High-power RF generation is required not only by various wireless communication applications, such as 4G and 5G cellular and satellite, but also by radar for airspace and weather monitoring, radar and communication jamming, imaging, DC/DC conversion, and even RF heating.
This power is delivered by the RF power amplifier (PA), the final stage of amplification before the antenna, with each application placing on the PA its own set of requirements in terms of frequency, bandwidth, load, power, efficiency, and linearity.
In communications, for instance, significant RF power may be needed to enable the transmission range goal to be met. A typical cellular communications application must deliver good signal coverage and high-speed data transfer with as little battery power consumption as possible. This interplay of requirements results in design tradeoffs between spectral efficiency, linearity, and power efficiency.
This RF power can be generated using any of a wide variety of techniques or amplifier modes of operation or classes. Each class differs in terms of the amount of time the transistor conducts and the shape of its output voltage and current waveforms, as well as the resulting unique set of tradeoffs.
This article is the first in a series that aims to refresh these considerations. We begin with a primer on basic waveform shapes and consider the power and efficiency they represent.
The third and final part in this series takes real-world waveforms and transistor behavior into account as it revisits gate biasing and efficiency.