Test & Measurement World, July/August 2012

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OSCILLOSCOPES In July, Agilent is releasing extensions on its EZJit jit- ter-measurement software. With that release, Agilent will provide amplitude-analysis and jitter-analysis algorithms that distinguish crosstalk from RJ and random noise. Ac- cording to Agilent, these enhancements will improve total-jitter estimates in the presence of crosstalk. Can crosstalk be corrected? When high-speed serial buses reached 5 Gbps, it seemed impossible to accommodate BERs of 10–12 and lower without replacing standard printed-circuit-board mate- rials with expensive new media that are less sensitive to intersymbol interference. But engineering innovation rose to the task, leading to the development of different equalization schemes that let receivers identify logic lev- els at the desired BERs in highly impaired signals whose eye diagrams are completely closed. Will some sort of signal compensation technique save the day? Zivny said, "I've heard techniques discussed going back to telegraph days: echo cancelation and hy- brid circuits." Sleigh added, "Once we've developed techniques to identify crosstalk, we'll have the under- standing we need to create techniques for solving the problem. Right now, we're working on identification." "Only compensation applied at the transmitter is likely to help, because that's where we know what's coming," Miller said. He concluded, "We'll be discussing crosstalk analysis for the next 15 years much the way we've been discussing jitter analysis for the last 15." T&MW REFERENCES 1. Derickson, D., and M. Müller, eds., Digital Communications Test and Measurement, Chapter 2, Prentice-Hall, 2008. 2. Stephens, R., and B. Fetz, et al., "Comparison of Different Jitter Analysis Techniques With a Precision Jitter Transmitter," DesignCon 2005, 3. Chow, D., and R. Stephens, "Methodology for Jitter Mea- surement Correlation and Consistency," Proceedings from DesignCon 2005. 4. Stephens, R., "Jitter Analysis: The dual-Dirac Model, RJ/DJ, and Q-Scale," Agilent Technologies White Paper, 5989- 3206EN, 2004. 5. Agoston, M., and P. Zivny, "Accurate Analytical Model of Bounded Uncorrelated Jitter and Noise Improves the Accu- racy of Crosstalk Impaired Link Evaluation: Theory, Validation, Practical Results," Proceedings from DesignCon 2012. 6. Resso, M., and E. Bogatin, Signal Integrity Characterization Techniques, International Engineering Consortium, 2009. Ransom Stephens, PhD, is a science writer and novelist who specializes in the electrodynamics of high-speed serial tech- nologies. After 15 years as a research physicist making pre- cise measurements of signals buried in noise at labs across the US and in Europe, he joined the private sector, became an expert on jitter, and is now trying to understand crosstalk in 40+ Gb/s systems. Test & Measurement World | JULY/AUGUST 2012 | –22–

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