Transistors are regarded as the basic building blocks that regulate the operation of almost all modern electronic circuits. They are solid-state semiconductor devices including diodes, triodes, field-effect transistors, thyristors, etc., sometimes referred to as bipolar devices. As a variable current switch, transistors can control the output current based on the input voltage. Different from ordinary mechanical switches such as Relay, transistors use electrical signals to control their own opening and closing, so their switching speed can be very fast and can reach more than 100GHz in the laboratory.
Transistor has three electrodes and there are also three ways to use them, namely emitter grounding (also known as common emitter amplification, CE configuration), base grounding (common base amplification, CB configuration), and collector grounding ( set amplification, CC configuration, emitter follower).
Due to their fast response and high accuracy, transistors are used for a wide variety of digital and analog functions, including amplification, switching, voltage regulation, signal modulation, and oscillators. Transistors can be packaged individually, but nowadays you may find billions of transistors embedded in a single integrated circuit.