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32 DESIGN007 MAGAZINE I NOVEMBER 2024 length of the trace radiating into the sur- rounding dielectric material and coupling energy to nearby trace segments. 2. In a multilayer board, each microstrip and each stripline configuration is isolated from the layers above or below. 3. Electric fields, which capacitively couple current into a nearby trace, are somewhat absorbed by the plane but still tend to radi- ate noise outward. 4. Magnetic fields refract at dissimilar dielec- tric boundaries and couple voltage induc- tively into a nearby trace. 5. A traveling, varying magnetic field is asso- ciated with a periodically changing electric field that may be conceived in terms of a displacement current. 6. EM fields do not merge but add vectori- ally, thereby distorting the signal. DESIGN007 Barry Olney is managing director of In-Circuit Design Pty Ltd (iCD), Australia, a PCB design service bureau that specializes in board- level simulation. The company developed the iCD Design Integrity software, incorporating the iCD Stackup, PDN, and CPW Planner. You can download the software at www.icd.com.au. To read past columns, click here. 9. e faster edge rate for the same frequency and same length trace creates ringing in the unterminated transmission line. is also has a direct impact on radiated emissions. 10. Transmission line effects become an important design consideration when the trace length approaches 1/6 of the wave- length of the signal being transported. 11. Any mismatch in impedance along the transmission path will result in a reduction in the quality of the signal and possibly radiation of noise. 12. Series terminations are generally required at fast edge rates to limit ringing. 13. Differential pair return current flows in the reference plane below each trace, not in the opposite signal. 14. An EM carrier wave can transport infor- mation, or it can supply energy to power an IC. 15. If the trace is too narrow, then the con- tained energy will dissipate as heat. EMC 1. Electromagnetic fields are produced when a logic driver delivers a high-speed, fast-rise time pulse into a trace. e elec- tromagnetic wave propagates down the Figure 7: Microstrip vs. stripline radiation.