Twin nonlinearity generator‐based analog predistorter for small‐cell power amplifiers

In this article, a simple analog predistorter (APD), named twin nonlinearity generator based APD (TNG-APD) using the pseudomorphic high electron mobility transistor (pHEMT), is proposed for linearizing small-cell radio frequency power amplifiers (RFPAs) in the fifth-generation mobile communication system (5G). The TNG-APD is composed of two cascaded common-source field effect transistors (FETs) and a phase shifter. To verify the linearization, a TNG-APD circuit operating at central frequency of 3.5 GHz is fabricated to linearize wideband RFPAs. The RFPA under the test in this article is a 1-W RFPA for 5G small-cell basestations. The measurement results show that the adjacent channel power ratio (ACPR) of the RFPA is suppressed by more than 15 dB under a 100 MHz bandwidth 5G new radio (5G-NR) signal with simultaneous quadrature phase shift keying (QPSK) modulation and 256-quadrature amplitude modulation (256QAM), and more than 7 dB under a 200 MHz bandwidth 64 QAM signal. The measured error vector magnitude (EVM) under the 100 MHz 5G-NR signal is improved from 6.2% to 2.3%. Therefore, the proposed TNG-APD has high potential to linearize wideband RFPAs in the 5G small-cell basestation.