Question

Write the truth table for the circuits given in figure. consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits.

Answer 1

In first case, $A$ acts as the two inputs of the NOR gate and $Y$ is the output. Hence, the output of the circuit is $\overline{A+A}$.

So, Output $Y=\overline{A}$.

Thus the gate is NOT gate.

The truth table is shown in the figure.

For second circuit, $A$ and $B$ are the inputs and $Y$ is the output of the given circuit. By using the result obtained in solution (a), we can infer that the outputs of the first two NOR gates are $\overline{A}$, $\overline{B}$. $\overline{A}$ and $\overline{B}$ are the inputs for the last NOR gate. Hence, the output for the circuit can be written as:

$Y=\overline{\overline{A}+\overline{B}}=A.B$

So this is a AND gate.

Truth table is shown in the figure.