JEE Physics 2026 Question with Solution

Given: Two $p\text{-}n$ junction diodes $D_1$ and $D_2$ are connected with a pull-up resistor $R$ to $+5 \, \text{V}$. Inputs are $A$ and $B$, and output is $C$.

Find: Which logic gate this circuit represents.

Concept: In diode logic, a forward-biased diode conducts and can pull the output node LOW, while a reverse-biased diode does not conduct.

Step 1: Understand the circuit A pull-up resistor $R$ connects the output node $C$ to $+5 \, \text{V}$. The diodes are oriented such that a LOW input can pull the output LOW.

Step 2: Truth table analysis

Explanation: If either $A = 0$ or $B = 0$, the corresponding diode conducts and pulls $C$ LOW. Only when both $A = 1$ and $B = 1$, both diodes are reverse-biased and the pull-up resistor makes $C$ HIGH.

Conclusion: The output is HIGH only when both inputs are HIGH. Therefore, the correct option is C, that is, AND Gate.