Question

You are given two circuits as shown in Figure. Which consists of NAND gates. Identify the logic operation carried out by the two circuits.

Answer 1

(a)

Here, the output of NAND gate is connected to NOT gate [obtained from NAND gate]. Let Y¹ be the output of NAND gate and final out put of the combination of two gates be Y. The out put of a NAND gate is 0 only when both the inputs are zero, while in NOT gate, the input gets inverted. Using these facts, the truth table for the given arrangement can be written as below.

It is the truth table of AND gate. Therefore the given Circuit acts as AND gate.

Here, the out puts of the NOT gates (obtained from NAND gates) are connected to NAND gate. Let Y_: and Y₂ be the outputs of the two NOT gates and the final out put of the combination of three gates be Y. In a NOT gate, the input gates inverted. While the out put of a NAND gate is 0 only when both the inputs are zero. Using these facts, the truth table for the given arrangement can be written as below:

It is the truth table of OR gate. Therefore, the given acts as OR gate.