Printed Circuit Design & Fab - August 2008 - (Page 22)

Consider a differential topology as displayed by Figure 13. It comprises a differential driver (U1), transmission lines (T1, T2, T3 and T4), termination resistor (Rt) and differential receiver U2. The concepts governing single-ended signaling can be extended to differential case, but it requires several important considerations. Differential signaling involves propagation of signals on a pair of coupled transmission lines. The degree of coupling influences impedance, signal velocity (timing) and termination requirements. The non-inverted signal Vp traveling on one line is the complement of an inverted signal Vn on the second line. For instance, if Vp is given by: 101011001110001010101111011000010101111001111 10001 Then Vn having opposite polarity (each “1” is replaced with a “0” and vice versa) consists of: 010100110001110101010000100111101010000110000 1110 The differential receiver acquires the difference Vp – Vn to ascertain the high or low state of the received signal. The reason for capturing the voltage difference is to minimize the commonmode noise. Mathcad scripts for treating differential topologies are described in Reference 3, found in Part 1 of this series. In conclusion, Mathcad can be effectively applied for analyzing signal-integrity concepts, solving complex signal-integrity expressions and simulating high-speed PCB topologies. PCD&F Dr. ABe (ABBAS) riAZi is a senior staff electronic design scientist with Broadcom Corp. in Irvine, CA, and can be reached at ariazi@ broadcom.com. reFereNCeS 18. Stephen H. Hall, Garrett W. Hall and James A. McCall. “High-Speed Digital System Design, A Handbook of Interconnect Theory and Design Practices, John Wiley and Sons Inc., 2000, p. 85. 19. “TDR and VNA Measurement Primer” Application Note, 2004, TDA Systems Inc. 20. Zack Settel and Cort Lippe. “Real-Time Frequency-Domain Digital Signal Processing on the Desktop, Proceedings of the 1998 International Com” puter Music Conference. San Francisco Music Association, pp. 142-149. 21. David Norte. Transmission Line Discontinuity With a Series RC Load” “ www.the-signal-and-power-integrity-institute.com. 22. Abe Riazi. “Stub or no Stub?” Printed Circuit Design and Manufacture, October 2004, p. 18. 23. Chih-Kong Ken Yang, Ramin Farjad-Rad and Mark A. Horowitz. “A 0.5-um CMOS 4.0-Gbits/s Serial Link Transceiver with Data Recovery Using Oversampling, IEEE Journal of Solid-State Circuits, vol. 33, no. 5, May ” 1998, pp. 713 - 722. ! Figure 12. The received signal bit sequence (a) and eye dia- gram (b). Figure 11. Mathcad code example for simulating single!ended configuration. ! Figure 13. Differential signaling. AUGUST 2008 22 PRINTED CIRCUIT DESIGN & FAB http://www.the-signal-and-power-integrity-institute.com

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - August 2008

Printed Circuit Design & Fab - July 2008 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar Software Performance Interconnect Strategies Final Finish Forum Product Development Challenges in a Global Market Innovative Modeling Supports Co-Design of the Power Supply Chain, Part 2 Low-Loss Fluoropolymer Copper Clad Laminate Qualifying PCBs Outsourced in Asia Copper Plating and Microvia Fill for Advanced PCBs Off the Shelf Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - August 2008

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