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

Explanation

(a) A acts as the two inputs of the NOR gate and Y is the output, as shown in the following figure. Hence, the output of the circuit is `bar(A+A)`.

`"Output", Y=bar(A+A)=barA`
The truth table for the same is given as:

This is the truth table of a NOT gate. Hence, this circuit functions as a NOT gate.
(b) 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 `barA" and "barB,` as shown in the following figure.

`barA" and "barB,` are the inputs for the last NOR gate. Hence, the output for the circuit can be written as:
`Y=bar(barA+barB)=barbarA.barbarB=A.B`
The truth table for the same can be written as:

This is the truth table of an AND gate. Hence, this circuit functions as an AND gate.