# Transistors and Basic logic gates

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1363 ## What is a transistor?

The transistor is an important component in electronic devices. Transistors are used as amplifiers and switch. As an amplifier, the transistor takes in a tiny electric current and produces an amplified current. One of the applications of the transistor as an amplifier is in hearing aids.

Transistors can also work as a switch. A small electric current flowing through one part of a transistor will make a much larger current flow through the other part of the transistor. A computer chip consists of millions of transistors which can be switched on and off individually. The transistors can store two different numbers zero and one since it can be in two different states.

The transistors are usually made using materials like silicon. Silicon is a semiconductor. Semiconductors are materials in which impurities are added by a process called doping to make it behave in a different way. If silicon is doped with impurities like arsenic or phosphorus, it gains some free electrons. This type of semiconductor is called n-type(negative type) since electrons are negatively charged. If silicon is doped with gallium or aluminium then the number of holes will be more. Therefore it is called p-type (positive type) semiconductors. These n-type and p-type semiconductors are combined to form a transistor.

## Working of Transistor

Three layers of silicon are sandwiched and electrical contacts joined to form a PNP transistor or NPN transistor. The three electrical contacts are called emitter, base and junction. The transistor starts working when the electrons or holes start moving across the junctions between the n-type and p-type.

## Basic Logic gates

Logic gates are electronic devices constructed using diodes and transistors. There are three basic logic gates called as NOT, AND, and OR gate. Logic gates are used to carry out logical operations on single or multiple binary inputs and give out one binary output. Boolean algebra is the mathematics that is used to analyze the logic gates. Boolean Algebra uses only two variables zero or one.

## Types of basic logic gates

The most basic gates are OR gate, AND gate and NOT gate. In addition to the basic logic gates, there are many combinations of gates. The basic gates are combined to form NAND gate, NOR gate, EXOR gate etc.

### OR gate

An OR gate has two inputs and a single output. The operation of the OR gate is such that the output of the gate is binary 1 if either one of the input is 1 or both the inputs are 1. The Boolean expression for the OR gate is given by Y = A + B.

### AND gate

The output of the AND gate is one only if both the inputs are one. The Boolean expression for AND gate is given by Y=A.B.

### NOT gate

This the most simple logic gate. NOR gate has only one input and one output. The output of the NOT gate is always opposite to the input. If the input is 0 then the output will be 1. If the input is 1 then the output is 0.