Modern RF and microwave engineers have many more types of amplifiers at their disposal to suit specific system needs than their predecessors ever dreamed of. Classes of amplifiers can more or less be lumped into two groups: the classical controlled conduction angle amplifiers and the so-called “switching” amplifiers. The first group consists of the high-fidelity Class-A and AB operating modes, the class-B and the reduced conduction-angle Class-C amplifier. The switchers include Class-D, E, F and inverse F.
This article focuses on a qualitative review of the Class A, B, AB and C amplifier modes as well as giving some explanation on where inefficiencies appear in each. Some of the advantages and disadvantages of each topology will be presented and the trade-offs will be briefly elaborated in an intuitive manner. The active devices will be assumed to be ideal (i.e. no or only resistive parasitics, no switching delays, etc.) to simplify the exposition. Naturally, the analysis and design of real-world amplifiers must consider the effects of parasitics. However, for clarity of exposition, effects of device parasitics are ignored.
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