Four-input AND gate requirement For a 4-input AND gate, how many inputs must be HIGH simultaneously for the output to go HIGH?

Introduction / Context:
AND gates implement logical multiplication. Understanding their threshold for producing a HIGH output is fundamental to building enable signals, interlocks, and multi-condition detectors in digital systems.

Given Data / Assumptions:

• Gate: 4-input AND.
• Positive logic conventions apply.
• No wired-AND or open-collector behavior; ideal logic only.

Concept / Approach:

The Boolean expression for a 4-input AND is Y = A · B · C · D. A product term evaluates to 1 only if every factor is 1. Therefore, any single 0 on any input forces the whole product to 0, keeping the output LOW.

Step-by-Step Solution:

Verification / Alternative check:

Truth table inspection confirms the output is HIGH only on the single row where A = B = C = D = 1. Any other combination includes at least one 0, yielding 0 at the output.

Why Other Options Are Wrong:

• “Any one/two/three” would describe OR-like thresholds or majority logic, not AND.
• “Always HIGH” is incorrect; AND is stringent, not permissive.

Common Pitfalls:

• Confusing AND with NAND, which inverts the final result.

Final Answer:

all four inputs