TTL logic-level windows Within standard TTL specifications, which range of output voltage is considered invalid (neither guaranteed LOW nor guaranteed HIGH)?

Introduction / Context:
Digital interoperability depends on clearly defined logic thresholds. TTL specifies guaranteed output LOW (VOL) and output HIGH (VOH) levels. The region between these guarantees is invalid/undefined for logic interpretation.

Given Data / Assumptions:

• Typical TTL guarantees: VOL(max) ≈ 0.4 V, VOH(min) ≈ 2.4 V at rated load.
• Inputs: VIL(max) ≈ 0.8 V, VIH(min) ≈ 2.0 V.
• Supply nominal: 5 V.

Concept / Approach:
The invalid window for outputs lies between VOL(max) and VOH(min). Any voltage in this band is not guaranteed to be recognized consistently by downstream inputs. Good design keeps dynamic signals moving quickly through this region and ensures steady-state levels meet margins.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets and logic family charts show identical thresholds and noise margins derived from these values.

Why Other Options Are Wrong:

• 0.0–0.4 V: Defined LOW.
• 2.4–5.0 V: Defined HIGH (within device limits).
• 0.0–5.0 V: Includes valid and invalid ranges; too broad.

Common Pitfalls:
Confusing input thresholds with output guarantees; remember the output invalid band is bracketed by VOL(max) and VOH(min).

Final Answer:
0.4–2.4 V