A Wideband Pulse-Modulated Polar Transmitter With Low-Complexity Digital Predistortion

In this letter, a wide bandwidth power amplifier (PA) using pulse modulation is presented. Pulse modulation significantly reduces the amount of thermal memory. However, with a large signal bandwidth, significant matching-related memory effect exists. A compensation equalization filter is proposed to compensate the in-band gain/phase variation, such that simple memoryless digital predistortion (DPD) can still be utilized. A prototype transmitter system is constructed using a commercially available base station PA for validation. Measurements are performed using a 256-QAM fifth-generation new radio (5G NR) downlink multicarrier modulated signal at 3500 MHz with an instantaneous bandwidth of 100 MHz. Using memoryless DPD and the proposed filter, the overall system achieved passing the -45-dBc downlink spectral requirements for the 5G NR standard showing negligible thermal memory effect in PAs using pulse modulation.