A logic gate is just a simple boolean function, in the sense that it has only either of two outputs. Either 1 or 0, high or low, true or false, whatever you call it. It is the most elementary tool in building a circuit. A logic gate performs a logical operation on an input and gives the appropriate output for it. Given below are the different logic gates, their symbols, descriptions and truth tables.

**NOT GATE:**

This function will have a single input only. It is also called an inverter as it gives the negative of the input function.

**AND GATE:**

Output will be 1 only if ‘all’ inputs are . It can have more than 1 input.

**NAND GATE:**

It is the NOT AND gate. The inverter bubble reverses the output of the AND gate logic, giving a 0 output only when all inputs are 1.

**OR GATE:**

If “any one” of the inputs are 1, the output is 1. Output is 0 only if all inputs are 0. It can have more than 1 input.

**NOR GATE:**

It is the NOT – OR gate. The inverter bubble reverses the output of the OR gate logic giving 1 as the output only if all inputs are 0. It can have more than 1 input.

**XOR GATE:**

It is the ‘Exclusive – OR’ gate. The output is 1 only when the one of the inputs (odd high) is 1.

**XNOR GATE:**

It is the ‘Exclusive – NOR’ gate. The output is 1 only when the both the inputs (even high) are the same.

**Universal Logic Gates:**

A universal logic gate is one which can implement any Boolean function {0,1}, without the use of any other logic gate. Simply put, a logic gate which can serve the function of ALL other logic gates, including itself.

The NAND and NOR gates are called universal logic gates because all the other gates can be created using these two.

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