IC refers to integrated circuits. In semiconductor, semiconductor is the most suitable material to realize transistor, and transistor is the core device of most circuits. But I want to write more here, starting from the beginning of "circuit". In physics class, everyone heard that Maxwell's equation predicted the existence of electromagnetic wave, and then Hertz's experiment proved the existence of electromagnetic wave. Finally, Marconi realized radio communication. The original radio receiver used a kind of device called "detector", but the performance of the detector as a receiver is very poor. First of all, its frequency response is difficult to control, resulting in a variety of chaotic interference signals will be triggered detector; On the other hand, it also requires high signal strength, resulting in a very high power at the transmitter. To make matters worse, the transmitting equipment at that time was also very simple. There were only devices such as spark plugs, which could only send signals similar to square waves. Those who had studied signals and systems knew how wide the square wave spectrum was... So the radios at that time could only communicate through Morse code, and FM and AM were inconceivable. In order to solve these problems, people have thought a lot of methods, but except for the realization of high-power sine generator through LC resonant circuit, there is little progress. With this improvement, in 1907, people finally achieved AM broadcasting successfully for the first time.