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30 The PCB Design Magazine • October 2014 • The faster edge rate, for the same frequen- cy and same length trace, creates ringing in the un-terminated transmission line. This also has a direct impact on radiated emissions. • Transmission line effects become an im- portant design consideration when the trace length approaches 1/6 of the wave-length of the signal being transported. • Impedance is the key factor that controls the stability of a design—it is the core issue of the signal integrity methodology. • Any mismatch in impedance along the transmission path, will result in a reduction in quality of the signal and possibly radiation of noise. • Series terminations are generally required at fast edge rates to limit ringing. • All drivers, whose trace length (in inches) is equal to or greater than the rise time (in ns), must have provision for termination. • Differential pair return current actually flows in the reference plane below each trace not in the opposite signal. PCBDESIGN References 1. Barry Olney's Beyond Design Columns: Practical Signal Integrity, Pre-Layout Simula- tion, Intro to Board-Level Simulation and the PCB Design Process, and Impedance Matching: Terminations. 2. Howard Johnson: High-speed Signal Prop- agation. 3. Henry Ott: Electromagnetic Compatibil- ity Engineering. The ICD Stackup and PDN Planner is distrib- uted globally Altium. Barry Olney is managing direc- tor of In-Circuit Design Pty Ltd (ICD), australia. This PCB design service bureau specializes in board-level simulation, and has developed the ICD Stackup Plan- ner and ICD PDn Planner software. To read past columns, or to contact Olney, click here. SIGNAL INTEGRITY, PART 1 OF 3 continues CliCk To View Video Interview vern Solberg of Solberg Techni- cal Consulting updates us on the status of IPC-7092, the standard that focuses on embedding pas- sive and active components. He explains why uS board shops have been slow to embrace em- bedding components in board layers, though he is seeing a change as companies try to keep work from going overseas. Embedded Components Standard Update by Real Time with... SMTAI beyond design

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