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NOVEMBER 2024 I DESIGN007 MAGAZINE 27 ded microstrip, symmetric, and dual asymmetric stripline configurations. 19. A transmission line is a series of conduc- tors that guide electromagnetic energy from one point to another. It is the move- ment of an electromagnetic field or energy—not voltage or current. 20. It is the electromagnetic energy that propagates down the transmission line— not electron flow. 21. As the electromagnetic energy propa- gates along a transmission line, current is induced into the conductors. is 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. 22. Current always flows in a loop, but it does not flow along the transmission line to the load and then return to the source. e propagating signal charges up each section as the rising edge propagates along the transmission line. 23. A distributed system disperses elements through the substrate along the entire length of the transmission line and is characterized by delay and scattered reflections. Stackup 1. e dielectric constant of FR-4 is ~4.0. is decreases as frequency increases. 2. e dielectric loss (dissipation factor) of FR-4 is ~0.02. is generally increases with frequency. 3. A 50-ohm microstrip will have a dielectric thickness of approximately half the trace width. 4. Solder mask covering a microstrip will decrease the impedance by 1–2 ohms. 5. Choosing the same dielectric materials as the Fab shop stocks will increase accuracy by ~5%. 6. A signal travels 13–17% faster in microstrip compared to stripline configurations. 7. All signal layers should be adjacent to a ref- erence plane, creating a clear return path and eliminating broadside crosstalk. 8. e signal end and differential impedance for several different technologies that must share the sample layers should be determined. 9. Microstrip layers should be closely coupled to the planes, reducing crosstalk. 10. Avoid broadside coupling by separating the internal signal layers with bulk core material. Figure 2: Six-layer stackup. (Source: iCD Stackup Planner)