AMS Interface · All levels

Sample Timing Contract: Comparison Matrix

Comparison Matrix for Sample Timing Contract.

Comparison matrix

Wrapper/calibration choices trade observability, complexity, and residual error.

diagram

+------------------+----------------+----------------+----------------+
| Approach         | Strength       | Weakness       | Best when      |
+------------------+----------------+----------------+----------------+
| Tight aperture   | accuracy       | jitter sensitive | precision mode |
| Relaxed aperture | robustness     | less precision | noisy conditions |
| Adaptive timing  | balanced       | complex FW     | dynamic systems |
| Fixed coarse     | simple         | poor margin    | low-cost flows |
+------------------+----------------+----------------+----------------+

When to choose each approach

Choose the smallest change that proves mechanism and preserves system margins.

Interview traps

Treating all AMS problems as analog-only
Skipping package and power evidence

Evidence comparison

diagram

AMS EVIDENCE MATRIX — Sample Timing Contract

+-------------------+------------------------+--------------------------+-------------------------+
| Evidence           | Tells you              | Does not prove           | Next action             |
+-------------------+------------------------+--------------------------+-------------------------+
| Waveform/log pair  | sequence behavior      | physical root cause      | correlate with signoff  |
| Signoff report     | metric movement        | contract correctness     | audit assumptions       |
| Floorplan view     | physical proximity     | dynamic mode behavior    | run stress mode         |
| Firmware trace     | state progression      | analog quality           | combine with lab data   |
| Dashboard summary  | closure status         | single-failure mechanism | inspect raw artifacts   |
+-------------------+------------------------+--------------------------+-------------------------+

AMS deep dive

Wrapper and sampling contracts determine data trustworthiness.

Concept diagram

diagram

CONVERTER DATA FLOW

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

Metric graph

diagram

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

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