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What is the Basic Logic Gate? Describe the OR, AND, NAND gate with the help of the truth table.

How ‘NOT’ operation can be performed using a transistor? Describe.

What is the difference between and NAND gates? Why do we use NAND gates instead of AND gates? What is the NAND gate truth table? What is an AND gate? What is the symbol of the NAND gate? Why is it called a NAND gate? What are NAND gates used for?

Ans: There are three types of Basic Logic gate i.e. AND, OR, and NOT gate.

AND gate:

A logic circuit whose output is HIGH only when all inputs are HIGH.

Symbol of AND gate :

The truth table of AND gate :

OR gate:

A logic circuit whose output is HIGH when at least one input is HIGH.

Symbol of OR gate :

The truth table of OR gate :

NOT Gate

The NOT Gate having a single input and single output device; which is also known as an Inverter because it performs the inversion of the applied binary signal, i.e., it converts 0 into 1 or 1 into 0.

NAND gate:

A logic circuit whose output is LOW when all inputs are HIGH.

Symbol of 2 input NAND gate :

the truth table of NAND gate

‘NOT’ operation can be performed using a transistor

When input 0 X = 0, the base of the transistor is low (0) and therefore transistor operates in the cut‐off region I_C  = 0, hence no voltage drop across R_C  and output Y is V_CC (HIGH)

When input X = 1, the base of the transistor is high (1) and therefore transistor operates in saturation region. In the saturation region V_CE  » 0.2 V . Hence output voltage 0.2 V, i.e logic 0 (Low).

Thus for the circuit shown in the figure output is the complement of input and we can say that it represents NOT gate.