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CN-122027078-A - Maximum likelihood sequence estimation on a real-time oscilloscope

CN122027078ACN 122027078 ACN122027078 ACN 122027078ACN-122027078-A

Abstract

A real-time oscilloscope includes one or more ports for connection to a Device Under Test (DUT) to establish a communication channel between the oscilloscope and the DUT, one or more analog-to-digital converters (ADCs) for sampling signals received from the DUT to convert the signals to waveforms, one or more processors for receiving and sampling runtime signals including actual symbols from the DUT to create runtime waveforms, resampling the runtime waveforms to locate samples at the center of each unit interval, estimating symbols in the runtime waveforms using a communication channel characterization, the samples at the center of each unit interval, a symbol constellation of the runtime waveforms, and a trace-back length configuration as inputs to a Maximum Likelihood Sequence Estimation (MLSE) process, and comparing the estimated symbols to the actual symbols to obtain symbol error ratios.

Inventors

  • TAN KAN

Assignees

  • 特克特朗尼克公司

Dates

Publication Date
20260512
Application Date
20251111
Priority Date
20251105

Claims (18)

  1. 1.A real-time oscilloscope, comprising: One or more ports for connecting to a Device Under Test (DUT) and establishing a communication channel between the oscilloscope and the DUT; One or more analog-to-digital converters (ADCs) for sampling signals received from the DUT to convert the signals to waveforms; One or more processors configured to execute code to cause the one or more processors to: Receiving and sampling a runtime signal comprising actual symbols from the DUT to create a runtime waveform; resampling the runtime waveform to locate samples at the center of each unit interval; estimating symbols in a runtime waveform using a communication channel characterization, samples at the center of each unit interval, a symbol constellation of the runtime waveform, and a back trace length configuration as inputs to a Maximum Likelihood Sequence Estimation (MLSE) process, and The estimated symbols are compared with the actual symbols to obtain symbol error ratios.
  2. 2. The real-time oscilloscope of claim 1 wherein said one or more processors are further configured to execute code to cause said one or more processors to characterize a communication channel.
  3. 3. The real-time oscilloscope of claim 2, wherein the code that causes the one or more processors to characterize the communication channel comprises code that causes the one or more processors to receive the communication channel characterization from a Vector Network Analyzer (VNA) or a Time Domain Reflectometer (TDR) instrument.
  4. 4. The real-time oscilloscope of claim 2 wherein code that causes the one or more processors to characterize a communication channel comprises code that causes the one or more processors to: Placing the oscilloscope in a training mode; applying a training signal having a known pattern to the communication channel; Receiving and sampling the training signal to create a training waveform; resampling the training waveform to produce a resampled training waveform having a predetermined number of samples per unit interval; extracting a linear fit impulse response (LFPR) from the resampled training waveform; deriving an impulse response from said LFPR, and Samples at the center of a unit interval around the peak of the impulse response are selected to estimate a communication channel characterization.
  5. 5. The real-time oscilloscope of claim 4 wherein code that causes said one or more processors to derive said impulse response comprises code that causes said one or more processors to: Constructing a matrix X from vectors of ideal impulse responses, and Deconvolving the matrix X from the LFPR.
  6. 6. The real-time oscilloscope of claim 5 wherein code that causes said one or more processors to deconvolute said matrix X from said LFPR comprises code that causes said one or more processors to deconvolute said matrix X using regularization.
  7. 7. The real-time oscilloscope of claim 4 wherein code that causes said one or more processors to characterize a communication channel comprises code that causes said one or more processors to: Determining that the communication channel has a longer impulse response duration, and An equalizer is applied to the samples to shorten the impulse response duration before deriving the impulse response.
  8. 8. The real-time oscilloscope of claim 7 wherein code that causes the one or more processors to determine that the channel has a long impulse response duration comprises code that determines an amount of time for stabilizing the impulse response comprises a time that exceeds a predetermined number of unit intervals.
  9. 9. The real-time oscilloscope of claim 7 wherein code that causes the one or more processors to apply an equalizer to the samples comprises code that causes the one or more processors to apply one of a Feed Forward Equalizer (FFE) or a continuous-time linear equalizer (CTLE).
  10. 10. A method, comprising: sampling a runtime signal received from a Device Under Test (DUT) over a communication channel as a runtime waveform; resampling the runtime signal to locate samples at the center of each unit interval; generating estimated symbols in a runtime signal using a communication channel characterization, a sample at the center of each unit interval, a symbol constellation of the waveform, and a configuration of trace-back lengths as inputs to a Maximum Likelihood Sequence Estimation (MLSE) process, and The estimated symbols are compared to the actual symbols to determine a symbol error rate.
  11. 11. The method of claim 10, further comprising characterizing the communication channel on a real-time oscilloscope using a training signal having a known or detected pattern to produce a communication channel characterization.
  12. 12. The method of claim 11, wherein characterizing the communication channel comprises receiving the channel characterization from a Vector Network Analyzer (VNA) or a Time Domain Reflectometer (TDR) instrument.
  13. 13. The method of claim 11, wherein characterizing the communication channel comprises: Placing the oscilloscope in a training mode; applying the training signal to a communication channel; Receiving and sampling the training signal to create a training waveform; Resampling the training waveform to have a predetermined number of samples per unit interval; Extracting a linear fit impulse response (LFPR) from the resampled training waveform; deriving an impulse response from said LFPR, and Samples at the center of a unit interval around the peak of the impulse response are selected to estimate a communication channel characterization.
  14. 14. The method of claim 13, wherein deriving the impulse response comprises: Constructing a matrix X from vectors of ideal impulse responses, and Deconvolving the matrix X from the LFPR.
  15. 15. The method of claim 14, wherein deconvoluting the matrix X from the LFPR comprises deconvolving the matrix X with regularization.
  16. 16. The method of claim 13, wherein characterizing the communication channel comprises: Determining that the communication channel has a long impulse response duration, and An equalizer is applied to the samples to shorten the impulse response duration before deriving the impulse response.
  17. 17. The method of claim 16, wherein determining that the communication channel has a long impulse response duration comprises determining an amount of time for stabilizing the impulse response comprises exceeding a predetermined number of unit intervals.
  18. 18. The method of claim 16, wherein applying an equalizer to the samples comprises applying one of a Feed Forward Equalizer (FFE) or a Continuous Time Linear Equalizer (CTLE).

Description

Maximum likelihood sequence estimation on a real-time oscilloscope Cross Reference to Related Applications The present disclosure is and claims the non-provisional application of U.S. provisional application No. 63/718,870, titled "MOST LIKELIHOOD SEQUENCE DETECTION ON REAL-TIME OSCILLOSCOPES," filed 11/2024, the entire contents of which are incorporated herein by reference. Technical Field The present disclosure relates to test and measurement instruments, and more particularly to symbol detection in transmission symbols, and more particularly to reducing errors in transmission symbols. Background PAM4 signaling has been developed to replace NRZ signaling for high speed serial data standards such as PCIE and IEEE 802.3 ethernet. An explicit solution was derived in U.S. patent No. 11,765,002 issued 2023, 9, 19 (the' 002 patent) for Decision Feedback Equalizer (DFE) taps based on a single extracted linear fit impulse response (LFPR). Tan et al "Multiple Linear Fit Pulse Responses for PAM4 Measurements",DesignCon 2024 Compiled Papers TR8-14,February 22, 2024,pp 438-453——, which may be obtained at https:// flip tml5.Com/mddwo/smbr/DesignCon _2024_completed_paper_tr_8-14, hereinafter referred to as "Tan et al," the contents of which are incorporated herein by reference in its entirety, describes a new method by which multiple LFPR may be extracted from a pattern waveform. Multiple LFPR hold more information about the signal. A new DFE structure, known as a multiple pulse-based DFE (MPDFE), which uses multiple LFPR, is described in U.S. patent application No. 18/754,871, filed on 6/26 at 2024, the contents of which are incorporated herein by reference. As signal speeds increase, equalizers in transmitters and receivers are widely used to improve system performance. The equalizer includes a continuous-time linear equalizer (CTLE), a feedforward equalizer (FFE), a Decision Feedback Equalizer (DFE), and a new multi-pulse DFE (MPDFE). Among these equalizers, DFEs and MPDFE detect symbols and then use the detected symbols to improve detection of subsequent symbols. If a symbol is incorrectly detected, because the wrong symbol is used in a feedback loop, as shown in fig. 1, the symbol error may result in a burst (burst) of multiple symbol errors, known as error propagation. Drawings Fig. 1 shows an embodiment of a decision feedback equalizer. Fig. 2 shows an embodiment of a real-time oscilloscope. Fig. 3 illustrates an embodiment of a trellis (trellis) structure used in the disclosed embodiments. Fig. 4 shows an example of a 4-level pulse amplitude modulation (PAM 4) waveform from a transmitted signal. Fig. 5 shows an enlarged view of the waveforms of fig. 4. Fig. 6 shows a linear fit impulse response extracted from the waveform of fig. 4 with samples at the center of the unit interval. Fig. 7 shows a linear fit impulse response with samples at the center of a unit interval around the peak of the impulse. Fig. 8 shows the result of Maximum Likelihood Sequence Estimation (MLSE) from PAM4 signal. Fig. 9 shows a flow chart of an embodiment of a method of detecting symbols in a waveform using MLSD. Fig. 10 shows an example of PAM4 waveform after passing through a channel with higher loss. Fig. 11 shows the impulse response of the channel of fig. 10. Fig. 12 shows the MLSE results of the PAM4 signal of fig. 10. Detailed Description The embodiments herein employ Maximum Likelihood Sequence Estimation (MLSE) to estimate symbols. MSLE is sometimes referred to as Maximum Likelihood Sequence Detection (MLSD). As discussed above, equalizers DFE and MPDFE detect symbols and then use the detected symbols to improve detection of subsequent symbols. If a symbol is incorrectly detected because the wrong symbol is used in a feedback loop, as shown in fig. 1, the symbol error may result in a burst of multiple symbol errors, known as error propagation. To achieve higher performance in symbol error rates, embodiments disclosed herein employ Maximum Likelihood Sequence Estimation (MLSE). MLSE provides an optimal solution for symbol estimation on signals with noise and inter-symbol interference (ISI). MLSE does not have the problem of error propagation as in DFE. Embodiments herein relate to a method of simulating an MLSE on a real-time oscilloscope. Real-time oscilloscopes typically digitize signals in real time to capture and display signal waveforms in a single continuous acquisition, typically using one or more high-speed analog-to-digital converters (ADCs) and an independent clock. They differ from equivalent time sampling oscilloscopes in that the sampling oscilloscopes require multiple samples over multiple signal periods to "build" a complete waveform over time. Fig. 2 shows an embodiment of a real-time oscilloscope 10. The real-time oscilloscope 10 includes one or more ports 12, and the ports 12 may be any electrical signaling medium. The port 12 may include a receiver, a transmitter, and/or a transceiver. Each port 12 is a channe