AMS Interface · All levels

Jitter Budgeting: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Jitter Budgeting.

Step-by-step analysis walkthrough

Use this when you own Jitter Budgeting during an AMS war room.

Capture failing mode and environmental condition.
Pull synchronized waveform, logs, and report artifacts.
Mark first boundary where legal behavior diverges.
Audit reset/clock/power sequence assumptions.
Check physical coupling contributors (floorplan/power/package) where relevant.
Assign single-thread ownership for the first fix.
Propose bounded change and define success criterion.
Run scenario and safety regressions.
Document findings in closure memo.
Update signoff dashboard and waiver state.

Artifacts to collect

jitter budget spreadsheet, phase-noise summary, STA uncertainty map
handoff contract
firmware/config tag
physical signoff snapshot
decision memo

Decision memo template

diagram

AMS DECISION MEMO — Jitter Budgeting
mode/condition:
metric:
hypothesis:
fix:
regression:
owners: timing lead, PLL owner, clock tree owner

Reference visuals

Jitter budget stack

diagram

TOTAL JITTER BUDGET
  source jitter
  + PLL intrinsic jitter
  + supply/package induced jitter
  + distribution skew/uncertainty
  = endpoint timing margin consumption

AMS deep dive

Clock quality evidence must include jitter and sequencing, not lock status alone.

Concept diagram

diagram

CLOCKING FLOW

reference -> PLL/DLL -> distribution -> endpoint margin

Metric graph

diagram

JITTER TREND

jitter ps
  ^
  |   o baseline
  |      o stress mode
  |         o failure edge

Reports and artifacts

jitter budget
lock/unlock counters
phase-noise snapshot
STA uncertainty deltas

Mini case study

False-lock condition released reset early; endpoint logic sampled unstable clock edge patterns.

Debug branches

Lock qualification policy
Reset sequencing check
Package/supply contributors

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

System timing margin is consumed by source jitter, transfer jitter, supply noise, and distribution skew; the budget must close from reference clock to endpoint sampler.

Metric: total jitter budget, deterministic/random split, downstream timing margin

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