Oscilloscope Pulse-Fit Analysis for Even/Odd Jitter Measurement
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Solution Overview
Problem
Existing methods struggle to accurately measure even/odd jitter (EOJ) in digital signals, particularly in even-length test patterns, due to confounding effects from data-dependent jitter (DDJ), especially in modern protocols like PCIe with PAM4 encoding, where defining a single threshold is difficult and edge measurements are sensitive, leading to reduced data statistics and inaccurate EOJ estimation.
Innovation Solution
A pulse-fit analysis is employed to generate separate pulse-fit vectors for even and odd symbols, measuring their widths to determine EOJ, utilizing a model symbol y=xe*pe+xo*po, where widths are compared to calculate EOJ as the absolute difference, ensuring sufficient statistical averaging to negate DDJ effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional threshold-based edge measurement methods are used, then measurement process is simple, but measurement precision deteriorates due to confounding effects from data-dependent jitter and difficulty in defining single threshold in PAM4 encoding
Solution Approach 1:
The patent segments the measurement process by separating even symbols and odd symbols into distinct groups. Two separate pulse-fit vectors are generated: one for even symbols (pe) and one for odd symbols (po). This segmentation allows independent analysis of each symbol type, enabling accurate EOJ measurement by comparing the widths of these separate vectors while eliminating confounding DDJ effects through statistical averaging within each group.
2Measurement precision
If sufficient data statistics are collected to average out DDJ effects, then measurement accuracy improves, but measurement time increases
Solution Approach 1:
The patent performs preliminary organization of data by separating even and odd symbols into distinct groups before analysis. This preliminary action structures the data in a way that enables efficient statistical averaging within each group. By pre-organizing the symbols and preparing separate pulse-fit vectors in advance, the method reduces the computational burden during actual measurement, allowing sufficient data collection for accurate EOJ estimation without excessive measurement time.
Data Source
AI summary
A method for measuring even/odd jitter (EOJ) in digital signals includes receiving a signal under test (SUT), where the SUT includes a waveform of even symbols and odd symbols constituting an even-length test pattern. The method further includes generating a first pulse-fit vector for the even symbols of the waveform and a second pulse-fit vector for odd symbols of the waveform, and determining the EOJ of the SUT by measuring and comparing respective widths of the first and second pulse-fit vectors.