Design of a broadband power amplifier using an optimized feedback network

This article presents a systematic design method for ultra broadband power amplifiers using an optimized feedback network. Based on the analysis using the network parameters for the open-loop circuit and feedback network, a design and optimization procedure was established. To make the gain response as flat as possible throughout the broad operating frequency band, the optimized component values of the feedback network were found using an optimization program which was built based on the least-mean-square-error algorithm in MATLAB. Single-ended broadband power amplifiers were implemented to verify the optimization results for various target gains, as well as source and load impedance sets. One of the single-ended amplifiers was selected for use as part of the push-pull power amplifier which includes broad-band 1:1 transmission line transformers. For the operational bandwidth from 8 to 800 MHz, the ultra broad-band push-pull power amplifier exhibited a flat gain response of ±0.331 dB from 17.2 dB, a P_1dB of more than 40.5 dBm, and high PAE from 26.7 to 45 % at each P_1dB point.