TTL source current vs. sink current capability: Evaluate the statement: “In TTL outputs, the HIGH-level source current is higher than the LOW-level sink current.”

Introduction / Context:Classic TTL output stages are asymmetric: they can sink substantially more current when driving a LOW than they can source when driving a HIGH. Recognizing this asymmetry matters for fan-out planning and interfacing to LEDs or other loads.

Given Data / Assumptions:

• Typical TTL VOH specification guarantees only a small source current (for example, -400 microampere) at a valid HIGH.
• Typical TTL VOL specification allows significant sink current (for example, 8–16 milliampere) at a valid LOW.
• Exact values vary by subfamily, but the asymmetry persists.

Concept / Approach:Because TTL can sink much more current than it can source, it is common to wire LEDs to Vcc with the TTL output sinking current when LOW. The statement claims the opposite relationship and is therefore incorrect.

Step-by-Step Solution:

Verification / Alternative check:Any TTL or 74LS/74ALS datasheet confirms the asymmetry; application notes recommend sinking loads for better current capability and logic-level compliance.

Why Other Options Are Wrong:

Common Pitfalls:Assuming symmetric drive because CMOS outputs are often near-symmetric; forgetting that TTL’s design heritage is different.

Final Answer:Incorrect