NOR Gate Truth Table | Nor Gate Circuit Diagram

What is NOR Gate?

The NOR gate is one of the universal gates. A NOR gate combines an OR gate and a NOT gate. So we can say it is an OR-NOT operation. It may have two or more inputs and an output.

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NOR Gate Symbol

The logical symbols of the NOR gate are shown:

NOR Gate Logical Expression

The logical expression for the output is

_     _     __
A + B = AB

It is clear from the truth table that the output is '1' only if all the inputs are at logic '0'. It can also say that if the inputs A' = B' = 1, the output Y is 1. Thus, the NOR gate is equivalent to the AND gate with inverted inputs, and it can be realized by a bubbled AND gate, as shown above.

NOR Gate Truth Table

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Circuit Diagram of NOR Gate

• The NOR gate is also called the active LOW AND gate.
• The switching circuit of a NOR gate is as shown:

When any of the switches, either A or B, is closed, the bulb will not glow.

NOR gate follows the commutative law as follows:

___    ___
A+B = B+A

However, it does not follow the associative law.

Enable and Disable Inputs

For a NOR Gate

If control = 0;

Thus, logic '0' enables input.
If control = 1;

Thus, logic '1' is disabled input.

Realization of the Logic Gate - Using NAND Gate and NOR Gate

NOT Gate Realization

Using NOR gate

For the NOT gate realization, we require 1 NOR gate, as shown in the circuit diagram:

AND Gate Realization

Using NOR gate

For the AND gate realization, we require 3 NOR gates if the inputs are not available in complement form, as shown in the circuit diagram:

OR Gate Realization

Using NOR gate

For the OR gate realization, we require 2 NOR gates, as shown in the circuit diagram:

EX-OR Gate Realization

Using NOR gate

For the EX-OR gate realization, we require 5 NOR gates, as shown in the circuit diagram:

EX-NOR Gate Realization

Using NOR Gate

For the EX-NOR gate realization, we require 4 NOR gates, as shown in the circuit diagram:

NOR Gate Realization Using NAND Gate

For the NOR gate realization using the NAND gate, we require 4 NAND gates, as shown in the circuit diagram:

Shortcuts for the realization of logic gates are as follows: