The transistor is the fundamental building block of modern electronic devices.
A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit.
A bipolar transistor has terminals labeled base, collector, and emitter. It is a current controlled device that a small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals.
Two basic function:
“switching” (digital electronics) or “amplification” (analogue electronics)
Three regions of operation
• Active Region – the transistor operates as an amplifier and Ic = β.Ib
• Saturation – the transistor is “Fully-ON” operating as a switch and
Ic = I(saturation)
• Cut-off – the transistor is “Fully-OFF” operating as a switch and
Ic = 0
Bipolar Transistor Construction