TTL output asymmetry: Is the HIGH-level source current capability of TTL typically smaller than the LOW-level sink current (i.e., TTL sinks more than it sources)?

Introduction / Context:
TTL outputs are asymmetric. Designers exploit this when selecting pull-ups, driving LEDs, or budgeting fan-out. Knowing which state offers stronger drive prevents logic-level violations and slow edges.

Given Data / Assumptions:

• Standard 74xx/74LS TTL family behavior.
• Typical IOH is small in magnitude; IOL is significantly larger.
• 5 V nominal supply.

Concept / Approach:
In TTL, the output transistor network sinks current efficiently at a logical LOW and sources less at a logical HIGH. Datasheets often show IOL in the range of 8–16 mA (or higher for drivers), while IOH is around -0.4 mA. This asymmetry shapes interface design.

Step-by-Step Solution:

Verification / Alternative check:
Practical lab tests show LEDs glow brighter with active-low connection through TTL because sinking current is stronger and VOH degrades with heavy sourcing.

Why Other Options Are Wrong:

• “Sources more than sinks” contradicts specifications.
• “Only for open-collector” is incorrect; asymmetry also exists in totem-pole outputs.
• “Always equal” is not true for TTL families.

Common Pitfalls:
Overloading a TTL output at HIGH, causing VOH to sag and violating VIH of the next stage.

Final Answer:
Correct — TTL typically sinks more current than it can source.