Question 1

Design a stack-up for a board with high-speed interfaces (MIPI, USB), analog circuits and a power section.

Accepted Answer

Say this first: Every signal layer next to a solid reference plane; high-speed signals on layers with continuous ground references (stripline inside for EMC, microstrip for short breakouts); a closely spaced power/ground pair for plane capacitance; symmetric stack for warpage. Example 8 layers: L1 signal/parts · L2 GND · L3 high-speed signal · L4 PWR · L5 GND · L6 signal · L7 GND · L8 signal/parts. Analog: placed in its own region, with its own local ground return paths over the same plane (no split), filtered supply. Power stage: wide pours on outer layers with many vias, its hot loop on the top layer.

Question 2

How do you handle grounding and partitioning between analog and digital circuits on one board?

Accepted Answer

Say this first: Use one continuous ground plane and partition by placement: keep digital return currents out of the analog area by routing, not by cutting the plane. Split planes create more problems than they solve (signals crossing gaps). Separate the supplies instead — e.g. 3.3 V digital and 3.3 V analog through ferrite/LC filters — and place the ADC across the boundary with its analog and digital pins on their own sides. When a split is justified: isolated sections or very high-precision designs, with signals crossing only through a bridge or isolator.

PCB Design Interview Questions

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