ANALOGUE ELECTRONICS I

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

Transistor = Transfer + Resistor. Transistor is a device which transfers its resistance from high to low. Due to this property a transistor amplifies any input signal and transfers it to the output part of the amplifier. We can control the amplification by changing resistance values of transistors.

There are two basic types of transistors:  the bipolar junction transistor (BJT) and the field-effect transistor (FET). The bipolar junction transistor is used in two broad areas of electronics: (1) as a linear amplifier to boost an electrical signal and (2) as an electronic switch.