Question

For the circuit below, identify the logic gate:

• A. AND
• B. OR
• C. NAND
• D. NOR

Hint:

In diode logic with a pull-up resistor, {output goes LOW if any diode conducts}, and {output stays HIGH only when all diodes are reverse biased}.

Answer 1

The Correct Option is A

Concept:
The given circuit is a diode logic circuit
with a pull-up resistor connected to \(+5\text{ V}\). Important principles:

A forward-biased diode conducts and pulls the output LOW.
A reverse-biased diode does not conduct.
A pull-up resistor forces the output HIGH when no diode conducts.

Step 1: Circuit Observation


Inputs \(A\) and \(B\) are connected to the output node through diodes.
The output \(y\) is connected to \(+5\text{ V}\) through a resistor.

Step 2: Input Condition Analysis


If any input is LOW
(\(A=0\) or \(B=0\)): The corresponding diode becomes forward biased and pulls the output \(y\) LOW.
If both inputs are HIGH
(\(A=1\), \(B=1\)): Both diodes are reverse biased, no current flows, and the pull-up resistor pulls \(y\) HIGH.

Step 3: Truth Table

Conclusion:
The output is HIGH only when both inputs are HIGH. Therefore, the circuit functions as an AND gate
.