Fan-Out in TTL — Define “ten TTL loads per TTL driver” In standard TTL terminology, the phrase “ten TTL loads per TTL driver” refers to which specification?

Introduction / Context:Fan-out quantifies how many standard logic inputs a single logic output can reliably drive while still meeting specified voltage thresholds for HIGH and LOW. It is a key system-level parameter for building combinational networks.

Given Data / Assumptions:

• For classic TTL, a “standard load” is defined by input current requirements at the recognized logic thresholds.
• Fan-out is often different for LOW vs. HIGH due to asymmetric sink/source capabilities.
• “Ten loads” implies the output can support ten standard inputs without violating VOH/VOL specs.

Concept / Approach:Fan-out reflects current-drive capability. A TTL output that can sink the sum of input LOW currents (and source the sum of input HIGH currents) for ten standard inputs has a fan-out of 10. Designers must check both LOW and HIGH cases, using the lower of the two limits as effective fan-out.

Step-by-Step Solution:Identify metric → number of input loads per output driver.Ensure compliance → sum of currents must not exceed driver limits.Interpret statement → “ten loads” is fan-out = 10.

Verification / Alternative check:Datasheets list IOH/IOL and IIH/IIL values; dividing driver capability by input demand yields the permissible fan-out for each logic level.

Why Other Options Are Wrong:

• noise immunity: A voltage margin metric, not a count.
• power dissipation: Measured in mW; unrelated to the count of loads.
• propagation delay: Time measure (ns), not a count.

Common Pitfalls:For mixed families, ensure the driven inputs truly match the “standard load” definition; otherwise, the real fan-out may be smaller.

Final Answer:fan-out