Linearity Trade-Off in the HPA Transmit Path

A major element in any communication system is the transmit chain, primarily the final amplifier or high-power amplifier (HPA). The purpose of the HPA is to increase the input signal (waveform) to a level that meets the link budget of the system. The key is to maximize efficiency, the conversion of DC power to RF power. HPA efficiency increases and tends to peak at and into compression towards device saturation, unfortunately amplitude modulated waveforms and frequency division multiplexed (FDM) schemes are susceptible to linearity. Heat dissipation, compression curve, device bandwidth and frequency response of the HPA device must be considered as well, which is determined by device construction and primarily material process. This note will discuss theses trade-offs.