Digital - Systems Testing And Testable Design Solution High Quality

Digital Systems Testing and Testable Design: High-Quality Solutions for Reliable Hardware

4.4 Analog/Mixed-Signal Test

Digital systems often contain PLLs, ADCs, and DACs. High-quality DFT injects analog test busses and on-chip oscillators to measure jitter and linearity without expensive RF testers.

Digital Systems Testing and Testable Design: The Blueprint for High-Quality Silicon

Part 7: Case Study – Automotive ISO 26262 Compliance

Consider an ADAS controller chip (16nm, 200M gates, 500MB memory). The requirement: Zero Defect ( < 1 DPPM).

The High-Quality DFT Solution implemented: Full scan with transition delay coverage >99

Full scan with transition delay coverage >99.5%.
Cell-aware fault models for all standard cells (detects intra-cell opens).
MBIST with ECC (Error Correction Code) and repair on all SRAMs.
Logic BIST for online periodic testing (every 10ms, test a slice of logic).
Mission-mode wrappers to isolate failing cores without shutting down the whole car.

Result: The chip passed AEC-Q100 Grade 1 (-40°C to +125°C) qualification. The test cost per device dropped by 40% due to compression, while DPPM remained under 2 for 100 million shipped units.

Example Checklist for Testable Design Review

Public APIs have clear contracts and versioning rules.
Components are small, single-responsibility, and independently testable.
Test hooks exist for critical subsystems and are gated from production.
CI pipeline runs unit, integration, and smoke tests automatically.
Observability (logs/traces/metrics) covers critical business flows.
Error handling and retry policies are tested via chaos/fault injection.
Security tests (static analysis, dependency scanning, fuzzing) are in place.

Part 5: The Testable Design Methodology (From RTL to Silicon)

A "high-quality solution" is not a tool; it is a methodology. Result: The chip passed AEC-Q100 Grade 1 (-40°C

4.1 Full Scan (Gold Standard)

Concept: Replace all flip-flops with scan cells (multiplexed DFF). Connect them into a shift register (scan chain).

Solution benefits:

Transforms sequential test into combinational test (reduces ATPG complexity from (O(2^N)) to (O(N^2))).
Achieves >99% fault coverage with minimal area overhead (~10–15%).

Operation:

Shift-in test pattern (N cycles).
Pulse capture clock (1 cycle).
Shift-out response while shifting next pattern.