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AMS Interface · All levels

Equalization Overview: Expanded Case Study

Expanded Case Study for Equalization Overview.

Extended case study

Signoff review: eye opening, BER vs EQ setting, adaptation convergence regressed after a change touching Equalization Overview.

Background

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

Symptoms observed

  • eye opening, BER vs EQ setting, adaptation convergence 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

Root cause tied to Equalization Overview: TX pre-emphasis and RX equalization compensate ISI and channel loss; over/under-equalization shifts noise sensitivity and error distribution.

Fix and validation

  • Bounded RTL/config/layout correction

  • Re-run EQ sweep report, eye diagram snapshot, adaptation log

  • Full cross-domain regression matrix

Lessons learned

  • Tag everything

  • Mechanism before commands

  • No signoff without owner agreement

diagram
CASE STUDY — Equalization Overview
baseline metric / regressed metric / post-fix metric

Sequence under stress

diagram
AMS BOUNDARY SEQUENCE — Equalization Overview

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

metric under watch: eye opening, BER vs EQ setting, adaptation convergence

AMS deep dive

SerDes closure requires protocol, training, and SI evidence together.

Concept diagram

diagram
SERDES FLOW

training -> equalization -> lane margin -> protocol stability

Metric graph

diagram
BER VS EQ

BER
 ^
 |  high  low  high
 +-----------------> EQ setting

Reports and artifacts

  • lane BER

  • training state transitions

  • EQ sweep report

  • link retry counters

Mini case study

Link looked protocol-clean but lane margin collapsed under thermal sweep.

Debug branches

  • Correlate LTSSM and lane metrics

  • Check SI margins

  • Review firmware timeout assumptions

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

TX pre-emphasis and RX equalization compensate ISI and channel loss; over/under-equalization shifts noise sensitivity and error distribution.

Metric: eye opening, BER vs EQ setting, adaptation convergence

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