Question

Digital circuit can be made by repetitive use of:
A. OR gates
B. AND gates
C. NOT gates
D. NAND gates

Answer 1

For the solution of this question, first understand how a digital circuit is made and what type of output is expected from the digital circuit, which will help us to get the final combination of gates. As the combination of gates will give us a kind of output and if we know the final output of a digital circuit, then we can construct an effective digital circuit from the gates.

Complete solution:
The NAND gate and the NOR gate can be said to be universal gates since combinations of them can be used to accomplish any of the basic operations and can thus produce an inverter, an OR gate or an AND gate. The non-inverting gates do not have this versatility since they can't produce an invert.
Since, NAND gate is called universal gate, thus any digital circuit can be made by appropriate repetitive use of NAND gate.

Therefore, the correct answer is Option (D).

Additional Information:
A universal gate is a gate which can implement any Boolean function without need to use any other gate type. The NAND and NOR gates are universal gates. In practice, this is advantageous since NAND and NOR gates are economical and easier to fabricate and are the basic gates used in all IC digital logic families.

Note:
Universal gates are a very useful tool, while solving any question related to gates. As using universal gates, we can produce any kind of circuit and also, we can produce any type of gates, that are, OR, AND & NOT gate. Just take care of the output the combination of the universal gates will produce, because that will let us know the final circuit that we have made.