a digital output signal using a differential analog-to-digital converter; and

[0031] Evaluating the digital output signal of the analog-to-digital converter to detect connection defects in the electrical connection between the capacitive sensor electrodes and the signal input of the charge amplifier.

[0032] The method according to the invention allows a continuous self-test of the sensor device, in particular in the case of a MEMS gyroscope.

[0033] In one possible embodiment of the inventive method for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, the generated signal has a single tone, a multiple tone or a pseudorandom sequence.

[0034] In one possible embodiment, it is possible to switch between the different signals. This increases the flexibility of the inventive method for different applications of the sensor device.

[0035] Possible embodiments of the detection circuit and the method according to the invention will be described in more detail below with reference to the attached figures.

[0036] Figure 1 shows a circuit diagram illustrating a possible

[0037] embodiment of the detection circuit according to the invention;

[0038] Fig. 2 shows a flowchart illustrating a possible embodiment of the method according to the invention.

[0039] As can be seen in Fig. 1, a detection circuit 1 according to the invention for detecting connection defects of an electrical connection between capacitive sensor electrodes 7A, 7B and a signal input 4A of a charge amplifier 4 (Current Sense Amplifier CSA) has a signal generator 2 in the embodiment shown there.

[0040] The connection defects can include, for example, a break in the bond wires between the sensor electrodes 7A, 7B and the signal input 4A of the charge amplifier 4. Detection of other connection defects is possible, such as a significant increase in the ohmic resistance of the electrical connection between the capacitive sensor electrodes 7A, 7B and the signal input 4A of the charge amplifier 4.

[0041] The signal generator 2 is designed to generate a signal that is applied as a common-mode signal to the signal input 4A of the differential charge amplifier 4 via a common-mode regulator 3 (ICMFB). The analog output signal of the differential charge amplifier 4, which is output by the signal output 4B of the differential charge amplifier 4, is converted into a digital output signal by a differential analog-to-digital converter 5A.

[0042] The digital output signal of the differential analog-to-digital converter 5A can be temporarily stored for evaluation if implemented. The clock or sampling rate of the differential analog-to-digital converter 5A is adjustable if the detection circuit 1 is implemented.

[0043] The detection circuit 1 also includes an evaluation unit 6, which is designed to evaluate the digital output signal of the analog-to-digital converter 5A for the detection of connection defects in the electrical connection between the capacitive sensor electrodes 7A,7B and the signal input 4A of the charge amplifier 4.

[0044] In a possible implementation, the evaluation unit 6 may have a processor that evaluates the digital output signal of the analog-to-digital converter 5A and the further analog-to-digital converter 5B shown in Fig. 1 in real time.

[0045] The signal generated by the built-in signal generator 2 can be fed into the signal input 4A of the charge amplifier 4 in a test operating mode of the front end (FEs) or continuously to determine whether a circuit-related impairment of the electrical connection between the capacitive sensor electrodes 7A,7B and the signal input 4A of the charge amplifier 4 already exists or is imminent.

[0046] In one possible embodiment of the detection circuit 1, the two capacitive sensor electrodes 7A, 7B are MEMS sensor electrodes. The capacitive sensor electrodes 7A, 7B can also have parasitic capacitances Cpar, as shown in Fig. 1. In one possible embodiment of the detection circuit 1, the MEMS sensor electrodes 7A, 7B are contained within a gyroscope.

[0047] In one possible embodiment of the detection circuit 1 according to the invention, the signal generated by the signal generator 2 has as a test signal a single tone ET, a multiple tone MT, or a pseudorandom sequence PRBS, as schematically shown in Fig. 1. The signal generator 3 can also generate a DC bias (DCB).

[0048] In a possible implementation, the signal provided by the signal generator 2 is applied as a common-mode signal to the signal input 4A via a reference signal input Vref,IN and the input common-mode controller 3, as shown in Fig.1.

[0049] In one possible embodiment of the detection circuit 1 for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input 4A of the charge amplifier 4, the electrical connection between the capacitive sensor electrodes 7A, 7B and the signal input 4A of the charge amplifier 4 has bond wires 8A, 8B, the impairment of which, in particular its mechanical interruption, is detectable by the evaluation unit 6 of the detection circuit 1.

[0050] In one possible embodiment of the detection circuit 1, the signal generator 2 contained therein can be operated via an interface. The interface comprises a user interface and / or a control interface to a control bus. In one possible implementation, a specific signal generated by the signal generator 2 can be selected via the interface, and its signal parameters can be set.

[0051] In one possible embodiment of the detection circuit 1, the charge amplifier 4 includes a differential operational amplifier 4C whose differential signal output 4B is connected to the differential signal input 4A of the operational amplifier 4C via feedback capacitors 4D. In one possible implementation, the non-inverting input (+) of the operational amplifier 4C of the charge amplifier 4 is connected to a virtual ground potential.

[0052] In one possible embodiment of the detection circuit 1, the input common-mode controller (ICMFB) 3 is provided at the differential signal input 4A of the operational amplifier 4C of the charge amplifier 4 for feeding in the signal generated by the signal generator 2.

[0053] The input common-mode controller (ICMFB) 3 can be connected to another analog-to-digital converter 5B, which provides another digital output signal to the evaluation unit 6, as shown schematically in Fig. 1.

[0054] In one possible embodiment of the detection circuit 1, an output common-mode controller (OCMFB) 9 is also provided at the differential signal output 4B of the operational amplifier 4C of the charge amplifier 4. As shown in Fig. 1, the output common-mode controller 9 can have a reference signal connection Vref,out. Furthermore, according to another aspect of the invention, a front-end circuit 10 for a MEMS gyroscope is provided, wherein the front-end circuit 10 includes an integrated detection circuit 1 for detecting connection defects in an electrical connection between capacitive sensor electrodes 7A, 7B and a signal input 4A of a charge amplifier 4.

[0055] The charge amplifier or current-sensing amplifier 4 contained in the gyroscope enables precise measurement of the angular velocity or rotational motion, which is important for a variety of applications in navigation, vehicle control, aviation, robotics and other technical fields.

[0056] Fig. 2 shows a simple flowchart illustrating a possible embodiment of a method according to the invention, which serves to detect connection defects of an electrical connection between capacitive sensor electrodes 7A, 7B and a signal input 4A of a charge amplifier 4.

[0057] The method shown in Fig. 2 essentially comprises three main steps S1, S2, S3.

[0058] In a first step S1, a signal is generated by a signal generator 2, which is applied as a common-mode signal to the signal input 4A of the differential charge amplifier 4 via a common-mode regulator 3.

[0059] In one possible embodiment of the method according to the invention, the signal generated by the signal generator 2 in step S1 comprises a predefined or selected test signal. In one possible embodiment, the generated test signal can consist of a single tone ET, a multiple tone MT, or a pseudorandom sequence PRBS.

[0060] In a further step S2, the analog output signal of the differential charge amplifier 4 is converted into a digital output signal by a differential analog-to-digital converter 5A. In a further step S3, the digital output signal of the analog-to-digital converter 5A is evaluated to detect connection defects in the electrical connection between the capacitive sensor electrodes 7A, 7B and the signal input 4A of the charge amplifier 4.

[0061] If a connection defect is detected by evaluation unit 6 in step S3, evaluation unit 6 can generate an error detection signal or...

[0062] A warning signal is generated and sent to a higher-level control system to initiate appropriate fault handling.

[0063] The detection circuit 1 and the method according to the invention use a common-mode excitation for the input of the charge-sensitive amplifier 4 and utilize an existing front-end circuit 10 for the detection of the injected common-mode signals.

[0064] Furthermore, the circuit 1 according to the invention enables online monitoring of the static capacitances of the MEMS as well as online detection of sudden defects in the bond wires 8A,8B, which connect the MEMS electrodes 7A,7B to the FE-ASIC.

[0065] In the circuit 1 according to the invention, a common-mode signal (a single tone ET, a multiple tone MT or a pseudorandom sequence PRBS) is introduced by the common-mode controller 3 at the input 4A of the charge amplifier 4, which excites the virtual ground of the charge-sensitive amplifier 4.

[0066] Any leakage of common-mode signals into differential signals indicates a change in the type of MEMS connection to the FE-ASIC and is automatically detected by the evaluation unit 6 of the detection circuit 1.

[0067] This differential signal can be digitized by an existing or a dedicated fully differential analog-to-digital converter 5A. The digitized signal is then used to correlate the presence of defects in the bond wires 8A and 8B. To ensure the highest safety standards in a sensor system, the detection circuit 1 according to the invention enables the detection and reporting of bond wire defects within a few milliseconds. The detection of a connection defect thus occurs within a short time span of a few milliseconds.

[0068] A test operating mode can be repeated cyclically during potential implementation. During potential implementation, it is possible to switch between a test operating mode and a normal operating mode for performing sensor measurements. The test operating mode can be triggered by an event, such as a detected strong mechanical shock to the front end.

[0069] Alternatively, the test signal generated by signal generator 2 is continuously fed into the sensor during normal sensor operation.

[0070] In one possible embodiment, the detection circuit 1 according to the invention is manufactured using a CMOS process. In another possible embodiment, the detection circuit 1 according to the invention is integrated into the MEMS sensor.

Claims

Claims:

1. Detection circuit (1) for detecting connection defects in an electrical connection between capacitive sensor electrodes (7A, 7B) and a signal input (4A) of a charge amplifier (4) comprising: a signal generator (2) for generating a signal which is applied as a common-mode signal to the signal input (4A) of the differential charge amplifier (4) via a common-mode regulator (3), the analog output signal of which is converted into a digital output signal by a differential analog-to-digital converter (5A); and an evaluation unit (6) which is designed to evaluate the digital output signal of the analog-to-digital converter (5A) for detecting connection defects in the electrical connection between the capacitive sensor electrodes (7A, 7B) and the signal input (4A) of the charge amplifier (4).

2. Detection circuit for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to claim 1, wherein the signal generated by the signal generator (2) comprises a single tone (ET), a multiple tone (MT) or a pseudorandom sequence (PRBS).

3. Detection circuit for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to claim 1 or 2, wherein the capacitive sensor electrodes (7A,7B) comprise MEMS sensor electrodes.

4. Detection circuit for detecting connection defects in an electrical connection between capacitive sensor electrodes and a Signal input of a charge amplifier according to claim 3, wherein the MEMS sensor electrodes (7A,7B) are contained in a gyroscope.

5. Detection circuit for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to one of the preceding claims 1 to 4, wherein the electrical connection between the capacitive sensor electrodes (7A, 7B) and the signal input (4A) of a charge amplifier (4) has bond wires (8A, 8B) whose impairment, in particular mechanical interruption, is detectable by the evaluation unit (6).

6. Detection circuit for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to one of the preceding claims 1 to 5, wherein the signal generator (2) contained therein can be actuated via an interface.

7. Detection circuit for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to one of the preceding claims 1 to 6, wherein the charge amplifier (4) has a differential operational amplifier (4C) whose differential signal output (4B) is connected to the differential signal input (4A) of the operational amplifier (4C) via feedback capacitors (4D).

8. Detection circuit for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to claim 7, wherein an input common-mode controller (3) for feeding the signal generated by the signal generator (2) is provided at the differential signal input (4A) of the operational amplifier (4) of the charge amplifier (4).

9. Detection circuit for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to claim 7 or 8, wherein at the A differential signal output (4B) of the operational amplifier (4C) of the charge amplifier (4) is provided with a common-mode output controller (9).

10. Front-end circuit (10) for a MEMS gyroscope, wherein the front-end circuit (10) comprises an integrated detection circuit (1) for detecting connection defects according to any one of claims 1 to 9.

11. Method for detecting connection defects in an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier, comprising the following steps: Generating (S1) a signal which is applied as a common-mode signal to the signal input of the differential charge amplifier via a common-mode controller, Converting (S2) the analog output signal of the differential charge amplifier into a digital output signal using a differential analog-to-digital converter; and Evaluation (S3) of the digital output signal of the analog-to-digital converter to detect connection defects in the electrical connection between the capacitive sensor electrodes and the signal input of the charge amplifier.

12. Method for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to claim 11, wherein the generated signal comprises a single tone (ET), a multiple tone (MT) or a pseudorandom sequence (PRBS).

13. Method for detecting connection defects of an electrical connection between capacitive sensor electrodes and a signal input of a charge amplifier according to claim 11 or 12, wherein the method is performed in a test operating mode or continuously.

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