In the first half of the twentieth century the radio was the main activity area of the electronics industry, and correspondingly, the RF circuits occupied a considerable part in the electronic engineering curriculum and books published in this period. Properties of the resonance circuits and electronic circuits using them: the single-tuned amplifiers as the input stages of receivers, the double-tuned circuits as the IF amplifiers, the RF sinusoidal oscillators and high power class-C amplifiers have been investigated in depth. It must be kept in mind that the upper limit of the radio frequencies of those days was several tens of MHz, the inductors used in tuned circuits were air-core or ferrite-core coils with inductance values in the micro-henries to milli-henries range, having considerably high quality factors, ranging from 100 to 1000, and the tuning capacitors were practically lossless.The knowledge developed for the vacuum-tube circuits easily adapted to the transistors with some modifications related to the differences of the input and output resistances of the devices. In the meantime, the upper limit of the frequency increased to about 100 MHz for FM radio and to hundreds of MHz for UHF-TV. The values of the inductors used in these circuits correspondingly decreased to hundreds to tens of nano-henries. But these inductors were still wound, high-Q discrete components.In the second half of the twentieth century, the emergence of the integrated circuits drastically increased the reach of electronic engineering. Digital electronics on one side and the analog electronics using the potentials of the operational amplifiers on the other side, forced the curricula and the textbooks to skip certain old and "already known" subjects (among them the resonance circuits and the tuned amplifiers), to open room to these new subjects. The development of the (inductorless) active filters that replaced the conventional passive LC filters extensively used in telecommunication systems, even decreased the importance of inductors.Rapid development of CMOS technology and the steady decrease of the dimensions of the devices according to "Moore's Law", led to the increase in complexity of ICs (from now on, the VLSI circuits) and the operating frequencies as well. In the digital realm this helped to improve the performances of digital computers and digital telecommunication systems. In the analog realm the operation frequencies of the circuits increased to the GHz region and correspondingly the inductance values decreased to below vii
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