Bandwidth broadening technique for harmonic-tuned power amplifiers at 5G new-radio FR2

Conventionally, harmonic-tuned power amplifier (PA) suffered from the difficulty of achieving broadband harmonic suppression for the performance enhancement. The main focus of this work is to figure out the dominant factor limiting the operating bandwidth of harmonic-tuned amplifier. Based on the theoretical analysis, the drain-to-source capacitance (C_ds) was identified as the dominant factor impacting the frequency dependence of the optimum load impedance. We thus proposed the stacked-FET configuration for C_ds reduction to achieve bandwidth broadening. The fabricated PA delivers a saturated output power (P_sat) of 30.6–30.8 dBm, and a maximum power-added-efficiency (PAE) of 34.9–37.7 % from 36 to 40 GHz. The measured PAE exhibits low variation with frequency across the operating band, which was achieved through reducing the C_ds for broadband harmonic tuning. Moreover, the linearity performance was evaluated using standard 400-MHz 256-QAM 5G NR signal, where an error-vector-magnitude (EVM) of −30.2 dB was measured while delivering an average output power of 25.2 dBm at 38 GHz.