Digital logic driving capability: A gate can drive a certain maximum number of standard load inputs. This limit is specified by which parameter?

Introduction / Context:
When interconnecting logic gates, each output has a limit to how many inputs it can reliably drive without violating logic-level specifications. Recognizing the correct parameter ensures signal integrity and reliable operation in larger designs.

Given Data / Assumptions:

• Logic families specify VOH/VOL, VIH/VIL, and input/output currents.
• Multiple receiving inputs load a single driving output.
• Standard loads are defined per family (e.g., TTL unit load).

Concept / Approach:
Fan-out is the maximum number of standard inputs that a gate output can drive while keeping output levels within guaranteed ranges. It is derived from the ratio of the driver’s available source/sink current to the required input current of the loads. Fan-in, by contrast, counts the number of inputs a gate possesses; supply voltage and noise margin are important parameters but do not count loads directly.

Step-by-Step Solution:
1) Identify the logic family (e.g., TTL, CMOS) and its unit load definitions.2) Obtain driver I_OH/I_OL and receiver I_IH/I_IL from datasheets.3) Compute allowable loads so that VOH/VOL remain within spec; this is reported as “fan-out.”4) Ensure total capacitive loading and wiring do not degrade edges excessively, even if static fan-out is met.

Verification / Alternative check:
Cross-check with family datasheets or design guides that list typical fan-out values and conditions.

Why Other Options Are Wrong:
“Supply voltage” sets operating range, not load count. “Noise margin” measures robustness against noise, not how many loads are driven. “Fan-in” is the count of inputs on a gate, unrelated to how many loads an output can drive.

Common Pitfalls:
Ignoring dynamic effects (capacitance) that reduce practical fan-out; mixing fan-in with fan-out terminology.

Final Answer:
fan-out