Universal Gate | NAND and NOR Gate as Universal GatePublished on 24/2/2012 & updated on Wednesday 11th of July 2018 at 12:23:51 AM
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NAND gate as Universal GateThe 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.
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 gateWe 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.
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