Oscilloscope and noise compensation method

Abstract

To compensate for noise in an oscilloscope.SOLUTION: An oscilloscope includes one or more ports to connect to a device under test (DUT) and receive a signal, one or more analog-to-digital converters (ADC) to generate a waveform of digital samples of the signal, and one or more processors to: acquire a noise waveform to obtain a measurement value, acquire a waveform of a repeating pattern from the ADC, obtains its frequency spectrum, identify a spectral impulse component of the frequency spectrum, obtain a measurement value of a flat component of the frequency spectrum, use the measurement value of the flat component and the measurement value of the noise waveform to generate a noise compensation ratio, perform scale adjustment on the flat component with the noise compensation ratio and combine it with the spectral impulse component of the frequency spectrum to generate a noise compensated frequency spectrum, convert the noise compensated frequency spectrum to a time domain waveform to measure performance of the DUT.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to oscilloscopes, and more particularly to techniques for reducing the effects of noise in oscilloscopes. [Background technology]

[0002] The accuracy of oscilloscope acquisition of high-speed signal waveforms is adversely affected by the oscilloscope's own noise. As of this writing, high-speed serial data signals are widely used in data centers and other applications, with speeds of 32 GBaud (gigabaud) PAM4 for PCI Express Gen 6 and 53 GBaud PAM4 for 400G Ethernet. See, for example, "PCI Express Base Specification 6.0" 2021, https: / / pcisig.com / specifications / 2021, and "IEEE 802.3ck 100 Gb / s, 200 Gb / s and 400 Gb / s Ethernet Standard" 2022, http: / / www.ieee802.org / 3 / . Transceivers for these applications are measured, and a pass / fail (pass / fail) decision is made based on the measurements. Noise in acquired waveforms can significantly impact link performance measurements such as Symbol Error Rate, SNDR, and TDECQ for electrical and optical signals because the test margins decrease as data rates increase. This can result in inaccurate measurements, causing devices to fail when they should pass and devices to pass when they should fail.

[0003] U.S. Patent Application Publication No. 2023 / 0280373, published September 7, 2023, entitled "Signal Processing Method and System" (hereinafter "Ramian"), describes a method for utilizing knowledge of noise introduced by a device under test (DUT) to obtain a cleaner signal for measurements such as error vector magnitude (EVM). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2023 / 0280373 [Patent Document 2] US Patent Application Publication No. 2024 / 0125837 [Patent Document 3] Japanese Patent Application Laid-Open No. 2024-54857 Summary of the Invention [Problem to be solved by the invention]

[0005] Oscilloscopes are widely used to measure high-speed signals because of their high bandwidth and versatile debugging capabilities. In this application, "RT oscilloscope" refers to an oscilloscope that acquires signals using real-time oversampling. Real-time oversampling typically ensures anti-aliasing through the acquisition system design. The instrument noise of these types of oscilloscopes affects measured jitter, eye opening and closure, and other measurements. The random component of instrument noise is scaled for measurements at very low bit error rates (BER). For example, random noise is converted to random jitter through the rising or falling edge of a signal, and in total jitter and eye opening measurements at a BER of 10e-12, the standard deviation of random jitter is 14 times larger. Typically, the dominant component of instrument noise is random. [Means for solving the problem]

[0006] Embodiments of the present application include real-time (RT) oscilloscopes that do not use knowledge of the DUT noise. Instead, the oscilloscopes of these embodiments use knowledge of the measurement device noise. The oscilloscope only needs to characterize the measurement device noise once, and then the oscilloscope uses that noise characterization to test and measure multiple DUTs. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 shows an embodiment of an oscilloscope device. [Figure 2] Figure 2 shows an example of a pattern waveform that complies with PCIE (Peripheral Component Interconnect Express) 6th generation. [Figure 3] FIG. 3 shows an example of the frequency spectrum of a waveform. [Figure 4] FIG. 4 shows an enlarged view of the frequency spectrum of the waveform. [Figure 5] FIG. 5 shows an enlarged view of the frequency spectrum of the noise-compensated waveform. [Figure 6] Figure 6 shows an example of an eye diagram before and after noise correction. DETAILED DESCRIPTION OF THE INVENTION

[0008] Because oscilloscopes sample signals in real time, in most test setups, they can acquire multiple repetitions of a test pattern in a short time. For example, for a 53 gigabaud (GBaud) PAM4 (4-level pulse amplitude modulation) signal, an oscilloscope can acquire 53 million symbols in 1 millisecond. High-bandwidth oscilloscopes typically have large acquisition memories, such as up to 1 gigabit of sample points per channel. For a typical PRBS13Q (Pseudo-Random Binary Sequence length 13) test pattern with 8191 symbols, an oscilloscope can acquire 100 repetitions of the pattern running at 53 GBaud in 16 microseconds. In contrast, a sampling oscilloscope may take several seconds to acquire just one repetition of the pattern. This is just one example of the repetitive patterns an oscilloscope can acquire.

[0009] FIG. 1 shows an embodiment of an oscilloscope in a test setup for a device under test (DUT) 30. In this setup, the DUT may include an optical transmitter, and therefore the test setup includes an optical-to-electrical (O / E) converter 34 as an accessory to the oscilloscope. If the signals from the DUT are not optical, the O / E converter 34 would not be present in the setup. The oscilloscope (also called a "scope") 10 receives signals from the DUT 30 through a measurement instrument probe (optical fiber for optical signals and cable for electrical signals 32). In the case of an optical transmitter, the probe typically has a test fiber coupled to an optical-to-electrical converter 34, which provides the signals to the test measurement instrument through one or more ports 14. Two ports may be used for differential signaling, and one port may be used for single-ended signaling. The test measurement instrument samples and digitizes the input waveform. Real-time oscilloscopes typically use a software clock recovery process and do not use clock recovery hardware.

[0010] The oscilloscope includes one or more processors represented by processor 12, memory 20, and a user interface 16. The memory may store executable instructions in the form of programs that, when executed by the processor, cause the processor to perform tasks. The test and measurement instrument's user interface 16 allows a user to interact with the test and measurement instrument 10, such as to enter settings and configure tests. The test and measurement instrument may also include a reference equalizer and analysis module 24.

[0011] One or more processors in the oscilloscope first characterize the oscilloscope's noise waveform in the absence of an input. This characterization occurs before any measurements are taken. U.S. patent application Ser. No. 18 / 478,556, filed Sep. 29, 2023, entitled "Adaptive Measurement Instrument Noise Rejection" (hereinafter referred to as "TAN"), the contents of which are incorporated herein by reference, describes an embodiment of this process. Many factors affect oscilloscope random noise, including sample rate, oscilloscope bandwidth, vertical gain and offset settings, and signal path compensation (SPC). For purposes of this description, oscilloscope noise measurements include the root mean square (RMS) of the oscilloscope noise, denoted scopeNoiseSpectrumRMS. RMS measurements of oscilloscope noise are used for optical signals, while standard deviation measurements of oscilloscope noise are used for electrical signals. In this description, oscilloscope noise, scopeNoiseSpectrumRMS, represents either RMS or standard deviation, depending on whether the signal is optical or electrical.

[0012] The oscilloscope then acquires a waveform from the DUT that repeats the data pattern multiple times. For example, one repetition of the 32 GBaud PAM4 PCIE Gen 6 (Peripheral Component Interface Express Generation 6) compliant pattern waveform is shown in Figure 2. This pattern is used as a standardized pattern to measure the DUT's compliance with the required performance of the standard.

[0013] Once the oscilloscope acquires multiple repetitions of this pattern, it determines the waveform's spectrum, which typically involves converting the waveform from the time domain to the frequency domain using something like a Fast Fourier Transform (FFT). Figure 3 shows the spectrum of an acquired waveform for a PCIE Gen 6 signal.

[0014] One or more processors within the oscilloscope then identify the spectral impulses associated with the repeating pattern. Figure 4 shows a close-up of the spectrum from Figure 3 near 16 GHz, showing multiple peaks or spectral impulses such as 40 highlighted with circles to stand out from the spectral floor. This identification essentially separates the waveform spectrum into two parts. One part is the spectral Y associated with the signal pattern. impulse The spectrum of the other part, Y, is shown as a spectral impulse. flat consists of the remaining spectral components not related to the signal pattern. See John Proakiss and Dimitris Manolakis, "Digital signal processing: principles, algorithms, and applications," Prentice-Hall, 1996.

[0015] Next, the spectrum Y without impulses flatis measured using RMS or similar and is referred to as signalFlatSpectrumRMS. The noise compensation ratio depends on the flat signal spectrum measurement and the oscilloscope noise measurement. In one embodiment, the oscilloscope noise compensation ratio is equal to:

number

[0016] In this equation, 100% of the oscilloscope noise is compensated for. Oscilloscope noise can also be partially compensated for; for example, 80% of the oscilloscope noise is compensated for. To do this, the signalFlatSpectrumRMS term in this equation is scaled by 80%.

[0017] Next, Spectrum Y flat The flat component of the waveform spectrum corresponding to the pattern is scaled by the oscilloscope noise correction factor, and then the scaled flat component is combined with the waveform component corresponding to the spectral impulse associated with the pattern. This results in an oscilloscope noise-corrected waveform spectrum. Figure 5 shows a close-up of the oscilloscope noise-corrected waveform spectrum. Note that although the spectral impulses, such as 50, are the same in Figures 4 and 5, the spectral noise floor in Figure 5 is lower than in Figure 4.

[0018] Once the oscilloscope noise-corrected spectrum is obtained, the oscilloscope noise-corrected waveform spectrum is then converted to a time-domain waveform, such as by an inverse FFT. The new waveform is constructed from the oscilloscope noise-corrected waveform. Figure 6 shows an eye diagram before (left) and after (right) applying oscilloscope noise correction. The eye diagram of the oscilloscope noise-corrected waveform shows a larger eye opening. The performance of the DUT may then be measured, such as measuring the symbol error rate, SNDR, TDECQ, and EVM.

[0019] Thus, these embodiments enable oscilloscopes to improve measurement fidelity by correcting their random noise. These embodiments apply to both electrical and optical signals, which can have a variety of modulation types. For example, when oscilloscope noise is corrected for the I and Q waveforms, EVM results improve. These embodiments provide more accurate measurements, improve the sensitivity of test and measurement equipment, improve measurement margins, and increase product yield. Improving the sensitivity of test and measurement equipment allows the same equipment to measure smaller or noisier signals than equipment with less sensitivity. While test and measurement equipment sensitivity is a key specification for measuring optical signals, it also applies to optical and electronic devices, enabling more accurate testing.

[0020] Aspects of the disclosed technology may operate on specially created hardware, firmware, digital signal processors, or specially programmed general-purpose computers, including processors that operate according to programmed instructions. The terms "controller" or "processor" herein contemplate microprocessors, microcomputers, ASICs, and dedicated hardware controllers, among others. Aspects of the disclosed technology may be implemented with computer-usable data and computer-executable instructions, such as one or more program modules, executed by one or more computers (including a monitoring module) or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., which, when executed by a processor in a computer or other device, perform particular tasks or implement particular abstract data types. Computer-executable instructions may be stored in computer-readable storage media, such as hard disks, optical disks, removable storage media, solid-state memory, RAM, etc. Those skilled in the art will appreciate that the functionality of the program modules may be combined or distributed as desired in various embodiments. Furthermore, such functionality may be embodied in whole or in part in firmware or hardware equivalents, such as integrated circuits, field programmable gate arrays (FPGAs), etc. Certain data structures may be used to more effectively implement one or more aspects of the disclosed technology, and such data structures are considered within the scope of the computer-executable instructions and computer-usable data described herein.

[0021] The disclosed aspects may, in some cases, be implemented in hardware, firmware, software, or any combination thereof. The disclosed aspects may also be implemented as instructions carried by or stored on one or more computer-readable media, which may be read and executed by one or more processors. Such instructions may be referred to as a computer program product. As used herein, computer-readable media refers to any medium that can be accessed by a computing device. By way of example and not limitation, computer-readable media may include computer storage media and communication media.

[0022] "Computer storage media" means any medium that can be used to store computer-readable information. By way of example and not limitation, computer storage media may include random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory and other memory technologies, compact disc read-only memory (CD-ROM), digital video disc (DVD) and other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage and other magnetic storage devices, and any other volatile or nonvolatile, removable or non-removable medium implemented in any technology. "Computer storage media" excludes signals themselves and transitory forms of signal transmission.

[0023] A communication medium means any medium usable for communicating computer-readable information. By way of example, and not limitation, communication media may include coaxial cable, fiber optic cable, air, or any other medium suitable for communicating electrical, optical, radio frequency (RF), infrared, acoustic, or other types of signals. Example

[0024] The following examples are provided to aid in understanding the technology disclosed in this application. Embodiments of the technology may include one or more of the examples described below, and any combination thereof.

[0025] Example 1 is an oscilloscope comprising one or more ports for connecting the oscilloscope to a device under test (DUT), one or more analog-to-digital converters (ADCs) for receiving a signal from the DUT, sampling the signal, and generating a digital sample of the signal as a waveform, and one or more processors, the one or more processors performing the following steps: acquiring a noise waveform of the oscilloscope when there is no input signal, determining a measurement value of the noise waveform; acquiring a waveform having multiple repetitions of a repeating pattern from the one or more ADCs; determining a frequency spectrum of the waveform; and calculating a spectral impulse associated with the repeating pattern in the frequency spectrum of the waveform as a spectral impulse component of the frequency spectrum. determining a measurement of a flat component of the frequency spectrum that is not associated with the repeating pattern; generating a noise correction factor using the measurement of the flat component of the frequency spectrum and the measurement of the noise waveform; scaling the flat component of the frequency spectrum by the noise correction factor and combining the scaled flat component with the spectral impulse component of the frequency spectrum to generate a noise corrected waveform frequency spectrum; converting the noise corrected waveform frequency spectrum to a time-domain noise corrected waveform; and measuring performance of the DUT using the time-domain noise corrected waveform.

[0026] A second embodiment is the oscilloscope of the first embodiment, further comprising an optical-to-electrical converter for converting an optical signal from the DUT into an electrical signal.

[0027] Example 3 is the oscilloscope of either example 1 or 2, wherein the repeating pattern includes a standard-compliant pattern.

[0028] A fourth embodiment is an oscilloscope according to any one of the first to third embodiments, wherein the program causing the one or more processors to perform a process of determining a measurement value of the noise waveform includes a program causing the one or more processors to perform a process of calculating either the root mean square (RMS) of the noise waveform in the case of an optical signal format or the standard deviation of the noise waveform in the case of an electrical signal format.

[0029] Example 5 is an oscilloscope according to any one of Examples 1 to 4, wherein the program causing the one or more processors to perform a process of determining the frequency spectrum of the waveform includes a program causing the one or more processors to perform a process of performing a fast Fourier transform on the waveform.

[0030] Example 6 is an oscilloscope according to any one of Examples 1 to 5, wherein the program causing the one or more processors to perform a process of determining a measurement value of the flat component of the frequency spectrum includes a program causing the one or more processors to perform a process of calculating a root mean square of the flat component of the frequency spectrum.

[0031] Example 7 is an oscilloscope according to any one of Examples 1 to 6, wherein the program causing the one or more processors to perform a process using the measurement value of the flat component of the frequency spectrum and the measurement value of the noise waveform includes a program causing the one or more processors to perform a process of calculating a value obtained by dividing the square root of the value obtained by subtracting the square of the measurement value of the noise waveform from the square of the measurement value of the flat component by the measurement value of the flat component.

[0032] Example 8 is the oscilloscope of Example 7, wherein the one or more processors are further configured to execute a program that causes the one or more processors to perform a process of scaling measurements of the flat component of the frequency spectrum to partially compensate for the noise generated by the oscilloscope.

[0033] Example 9 is the oscilloscope of any one of Examples 1 to 8, wherein the program that causes the one or more processors to perform a process of measuring the performance of the DUT using the time-domain noise-corrected waveform includes a program that causes the one or more processors to perform a process of measuring one or more of a symbol error rate, a signal to noise distortion rate (SNDR), a transmitter and dispersion eye closure quaternary (TDECQ), and an error vector magnitude (EVM).

[0034] Example 10 is a method comprising: acquiring a noise waveform from an oscilloscope when there is no input signal and determining a measurement of the noise waveform; acquiring a waveform having a repeating pattern repeated multiple times from a device under test (DUT); determining a frequency spectrum of the waveform; identifying a spectral impulse in the frequency spectrum of the waveform associated with the repeating pattern as a spectral impulse component of the frequency spectrum; determining a measurement of a flat component of the frequency spectrum that is not associated with the repeating pattern; generating a noise correction factor using the measurement of the flat component of the frequency spectrum and the measurement of the noise waveform; scaling the flat component of the frequency spectrum by the noise correction factor and combining the flat component with the spectral impulse component of the frequency spectrum to generate a noise corrected waveform frequency spectrum; converting the noise corrected waveform frequency spectrum to a time domain noise corrected waveform; and measuring performance of the DUT using the time domain noise corrected waveform.

[0035] Example 11 is the method of example 10, further comprising converting the optical signal from the DUT to an electrical signal using an optical-to-electrical converter.

[0036] Example 12 is the method of any of examples 10 or 11, wherein the repeating pattern comprises a standard-compliant pattern.

[0037] A thirteenth embodiment is the method according to any one of the tenth to twelfth embodiments, wherein the step of determining a measurement value of the noise waveform includes a step of calculating a root mean square of the noise waveform.

[0038] A fourteenth embodiment is the method according to any one of the tenth to thirteenth embodiments, wherein the process of obtaining the frequency spectrum of the waveform includes a process of performing a fast Fourier transform on the waveform.

[0039] A fifteenth embodiment is the method of any one of the tenth to fourteenth embodiments, wherein the process of determining the measurement value of the flat component of the frequency spectrum includes a process of calculating either the root mean square of the noise waveform in the case of an optical signal format or the standard deviation of the noise waveform in the case of an electrical signal format.

[0040] Example 16 is a method according to any one of Examples 10 to 15, wherein the process of using the measurement value of the flat component of the frequency spectrum and the measurement value of the noise waveform includes a process of calculating a value obtained by dividing the square root of the square of the measurement value of the flat component by the measurement value of the flat component, minus the square of the measurement value of the noise waveform.

[0041] Example 17 is the method of example 16, further comprising scaling the flat component measurements to partially compensate for the noise introduced by the oscilloscope.

[0042] Example 18 is the method of any of Examples 10 to 17, wherein measuring the performance of the DUT using the time-domain noise-compensated waveform includes measuring one or more of a symbol error rate, a signal to noise distortion rate (SNDR), a transmitter and dispersion eye closure quaternary (TDECQ), and an error vector magnitude (EVM).

[0043] Although the above-described versions of the presently disclosed subject matter have many advantages that have been described or that will be apparent to those skilled in the art, not all of these advantages or features are required in every version of the disclosed devices, systems, or methods.

[0044] Additionally, the description of this application refers to specific features. It should be understood that the disclosure herein includes all possible combinations of these specific features. When a specific feature is disclosed in connection with a particular aspect or example, that feature can also be used in connection with other aspects and examples, to the extent possible.

[0045] Furthermore, when this application refers to a method having two or more defined steps or processes, these defined steps or processes may be performed in any order or simultaneously, unless the circumstances do not preclude this possibility.

[0046] All features disclosed in the specification, claims, abstract and drawings, and all steps in any disclosed method or process, may be combined in any combination, except where at least some of such features or steps are mutually exclusive combinations. Each feature disclosed in the specification, abstract, claims and drawings may be replaced by an alternative feature serving the same, equivalent or similar purpose, unless expressly stated otherwise.

[0047] Although specific embodiments of the invention have been illustrated and described for purposes of illustration, it will be appreciated that various modifications can be made therein without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims. [Explanation of symbols]

[0048] 10 Oscilloscope 12 processors 14 ports 16 User Interface (U / I) 20 memory 24 Reference Equalizer and Analysis Module 30 Device Under Test (DUT) 32 Measuring device probe (optical signal fiber or electrical signal cable) 34 Photoelectric (O / E) converter

Claims

1. 1. An oscilloscope, one or more ports for connecting the oscilloscope to a device under test (DUT); one or more analog-to-digital converters (ADCs) that receive signals from the DUT, sample the signals, and generate digital samples of the signals as waveforms; one or more processors Equipped with the one or more processors acquiring a noise waveform of the oscilloscope when there is no input signal and determining a measurement value of the noise waveform; acquiring a waveform having multiple repetitions of a repeating pattern from the one or more ADCs; A process of determining a frequency spectrum of the waveform; identifying spectral impulses associated with the repeating pattern in the frequency spectrum of the waveform as spectral impulse components of the frequency spectrum; determining a measure of a flat component in the frequency spectrum that is not associated with the repeating pattern; generating a noise correction factor using the measurement of the flat component of the frequency spectrum and the measurement of the noise waveform; scaling the flat component of the frequency spectrum by the noise correction factor and combining the scaled flat component with the spectral impulse component of the frequency spectrum to generate a noise corrected waveform frequency spectrum; converting the noise-compensated waveform frequency spectrum into a time-domain noise-compensated waveform; measuring the performance of the DUT using the time-domain noise-corrected waveform; an oscilloscope configured to execute a program that causes the one or more processors to perform the following:

2. 2. The oscilloscope of claim 1, wherein the program that causes the one or more processors to perform a process to obtain a measurement value of the noise waveform includes a program that causes the one or more processors to perform a process to calculate either the root mean square of the noise waveform in the case of an optical signal format or the standard deviation of the noise waveform in the case of an electrical signal format.

3. 2. The oscilloscope of claim 1, wherein the program causing the one or more processors to perform processing to determine the measurement value of the flat component of the frequency spectrum includes a program causing the one or more processors to perform processing to calculate the root mean square of the flat component of the frequency spectrum.

4. 2. The oscilloscope of claim 1, wherein the program that causes the one or more processors to perform processing using the measurement value of the flat component of the frequency spectrum and the measurement value of the noise waveform includes a program that causes the one or more processors to perform processing to calculate a value obtained by dividing the square root of the value obtained by subtracting the square of the measurement value of the noise waveform from the square of the measurement value of the flat component by the measurement value of the flat component.

5. 5. The oscilloscope of claim 4, wherein the one or more processors are further configured to execute a program that causes the one or more processors to scale measurements of the flat component of the frequency spectrum to partially compensate for the noise introduced by the oscilloscope.

6. acquiring a noise waveform on an oscilloscope when there is no input signal and determining a measurement value of the noise waveform; acquiring a waveform from a device under test (DUT) having a repeating pattern repeated multiple times; A process of determining a frequency spectrum of the waveform; identifying spectral impulses in the frequency spectrum of the waveform associated with the repeating pattern as spectral impulse components of the frequency spectrum; determining a measure of a flat component of the frequency spectrum that is not associated with the repeating pattern; generating a noise correction factor using the measurement of the flat component of the frequency spectrum and the measurement of the noise waveform; scaling the flat component of the frequency spectrum by the noise correction factor and combining the flat component with the spectral impulse component of the frequency spectrum to generate a noise-corrected waveform frequency spectrum; converting the noise-compensated waveform frequency spectrum into a time-domain noise-compensated waveform; measuring the performance of the DUT using the time-domain noise-corrected waveform; A noise correction method comprising:

7. 7. The method of claim 6, wherein the repeating pattern comprises a standard-compliant pattern.

8. 7. The noise correction method according to claim 6, wherein the process of determining the measurement value of the flat component of the frequency spectrum includes a process of calculating either the root mean square of the noise waveform in the case of an optical signal format or the standard deviation of the noise waveform in the case of an electrical signal format.

9. 7. The noise correction method according to claim 6, wherein the process using the measurement value of the flat component of the frequency spectrum and the measurement value of the noise waveform includes a process of calculating a square root of the difference between the square of the measurement value of the flat component and the square of the measurement value of the noise waveform, divided by the measurement value of the flat component.

10. 10. The method of claim 9, further comprising scaling the flat component measurements to partially compensate for the noise introduced by the oscilloscope.

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