Analog Supply Noise: Worked Example

Worked example

Worked Example 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.

A stress workload shows supply ripple, spur coupling, analog performance degradation. The first review mistake is broad blame. A better review tracks one boundary transition, validates contract assumptions, and proves the first failing mechanism in Analog Supply Noise.

Sequence under inspection

AMS BOUNDARY SEQUENCE — Analog Supply Noise

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

metric under watch: supply ripple, spur coupling, analog performance degradation

Supply noise path

digital burst current -> shared impedance -> analog ripple/spurs -> performance loss

1. Capture tagged waveform/log/report set.

2. Mark mode boundary and first failure timestamp.

3. Map to contract and owner.

4. Compare against supply noise simulation, ripple spectrum, decap strategy report.

5. Propose one reversible fix and predefine regression matrix.

Did the fix work?

BEFORE / AFTER — Analog Supply Noise

health score
  ^
  |                     --- target
  |         o regressed
  |               o before fix
  |                    o after bounded fix
  +--------------------------------------> debug iteration

Prove signal quality, timing margin, and integration safety together.

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