High-Speed Jitter Testing of XFP Transceivers

Jitter is a key performance factor in high-speed digital transmission systems, such as synchronous optical networks/synchronous digital hierarchy (SONET/SDH), optical transport networks (OTN), and 10 Gigabit Ethernet (GE). This paper outlines the differences between telecom and datacom jitter standards and describes the various jitter applications for compliance testing of 10 G small form-factor pluggable (XFP) transceivers, which have become the dominant 10 G optical interface for telecom and datacom applications. By Andreas Alpert Introduction Accurate jitter measurements are essential for ensuring error-free high-speed data transmission lines. Jitter which is any phase modulation above 10 Hz in a digital signal, is unwanted and always present within devices, systems, and networks. To ensure interoperability between devices and to minimize signal degradation due to jitter accumulation, limits must be set for the maximum level of jitter for an output interface as well as the maximum level tolerated at an input. Standards bodies determined these limits which can be divided into two categories: telecommunications and data communications. The major telecom standards organizations are International Telecommunications Union (ITU-T) and Telcordia, while the Institute of Electrical and Electronic Engineers (IEEE) is the main datacom standardization organization. Jitter Aspects and Characteristic Values for 10 G Telecom and datacom technologies use different timing methods. The system components in synchronous systems, such as SDH/SONET, synchronized to a common clock. In asynchronous and serial systems, such as 10 GE, distributed clocks or clock signals recovered from the data provide the component timing. While it is important to limit jitter generated by components jitter transferred from one component to another is less important than that for synchronous systems, where jitter can increase as it transfers from component to component. Well-defined band-limited jitter generation, tolerance, and transfer requirements exist for SDH/SONET/OTN.