We can obtain the different gates by the repeated use of three basic gates, i.e., OR, and NOT gates.
The repeated use of NAND gate can produce all the three basic gates. Thus, in digital circuits, NAND gate serves as a building block. So, NAND gate is called a universal gate.
AND gate by using the NAND gate :
Suppose that the output of NAND gate is connected to the NOT gate, made from NAND gate by joining two inputs, as given in figure below :
The truth table for the circuit is as given here.
(i) the impedance of the circuit and
(ii) peak value of current in the circuit.