Sensor interface for functional safety applications

Abstract

A sensor interface for functional safety applications is disclosed. A sensor interface circuit (100) comprising: at least two sensor inputs (111, 112) and at least two front-end circuits (121, 122) to obtain sensor signal acquisitions from the at least two sensor inputs; a test circuit (131, 132) configured to test at least part of one of the front-end circuits (121, 122) for correct functionality by applying a test input to the front-end circuit under test, by reading a test output of the front-end circuit, and by comparing the test output with an expected result to obtain at least one test result, wherein the test input is applied intermittently between the sensor signal acquisitions; a processing device (140) configured for comparing the sensor signal acquisitions from different sensor inputs and for combining the comparison with the at least one test result to evaluate correct functionality of the sensor interface circuit.

Description

Technical Field

[0001] This invention relates to the field of sensors. More specifically, it relates to sensor interface circuits for functional safety applications. Background Technology

[0002] In safety-critical applications, such as automotive applications, it is crucial that the acquired sensor data is reliable and that incorrect sensor data be identified. In the automotive industry, vehicle safety integrity levels are defined in standards such as ISO 26262.

[0003] Often, at least two sensors are used to measure the same physical parameter. For example, this could be pressure. Typically, these two sensors are read out through a sensor interface circuit, which includes two independent analog front-ends, such as... Figure 1 The sensor interface circuit 10 is shown in the diagram. The first analog front-end (AFE1) has input pins 11 and 12, and a ground input pin 13. The second analog front-end (AFE2) has input pins 14 and 15, and a ground input pin 16. The outputs of the analog front-ends are connected to the digital module DM, which performs analog-to-digital conversion and may also perform digital processing. In this example, the output of the digital module is connected to the analog back-end (ABE), and the output of the analog back-end ABE is connected to output pin 17. Alternatively, both ABEs can output the two outputs of the AFEs. The analog front-end, digital module, and analog back-end are powered by a power supply system PS that can be powered via interface 16.

[0004] In these types of sensor systems, a primary signal (e.g., measured by analog front-end 1) is used as the main output. Secondary signals in these systems can be used to check the correctness of the primary signal through digital processing. In the case of two analog signals with different outputs (ABEs), the check can be performed by an external control unit (ECU).

[0005] US9346441B2 or US9874609B2 discloses examples of prior art solutions for dual-path sensor arrangements, wherein a monolithic integrated circuit sensor system implemented on a single semiconductor chip includes: a first sensor device having a first signal path on the semiconductor chip for a first sensor signal; and a second sensor device having a second signal path on the semiconductor chip for a second sensor signal, the second signal path being different from the first signal path, wherein a comparison between the first signal path signal and the second signal path signal provides a self-test for the sensor system.

[0006] However, both existing technological solutions involve monolithic integration of two sensors and signal paths. In many cases, monolithic integration is not feasible or beneficial, for example, when the sensor chip uses a different manufacturing technology than the interface chip. An example of this is when the sensor is manufactured using MEMS technology with a small number of metal layers (e.g., one or two) for connectivity, and the interface chip uses CMOS technology with more than six metal layers. In these cases, each sensor chip needs to be connected to the interface chip outside the sensor chip's die, for example, using electrical connections (e.g., solder pads). When using such long electrical connections to interconnect the sensor chip and the interface chip, the signal from the sensor becomes sensitive to electromagnetic compatibility (EMC) events, which can distort the sensor output signal.

[0007] The two analog front-ends typically use the same or nearly identical design. While this helps improve the safety level, it can still encounter common-cause failures such as design flaws, manufacturing defects, EMC events, and mechanical stress. Some diversity can be created by swapping the polarity of the differential inputs; for example, as physical parameters increase, the inputs and outputs of the first analog front-end increase, while those of the second analog front-end decrease. However, this may not be sufficient.

[0008] Alternatively, two completely different analog front-ends could be used. This could reduce common-cause failures, but it would double the design workload. Furthermore, making the designs truly diverse can be complex; for example, they might use the same type of components.

[0009] For the reasons mentioned above, there remains a need to find solutions on how to detect common causes. Summary of the Invention

[0010] The purpose of embodiments of the present invention is to provide good sensor interface circuits and methods that can provide indications of the correct function (e.g., performance) of the sensor interface circuits.

[0011] The above objectives are achieved by the method and apparatus according to the present invention.

[0012] In a first aspect, embodiments of the present invention relate to a sensor interface circuit, the sensor interface circuit comprising:

[0013] - At least two sensor inputs, each configured to connect to a separate sensor for measuring the same physical parameter.

[0014] - At least two front-end circuits, wherein each sensor input is configured to be connected to one of the front-end circuits, and wherein each front-end circuit is configured to modulate the signal from the connected sensor input, thereby obtaining sensor signal acquisition from at least two sensor inputs.

[0015] - A test circuit configured to test the correct function of at least a portion of a front-end circuit (e.g., by checking whether performance meets predefined requirements) by applying a test input to the front-end circuit under test, reading the test output of the front-end circuit, and obtaining at least one test result by comparing the test output with an expected result, wherein the test output is caused by the test input, and wherein the test input is applied intermittently between sensor signal acquisitions.

[0016] - A processing device configured to compare sensor signal acquisitions from different sensor inputs and to combine the comparison with at least one test result to evaluate the correct functioning of the sensor interface circuitry.

[0017] The advantage of this invention is that the safety integrity level can be improved through the test circuit while maintaining redundancy of at least two front-end circuits.

[0018] An advantage of embodiments of the present invention is that problems related to the signal path from the sensor to the output of the front-end circuitry can be detected. This test, performed by the test circuitry, can be completed before the signal is converted to a digital signal, or more preferably afterward (as this is easier and leads to potentially better performance testing). This testing is particularly advantageous when the sensor and sensor interface circuitry reside on separate dies. In these cases, the signal path of the interface die begins at the input pin connecting the interface die to the sensor die, and the signal path within the interface die includes the analog front-end circuitry. Compared to sensor interface circuitry without testing, embodiments of the present invention offer the advantage of improved safety integrity levels for the sensor interface circuitry. This can be achieved without significantly increasing the complexity of the sensor interface circuitry.

[0019] In an embodiment of the invention, the test input is a signal that spans the operating range of the sensor interface circuit.

[0020] The test input can be a sine wave signal.

[0021] Alternatively, the test input may include one or more constant signals. One of the one or more constant signals may be substantially zero.

[0022] In an embodiment of the invention, the test circuit includes a test input circuit. The test input circuit includes a switch for the following:

[0023] - Connect one of the sensor input pins to an input contact in the front-end circuit to obtain sensor signal acquisition.

[0024] - Connect one of the sensor input pins to two input contacts in the front-end circuit, and disconnect the other sensor input from the front-end circuit to obtain a test result. The test input circuit may include a capacitor that can be connected to one of the input contacts.

[0025] In embodiments of the present invention, the processing device is configured to compare sensor signal acquisitions by comparing the difference between sensor signal acquisitions and a predefined threshold, and

[0026] - Used to determine if sensor signal acquisition is unreliable when the difference is greater than a threshold, and

[0027] - Used to determine if sensor signal acquisition is unreliable when the difference is less than a threshold and the test result of one of the front-end circuits indicates that the front-end circuit is malfunctioning, and

[0028] - Used to determine that sensor signal acquisition is reliable when the difference is less than a threshold and one or more test results of one or more front-end circuits under test indicate that they are working correctly.

[0029] In embodiments of the present invention, the sensor interface circuit includes a separate test input circuit for each front-end circuit or a single test input circuit for testing all front-end circuits.

[0030] In embodiments of the present invention, the processing device is configured to:

[0031] Sensor signal acquisitions are compared by comparing the difference between sensor signal acquisitions from at least two sensor inputs with a predefined threshold, and if the difference is greater than the threshold,

[0032] - Used to determine that sensor signal acquisition is unreliable when at least one test result for each front-end circuit indicates that all front-end circuits are malfunctioning, or when test results for all test input circuits indicate that all front-end circuits are malfunctioning.

[0033] - Used to determine the sensor signal acquisition of the front-end circuit that should be used when the test results of at least one front-end circuit indicate that the front-end circuit is not working correctly.

[0034] And, if the difference is less than a threshold, then it is used to obtain the test result of one of the front-end circuits, and

[0035] - Used to determine if sensor signal acquisition is unreliable when test results indicate that the front-end circuit is malfunctioning.

[0036] - Used to determine that sensor signal acquisition is reliable when test results indicate that the front-end circuit is working correctly.

[0037] In embodiments of the present invention, the front-end circuit may include an analog-to-digital converter (ADC).

[0038] In embodiments of the present invention, the sensor system may include a controller configured to trigger at least one test input circuit to obtain test results.

[0039] In an embodiment of the present invention, the sensor interface circuit includes an external controller for controlling the sensor interface circuit.

[0040] In a second aspect, embodiments of the invention relate to a method for controlling the integrity of a sensor interface circuit, the sensor interface circuit including at least two sensor inputs, each sensor input being configured to be connected to a different sensor for measuring the same physical parameter, and each sensor input being configured to be connected to a front-end circuit for modulating signals from the sensor, the method comprising:

[0041] -Signals are acquired from the front-end circuitry to obtain sensor signal data.

[0042] - Intermittently apply a test signal to at least one of the front-end circuits and read the test output of the front-end circuit caused by the test signal.

[0043] - Compare the test output with the expected result to obtain at least one test result.

[0044] - Compare sensor signal acquisitions from different sensor inputs and combine the comparison with at least one test result to evaluate the correct functioning of the sensor interface circuit.

[0045] In embodiments of the present invention, the method can be used in a sensor interface circuit, which may have a front-end circuit with differential inputs. In this case, the method may include:

[0046] Connect one of the sensor input pins to an input contact of the front-end circuit to obtain sensor signal acquisition.

[0047] - Connect one of the sensor input pins to the two input contacts of the front-end circuit, and disconnect the other sensor input from the front-end circuit to obtain test results.

[0048] Specific and preferred aspects of the invention are set forth in the appended independent and dependent claims. Features from the dependent claims may be suitably combined with features of the independent claims and other dependent claims, and not merely as expressly set forth in the claims.

[0049] These and other aspects of the invention will be apparent from the embodiments described herein, and are illustrated with reference to these embodiments. Attached Figure Description

[0050] Figure 1 A schematic diagram of a typical prior art sensor interface circuit is shown.

[0051] Figure 2 A schematic diagram of a sensor interface circuit according to an embodiment of the present invention is shown.

[0052] Figure 3 A schematic diagram of a sensor interface circuit including an external controller according to an embodiment of the present invention is shown.

[0053] Figure 4 and Figure 5 Typical method steps that can be implemented in a sensor interface circuit according to an embodiment of the present invention are shown.

[0054] Figure 6 A schematic diagram of a sensor interface circuit (wherein the test input circuit includes a switch) according to an embodiment of the present invention is shown.

[0055] Figure 7 A schematic diagram of a sensor interface circuit (wherein the test input circuit additionally includes a capacitor) according to an embodiment of the present invention is shown.

[0056] Any reference numerals in the claims should not be construed as limiting the scope.

[0057] In different accompanying drawings, the same reference numerals refer to the same or similar elements. Detailed Implementation

[0058] The invention will be described with reference to specific embodiments and certain accompanying drawings, but the invention is not limited thereto but is defined solely by the claims. The described drawings are illustrative only and not restrictive. In the drawings, some elements may be enlarged and not drawn to scale for illustrative purposes. Dimensions and relative dimensions do not correspond to an actual reduction in the implementation of the invention.

[0059] The terms "first," "second," etc., used in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe a temporal, spatial, hierarchical, or any other order. It should be understood that such terms are interchangeable where appropriate, and embodiments of the invention described herein can be operated in a different order than those described or illustrated herein.

[0060] It should be noted that the term "comprising" as used in the claims should not be construed as limiting oneself to the means listed thereafter; it does not exclude other elements or steps. Therefore, the term should be interpreted as specifying the presence of the features, integers, steps, or components stated as mentioned, but does not exclude the presence or addition of one or more other features, integers, steps, or components, or groups thereof. Thus, the scope of the statement "device comprising means A and B" should not be limited to a device consisting solely of components A and B. It means that for the purposes of this invention, the only relevant components of the device are A and B.

[0061] Throughout this specification, the reference to "an embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the phrase "in one embodiment" or "in an embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, but may refer to the same embodiment. Furthermore, in one or more embodiments, as will be obvious to those skilled in the art from this disclosure, particular features, structures, or characteristics can be combined in any suitable manner.

[0062] Similarly, it should be understood that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, drawing, or description for the purpose of simplification and aiding in the understanding of one or more of the various inventive aspects. However, this method of disclosure should not be construed as reflecting an intention to claim more features than are expressly recited in each claim. Rather, as reflected in the appended claims, inventive aspects exist in fewer features than all the features of a single foregoing disclosed embodiment. Therefore, the claims appended following the detailed description are thus explicitly incorporated into this detailed description, wherein each claim itself represents a separate embodiment of the invention.

[0063] Furthermore, while some embodiments described herein include features that are included in other embodiments but not others, it will be understood by those skilled in the art that combinations of features from different embodiments are intended to fall within the scope of the invention and form different embodiments. For example, any embodiment of the claimed embodiments in the appended claims can be used in any combination.

[0064] Numerous specific details are set forth in the description provided herein. However, it should be understood that embodiments of the invention can be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description.

[0065] In a first aspect, embodiments of the present invention relate to a sensor interface circuit 100. Figure 2 An example of such a sensor interface circuit is shown. The sensor interface circuit 100 includes at least two sensor inputs 111, 112, each sensor input being configured to connect to a separate sensor for measuring the same physical parameter.

[0066] Furthermore, the sensor interface circuit includes at least two front-end circuits 121 and 122. Each sensor input 111 and 112 is configured to connect to one of the front-end circuits 121 and 122, and each front-end circuit 121 and 122 is configured to modulate the signal from the connected sensor input, thereby obtaining sensor signal acquisition from at least two sensor inputs. Thus, at least two signal paths are formed, each starting from a sensor input and passing through a front-end circuit. In embodiments of the invention, the sensor interface circuit may include more than two sensor inputs, and more than two signal paths may exist. The sensor interface circuit may, for example, include a multiplexer, allowing one or more front-ends to connect to the sensor inputs. In some embodiments, the sensor interface circuit may include, for example, three or more sensor inputs and two front-ends, wherein at least one front-end can read from multiple sensors. In this configuration, each sensor can measure the same physical parameter.

[0067] Furthermore, the sensor interface circuit also includes a test circuit comprising test input circuits 131 and 132, configured to test the correct function of at least a portion of one of the front-end circuits 121 and 122. For example, correct function can be tested by checking whether performance meets predefined requirements. For example, if performance does not meet one or more predefined thresholds, the function is considered incorrect. Therefore, the test circuit can be configured to apply a test input to the front-end circuit under test and read the test output of the front-end circuit. For example, voltage or current can be applied as a test input. The test output is caused by the test input. The test circuit is configured to apply the test input intermittently between sensor signal acquisitions. The test circuit is configured to compare the test output with the expected result to obtain at least one test result. The functionality of the test circuit can be distributed across different components. For example, the reading and comparison of test outputs can be implemented in the processing device 140.

[0068] In an embodiment of the present invention, the sensor interface circuit 100 includes test input circuits 131, 132 for each front-end circuit 121, 122.

[0069] In embodiments of the invention, the test signal of one test input circuit can be interleaved with the test signal of another test input circuit. This allows sensor signals to be acquired at at least one of the front-end circuits.

[0070] In addition, the sensor interface circuit includes a processing device 140 configured to compare sensor signal acquisitions from different sensor inputs and to combine the comparison with at least one test result in order to evaluate the correct functioning of the sensor interface circuit.

[0071] The front-end circuitry includes analog front-end circuitry for processing sensor signals in the analog domain. This may include amplification, filtering, or any other desired processing.

[0072] In embodiments of the invention, the front-end circuitry may additionally include an ADC for converting the output of the analog front-end into a digital representation. This digital representation can be used as an input to a processing device.

[0073] The analog-to-digital (A / D) conversion is preferably performed separately for different signal paths, and alternatively, different types of A / D converters can be used between paths. In principle, an A / D converter and time multiplexing can be used between the analog outputs of a path, but this reduces redundancy between paths, thus compromising safety integrity. Therefore, each path preferably (but not necessarily) has an A / D converter.

[0074] In embodiments of the present invention, at least two signal paths exist. The first path passes through a first sensor input and a first front-end circuit, while the second path passes through a second sensor input and a second front-end circuit. Each path may contain a test input circuit, or may contain only one test input circuit.

[0075] In embodiments of the present invention, the test input circuit may be applied only to the second path, or it may be applied more thoroughly to the second path.

[0076] In some embodiments of the invention, the sensor interface may include test input circuitry for the second path only. The second front-end circuitry may multiplex the signal from the sensor and the test output. For the second path, a slower update cycle for sensor signal acquisition may be implemented, allowing a self-test using the test circuitry to be performed between updates.

[0077] Sensor signal acquisition in the second path can be performed alternately with test output acquisition. The overall update cycle for sensor signal acquisition and test output acquisition in the second path can be the same as the update rate for sensor signal acquisition in the first path. However, some samples in the sample will be related to the test circuit (also known as the built-in self-test BIST) and some related applications. Therefore, the update rate for applications related to the sample can be lower than the update rate in the first path.

[0078] In various applications, the requirements for the update rate of the second signal path are not as stringent as those for the first path. This results in significantly more self-tests applied to the second front-end circuitry (and optionally the secondary sensor) than to the first front-end circuitry. In such applications, a test input circuitry for the first path is not required. It may exist due to symmetry. In this case, it can be disabled (during normal operation) to guarantee the full sensor signal update rate of the first path. For example, it can be disabled during normal operation and enabled at startup. In some embodiments of the invention, the first analog front-end can be checked upon request (e.g., when there is a question regarding proper performance).

[0079] The sensor interface circuit can be configured to trigger the test circuit to test the correct functioning of the first and second front-end circuits during startup or production testing.

[0080] In an embodiment of the present invention, the interface circuit includes a controller 150, which is configured to trigger at least one test input circuit 131, 132 to obtain test results.

[0081] In embodiments of the present invention, the controller and the processing device can be the same device. For example, a microprocessor, a field-programmable gate array, or a digital signal processor can be used. They can also be separate devices.

[0082] The controller 150, configured to trigger at least one test input circuit 131, 132, can also control the front-end circuit and is also referred to as the front-end control block. Figure 2 An example of such a control block 150 is shown in the figure. Figure 2 In this circuit, the operation of (multiple) test input circuits is controlled by a controller within the sensor interface circuit (this can be on the same chip / die). The sensor interface circuit can be configured to disconnect the sensor signal from the front-end circuit when the test input circuit is triggered to test the correct function of the corresponding front-end circuit. This can be achieved using a switch controlled by controller 150.

[0083] The test circuit is configured to test the correct function (e.g., performance) of at least a portion of the front-end circuitry. For example, the test input circuitry may not be located entirely before the analog front-end (AFE), such as... Figure 2 As shown, it is not a separate entity, but rather a part of it. For example, filtering of signals from sensor inputs can be accomplished by a filtering circuit at the beginning of the analog front-end. Therefore, for EMC reasons, it is best if there are no switches or other active components before this filter. In this case, the test input circuit is also preferably implemented after the filter. Additionally, the test input circuit can also be configured to use an ADC converter for testing the front-end circuitry.

[0084] As discussed below, the test circuit can be configured to modify the front-end circuit to obtain an oscillating front-end circuit (the analog portion of the front-end circuit is oscillating).

[0085] In embodiments of the invention, the comparison between the test output and the expected result can be implemented in the processing device to obtain at least one test result. Therefore, the controller 150 can instruct the processing device 140 at what time which test input to apply. This is indicated by the dashed line from the controller 150 to the processing device 140.

[0086] In embodiments of the invention, the outputs of front-end circuits 121 and 122 include ADCs for converting the analog output of the analog front-end into a digital signal for processing device 140 (e.g., a DSP block). This processing device is configured to process the outputs of front-end circuits 121 and 122. The processing device may be configured to detect faulty operation of the analog front-end, for example, by comparing the outputs of two paths and combining this comparison with the result of a test circuit operation.

[0087] The test result of the test circuit operation can be pass or fail, or in some implementations, for example, indeterminate. In this case, the sensor interface circuit can be configured to perform more detailed testing of the second front-end circuit, at the cost of interrupting the sensor signal acquisition of the second front-end circuit, for example, by triggering the test input circuit to run an oscillation test (which will be discussed later). In this case, the sensor interface circuit can also be configured to run tests together with the test input circuit of the first front-end circuit.

[0088] In embodiments of the present invention, the front-end control and DSP block in the interface circuit die can be implemented in a single block, or their functions can be distributed across different processing devices. The test circuit includes test input circuits 131 and 132 for providing test inputs to the device under test (e.g., front-end circuitry). Furthermore, the test circuit includes additional functions, such as comparing the output of the device under test with the expected output, or triggering test inputs to the device under test. These functions can be implemented in the test input circuits or in shared circuitry of the distributed processing devices.

[0089] The test input circuitry can be implemented separately for each path, or it can be shared between paths, or parts of the test input circuitry can be shared. In embodiments of the invention, test inputs can be applied, for example, simultaneously to two paths or in a time-multiplexed manner. Even Figure 2 The blocks representing test input circuit 131 and test input circuit 132 are drawn as separate blocks, but their functional parts can also be implemented as shared circuits. Figure 2 In the diagram, block 131, representing the test circuit of the first path, is drawn with a dashed line to indicate that block 131 is optional.

[0090] exist Figure 3 In the exemplary embodiment shown, a built-in self-test is performed on both front-end circuits of the sensor interface circuit. However, it may be advantageous to test the other front-end while one of the front-ends is operating in normal application mode, so that at least one of the two sensor signals is available at any given time.

[0091] In embodiments of the invention, the sensor interface circuit is configured to connect to an external controller for controlling the sensor interface circuit. For example, an external controller can be used to trigger a test circuit. The comparison of sensor signal acquisitions and test outputs with expected results, as well as the combination of comparisons between test results and sensor signal acquisitions, can be performed internally, on a separate die or chip (e.g., at an external controller), or both internally and externally. This is in... Figure 3 As shown, the processing device is a distributed device comprising an internal controller 140a (e.g., a DSP) and an external controller 140b. Both can be implemented on separate chips / dies. Figure 3 In the example, the external controller is the engine control unit (ECU). As previously described, the DSP block can perform analysis between the outputs of the two signal paths and transmit the comparison results to the external controller. In some embodiments of the invention, the comparison results can be combined with test results in the DSP block, and the combined output can be transmitted to the external controller (the processing device is a distributed device). In embodiments of the invention, both the output values ​​of the two paths (sensor signal acquisition) and the test results can be transmitted to the external controller, but this requires a larger bandwidth for the data compared to this part of the processing completed before data transmission.

[0092] As explained previously, the external controller 140b can optionally be used to trigger test operations. This can be done, for example, when there is doubt about the correct operation of the front-end circuitry (e.g., the analog portion of the front-end circuitry). In embodiments of the invention, the external controller can be configured to request test operations by communicating with an internal controller (e.g., a DSP), which in turn is connected to the front-end control block 150. The external controller can also be directly connected to the front-end control block 150, or even directly connected to (or more) test input circuits.

[0093] The processing device can be configured to perform a method including the following steps ( Figure 4 A flowchart illustrating an exemplary method according to an embodiment of the present invention is shown. The processing device can be configured to compare sensor signal acquisitions by comparing the difference between sensor signal acquisitions and a predefined threshold.

[0094] - Used to determine if sensor signal acquisition is unreliable when the difference is greater than a threshold, and

[0095] - Used to determine if sensor signal acquisition is unreliable when the difference is less than a threshold and a test result of one of the front-end circuits indicates that the front-end circuit is malfunctioning, and

[0096] - Used to determine that sensor signal acquisition is reliable when the difference is less than a threshold and the test results of one or more of the tested front-end circuits indicate that they are working correctly.

[0097] An advantage of embodiments of the present invention is that the test circuit according to embodiments of the present invention can detect errors in the front-end circuit that would otherwise remain unnoticed when comparing the differences between sensor signal acquisitions.

[0098] For two front-ends, a fault in one of them can be detected by comparing the results of the two front-ends. However, both front-ends can exhibit the same or similar faults because there can be some correlation between them. For example, if the second front-end is extensively tested during the operation of the sensor interface circuit, a fault can be detected in the second analog front-end. If there is a correlation between the front-ends, a related fault occurring simultaneously in both front-ends can be detected.

[0099] An advantage of embodiments of the present invention is that the test circuitry and corresponding test operations allow for the detection of subordinate faults affecting both analog front-ends. Therefore, it should be noted that by comparing the signal acquisitions from the two front-ends, a fault affecting only one front-end can be detected regardless, since the physical parameters measured by the two sensors are identical, and thus the outputs of the front-ends should be the same.

[0100] Some examples of dependent faults include:

[0101] -EMC events (EMC events can be coupled to the sensor input or to other locations, such as, for example, through the power supply);

[0102] - Low power supply voltage or interference;

[0103] - Leakage current or other process deviations of components used in both front ends (e.g., MIM capacitors);

[0104] - Drift over life (this design is designed to prevent drift over life).

[0105] An advantage of embodiments of the present invention is that it can increase the availability of sensor interface circuitry. If a difference is detected between two front-ends, but one front-end proves to be fault-free, that front-end can still be used to generate an output signal. This is in... Figure 5 As shown in the image.

[0106] Figure 5 The flowchart illustrates an exemplary method according to an embodiment of the present invention. A processing device is configured to compare sensor signal acquisitions from two front-ends. If the difference is greater than a predefined threshold, if the test results of the two front-ends with test inputs from the test input circuit indicate that both front-end circuits are not functioning correctly, or if the test results of the two front-ends with test inputs from the test input circuit indicate that both front-end circuits are functioning correctly, the processing device concludes that the sensor signal acquisition is unreliable. If both front-ends with test inputs from the test input circuit fail the test, the output can be concluded to be unreliable, which may be due to a common cause. If both front-ends pass, the sensor signal acquisition (output) is unreliable, which may be due to a portion not covered by the test circuit (e.g., the sensor itself, if the sensor is not covered by the test circuit).

[0107] If one front-end circuit passes the test while the other fails, the output can be generated using the one that passed the test. It should be noted that reliability is reduced in this case. This can be flagged by the processing device to indicate a decrease in the reliability of the sensor interface circuitry. In fact, if one path of the two sensor systems fails the test, no additional faults (such as sensor drift) will be detected.

[0108] If the difference is less than a predefined threshold, the processing device's conclusion depends on the test results of the second front-end (in this example, the second front-end is tested, but it could be another front-end). If the test results show a fault, the conclusion is that both simulated front-ends are faulty. If the test results show a correct result, the conclusion is that the output is reliable.

[0109] Alternatively, if the difference between sensor signal acquisitions is less than a predefined threshold, all front-ends can be tested instead of just one.

[0110] In this case, the following conclusions can be drawn:

[0111] - If the test results of one of the front-ends are still correct, then it can be concluded that the output of that front-end is reliable;

[0112] -If all front-end test results are correct, then it can be concluded that all front-end outputs are reliable;

[0113] - If all front-end test results are incorrect, then it can be concluded that all outputs are unreliable.

[0114] For example, this could apply to a scenario with two front-ends, where the first front-end works 100% correctly, and the second front-end works for small input signals but not for large signals (e.g., clamping or gain error). If the application input is very small, both will give correct outputs, and their difference will be small. However, the second front-end may not pass the BIST. While the second front-end works correctly with small application inputs, it becomes unreliable with large application inputs.

[0115] In embodiments of the present invention, the test circuits can be configured not only to test the correct function of the front-end circuit, but also to test the correct function of the sensor itself.

[0116] Externally induced faults (such as EMC events) can severely interfere with sensor inputs connected to the sensor. These errors may be temporary, but they can persist long enough to cause safety issues. Such errors may go unnoticed if the sensor input is replaced with an internal test signal to check if the front-end is functioning correctly. Note that EMC interference is primarily a common-mode signal in most cases. Small differential signals can also be generated, for example, due to some difference in parasitic capacitance. However, one should always strive (through design) to make the connections of sensor elements, readout circuitry, and differential inputs as symmetrical as possible. Because the interference can be too large, errors may still be obtained that exceed the common-mode input range of the analog front-end, causing deviations in its output.

[0117] To detect such interference, the test circuit according to an embodiment of the present invention is configured to apply a test input derived from the actual input pin as an alternative to or supplement to applying an internally generated test input.

[0118] Therefore, in embodiments of the present invention, the input nodes of the front end (two input nodes for receiving differential signals) can be connected to the same input pin of the interface circuit (e.g., Figure 6The test input is generated using the INP2 pin (in the input pin). In this configuration, the test signal differential is 0, but it has a common-mode equal to that of one of the input pins that is susceptible to EMC interference. This is in Figure 6 As shown, the secondary path test input circuitry also includes a switch configuration that connects the input nodes to the same potential. Naturally, depending on which input pin provides the common potential, the other input pin needs to be disconnected from the measurement.

[0119] Generally speaking, it is also like Figure 7 As shown, test input circuit 131 and test circuit 132 may include switches for the following:

[0120] Connect one of the sensor input pins 112 to an input contact of the front-end circuit 122 for acquiring sensor signals.

[0121] - Connect one of the input pins of sensor input 112 to the two input contacts of front-end circuit 122, and disconnect the other sensor input 112 from front-end circuit 122 to obtain test results.

[0122] For the sake of simplicity, Figure 6 and Figure 7 An AD converter is not shown. The AD converter may be located, for example, before the input of the processing device 140, or may be part of the processing device 140.

[0123] Therefore, an advantage of embodiments of the present invention is that errors in sensor signals caused by MC events can be detected.

[0124] Alternatively, a small asymmetry can be created between the two sides of the differential test signal path by adding, for example, a small capacitor on only one side, to simulate the worst-case asymmetry on a real sensor signal path. Alternatively, an RC filter might be used instead of a single capacitor, but in practice, the resistance of the switch is sufficient, so only a capacitor is needed. For example, the capacitor could have a capacitance of less than 1 pF or even less than 100 fF.

[0125] An alternative method for detecting EMC effects can be achieved by simply adding (or removing) some extra capacitors (or RC capacitors) to, for example, the INM2 line, without short-circuiting INP2 and INM2. Without EMC (and assuming the useful signal changes not rapidly), both front-end circuits should still give the same results. This is easier, but the downside is that the system's "availability" may decrease because an EMC problem may have already been detected, even if it's not a problem for normal applications.

[0126] In embodiments of the invention, the test input circuit can be configured to apply an internally created stable zero-differential input. The test circuit can be configured to compare the outputs of two tests with a short-circuited input, which typically produces the same result.

[0127] Configurations related to EMC detection, such as Figure 7 As shown, the test input circuit includes a switch and a switchable capacitor.

[0128] In this diagram, the test input circuit additionally includes a capacitor (or RC filter) that can be connected to one of the input contacts. This has the advantage of further increasing sensitivity to EMC events. For example, the capacitor (or RC filter) can be connected between one of the input contacts and ground or another reference voltage. The RC filter can be a low-pass filter.

[0129] In addition to applying a zero-differential input and checking the output against the expected result, the test input circuit according to an embodiment of the invention can also be configured to apply an additional input signal to increase coverage.

[0130] In embodiments of the invention, the test input can be, for example, a signal spanning the operating range of the sensor interface circuitry. In a preferred embodiment, the test input covers the entire input range of the analog front-end. An advantage of embodiments of the invention is that it tests the correct operation of the front-end circuitry across its entire operating range. In embodiments of the invention, not only can 0 be applied as a differential input, but signals, for example, close to the sensor's full-scale value, can also be applied. If the sensor is supplied with a voltage VDDA by an analog regulator (and assuming the sensor output is proportional to its power supply), the test input circuitry can be configured to internally generate a differential signal of 10% VDDA. Pure gain error cannot be detected with a single signal. If good coverage of nonlinear errors is required, the test input circuitry needs to be configured with more than two signals (preferably significantly more than two), such as 1% VDDA, 2% VDDA, etc.

[0131] In most cases, sensor interfaces have low bandwidth requirements, so applying only a DC signal as a test input may suffice. One or more constant signals can be applied. The levels of the constant signals allow them to span the operating range of the sensor interface circuitry. The advantage of applying (multiple) constant signals is that the input can be easily generated, and the output can be easily examined. In other cases, it may be necessary to apply different signals; for example, a sine wave may need to be applied. The output can be examined, for example, by performing a Fast Fourier Transform (FFT) to check the spectrum.

[0132] The examples above are functional tests, as they check the proper functioning of components. In some cases, structural testing can help uncover defects (potentially in conjunction with some functional testing). Therefore, test input circuitry can be configured to modify the front-end circuitry so that it begins to oscillate. For example, the amplifier in the front-end circuitry might be configured with positive feedback, whereas in normal applications it uses negative feedback. The advantage is that the test input is inherently generated as a result of the oscillation. In such embodiments, the test output can include the frequency and amplitude of the oscillation. Such an oscillation signal can also be used to test an ADC.

[0133] In embodiments of the invention, the processing device is configured to compare sensor signal acquisitions from different sensor inputs. For example, their differences can be compared to a threshold. The threshold can be predefined.

[0134] Sensor performance can affect the safety of interface circuitry. When comparing two front-end outputs, a predefined threshold can depend on the expected difference between the two inputs from the sensor in the absence of a fault.

[0135] For example, if two sensor inputs can each drift (without fault) by 1%, and the difference between these two sensor signals can drift by 1.5%, then the difference between the two outputs of the processed sensor signal can also drift by 1.5%, even though there are no faults in the interface circuitry used for sensor processing. Therefore, the threshold used for output comparison should be at least 1.5% of the full-scale signal range, and often even higher, to provide some headroom for the interface circuitry. This means that faults in the interface that cause 1.5% or lower errors cannot be detected. If the sensor drifts 1.5% in the opposite direction, it might even be impossible to detect faults in the interface that cause 3% errors. Smaller deviations in the interface chip are generally preferred for detection.

[0136] Therefore, in some embodiments of the invention, the processing device is configured to compensate for sensor drift. This can be achieved, for example, through automatic zeroing. This means that the processing device measures the drift at a certain moment and subtracts it from the result of subsequent measurements. This can be repeated periodically. If the physical input is known, this can be done separately on the two outputs (signal acquisitions from different sensors). This operation can also be done based on the difference between the two outputs, with the advantage that the physical input does not need to be known (assuming the two sensors measure the same physical input).

[0137] In embodiments of the invention, the processing device may be configured to examine the output difference without drift compensation and the output difference with drift compensation, each output difference having its own threshold. Instead of examining the drift without compensation, the processing device may be configured to examine the magnitude of the required compensation, which is essentially the reciprocal of the drift.

[0138] Uncompensated checks are performed to inspect for sensor drift, which is typically slow. Compensated checks can use stricter constraints to cover rapid drift in the interface circuitry and the sensor. The processing device can be configured to track slow sensor drift, rather than measuring and compensating for it at one or a few discrete moments. The sensor interface circuitry may include a low-pass filter with a sufficiently high time constant (e.g., 1 minute) to reduce the effects of rapid changes caused by internal or external faults, including EMC-related biases.

[0139] In some cases, there may be more than two sensors sharing two analog front ends, such as three sensors and two front ends.

[0140] In embodiments of the present invention, the analog front end may have the same design.

[0141] Individual sensors can each exist on a separate die. Alternatively, individual sensors can exist on a single die with a single membrane, where different sensors use only a different set of piezoelectric resistors.

[0142] In a second aspect, embodiments of the invention relate to a method for controlling the integrity of a sensor interface circuit, the sensor interface circuit including at least two sensor inputs, each sensor input being configured to be connected to a different sensor for measuring the same physical parameter, and each sensor input being configured to be connected to front-end circuitry for modulating signals from the sensors. Similar to the sensor interface circuits broadly described above, the method includes:

[0143] -Signals are acquired from the front-end circuitry to obtain sensor signal data.

[0144] - Intermittently apply a test signal to at least one of the front-end circuits and read the test output of the front-end circuit caused by the test signal.

[0145] - Compare the test output with the expected result to obtain at least one test result.

[0146] - Compare sensor signal acquisitions from different sensor inputs and combine the comparison with at least one test result to evaluate the correct functioning of the sensor interface circuit.

[0147] In embodiments of the present invention, the method may include:

[0148] Connect one of the sensor input pins to an input contact of the front-end circuit to obtain sensor signal acquisition.

[0149] - Connect one of the sensor input pins to the two input contacts of the front-end circuit, and disconnect the other sensor input from the front-end circuit to obtain test results.

[0150] The method according to embodiments of the present invention may include additional features, which are also described above.

Claims

1. A sensor interface circuit (100), the sensor interface circuit comprising: At least two sensor inputs (111, 112), each of which is configured to be connected to a separate sensor for measuring the same physical parameter. At least two front-end circuits (121, 122) are provided, wherein each sensor input (111, 112) is configured to be connected to one of the front-end circuits (121, 122), and wherein each front-end circuit (121, 122) is configured to modulate the signal from the connected sensor input, thereby obtaining sensor signal acquisition from the at least two sensor inputs. A test circuit, configured to test the correct function of at least a portion of one of the front-end circuits (121, 122) by applying a test input to the front-end circuit under test using test input circuits (131, 132), reading the test output of the front-end circuit, and obtaining at least one test result by comparing the test output with an expected result, wherein the test output is caused by the test input, and wherein the test input is applied intermittently between sensor signal acquisitions. A processing device (140) is configured to compare sensor signal acquisitions from different sensor inputs and to combine the comparisons with the at least one test result to evaluate the correct functioning of the sensor interface circuit.

2. The sensor interface circuit (100) as described in claim 1, wherein, The test input is a signal that spans the operating range of the sensor interface circuit.

3. The sensor interface circuit (100) as described in claim 1, wherein, The test input is a sine wave signal.

4. The sensor interface circuit (100) as described in claim 1, wherein, The test input includes one or more constant signals.

5. The sensor interface circuit (100) as described in claim 4, wherein, One of the one or more constant signals is essentially zero.

6. The sensor interface circuit (100) as described in claim 1, wherein, The test input circuit (132) includes switches for the following: Connect one of the sensor input pins of the sensor input (112) to an input contact of one of the front-end circuits (122) to obtain sensor signal acquisition. Connect one of the input pins of the sensor input (112) to the two input contacts of the front-end circuit (122), and disconnect the other sensor input (112) from the front-end circuit (122) to obtain the test result.

7. The sensor interface circuit (100) of claim 6, wherein the test input circuit includes a capacitor that can be connected to one of the input contacts.

8. The sensor interface circuit (100) as described in claim 1, wherein, The processing device (140) is configured to compare sensor signal acquisitions by comparing the difference between the sensor signal acquisitions and a predefined threshold. Used to determine that the sensor signal acquisition is unreliable when the difference is greater than the threshold, and Used to determine that the sensor signal acquisition is unreliable when the difference is less than the threshold and the test result of one of the front-end circuits indicates that the front-end circuit is malfunctioning, and The sensor signal acquisition is deemed reliable when the difference is less than the threshold and the test results of the one or more front-end circuits under test indicate that they are working correctly.

9. The sensor interface circuit (100) as claimed in claim 1, wherein the sensor interface circuit (100) includes a separate test input circuit (131, 132) for each front-end circuit (121, 122) or a single test input circuit for testing all front-end circuits.

10. The sensor interface circuit (100) as described in claim 9, wherein, The processing device (140) is configured to: The sensor signal acquisitions are compared by comparing the difference between the sensor signal acquisitions from the at least two sensor inputs with a predefined threshold, and if the difference is greater than the threshold, This is used to determine that the sensor signal acquisition is unreliable when at least one test result for each front-end circuit indicates that all front-end circuits are malfunctioning, or when the test results indicate that all front-end circuits are malfunctioning. The sensor signal acquisition is used to determine which front-end circuit should be used when the test results of at least one front-end circuit indicate that the front-end circuit is not malfunctioning. And, if the difference is less than the threshold, then the test result of one of the front-end circuits is obtained, and This is used to determine that the sensor signal acquisition is unreliable when the test results indicate that the front-end circuit is malfunctioning. This is used to determine that the sensor signal acquisition is reliable when the test results indicate that the front-end circuit is working correctly.

11. The sensor interface circuit (100) as described in claim 1, wherein, The front-end circuitry includes an analog-to-digital converter (ADC).

12. The sensor interface circuit (100) of claim 1, wherein the sensor interface circuit includes a controller (150) configured to trigger at least one test input circuit (131, 132) to obtain a test result.

13. The sensor interface circuit (100) of claim 1, wherein the sensor interface circuit (100) is configured to connect to an external controller for controlling the sensor interface circuit.

14. A method for controlling the integrity of a sensor interface circuit, the sensor interface circuit including at least two sensor inputs, each sensor input being configured to connect to a different sensor for measuring the same physical parameter, and each sensor input being configured to connect to front-end circuitry for modulating signals from the sensor, the method comprising: Signals are acquired from the front-end circuit to obtain sensor signal acquisition. A test signal is intermittently applied to at least one of the front-end circuits, and the test output of the front-end circuit caused by the test signal is read. The test output is compared with the expected result to obtain at least one test result. The sensor signal acquisitions from different sensor inputs are compared, and the comparison is combined with the at least one test result to evaluate the correct functioning of the sensor interface circuit.

15. The method of claim 14, used in a sensor interface circuit, the sensor interface circuit having a front-end circuit having a differential input, the method comprising: Connect one of the sensor input pins to an input contact of one of the front-end circuits to obtain sensor signal acquisition. Connect one of the input pins of the sensor input to the two input contacts of the front-end circuit, and disconnect the other sensor input from the front-end circuit to obtain the test result.

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