Sample Timing Contract: Worked Example

Worked example

Worked Example for Sample Timing Contract focuses on aperture budget compliance, sample alignment error, control-loop jitter. The goal is to connect observed symptom to boundary mechanism, ownership, and signoff risk.

A stress workload shows aperture budget compliance, sample alignment error, control-loop jitter. The first review mistake is broad blame. A better review tracks one boundary transition, validates contract assumptions, and proves the first failing mechanism in Sample Timing Contract.

Sequence under inspection

AMS BOUNDARY SEQUENCE — Sample Timing Contract

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

metric under watch: aperture budget compliance, sample alignment error, control-loop jitter

Sampling contract

sample edge alignment + aperture budget + CDC boundary
=> valid digital sample interpretation

1. Capture tagged waveform/log/report set.

2. Mark mode boundary and first failure timestamp.

3. Map to contract and owner.

4. Compare against timing contract table, phase alignment report, calibration captures.

5. Propose one reversible fix and predefine regression matrix.

Did the fix work?

BEFORE / AFTER — Sample Timing Contract

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

Wrapper and sampling contracts determine data trustworthiness.

Concept diagram

CONVERTER DATA FLOW

sampling clock -> wrapper -> sync boundary -> system consumer

Metric graph

INVALID SAMPLE BURSTS

time --->  _|¯¯|__|¯¯¯|____|¯|_

Reports and artifacts

• sample validity ratio

• calibration convergence

• CDC audit

• overflow/stale sample counters

Mini case study

Mode transition changed sample phase and invalidated wrapper framing assumptions.

Debug branches

• Sample timing contract

• Calibration hook behavior

• Wrapper CDC integrity

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

Sampling quality depends on clock phase relationships, aperture uncertainty, and synchronization boundaries between converter clocks and system clocks.

Metric: aperture budget compliance, sample alignment error, control-loop jitter