Analysis and Design of Power Amplifier Using Parallel-Combined Multisegment Transformer

This letter presents a highly efficient power amplifier (PA) using a parallel combined vertical multi-segment transformer for 5G new radio (NR) applications operating in bands n257 and n258, in a 65-nm bulk CMOS process. A multi-segment transformer facilitates a lower provided input impedance than a conventional transformer, enabling the PA to achieve a higher output power. The vertical multi-segment transformer also offers lower insertion loss than the conventional transformer owing to its high coupling factor. In addition, this work demonstrates that utilizing the compact parallel T-line with vertical multi-segment transformers, a low-loss characteristic can be achieved by providing an appropriately low input impedance for high output power. To achieve high efficiency in low-power region, the PA operates in dual-mode by applying discrete power control. The PA achieves 24.87-dBm saturated output power with 40.27% peak power-added efficiency (PAE) at 27 GHz. Furthermore, it achieves average output powers of 17.6 and 13.8 dBm with average PAEs of 14.02 and 12.31% in the high- and low-power modes, respectively, using 800 Msym/s of 5G OFDM using 64-QAM with –25 dB error vector magnitude.