IC refers to integrated circuits, which are made on semiconductors because semiconductors are the most suitable materials for realizing transistors, and transistors are the core devices of most circuits now. However, I want to write more here, tracing back to the origin, starting from the beginning of "circuit". In physics class, everyone heard that Maxwell's equation predicted the existence of electromagnetic waves, then Hertz's experiment proved the existence of electromagnetic waves, and finally Marconi realized radio communication. The original radio receiver used a kind of device called "detector", but the performance of detector as a receiver is very poor. First of all, its frequency response is difficult to control, resulting in all kinds of messy interference signals will be triggered detector; On the other hand, it also requires high signal strength, resulting in the power of the transmitter must be very large. What's worse, the transmitting equipment at that time was also very simple, only devices such as spark plugs, which could only send signals similar to square waves, and those who had studied signals and systems knew how wide the spectrum of square waves was... So the radio at that time could only communicate through Morse code, and FM and am were all Arabian Nights. In order to solve these problems, people think a lot of methods, but in addition to the realization of high-power sinusoidal generator through LC resonant circuit, there is little progress. With this improvement, in 1907, people finally realized AM broadcasting for the first time