Question

Four NAND gates are connected as shown in Fig. The arrangment is equivalent to

(1) One NAND gate

(2) One OR gate

(3) One NOR gate

(4) One NOT gate

Answer 1

(1) One NAND gate

Gate I and II are used as NAND gates. Let their output be C₁ and C₂ respectively. C₁ and C₂ are inputs of gate III used as a NAND gate. Its output is C₃ . C₃ is input of gate IV used as a NOT gate. The final output C. The truth–table of the arrangement is

From the truth–table we can make truth–table showing A, B and C only. This is truth–table of a NAND gate. The arrangment therefore is equivalent to a single NAND gate.