Differential Signaling and Discontinuity Modeling in PCBs

The differential transmission technique is the best way to ensure high-speed data functionality and immunity to the system for signaling at PCB and cable level. The advantages of using differential-mode (DM) transmission versus single-ended transmission are presented in this last chapter. Techniques for implementing differential signal transmission in a system are outlined, referring to the Advanced Telecommunications Computing Architecture (ATCA) standard. This standard is adopted by many companies involved in the development of very high-speed systems for telecommunications. LVDS is one of the most popular devices for differential-mode transmission. For this reason, LVDS characteristics and performances are shown in comparison with other families. The results obtained in terms of signal integrity (SI) and induced noise from an experimental set-up that uses test boards with LVDS drivers and receivers are presented and discussed. It is also shown that, by adding pulse transformers at driver and receiver locations, the immunity of the LVDS to a common-mode (CM) noise voltage can rise over 40 V instead of the specified ±1 V. Crosstalk in differential signaling with overhead and coplanar traces is investigated by SPICE simulations. Moreover, some design rules are provided for trace routing. An example of the realization of a motherboard according to the ATCA standard is presented, and its performance in terms of crosstalk ...

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