What are the critical considerations for mixed-signal PCB design in precision instrumentation?

Mixed-signal PCB design considerations: partitioning (separate analog and digital sections physically, separate ground planes joined at single point near power supply), power distribution (separate LDO regulators for analog, ferrite bead or LC filtering between domains), component placement (ADCs at boundary, analog components grouped away from digital noise sources), routing (no digital traces under or near analog sections, guard rings around sensitive nodes, differential pairs tightly coupled). Address: return current paths (every signal has return current, ensure low-impedance path), decoupling hierarchy (bulk to local, ceramic close to pins), and EMC (internal layers for shielding, proper connector design). Use simulation for power integrity and signal integrity validation.