Identify the diode logic circuit

In such standard electronic-device questions, two inputs $A$ and $B$ are connected through diodes to a common output node $C$, with a resistor connected so that the output is pulled low unless at least one input drives it high.

Work out the output for different inputs

For a diode OR gate:

• If $A=0$ and $B=0$, no diode conducts, so $C=0$.
• If $A=1$ and $B=0$, the diode from $A$ conducts and makes $C=1$.
• If $A=0$ and $B=1$, the diode from $B$ conducts and makes $C=1$.
• If $A=1$ and $B=1$, at least one conducting path exists, so $C=1$.

Thus the truth table is:

Match with logic gate

This is exactly the truth table of an OR gate.

Evaluate options

• A: NOR gate $\rightarrow$ Incorrect
• B: AND gate $\rightarrow$ Incorrect
• C: NAND gate $\rightarrow$ Incorrect
• D: OR gate $\rightarrow$ Correct

Final answer

The circuit represents an OR gate.