ECL interfacing drawback: Evaluate — “A major drawback when using ECL with TTL or MOS circuits is its negative supply and logic level conventions.”

Introduction / Context:
While Emitter-Coupled Logic (ECL) offers very high speed due to non-saturating operation, it traditionally uses negative supply rails (e.g., VEE = −5.2 V, with ground as the positive rail), resulting in logic levels that are negative with respect to ground. Interfacing this directly with TTL or MOS logic families adds complexity.

Given Data / Assumptions:

• ECL logic levels are negative-referenced; TTL and CMOS are usually ground-referenced positive supplies.
• Level translation or special interfacing devices are required.
• Power supply arrangements differ, increasing design complexity.

Concept / Approach:
Because logic thresholds and common-mode ranges differ markedly, translating between ECL and TTL/MOS often requires dedicated translator ICs or bias networks. Additionally, ECL’s constant-current operation and rail conventions complicate mixed-signal power distribution compared to single positive-rail systems.

Step-by-Step Solution:

Verification / Alternative check:
Design guides for ECL-to-TTL/CMOS interfacing specify translators (e.g., MC10/100 series, PECL/LVPECL variants) to bridge level differences.

Why Other Options Are Wrong:

• Incorrect / PECL-only / high-voltage-only / fan-out-only: The core issue is level convention and supply polarity, not merely drive strength or unusually high supply voltages. PECL uses positive supplies but still requires careful level management.

Common Pitfalls:
Assuming direct connection without translators; mixing grounds improperly; neglecting termination practices needed for high-speed ECL signals.

Final Answer:
Correct