Experiment 2 - The Transistor as a Quadripole

A transistor is often described as a Quadripole, Four-terminal device or Two-port. What is this all about? The transistor has nevertheless only three terminals?

Consider the illustration shown. A generic amplifier is often described as a "Black Box". It has an input (port) and an output (port) with two terminals each. As you have seen, a transistor is an amplifier, but has only three terminals. How does this go together?

A quadripole (also four terminal or two port).

A transistor circuit therefore has one terminal which is common to the input and output. Thus, you automatically obtain three possible transistor circuits...

• common emitter...Common Emitter Circuit, 
• common collector...Common Collector Circuit und 
• common base...Common Base Circuit. 

Common emitter circuit.

Common collector circuit.

Common base circuit.

But are these really amplifier circuits? If so, how do they differ, and how are they used...?

In the further course you build these circuits and investigate their characteristics...