Method for testing an analog-digital conversion unit by means of delta-sigma modulation

Abstract

The invention relates to a method for testing an analog-digital conversion unit (1) which is provided for converting an analog input signal (100) into a digital output signal (200) according to a Delta-Sigma modulation, the method having the following steps: generating an analog input signal (100), applying a predefined disturbance signal (300) to the analog input signal (100) and storing the resulting digital output signal (200) as a test result, finding a fault condition when a transfer function of the analog-digital conversion unit (1) which is determined from the test result and the input signal (100) has a deviation from a predefined target transfer function which is greater than a predefined reference value, wherein a fault notification is output in the event of a fault condition being found.

Description

Background Technology

[0001] This invention relates to a method for testing an analog-to-digital converter (ADC). The ADC is based on Delta-Sigma modulation. Furthermore, this invention relates to an ADC with a corresponding self-test module.

[0002] Analog-to-digital converters (ADCs) are known from existing technologies. Such ADCs can be based on Delta-Sigma modulation, in which an adjustment loop is implemented, wherein the analog input signal is quantized to subsequently adjust for quantization errors. Such ADCs offer the potential for very high accuracy, where the quality of the ADC is related to the quality of the implemented adjustment loop. Summary of the Invention

[0003] The method according to the invention enables accurate testing of analog-to-digital converters based on Delta-Sigma modulation. Thus, the dead zone in the transfer function of the analog converter can be reliably determined with reduced effort. This allows for and guarantees high accuracy in analog-to-digital conversion. In particular, the method preferably performs testing on the adjustment loop, as this test significantly affects the transfer function. Therefore, other effects can be ignored, thereby avoiding tedious verification of the overall input-output behavior of the analog-to-digital converter.

[0004] A method for testing an analog-to-digital converter (ADC) unit that converts an analog input signal to a digital output signal according to Delta-Sigma modulation comprises the following steps: First, an analog input signal is generated, which serves as a test signal. Additionally, a predefined interference signal is applied to the analog input signal, and the resulting digital output signal is stored as a test result. Finally, a fault condition is detected based on the deviation from a predefined target transfer function. For this purpose, the transfer function of the analog-to-digital converter is determined. This transfer function can be extracted from the transfer behavior of the analog-to-digital converter unit, i.e., based on the input and output signals. A fault condition is detected when the deviation between the determined transfer function and the predefined target transfer function is greater than a predefined reference value. In the event of a fault condition, a fault notification is output. Particularly advantageously, the test can be performed on only a single part of the transfer function, such as at zero. This simplifies the execution of the test.

[0005] The occurrence of dead zones in the transfer function is particularly due to excessively low regulator gain within the adjustment loop. Therefore, according to the invention, instead of examining the direct input-output behavior of Delta-Sigma modulation, only the regulator gain is checked. If an interference signal is applied, ideally, this interference signal should be adjusted through the adjustment loop. Conversely, if the adjustment loop is malfunctioning and therefore has excessively low regulator gain, the deviation remains in the digital output signal, which can be reliably detected using the aforementioned method. Thus, the presence of faults in the analog-to-digital conversion unit can be easily and effortlessly discovered.

[0006] The content of the dependent claims is a preferred extension of the present invention.

[0007] Preferably, the analog-to-digital conversion unit has a loop filter and a quantizer as components for Delta-Sigma modulation. A predefined interference signal is applied between the loop filter and the quantizer. Therefore, the interference signal directly affects the quantization, but is not affected by other components of the Delta-Sigma modulation. Furthermore, this method can be implemented easily and effortlessly because the interference signal only needs to be applied to the analog-to-digital conversion unit at a predefined location.

[0008] Advantageously, the interfering signal is an offset signal, which can be implemented using a DC voltage. Alternatively or additionally, the interfering signal is advantageously a sinusoidal signal and / or pseudo-random noise. Depending on the available information about the aforementioned loop filter, a particularly advantageous interfering signal can be determined to perform the method particularly efficiently. However, in the simplest case, it is sufficient to apply only the offset signal as the interfering signal so as to detect, and thus detect, the behavior of the Delta-Sigma modulation conditioning loop and therefore the conversion quality of the entire analog-to-digital converter.

[0009] Fault conditions are presented in particular through a plateau of the transfer function of the analog-to-digital converter. This plateau visualizes the aforementioned dead zone because at this location, the output signal cannot be definitively and uniquely assigned to the incoming input signal. The test results and / or additional test results and / or the difference between the test results and additional test results is here used as a scale (Maβ) for this plateau.

[0010] Preferably, after applying a predefined interference signal, a negative (negierte) predefined interference signal is also applied to the analog input signal, and the resulting digital output signal is stored as an additional test result. This method is particularly advantageous because a fault condition exists when the difference between the test result and the additional test result exceeds a predefined reference value. Therefore, dead zones within the transfer function can be detected safely and reliably, thereby enabling easy and effortless testing of the analog-to-digital converter unit.

[0011] Advantageously, the same input signal exists for obtaining both the test results and additional test results. As mentioned earlier, the input signal is generated for testing purposes. Therefore, it is preferable that the input signal is generated in the same way not only for obtaining the test results but also for obtaining the additional test results. Thus, the only area in obtaining the test results and additional test results is the applied interference signal, making it possible to detect the full effect of the interference signal. As mentioned earlier, ideally, there should be a complete adjustment to the interference signal, i.e., the change in the output signal should not be identifiable. Conversely, if the change in the output signal is greater than a predefined reference value, a fault in the analog-to-digital conversion unit can be inferred.

[0012] Furthermore, the present invention relates to an analog-to-digital conversion unit. This unit includes a Delta-Sigma modulator configured to convert an analog input signal into a digital output signal according to Delta-Sigma modulation. Additionally, the unit includes a self-test module configured to perform the following activities: First, the self-test module is configured to generate an input signal. This input signal is intended for self-testing the Delta-Sigma modulator. Therefore, the generated input signal is advantageously output from the self-test module to the input of the Delta-Sigma modulator. Furthermore, the self-test module is configured to apply a predefined interference signal to the analog input signal. Additionally, the self-test module is configured to store the resulting digital output signal as a test result. Thus, the self-test module can achieve the storage of a digital output signal as a test result in the presence of both the generated input signal and the predefined interference signal. Finally, the self-test module is configured to detect fault conditions based on deviations from a predefined target transfer function. For this purpose, the self-test module is configured to determine the transfer function of the analog-to-digital unit. The transfer function can be extracted from the transfer behavior of the analog-to-digital converter, i.e., based on the input and output signals. When the deviation between the obtained transfer function and the predefined target transfer function exceeds a predefined reference value, the self-test module detects a fault condition. Finally, the self-test module is configured to output a fault signal upon detection of the fault condition. Therefore, the self-test module enables reliable and efficient self-testing of the Delta-Sigma modulator, particularly reliably identifying dead zones in the transfer function of the Delta-Sigma modulator and therefore the analog-to-digital converter. The details of the identification process mechanism are as described above, and therefore refer to the disclosure above.

[0013] Particularly advantageously, the Delta-Sigma modulator includes a loop filter and a quantizer. Preferably, a coupling point is provided between the loop filter and the quantizer, on which a predefined interference signal can be applied. Therefore, a simple and cost-effective implementation of the self-test module is achieved, as only minimal modification to the Delta-Sigma modulator is required—namely, embedding the coupling point between the quantizer and the loop filter. This coupling point allows the interference signal to be reliably applied to the input signal, so that the interference signal directly affects the quantizer, but is not affected by other components of the Delta-Sigma modulator. Thus, efficient testing of the Delta-Sigma modulator can be achieved.

[0014] Preferably, the self-test module is configured to provide an offset signal and / or a sinusoidal signal and / or pseudo-random noise as an interference signal. These different signal types have different advantages, particularly as previously described, and therefore reference is made herein to the disclosure above.

[0015] Preferably, the self-test module is configured to determine faults in the control loop that cause plateaus in the transfer function of the analog-to-digital converter (ADC). Therefore, this transfer function is preferably that of the Delta-Sigma modulator or the ADC. Here, the plateau is visualized by the aforementioned dead zone in the transfer function. The test result and / or additional test result and / or the difference between the test result and the additional test result constitutes a scale for the plateau. Therefore, the plateau or dead zone in the transfer function can be easily and effortlessly deduced from the determined parameters, where the input and output signals cannot be definitively and uniquely assigned on the plateau or in the dead zone, especially since multiple different input signals are converted to the same output signal. Thus, a reliable and efficient determination of fault conditions in the Delta-Sigma modulator is achieved.

[0016] Advantageously, the self-test module is configured to apply a negative predefined interference signal to the analog input signal after applying a predefined interference signal. Furthermore, the self-test module is configured to store the resulting digital output signal as an additional test result. Therefore, for the self-test module, there are two distinct results derived from the interfered analog input signal when both the interference signal and the negative interference signal are applied. Thus, the self-test module is constructed to detect a fault condition when the difference between the test result and the additional test result exceeds a predefined reference value. Consequently, the self-test module can reliably and effortlessly identify fault conditions.

[0017] Advantageously, the self-test module is configured to generate the same input signal during the acquisition of both the test result and the additional test result. Therefore, the test result and the additional test result are acquired based on the same fundamental preconditions, where only the interference signal differs. Since the interference signal is ideally fully adjusted, a change in the output signal can ideally be expected such that the difference between the test result and the additional test result becomes zero. However, if the difference is greater than a predefined reference value, a failure of the Delta-Sigma modulator can be considered, as the Delta-Sigma modulator's adjustment loop has too low a gain, insufficient to adjust the interference signal. Therefore, failures and malfunctions of the Delta-Sigma modulator, and thus the analog-to-digital converter, can be reliably identified. Attached Figure Description

[0018] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The drawings show:

[0019] Figure 1 A schematic view of an analog-to-digital conversion unit according to an embodiment of the present invention is shown.

[0020] Figure 2 A schematic view showing the ideal and actual transfer functions of an analog-to-digital conversion unit according to an embodiment of the present invention is provided. Detailed Implementation

[0021] Figure 1 An analog-to-digital converter (ADC) unit 1 according to an embodiment of the invention is illustrated schematically. The ADC unit 1 includes a Delta-Sigma modulator 10 and a self-test module 11. The Delta-Sigma modulator 10 is configured to convert an analog input signal 100 into a digital output signal 200 according to Delta-Sigma modulation. Additionally, the ADC unit 1 may advantageously include a low-pass filter 7 and a sampling rate converter 8, which affect the output signal 200. However, the latter two components are not essential to the embodiment of the invention and are therefore not described in detail below.

[0022] The Delta-Sigma modulator 10 has a loop filter 2 and a quantizer 3, such that the input signal 100 is converted into a digital signal by the quantizer 3 after passing through the loop filter 3. The quantizer 3 can be, for example, a comparator that compares the input signal with a predefined reference signal 500. An adjustment loop is implemented by a feedback device 9, which is used to adjust the quantization error of the quantizer 3. For this purpose, the analog input signal 100 is superimposed on the feedback signal at the feedback section 6, wherein the feedback signal is converted into an analog signal by means of a digital-to-analog converter 5. The digital-to-analog converter 5 uses the output signal 200 from the quantizer 3 and converts the output signal back into an analog signal, wherein this is advantageously performed only by 1 / bit conversion, such that the reference voltage V is either positive or negative. Ref It is superimposed on the analog input signal 100.

[0023] To identify faults in the Delta-Sigma modulator 10, the loop filter 2 is examined in particular. This loop filter 2 typically has at least one integrator by which the quantization error is integrated so that the quantization error can be adjusted. If this integrator has too low a gain, the regulator gain of the regulation loop of the Delta-Sigma modulator 10 is insufficient. This excessively low regulator gain is particularly evident in the case of a Delta-Sigma modulator failure. This can be determined using the self-test module 11.

[0024] The self-test module 11 is first used to generate an input signal 100, which should be used for testing purposes. Additionally, the self-test module 11 generates an interference signal 300. The interference signal 300 is applied to the coupling point 4 between the loop filter 2 and the quantizer 3. Therefore, the interference signal 300 directly affects the quantizer 3, thereby avoiding the influence of other components of the Delta-Sigma modulator 10. Under normal operating conditions of the regulation loop, the Delta-Sigma modulator 10 adjusts the interference signal 300 so that no or almost no change can be detected in the output signal 200. However, if the regulator gain is insufficient, adjustment cannot be made.

[0025] Therefore, the self-test module 11 is configured to first apply a predefined interference signal 300 so as to store the resulting output signal 200 as a test result. Additionally, the self-test module 11 is configured to apply a negative predefined interference signal 300 so as to store the resulting output signal 200 as an additional test result. The generated input signal 100 remains the same during the determination of the test result and the additional test result. Therefore, the only difference between the test result and the additional test result is the presence of a different interference signal 300 during the detection of said result.

[0026] As previously stated, ideally, it is expected that there will be no change in the output signal 200 under the interference signal 300. Therefore, the self-test module 11 forms a difference between the test result and the additional test result. If the difference is higher than a predefined reference value, the failure of the adjustment can be inferred, and therefore the failure of the Delta-Sigma modulator 10 can be inferred. In this case, the self-test module 11 is configured to output a fault notification. Therefore, a particularly simple special case of the general principle is described here, namely, inferring the transfer function based on the transmission behavior of the analog-to-digital conversion unit 1, wherein the transfer function is compared with a predefined target transfer function. If the deviation is greater than the predefined reference value, the failure is found.

[0027] In its simplest case, the interference signal 300 is an offset signal generated by a DC voltage. Similarly, the interference signal 300 can also be a sinusoidal signal and / or pseudo-random noise. Depending on the available information about the loop filter 2, different interference signals 300 can be used to achieve optimal testing.

[0028] In an alternative configuration, the application of the negative interference signal 300 can be omitted. This is especially true when the interference signal 300 is not a simple offset signal.

[0029] Figure 2The transfer function 400 of the analog-to-digital conversion unit 1 is shown, i.e., the association between the input signal 100 and the output signal 200. If an ideal transfer function 400a exists, each input signal 100 can be definitively and uniquely assigned to one output signal 200, i.e., each analog input signal 100 will be converted into a definitively and uniquely digital output signal 200. However, the transfer function 400 may have a plateau 401, thereby creating a dead zone. In this dead zone, the definitively and uniquely assigned relationship between the input signal 100 and the output signal 200 cannot be guaranteed. The plateau 401 can be reliably identified according to the aforementioned method steps performed by the aforementioned self-test module 11. The test result and / or additional test result and / or the difference between the test result and the additional test result constitute the scale for the plateau 401. In particular, the local shift 402 of the transfer function 400 shown by the plateau 401 can be determined based on these parameters. In particular, the following association exists: if the interference signal 300 is described as Q OS Then we can expect to see the D described below. out The following effects of the output signal 200:

[0030] D out =kQ Q OS / H(f=0)+x

[0031] Where kQ is the gain of quantizer 3, and x is the digital output signal 200, which is converted from input signal 100 in the absence of interference signal 300. Therefore, complete adjustment of interference signal 300 can only be expected when the gain of the loop filter increases accordingly. If this is not the case, adjustment cannot be made, and the platform 401 is retained, the position of which can be determined according to parameters kQ. OS The result is obtained from / H (f = 0). If, as mentioned before, the difference between the test results and the additional test results forms a difference, then the result is exactly the parameter, because the difference D... out ,1-D out ,2 leads to the elimination of the same value x under the same input signal 100.

[0032] In addition to the position 402 of platform 401, the width 403 of the platform can also be determined. Advantageously, in the event of a failure of the Delta-Sigma modulator 10 or the analog-to-digital converter 1, platform 401 is output as the aforementioned fault notification. Therefore, the analog-to-digital converter 1 can be reliably and accurately tested in a simple manner. In particular, fault conditions can be reliably and quickly identified. In this case, the self-test module 11 reliably outputs the corresponding fault notification.

Claims

1. A method for testing an analog-to-digital converter (1), the analog-to-digital converter being configured to convert an analog input signal (100) into a digital output signal (200) according to Delta-Sigma modulation, the method comprising the following steps: Generate an analog input signal (100). A predefined interference signal (300) is applied to the analog input signal (100), and the resulting digital output signal (200) is stored as the test result. When the transfer function obtained by the analog-to-digital conversion unit (1) from the test results and the input signal (100) deviates from the predefined target transfer function by a value greater than a predefined reference value, a fault is detected. Upon detecting a fault, a fault notification will be output. The analog-to-digital conversion unit (1) has a loop filter (2) and a quantizer (3) as components of the Delta-Sigma modulation, wherein the predefined interference signal (300) is applied between the loop filter (2) and the quantizer (3).

2. The method according to claim 1, characterized in that, The interference signal (300) is an offset signal and / or a sinusoidal signal and / or pseudo-random noise.

3. The method according to claim 1 or 2, characterized in that, After applying the predefined interference signal (300), a negative predefined interference signal (300) is applied to the analog input signal (100) and the resulting digital output signal (200) is stored as an additional test result, wherein a fault is found when the difference between the test result and the additional test result is greater than a predefined reference value.

4. The method according to claim 3, characterized in that, There is a common input signal (100) used to obtain the test result and the additional test result.

5. An analog-to-digital converter (1) having: Delta-Sigma modulator (10), the Delta-Sigma modulator being configured to convert an analog input signal (100) into a digital output signal (200) according to Delta-Sigma modulation. Self-test module (11), the self-test module is configured to: Generate an analog input signal (100). A predefined interference signal (300) is applied to the analog input signal (100), and the resulting digital output signal (200) is stored as the test result. When the transfer function obtained by the analog-to-digital conversion unit (1) from the test results and the input signal (100) deviates from the predefined target transfer function by a value greater than a predefined reference value, a fault is detected. The self-test module (11) is configured to output a fault signal when a fault condition is detected. The Delta-Sigma modulator (10) has a loop filter (2) and a quantizer (3), wherein the predefined interference signal (300) can be applied through the coupling portion (4) between the loop filter (2) and the quantizer (3).

6. The analog-to-digital conversion unit (1) according to claim 5, characterized in that, The self-test module (11) is configured to provide an offset signal and / or a sinusoidal signal and / or pseudo-random noise as an interference signal (300).

7. The analog-to-digital conversion unit (1) according to claim 5 or 6, characterized in that, The self-test module (11) is configured to, after applying the predefined interference signal (300), apply a negative predefined interference signal (300) to the analog input signal (100) and store the resulting digital output signal (200) as an additional test result, wherein a fault is found when the difference between the test result and the additional test result is greater than a predefined reference value.

8. The analog-to-digital conversion unit (1) according to claim 7, characterized in that, The self-test module (11) is configured to generate the same input signal (100) during the determination of the test result and the additional test result.

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