Signal processing method and measurement system

Abstract

A signal processing method for reducing measurement uncertainty is described, comprising the steps of: receiving an analog measurement signal from a device under test by means of a first measurement unit; digitizing the analog measurement signal by means of the first measurement unit to obtain a digital measurement signal; removing noise from the digital measurement signal by means of a first noise reduction unit to obtain a noise-corrected measurement signal; receiving an analog reference signal by means of a second measurement unit, wherein the device under test generates an analog measurement signal based on the analog reference signal; digitizing the analog reference signal by means of a second measuring unit to obtain a digital reference signal; removing noise from the digital reference signal by means of a second noise reduction unit to obtain a noise-corrected reference signal; and determining, by means of a subtraction unit, a digital difference signal on the basis of the noise-corrected measurement signal and the noise-corrected reference signal. Furthermore, a measurement system is described.

Description

Technical Field

[0001] The present invention generally relates to a signal processing method for reducing measurement uncertainty. The present invention also relates to a measurement system. Background Art

[0002] For high-precision measurements of a device under test using a measurement instrument, it is very important to remove noise generated by sources other than the device under test.

[0003] For example, it is necessary to consider the noise generated by the signal generator that provides the test signal to the device under test and the noise generated by the measurement instrument itself.

[0004] Different techniques are known in the art to remove noise generated by sources external to the device under test. Summary of the invention

[0005] It is an object of the present invention to provide a signal processing method and a measuring system which further improve the noise cancellation of noise generated by sources external to the device under test.

[0006] According to the invention, this problem is solved by a signal processing method for reducing measurement uncertainty. The signal processing method comprises the following steps:

[0007] - receiving an analog measurement signal from the device under test by means of a first measurement unit;

[0008] - digitizing the analog measurement signal by means of the first measurement unit, thereby obtaining a digital measurement signal;

[0009] - removing noise from the digital measurement signal by means of a first noise reduction unit, thereby obtaining a noise-corrected measurement signal;

[0010] - receiving an analog reference signal by means of a second measuring unit, wherein the device under test generates an analog measurement signal based on the analog reference signal;

[0011] - digitizing the analog reference signal by means of a second measuring unit, thereby obtaining a digital reference signal;

[0012] - removing noise from the digital reference signal by means of a second noise reduction unit, thereby obtaining a noise-corrected reference signal; and

[0013] - Determining a digital difference signal based on the noise-corrected measurement signal and the noise-corrected reference signal by means of a subtraction unit.

[0014] Therein and hereinafter, the term “the device under test generates an analog measurement signal based on the analog reference signal” is understood to mean that the device under test can process and output an analog reference signal generated by an external signal generator.

[0015] Alternatively, the term may mean that the device under test processes and outputs an analog reference signal produced by a signal generator integrated into the device under test.

[0016] Furthermore, the term “noise removal” is understood to mean that noise originating from the first measuring unit and / or the second measuring unit is removed.

[0017] Among other things, any suitable noise cancellation technique may be used to remove the noise, which will be described in more detail below.

[0018] The noise-corrected measurement signal includes the noise generated by the device under test and the noise generated by the signal generator that produces the analog reference signal.

[0019] On the other hand, the noise-corrected reference signal includes noise generated by a signal generator that generates an analog reference signal.

[0020] Therefore, when determining the difference signal, the noise generated by the signal generator cancels out.

[0021] Therefore, the resulting signal, ie the digital difference signal, comprises only the noise generated by the device under test, in particular the statistical noise generated by the device under test and the noise originating from defects in the device under test.

[0022] In fact, the digital difference signal may only include the noise generated by the device under test, ie no other signal components.

[0023] In other words, the digital difference signal corresponds to the DUT-specific errors included in the digital measurement signal.

[0024] Therefore, the performance of the device under test can be evaluated based on the digital difference signal. More precisely, the noise generated by the device under test can be analyzed based on the digital difference signal that only includes the noise generated by the device under test.

[0025] For example, the noise contribution of a device under test can be analyzed over frequency.

[0026] Therefore, the signal processing method according to the present invention further reduces the measurement uncertainty associated with noise generated by sources external to the device under test.

[0027] The signal processing method according to the invention thus allows the performance of a device under test to be assessed with high accuracy, since an advance noise cancellation of noise originating from all other sources is provided.

[0028] Thus, additional measurement uncertainties that may originate from frequency response or nonlinearities not caused by the device under test are removed.

[0029] According to one aspect of the invention, before determining the digital difference signal, the signal level of the noise-corrected measurement signal and / or the signal level of the noise-corrected reference signal is adapted. By adapting the signal level of the noise-corrected measurement signal and / or the signal level of the noise-corrected reference signal, a cancellation of noise originating from outside the device under test is ensured. In particular, a complete cancellation of noise originating from outside the device under test is ensured.

[0030] In an embodiment of the invention, the signal level of the noise-corrected measurement signal and / or the noise-corrected reference signal is adapted so that the noise-corrected measurement signal and the noise-corrected reference signal have substantially equal signal levels, in particular equal signal levels. By adapting the signal level of the noise-corrected measurement signal and / or the signal level of the noise-corrected reference signal in this way, it is ensured that noise originating from outside the device under test is completely cancelled.

[0031] Herein, the term "substantially equal" is understood to mean that the signal levels are within 5% of each other, and in particular within 2% of each other.

[0032] According to another aspect of the present invention, the analog reference signal is generated based on a digital waveform. The digital waveform can be provided by means of a digital waveform generator.

[0033] Typically, the digital waveform corresponds to a waveform to be applied to a device under test in order to evaluate the performance of the device under test.

[0034] In another embodiment of the invention, the digital waveform is forwarded to the first noise reduction unit and / or the second noise reduction unit, wherein noise is removed from the digital measurement signal and / or from the digital reference signal based on the digital waveform. In this way, it is ensured that when removing the noise, parts of the digital measurement signal and / or the digital reference signal corresponding to the digital waveform are not removed.

[0035] Another aspect of the present invention provides that the digital waveform comprises a modulated signal and / or a continuous wave signal scan. In fact, the digital waveform may correspond to an IQ data signal.

[0036] In particular, the digital difference signal and the digital waveform are summed by means of a summing unit, thereby obtaining a digital summed signal. The obtained signal, namely the digital summed signal, only includes the digital waveform and noise originating from the device under test.

[0037] According to another aspect, the digital summation signal is provided to a measurement application.

[0038] In fact, the performance of the device under test can be evaluated based on the digital summation signal. More precisely, the noise generated by the device under test can be analyzed based on the digital summation signal including only the noise originating from the device under test and the digital waveform, especially by means of a measurement application.

[0039] For example, the noise contribution of the device under test can be analyzed over frequency based on the digital summed signal.

[0040] In another embodiment of the invention, the impedance mismatch between the signal generator generating the analog reference signal and the device under test is corrected. Thus, undesired reflections at the input port of the device under test are reduced, in particular avoided.

[0041] The impedance mismatch may be corrected using any suitable impedance matching technique known in the art.

[0042] Alternatively or additionally, an impedance mismatch between the signal generator generating the analog reference signal and the second measuring unit is corrected. Thus, undesired reflections at the second measuring unit are reduced, in particular avoided.

[0043] The impedance mismatch may be corrected using any suitable impedance matching technique known in the art.

[0044] According to the present invention, the problem is further solved by a measurement system. The measurement system comprises a first measurement unit, a second measurement unit, a first noise reduction unit, a second noise reduction unit and a subtraction unit. The measurement system is configured to perform the above signal processing method.

[0045] With regard to further advantages and properties of the measuring system, reference is made to the explanations given above with regard to the signal processing method, which also apply to the measuring system and vice versa.

[0046] In an embodiment of the present invention, the first measuring unit, the second measuring unit, the first noise reduction unit, the second noise reduction unit and the subtraction unit are integrated into a measuring instrument.

[0047] According to one aspect of the invention, the measuring instrument is designed as an oscilloscope, in particular a digital oscilloscope, a signal analyzer, a vector network analyzer or a measuring receiver.

[0048] However, it should be understood that the measuring instrument may be configured as any other suitable type of measuring instrument.

[0049] The measurement system may further comprise an external signal generator, wherein the external signal generator is configured to generate the analog reference signal, in particular based on the digital waveform.

[0050] Therein and hereinafter, the term “external” is understood to mean that the signal generator is set up separately from the measuring instrument.

[0051] However, it is also conceivable to integrate the signal generator into the measuring instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The foregoing aspects and many of the attendant advantages of the claimed subject matter will become more readily appreciated as they become better understood upon reference to the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0053] - Figure 1 A measuring system according to the invention is schematically shown;

[0054] - Figure 2 Shows Figure 1 A front view of the measuring instrument of the measuring system; and

[0055] - Figure 3 A flow chart of a signal processing method according to the present invention is shown. DETAILED DESCRIPTION

[0056] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of various embodiments of the disclosed subject matter, and is not intended to represent the only embodiments, wherein like reference numerals refer to like elements. Each embodiment described in the present disclosure is provided only as an example or illustration, and should not be construed as preferred or superior to other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the claimed subject matter to the precise form disclosed.

[0057] For purposes of this disclosure, the phrase "at least one of A, B, and C," for example, means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all other possible permutations when more than three elements are listed. In other words, the term "at least one of A and B" generally refers to "A and / or B," i.e., "A" alone, "B" alone, or "A and B."

[0058] Figure 1 A measurement system 10 is shown that includes a measurement instrument 12 and a device under test 14 .

[0059] Generally, the measurement instrument 12 is configured to perform measurements on the device under test 14, and more specifically, to perform measurements on electrical signals received from the device under test.

[0060] The device under test 14 may be any type of electronic device configured to generate and / or process analog electrical signals.

[0061] For example, the device under test 14 may be an amplifier, a mixer, a filter, a mobile phone, or any other electronic component or device configured to generate and / or process electrical signals.

[0062] exist Figure 1 In the particular example shown, device under test 14 is a two-port device configured to receive an analog signal from signal generator 16 .

[0063] The device under test 14 processes the analog signal, thereby generating an analog measurement signal that is forwarded to the measuring instrument 12 .

[0064] However, it should be understood that the device under test 14 may also be configured to generate a measurement signal.

[0065] In this case, the signal generator 16 may be integrated into the device under test 14 .

[0066] Furthermore, it is also conceivable that the signal generator 16 can be integrated into the measuring device 12 .

[0067] Generally, the type of measurement instrument 12 may depend on the type of device under test 14 to be tested.

[0068] For example, the measuring instrument 12 can be designed as an oscilloscope, in particular a digital oscilloscope, a signal analyzer, a vector network analyzer or a measuring receiver.

[0069] However, it should be understood that the measuring instrument 12 may be configured as any other suitable type of measuring instrument.

[0070] The measuring instrument 12 comprises a first measuring port 18 and a signal processing circuit 19 having a first measuring unit 20 , wherein the first measuring unit 20 is connected to an output of the device under test 14 via the first measuring port 18 .

[0071] The measuring instrument 12 further comprises a second measuring port 22 connected to the output of the signal generator 16 .

[0072] The signal processing circuit 19 comprises a second measuring unit 24 , wherein the second measuring unit 24 is connected to the output of the signal generator 16 via a second measuring port 22 .

[0073] Therein and hereinafter, the term "unit" is understood to describe suitable hardware, suitable software or a combination of hardware and software configured to have a certain function.

[0074] The hardware may include, among other things, a CPU, a GPU, an FPGA, an ASIC, or other types of electronic circuitry.

[0075] The signal processing circuit 19 further includes a first noise reduction unit 26 disposed downstream of the first measurement unit 20 and a second noise reduction unit 28 disposed downstream of the second measurement unit 24 .

[0076] A gain unit 30 interconnected between the first noise reduction unit 26 and the second noise reduction unit 28 is provided.

[0077] Furthermore, a multiplication unit 32 is provided, which is connected downstream of the second noise reduction unit 28 to the second noise reduction unit 28 and is connected downstream of the gain unit 30 to the gain unit 30 .

[0078] The measuring instrument 12 further comprises a subtraction unit 34 which is arranged downstream of the first noise reduction unit 26 and downstream of the multiplication unit 32 .

[0079] The measurement system 10 may further include a digital waveform generator (DWG) 35 , which may be established separately from the signal generator 16 .

[0080] In this case, the signal generator 16 may be connected to the digital waveform generator 35 so as to receive the digital waveform generated by the digital waveform generator 35 .

[0081] However, it is also conceivable that the digital waveform generator 35 may be integrated into the signal generator 16 or the measuring instrument 12 .

[0082] The signal processing circuit 19 may also include a digital waveform input 36 connected to the digital waveform generator 35 , for example via an additional input port of the measurement instrument 12 .

[0083] The first noise reduction unit 26 and the second noise reduction unit 28 may be connected to the digital waveform input 36 to receive the digital waveform generated by the digital waveform generator 35 .

[0084] The measuring instrument 12 may further include a summing unit 38 connected to the subtraction unit 34 downstream of the subtraction unit 34 and to the digital waveform input 36 for receiving the digital waveform generated by the digital waveform generator 35 .

[0085] The signal processing circuit 19 may also include a signal output 40 connected to a measurement circuit 42 .

[0086] For example, measurement circuitry 42 may be configured to execute a measurement application configured to analyze output signals of device under test 14 processed by signal processing circuitry 19 .

[0087] The functions of the various units and other components of the measurement system 10 will be described in more detail below.

[0088] Figure 2 A front view of the measuring instrument 12 is shown.

[0089] like Figure 2 As shown, the measurement instrument 12 may include a display 44 configured to display a user interface and / or measurement data obtained by the measurement instrument 12 .

[0090] The measuring instrument 12 may also include an input device 46 such as a button, a knob, a touch-sensitive display, or the like.

[0091] Generally, a user may control measurement settings of the measurement instrument 12 and / or may adjust data visualization on the display 44 via the input device 46 .

[0092] The measurement system 10 is configured to perform the following reference Figure 3 Describe the signal processing method.

[0093] A digital waveform is generated by means of the digital waveform generator 35 (step S1).

[0094] Typically, the digital waveform corresponds to a signal to be applied to the device under test 14 in order to test the device under test 14 , ie, in order to evaluate the performance of the device under test 14 .

[0095] For example, a digital waveform includes a modulated signal and / or a continuous wave signal sweep.

[0096] In particular, the digital waveform may correspond to an IQ data signal.

[0097] It should be noted that Figure 1 In the figure, digital signals are represented by solid arrows, while analog signals are represented by dashed arrows.

[0098] The digital waveform is forwarded to the signal generator 16 , the first noise reduction unit 26 , and the second noise reduction unit 28 .

[0099] An analog reference signal is generated by means of the signal generator 16 based on the digital waveform (step S2 ).

[0100] The analog reference signal is forwarded to the device under test 14 and to the second measurement unit 24 .

[0101] Therein, the impedance mismatch between the signal generator 16 and the device under test 14 can be corrected by means of the signal generator 16 in order to minimize reflections at the input port of the device under test 14 .

[0102] Alternatively or additionally, an impedance mismatch between the signal generator 16 and the second measuring unit 24 can be corrected by means of the signal generator 16 in order to minimize reflections at the second measuring port 22 of the measuring instrument 12 .

[0103] The analog reference signal is processed by means of the device under test 14, thereby obtaining an analog measurement signal (step S3).

[0104] The analog measurement signal is forwarded to the first measuring unit 20 .

[0105] The analog measurement signal is digitized by means of the first measurement unit 20, so that a digital measurement signal is obtained (step S4).

[0106] Therefore, the first measuring unit 20 may include at least one analog-to-digital converter configured to digitize the analog measurement signal.

[0107] The analog reference signal is digitized by means of the second measuring unit 24, thereby obtaining a digital reference signal (step S5).

[0108] Therefore, the second measuring unit 24 may include at least one analog-to-digital converter configured to digitize the analog reference signal.

[0109] The noise is removed from the digital measurement signal by means of the first noise reduction unit 26, so that a noise-corrected measurement signal is obtained (step S6).

[0110] In particular, based on the digital waveform provided by the digital waveform generator 35 , noise is removed from the digital measurement signal.

[0111] The removed noise may correspond to the noise generated by the measuring instrument 12 , in particular the noise generated by the first measuring unit 20 .

[0112] Therein, any suitable noise cancellation technique may be used to remove noise from the digital measurement signal.

[0113] In one specific example, noise can be removed as follows:

[0114] The DUT noise contribution of the device under test 14 to the digital measurement signal is determined.

[0115] The DUT noise contribution corresponds to the noise originating from the device under test 14 .

[0116] The DUT noise contribution may be determined by means of any suitable technique, in particular by means of any suitable technique known in the prior art. For example, the DUT noise contribution may be determined using the technique described in granted US Pat. No. US10,761,134B2.

[0117] Based on the determined DUT noise contribution and based on the digital waveform, a noise level of the digital measurement signal is reduced to a noise level of the DUT noise contribution, thereby obtaining a noise-corrected measurement signal.

[0118] Thus, the noise-corrected measurement signal includes the noise generated by the device under test 14 and the noise generated by the signal generator 16, since the noise generated by the measuring instrument 12 has been removed.

[0119] Noise is removed from the digital reference signal by means of the second noise reduction unit 28, thereby obtaining a noise-corrected reference signal (step S7).

[0120] In particular, based on the digital waveform provided by the digital waveform generator 35 , noise is removed from the digital reference signal.

[0121] The removed noise may correspond to the noise generated by the measuring instrument 12 , in particular the noise generated by the second measuring unit 24 .

[0122] Any suitable noise cancellation technique may be used to remove noise from the digital reference signal.

[0123] For example, the noise may be removed similarly to step S7 described above, where the DUT noise contribution is replaced by the noise contribution of the signal generator 16 (in other words, the signal generator 16 corresponds to the DUT).

[0124] Thus, the noise-corrected reference signal includes the noise generated by the signal generator 16, since the noise generated by the measuring instrument 12 has been removed.

[0125] The signal level of the noise-corrected reference signal is adapted by means of the gain unit 30 and the multiplication unit 32 (step S8).

[0126] More precisely, the signal level of the noise-corrected reference signal is adapted such that the noise-corrected measurement signal and the noise-corrected reference signal have substantially equal signal levels, in particular equal signal levels.

[0127] The gain unit 30 may determine a signal level g1 of the noise-corrected measurement signal and a signal level g2 of the noise-corrected reference signal.

[0128] The gain unit 30 may determine the gain factor G based on the determined signal levels g1 , g2 according to G=g1 / g2 .

[0129] The signal level of the noise-corrected reference signal can then be adapted by multiplying the noise-corrected reference signal by a gain factor G by means of a multiplication unit 32 .

[0130] Of course, the signal level of the noise-corrected measurement signal can also be adapted as an alternative.

[0131] In this case, the noise-corrected measurement signal can be multiplied by the multiplication unit 32 by the gain factor G ′ =g2 / g1 is multiplied to adapt the signal level of the noise-corrected measurement signal.

[0132] After adaptation of the signal levels, the noise-corrected measurement signal and the noise-corrected reference signal are forwarded to a subtraction unit 34 .

[0133] Based on the noise-corrected measurement signal and the noise-corrected reference signal, a digital difference signal is determined by means of the subtraction unit 34 (step S9),

[0134] More precisely, the subtraction unit 34 may subtract the noise-corrected reference signal from the noise-corrected measurement signal, thereby obtaining a digital difference signal.

[0135] Alternatively, the subtraction unit 34 may subtract the noise-corrected measurement signal from the noise-corrected reference signal, thereby obtaining a digital difference signal.

[0136] As described above, the noise-corrected measurement signal includes the noise generated by the device under test 14 and the noise generated by the signal generator 16 , while the noise-corrected reference signal includes the noise generated by the signal generator 16 .

[0137] Therefore, in the digital difference signal, the noise generated by the signal generator 16 cancels out, so that the digital difference signal only includes the noise generated by the device under test 14 .

[0138] In fact, since both the noise-corrected measurement signal and the noise-corrected reference signal comprise digital waveforms (and since the signal levels of the noise-corrected reference signal and / or the noise-corrected measurement signal are adapted), the digital waveforms may also cancel.

[0139] Therefore, the digital difference signal may include only the noise generated by the device under test 14 .

[0140] like Figure 1 As shown by the dashed arrow in , the digital difference signal can be forwarded to the measurement circuit 42 for analyzing the noise generated by the device under test 14, in particular for evaluating the performance of the device under test 14.

[0141] Furthermore, the digital difference signal and the digital waveform may be summed by means of the summing unit 38 to obtain a digital summed signal (step S10 ).

[0142] The digital summation signal corresponds to a digital waveform superimposed with the noise generated by the device under test 14 .

[0143] The digital summation signal may be forwarded to measurement circuitry 42 for analyzing the noise generated by device under test 14 , in particular for evaluating the performance of device under test 14 .

[0144] Certain embodiments disclosed herein, in particular corresponding modules and / or units, utilize circuit systems (e.g., one or more circuits) to implement the standards, protocols, methods, or techniques disclosed herein, operably couple two or more components, generate information, process information, analyze information, generate signals, encode / decode signals, convert signals, send and / or receive signals, control other devices, etc. Any type of circuit system may be used.

[0145] In one embodiment, the circuit system includes, among other things, one or more computing devices, such as a processor (e.g., a microprocessor), a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a system on a chip (SoC), etc. or any combination thereof, and may include discrete digital or analog circuit elements or electronic devices or combinations thereof. In one embodiment, the circuit system includes a hardware circuit implementation (e.g., an implementation in an analog circuit system, an implementation in a digital circuit system, etc. and a combination thereof).

[0146] In one embodiment, the circuit system includes a combination of circuits and computer program products having software or firmware instructions stored on one or more computer readable memories that work together to cause the device to perform one or more protocols, methods, or techniques described herein. In one embodiment, the circuit system includes circuits that require software, firmware, etc. to operate, such as, for example, a microprocessor or a portion of a microprocessor. In one embodiment, the circuit system includes one or more processors or portions thereof and accompanying software, firmware, hardware, etc.

[0147] The present application may quote quantities and numbers. Unless otherwise specified, these quantities and numbers are not considered to be restrictive, but examples of possible quantities or numbers associated with the present application. Also in this regard, the present application may use the term "plurality" to refer to quantities or numbers. In this regard, the term "plurality" refers to any number greater than one, for example, two, three, four, five, etc. The terms "approximately", "approximately", "close to", etc. refer to plus or minus 5% of the value.

Claims

1. A signal processing method for reducing measurement uncertainty, the signal processing method comprising the following steps: - receiving an analog measurement signal from a device under test (14) by means of a first measurement unit (20); - digitizing the analog measurement signal by means of the first measurement unit (20) to obtain a digital measurement signal; - removing noise from the digital measurement signal by means of a first noise reduction unit (26), thereby obtaining a noise-corrected measurement signal; - receiving an analog reference signal by means of a second measuring unit (24), wherein the device under test (14) generates the analog measurement signal based on the analog reference signal; - digitizing the analog reference signal by means of a second measuring unit (24) to obtain a digital reference signal; - removing noise from the digital reference signal by means of a second noise reduction unit (28), thereby obtaining a noise-corrected reference signal; and - Determining a digital difference signal based on the noise-corrected measurement signal and the noise-corrected reference signal by means of a subtraction unit (34).

2. The signal processing method according to claim 1, wherein: Before the digital difference signal is determined, the signal level of the noise-corrected measurement signal and / or the signal level of the noise-corrected reference signal is adapted.

3. The signal processing method according to claim 2, wherein: The signal level of the noise-corrected measurement signal and / or the signal level of the noise-corrected reference signal is adapted such that the noise-corrected measurement signal and the noise-corrected reference signal have substantially equal signal levels, in particular equal signal levels.

4. A signal processing method according to any one of the preceding claims, wherein: The analog reference signal is generated based on a digital waveform.

5. The signal processing method according to claim 4, wherein: The digital waveform is forwarded to the first noise reduction unit (26) and / or the second noise reduction unit (28), and wherein the noise is removed from the digital measurement signal and / or from the digital reference signal based on the digital waveform.

6. The signal processing method according to claim 4 or 5, wherein: The digital waveform includes a modulated signal and / or a continuous wave signal scan.

7. The signal processing method according to any one of claims 4 to 6, wherein: The digital difference signal and the digital waveform are summed by means of a summing unit (38) to obtain a digital summation signal.

8. The signal processing method according to claim 7, wherein: The digital summed signal is provided to a measurement application.

9. The signal processing method according to claim 7 or 8, wherein: The performance of the device under test (14) is evaluated based on the digital summation signal.

10. The signal processing method according to any one of the preceding claims, wherein: Impedance mismatch between a signal generator (16) generating the analog reference signal and the device under test (14) is corrected.

11. A signal processing method according to any one of the preceding claims, wherein: An impedance mismatch between a signal generator (16) generating the analog reference signal and the second measuring unit (24) is corrected.

12. A measurement system, the measurement system (10) comprising a first measurement unit (20), a second measurement unit (24), a first noise reduction unit (26), a second noise reduction unit (28) and a subtraction unit (34), wherein: The measurement system (10) is configured to perform the signal processing method according to any of the preceding claims.

13. The measurement system according to claim 12, wherein: The first measuring unit (20), the second measuring unit (24), the first noise reduction unit (26), the second noise reduction unit (28) and the subtraction unit (34) are integrated into a measuring instrument (12).

14. The measurement system according to claim 13, wherein: The measuring instrument (12) is designed as an oscilloscope, in particular a digital oscilloscope, a signal analyzer, a vector network analyzer or a measuring receiver.

15. The measuring system according to any one of claims 12 to 14, further comprising an external signal generator (16), wherein: The external signal generator (16) is configured to generate an analog reference signal, in particular based on a digital waveform.

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