What is the role of the transistor?

A transistor is a solid-state semiconductor device that can be used for detection, rectification, amplification, switching, voltage regulation, signal modulation, and many other functions. As a variable switch, the transistor controls the current flowing out based on the input voltage. Therefore, the transistor can be used as a current switch. The difference between a transistor and a general mechanical switch (such as Relay and Switch) is that the transistor is controlled by an electrical signal, and the switch is switched. The speed can be very fast, and the switching speed in the laboratory can reach more than 100GHz.

A semiconductor transistor is a semiconductor device having two PN junctions inside and three external extraction electrodes. It has the functions of amplification and switching of electrical signals, and is widely used. Both the input stage and the output stage use a transistor logic circuit called a transistor-transistor logic circuit. In books and practical applications, it is simply referred to as a TTL circuit. It belongs to a type of semiconductor integrated circuit, and the most common one is TTL NAND gate.