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September 2008 EEEL Researchers Develop Robust Algorithm for Eye-Diagram Analysis |
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EEEL researchers Jeffrey Jargon and Paul Hale, along with Chih-Ming Wang from the NIST Statistical Engineering Division, have developed a new method for analyzing eye diagrams. Eye-diagrams are multivalued displays used for assessing the quality of high-speed digital signals [1]. They are usually constructed by applying a data waveform to the input of a sampling oscilloscope, and then overlapping all possible one-zero combinations on the instrument’s display. Eye diagram measurements have a huge economic impact on the optical and electrical communications industries. With cost pressures driving manufacturers to create products that just meet specifications, the ability to make accurate and repeatable measurements for equipment testing is becoming more important. Conflicts may arise between component manufacturers and their customers when different test equipment leads to measurement inconsistencies. These discrepancies can be attributed to both software and hardware differences. The focus of the current work is on an algorithmic method that can be implemented in software The NIST algorithm makes use of a robust, least-median-of-squares (LMS) location estimator. In contrast to commonly used histogram techniques, the LMS algorithm provides a repeatable solution that is insensitive to outliers and data distributions. The motivation for developing this algorithm was to create an independent, benchmark method that is both amenable to a thorough uncertainty analysis and can function as a comparison tool since no standardized industry algorithms currently exist. Utilizing this technique, the researchers can calculate the fundamental parameters of an eye diagram, namely the one and zero levels, as well as the time and amplitude crossings. With these parameters determined, eye-mask alignment can be performed and various performance metrics can be derived, such as extinction ratio and root-mean-square jitter. The algorithm in its entirety will be published in an upcoming issue of the IEEE Journal of Lightwave Technology. [1] D. Derickson, Fiber Optic Test and Measurement, Prentice-Hall, 1998. |