01
Target-impedance budget
Z(f) derived from the load’s transient current and ripple spec — the number every decap decision flows from.
Rails that stay quiet under load.
We derive your target impedance from the silicon, place decoupling that actually works, kill plane resonances, and prove the rail with DC IR-drop and AC PDN analysis.
< mΩIR-drop resolution
Z(f)target-impedance method
DC + ACPDN analysis
TRMcoupled thermal + PDN
The deliverables.
02
Decoupling strategy
Cap values, counts, and placement chosen against the impedance profile — not a copy-pasted “0.1 µF everywhere.”
03
DC IR-drop map
Layer-by-layer voltage drop across the PDN so the far-end rail still meets tolerance at full load.
04
AC PDN + resonance
Impedance-vs-frequency with anti-resonance peaks identified and damped before they bite.
The full power picture.
DC domain
- Static IR-drop per rail
- Current-density hotspots
- Via + plane sizing
- Connector + shunt placement
AC domain
- Target impedance Z(f)
- Decap network optimization
- Plane resonance + damping
- Anti-resonance mitigation
Coupled effects
- Thermal-aware resistance (TRM)
- Split-plane return paths
- SSN / ground bounce
- Brown-out / inrush scenarios
A 25 A buck with a sliced plane.
The brief
A telecom DC-DC was failing intermittently under load. The team suspected the regulator; it was the plane.
What we found
- A routing channel had sliced the power plane, forcing 25 A through a 40-mil neck.
- IR-drop at the load was 180 mV — enough to trip the downstream UVLO during transients.
- Decoupling was all 0.1 µF; the bulk-to-ceramic gap left an anti-resonance right at the switching frequency.
Outcome
Re-routed the offending channel to an inner layer, restored the plane, and re-built the decap network against the target impedance. IR-drop fell to 41 mV; the intermittent fault disappeared.
Common questions.
Do you need IBIS / vendor models?
Helpful but not required. We can derive a target impedance from the datasheet’s transient-current and ripple specs and refine if models are available.
Is this separate from thermal sign-off?
Related — TRM couples PDN and thermal (copper resistance rises with temperature). For mission-critical boards we bundle both into PhySignoff.
Can you review an existing board’s PDN?
Yes — that’s a PhyVerify engagement. We’ll tell you where the rail is at risk and what to change.
Keep the rail quiet.
Target-impedance-driven PDN design, DC + AC verified. Fixed-fee band in 60 seconds.