Review of Basic Amplifiers
After a weak radio frequency (RF) signal has arrived at the antenna, it is channelled to the input terminals of the RF amplifier through a passive matching network that enables maximum power transfer of the receiving signal by equalizing the antenna imped
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Review of Basic Amplifiers
After a weak radio frequency (RF) signal has arrived at the antenna, it is channelled to the input terminals of the RF amplifier through a passive matching network that enables maximum power transfer of the receiving signal by equalizing the antenna impedance with the RF amplifier input impedance. Then, it is job of the RF amplifier to increase the power of the received signal and prepare it for further processing. In the first part of this chapter, we review the basic principles of linear baseband amplifiers and common circuit topologies. In the second part of the chapter, we introduce RF and IF amplifiers. Aside from their operating frequency, for all practical purposes, there is not much difference between the schematic diagrams of RF and IF amplifiers. In this book, unless we need to specifically separate the two functions, we refer to all tuned amplifiers as RF amplifiers.
6.1
General Amplifiers
The topic of linear baseband amplifiers is usually covered in introductory undergraduate courses in electronics, thus there is a large number of excellent textbooks available with a thorough treatments of the subject, some of them listed in the reference section. Here, however, we introduce the “back of the envelope” circuit analysis approach with the intent to develop intuition for the circuits and to adopt rapid techniques for circuit analysis. Even though the “back of the envelope” approach is more than often based on very rough approximations, and it leads into conclusions that are sometimes order of magnitude off the “correct” numerical solution, its usefulness is in enabling circuit designer to focus on the underlying principles of the circuit operation instead on the fine and obscuring numerical details. As a result, the amount of time spend to reach correct conclusions is often measured in seconds. By practicing rapid circuit analysis the designers, eventually, develop intuition for the underlying principles and ability to spot possible problems, the circuit limitations, or improvements. Indeed, the machines and simulators still cannot solve problems and improve existing solutions, they merely produce numbers that may or may not have anything to do with the problem at hand. Until we reach the age of intelligent machines, our brain is still the only tool we have that is capable of creative reasoning. In addition, we note that the very notion of “correct” answer is more than often fuzzy. The point is that circuit’s internal states keep changing in both time and frequency domains. That is, even before the signal-processing operation is finished, the circuit’s internal voltage and current levels have changed many times. Therefore, it is valid question to ask “which of the states is the “correct” © Springer Nature Switzerland AG 2021 R. Sobot, Wireless Communication Electronics, https://doi.org/10.1007/978-3-030-48630-3_6
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6 Basic Amplifiers
one?” The answer is “all of them, but not all of the time”, and that is why the numerical simulators are useful. They enable designers
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