Metastability & Synchronizers

Section goal

Metastability physics, MTBF modeling, synchronizer design patterns, and safe single-bit vs multi-bit crossings.

How to study this section

1. Start with topic hubs to classify problem shapes.

2. Use mechanism and reports pages to connect risk signals to evidence.

3. Practice debug and worked examples before signoff reviews.

4. Close with checklist and silicon impact before approving fixes or waivers.

Topics

1. mtbf-and-synchronizers/ — MTBF & Synchronizer Math

2. two-flop-sync/ — Two-Flop Synchronizers in Practice

3. multi-bit-cdc-hazards/ — Multi-bit CDC Hazards

4. sync-selection-guide/ — Synchronizer Selection Guide

Related topics

• CDC/RDC course hub

CDC/RDC deep dive

Metastability is managed risk, not eliminated risk.

Concept diagram

METASTABILITY FLOW

async event -> first sample may metastabilize
 -> settle window
 -> downstream sample confidence

Metric graph

MTBF TREND

target MTBF ---------
current design   ____/

Reports and artifacts

• MTBF assumptions

• synchronizer inventory

• crossing class summary

• critical waivers

Mini case study

Pulse sync chosen for a level signal caused intermittent stuck state under voltage stress.

Debug branches

• Validate crossing class first

• Check pulse width assumptions

• Audit synchronizer template usage

Senior review question

Ask: what evidence proves this risk is closed for silicon, not just tool-clean?