Debug playbook

Debug Playbook for Analog Supply Noise focuses on supply ripple, spur coupling, analog performance degradation. The goal is to connect observed symptom to boundary mechanism, ownership, and signoff risk.

AMS debug is a hunt for first divergence, not downstream symptom management. Most costly delays come from wrong-owner first actions.

Root-cause tree

ROOT-CAUSE TREE — Analog Supply Noise

supply ripple, spur coupling, analog performance degradation regressed
        |
same silicon / run tags?
   /            \
 no              yes
 |                |
env mismatch    boundary contract or
tag mismatch    true physical issue
 /   \             |
clk   reset      isolate first failing
map   sequence   boundary transition

1. Freeze reproducer: mode, firmware/config, and evidence tags.

2. Find the first boundary signal that diverges.

3. Map divergence to contract clause and owner.

4. Classify failure: contract, sequencing, coupling, package, or tool-view mismatch.

5. Prove mechanism with one reduced reproducer.

6. Apply smallest reversible fix and rerun cross-domain regressions.

Review memo template

STAFF AMS REVIEW MEMO — Noise & IR at the Boundary / Analog Supply Noise

1. Symptom
   - Watched metric: supply ripple, spur coupling, analog performance degradation
   - Failing mode/condition: <power/clock/temp/workload>
   - Boundary under suspicion: <macro/wrapper/interface/lane/island>
   - Repro setup: <sim/emulation/lab + firmware/config tags>

2. Mechanism hypothesis
   - Primary mechanism: Switching current bursts from digital domains couple through shared impedance and package parasitics, modulating analog supply quality and phase noise.
   - Competing hypothesis: <contract gap, sequencing, physical coupling, package, tooling>
   - Missing evidence: <waveform, report, scope/analyzer capture, dashboard snapshot>

3. Proposed action
   - Minimal reversible change: <RTL/config/layout/policy>
   - Expected metric movement: <delta and conditions>
   - Regression risk: timing, noise, power, performance, compatibility

4. Signoff
   - Re-run artifact: supply noise simulation, ripple spectrum, decap strategy report
   - Required owners: PI owner, analog lead, package owner
   - Final decision: fix, waive with controls, or escalate

AMS deep dive

AMS signoff is a combined noise, IR, timing, and package decision.

Concept diagram

BOUNDARY SIGNOFF

noise + IR + package + timing -> release decision

Metric graph

RISK DASHBOARD

open blockers █████
waivers       ███

Reports and artifacts

• supply ripple spectrum

• IR around analog islands

• package PI summary

• release dashboard

Mini case study

IR hotspot at analog island caused jitter spikes only under burst traffic.

Debug branches

• Correlate droop and jitter

• Check package return path

• Validate mode-specific activity profile

Senior review question

Ask: what boundary condition proves this topic is actually closed?

Key takeaways

• State boundary, mode, and evidence tag with every claim.

• Always align analog, digital, and physical owners before signoff decisions.

Common pitfalls

• Fixing averages while tails still fail.

• Skipping package/supply evidence in jitter or SerDes issues.

• Shipping with waivers that lack owner and expiration criteria.

Principal AMS review addendum

Switching current bursts from digital domains couple through shared impedance and package parasitics, modulating analog supply quality and phase noise.

Metric: supply ripple, spur coupling, analog performance degradation