Extended case study

Signoff review: keepout violation count, analog disturbance incidents, ECO rework regressed after a change touching AMS Floorplan Keepouts.

Background

Team had prior closure; latest integration run shows instability concentrated in one operating condition.

Symptoms observed

• keepout violation count, analog disturbance incidents, ECO rework degradation

• Cross-team disagreement on root cause

• Directed tests pass but system scenario fails

Investigation timeline

1. Hour 0: freeze data tags, firmware build, and environmental conditions

2. Hour 1: diff boundary assumptions and handoff revisions

3. Hour 2: isolate first failing mode and trigger sequence

4. Hour 3: correlate waveform/log/report evidence

5. Hour 4: classify root cause and ownership

6. Hour 5: apply bounded fix

7. Hour 6: execute full regression and issue signoff memo

Root cause

Late floorplan compaction violated quiet-zone assumptions and increased coupling into adjacent analog macro.

Fix and validation

• Bounded RTL/config/layout correction

• Re-run floorplan keepout map, congestion overlay, integration signoff note

• Full cross-domain regression matrix

Lessons learned

• Tag everything

• Mechanism before commands

• No signoff without owner agreement

CASE STUDY — AMS Floorplan Keepouts
baseline metric / regressed metric / post-fix metric

Sequence under stress

AMS BOUNDARY SEQUENCE — AMS Floorplan Keepouts

analog macro -> wrapper / boundary cell -> synchronizer or sampler -> digital consumer
      |                 |                         |                     |
  analog assumptions    legal voltage/state       clock/reset contract   protocol/data validity

metric under watch: keepout violation count, analog disturbance incidents, ECO rework

AMS deep dive

Physical proximity and boundary rules are functional constraints in AMS SoCs.

Concept diagram

INTEGRATION FLOW

floorplan keepouts -> guard strategy -> abutment policy -> PV signoff

Metric graph

INTEGRATION ESCAPES

layout boundary issues ███████
waiver drift           ████

Reports and artifacts

• keepout violations

• guard-ring checks

• abutment DRC

• mixed-signal PV dashboard

Mini case study

Late macro move violated quiet-zone assumptions and caused intermittent converter noise excursions.

Debug branches

• Review macro adjacency

• Re-check guard assumptions

• Re-run PV with correct deck variant

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

Keepout regions protect analog blocks from aggressor routing, switching clusters, and noisy clocks that inject disturbance through substrate and supplies.

Metric: keepout violation count, analog disturbance incidents, ECO rework