We have discussed different types of logic gates in previous articles. Now coming to the topic of this article we are going to discuss the Universal Gate. AND, NOT and OR gates are the basic gates; we can create any logic gate or any Boolean expression by combining a mixture of these gates.
But NOR gates and NAND gates have the particular property that any one of them can create any logical Boolean expression if appropriately designed. Meaning that you can create any logical Boolean expression using ONLY NOR gates or ONLY NAND gates. Other logical gates do not have this property. If you which to play around with these universal gates as part of an electronics project, many of the best Arduino starter kits contain these universal NOR and NAND gates.
Now we will look at the operation of NOR gates and NAND gates as universal gates.
NAND gate as Universal Gate
The below diagram is of a two input NAND gate. The first part is an AND gate and second part is a dot after it represents a NOT gate. So it is clear that during the operation of NAND gate, the inputs are first going through AND gate and after that, the output gets reversed, and we get the final output. Now we will look at the truth table of NAND gate.
We will consider the truth table of the above NAND gate i.e. a two-input gate. The two inputs are A and B.
Now we will see how this gate can be used to make other gates.
This is the circuit diagram of a NAND gate used to make work like a NOT gate, the original logic gate diagram of NOT gate is given besides.
The above diagram is of an OR gate made from combinations of NAND gates, arranged in a proper manner. The truth table of an OR gate is also given beside the diagram.
Now we will see the design of an AND gate from NAND gates.
The above diagram is of an AND gate made from NAND gate. So we can see that all the three basic gates can be made by only using NAND gates, that’s why this gate is called Universal Gate, and it is appropriate.
NOR gate as universal gate
We have seen how NAND gate can be used to make all the three basic gates by using that alone. Now we will discuss the same in case of NOR gate.
The above diagram is of an OR gate made by only using NOR gates. The output of this gate is exactly similar to that of a single OR gate. We can see the circuit arrangement of OR gate using, NOR gate is similar to that of AND gate using NAND gates.
The above diagram as the name suggests is of AND gate using only NOR gate, again we can see that the circuit diagram of AND gate using only NOR gate is exactly similar to that of OR gate using only NAND gates. Now we will finally see how we can make a NOT gate by using only NOR gates.
The above diagram is of a NOT gate made by using a NOR gate. The circuit diagram is similar to that of NOT gate made by using only NAND gate.
So, from the above discussion, it is clear that all the three basic gates (AND, OR, NOT) can be made by only using NOR gate. And thus, it can be aptly termed as Universal Gate.