Band-Split Forward-Path Cartesian Feedback for Multicarrier TETRA RF Power Amplifiers

This paper demonstrates a TETRA base-station RF power amplifier (RFPA) with state-of-the-art linearity and noise performance for the UHF band. Very high linearity is achieved at considerable power levels using a combination of a linear class-A/B RFPA, a novel dual-path Cartesian-feedback structure with RF reference injection, and high-order loop filters. It is demonstrated how the limitation on linearization bandwidth imposed by RFPA group delay can be alleviated by the introduction of an auxiliary low-power RFPA to the system. A 10-MHz (baseband) bandwidth loop is closed around a 200-W LDMOS RFPA with 20-ns group delay. Basic small-signal and noise/distortion analysis of the adopted approach is presented. Experimental validation of the approach is done with a noncontiguous dual-carrier TETRA signal with 25-500-kHz carrier spacing. Intermodulation performance in the -80-dBc area is demonstrated along with a linearization system noise floor of -130 to -110 dBc, all achieved from a +45- to +46-dBm RF output power level with 23-27% LDMOS RFPA drain efficiency.