Output loading in logic families – as more load-gate inputs are connected to a driver output, does the total sink current required by the driving gate decrease, increase, or stay the same?

Introduction / Context:
Fan-out describes how many inputs a logic output can reliably drive. The electrical consequence of attaching more inputs to one output is a classic consideration in digital electronics. This question focuses specifically on sink current and how it changes as additional loads are attached.

Given Data / Assumptions:

• The driver output must meet guaranteed logic-level voltages under load.
• Each load input presents some current requirement (DC and dynamic).
• Sink current refers to current flowing into the driver when it pulls the line to logic 0.

Concept / Approach:
In TTL, each input sources a small current when high and demands current be sunk by the driver when low. More connected inputs add to the total current that must be sunk by the driver to hold a valid low level. Even with CMOS inputs (which have negligible DC input current), dynamic currents due to input capacitance increase with more loads, raising transient sink/source current and slowing edges if the driver is not strong enough.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets specify IOH/IOL (source/sink limits) and fan-out ratings. Exceeding these limits degrades VOL/VOH margins and rise/fall times, confirming the increased current requirement with more loads.

Why Other Options Are Wrong:
Decrease is the opposite of reality; “stays the same” ignores additive loading; oscillation or zero current claims are nonphysical for practical logic families.

Common Pitfalls:
Confusing CMOS near-zero DC input current with zero total demand; dynamic switching still requires charging/discharging input capacitances, increasing transient current with more loads.

Final Answer:
It increases because additional inputs require more current to sink