When Digital Breaks Down#

Where the abstraction leaks. Digital design depends on a clean separation between HIGH and LOW, between one clock cycle and the next, between signal and noise. Most of the time, this works. But at the edges — fast transitions, tight margins, high pin counts, noisy power rails — the underlying analog reality reasserts itself.

Metastability violates the assumption that flip-flops always settle cleanly. Power integrity problems corrupt logic levels from underneath. High-speed effects turn traces into transmission lines and edges into RF events. Understanding these failure modes is not optional for anyone designing digital systems that must work reliably at real speeds, on real boards.

What This Section Covers#

• Metastability — Why it exists; why it never fully goes away; synchronizers and MTBF calculation intuition.
• Power Integrity — Switching noise; ground bounce; simultaneous switching output (SSO); decoupling from the digital designer’s perspective.
• High-Speed Effects — Edges as analog events; why fast digital becomes RF; crosstalk; controlled impedance.