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24 DESIGN007 MAGAZINE I SEPTEMBER 2025 S ignal integrity has become a critical factor in ensuring reliable performance in high-speed digital systems. As data rates continue to increase, engineers must understand the fundamental prin- ciples that govern how signals propagate through transmission lines and how to mitigate common issues that can degrade signal quality. Several decades ago, signal speeds were very slow (compared to today's signal speed). Signal integrity (SI) didn't seem to be a high priority, and balanced PCB structures, impedance require- ments, routing techniques such as microstrip and F E AT U R E A RT I C L E by S te p h e n V. C h a vez , S i e m e n s E DA Understanding Signal Integrity, the Foundation of High-speed Digital Design stripline, were not a major requirement or focus to address. We could and were getting by with simply "making the point-to-point connections" without much thought, regarding the performance of a PCB when routing our signal traces. Well, those days are long gone. This article will address the core concepts of understanding SI and why it's important, with a focus on transmission lines, impedance discontinuities, reflections, and termination tech- niques—the foundation of reliable high-speed digital design.