Sample Timing Contract: Interview Drills

Interview drills

Interview Drills 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.

PROMPT
You see aperture budget compliance, sample alignment error, control-loop jitter on Sample Timing Contract. Walk through root cause and fix.

STRONG ANSWER
1. Names boundary and mode.
2. Explains Sampling quality depends on clock phase relationships, aperture uncertainty, and synchronization boundaries between converter clocks and system clocks.
3. Requests timing contract table, phase alignment report, calibration captures.
4. Proposes one bounded fix and full regression.

WEAK ANSWER
Jumps to random tuning or tool commands without proving mechanism and ownership.

Diagram to draw on whiteboard

Sampling contract

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

Root-cause tree to narrate

ROOT-CAUSE TREE — Sample Timing Contract

aperture budget compliance, sample alignment error, control-loop jitter regressed
        |
same silicon / run tags?
   /            \
 no              yes
 |                |
env mismatch    boundary contract or
tag mismatch    true physical issue
 /   \             |
clk   reset      isolate first failing
map   sequence   boundary transition

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