Digital IC drive capability: how is the fan-out of a logic gate or building block defined in practical digital design?

Introduction / Context:
Fan-out quantifies how many standard inputs a logic output can reliably drive without violating voltage levels or timing specifications. It is a key parameter for designing robust digital systems and avoiding signal integrity issues.

Given Data / Assumptions:

• Standardized input load per gate family (e.g., TTL, CMOS).
• Output must meet logic-high/low thresholds under load.
• Capacitive loading and DC current levels affect fan-out.

Concept / Approach:
For TTL, fan-out historically references the ratio of available output current to required input current. For CMOS, static current is tiny, so fan-out is largely limited by capacitive loading and timing (rise/fall times). In both cases, the definition remains: how many inputs can one output reliably drive.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets list “fan-out” explicitly as the maximum number of standard inputs permitted per output for a given family and supply condition.

Why Other Options Are Wrong:

Common Pitfalls:
Ignoring dynamic effects (capacitance) in CMOS; assuming static definitions apply identically across families without timing considerations.

Final Answer:
the number of inputs that one output can transmit to