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44 The PCB Design Magazine • May 2014 • It is the electromagnetic energy that prop- agates down the transmission line—not elec- tron flow. • As the electromagnetic energy propagates along a transmission line, current is induced into the conductors. This current flows along the conductors, charging the first section's parasitic capacitance and then flows back on the return conductor (reference plane) to the source. • Current always flows in a loop. But is does not flow along the transmission line to the load and then return to the source. The propagating signal charges up each section, in turn, as the rising edge propagates along the transmission line. • Closed-form equations are approxima- tions only and a 2D field solver is required to accurately model impedance of multilayer PCB traces. PCBDESIGN References 1. Henry Ott, Electromagnetic Compatibil- ity Engineering 2. Howard Johnson, High-speed Signal Prop- agation 3. Bob Holmes, Bush Telegraph and New Sci- entist Magazine 4. Telegrapher's equations, Wikipedia 5. The ICD Stackup Planner and PDN Plan- ner can be downloaded from www.icd.com.au Barry olney is managing director of in-Circuit Design Pty ltd (iCD), Australia. This PCB design service bureau specializes in board-level simulation, and has developed the iCD stackup Planner and iCD PDn Planner software. To read past columns, or to contact olney, click here. realtimewith.com CliCk To View Video Interview halil ibrahim yaslak probably traveled a lot farther than most Designers Forum attendees. halil is a PCB designer with the Turk- ish company Aselsan; you may remember that halil won a Men- tor Technology leadership Award in the milaero category in 2012. he and editor Kelly Dack discuss his company's cutting-edge work and the different challenges faced by designers worldwide. PCB Design From a Turkish Perspective by Real Time with... Designers Forum TRANSMISSION LINES continues beyond design