Overview

During the early days of radio design, the tuned amplifier was one of the most important subjects of electronic engineering. It was used as the input RF amplifier of radio receivers tunable in a certain frequency range and as an intermediate frequency (IF) amplifier tuned to a fixed frequency. From the 1930s to 1950s RF amplifiers using electron tubes were one of the most important and interesting research areas of electronics engineering and were investigated in depth. TV and all other wireless systems were other application areas for tuned amplifiers.

After the emergence of transistor circuits in the 1950s, the knowledge already acquired was sufficient for transistorized tuned amplifiers, because the frequency range was still limited to several hundreds of MHz. Active filters, one of the benefits of analog ICs, largely replaced another class of frequency-selective circuits, i.e. L-C filters. As a result of these developments the importance of inductors and circuits containing inductors decreased and eventually these subjects disappeared from many electronic engineering curricula and textbooks.

The rapid expansion of wireless personal communication and data communication during the recent decade, and the developments in IC technology that extended the operation frequencies into the GHz range, resulted in the re-birth of frequency-selective circuits containing inductors. In parallel to the increase of operating frequencies reaching up to multi-GHz range, the necessary inductance values decreased to nanohenry level that are now possible to realize as an integral part of ICs, as mentioned in Chapter 1. But the quality factor of these...