Dynamic Supply Voltage Control for PA Output Power Correction Under Variable Loading Scenarios

This article presents an automatic system that is able to dynamically restore the output power capability of a power amplifier (PA) under variable loading scenarios. This is accomplished by dynamically adapting the supply voltage, VDD, of the PA according to the developed theoretical model. To dynamically vary VDD, a GaN dc-dc converter, based on the commercial EPC 9067 Demo Board, was used. The load is measured using an impedance meter, which is based on the slotted line principle and was specifically designed for low insertion loss. This impedance meter also generates a load-dependent pulsewidth modulated signal that controls the dc-dc converter switching, regulating VDD. The prototype was designed for 3.55 GHz and tested with CW and modulated signal excitations, being able to compensate the output power degradation under variable loading conditions inside a 2.1 voltage standing wave ratio circle. For a constant gain compression level, the average efficiency degradation over the tested range of impedances is less than 5%, and the average power improvement is 0.7 dB. The worst case measured output power of the PA is compensated from 37.0 to 39.9 dBm, which corresponds to a 2.9 dB improvement. Using a modulated signal excitation, the peak envelope power, which is compressed by almost 3 dB without VDD compensation, is restored, and the average output power is improved by 0.6 dB. The system can track the load and adjust VDD with a worst case step-up delay of 25 ms.