Ka-Band CMOS Stacked-FET Power Amplifier With Pre-Distorted Driver Stage for 5G Applications

In this study, we proposed a pre-distorted driver of a power amplifier in which the driver stage can serve as a pre-distorter of the power stage. In order to secure the linearity of the power amplifier, AM-PM distortions according to the input power of the common-source (CS) and two stacked-FET structures were analyzed and compared with the simulated results. Based on the analyzed AM-PM distortions of the two structure, it was verified that the driver stage with CS structure can act as a pre-distorter of the power stage with the two stacked-FET structure by optimizing the bias voltages of the two structures. The Ka-band power amplifier was designed with a 65-nm CMOS process to verify the feasibility of the proposed pre-distorted driver stage. At 28 GHz, the measured P1dB, saturated output power (P $_{\mathrm {SAT}}$ ), and peak power-added efficiency (PAE) were 18.6 dBm, 19.7 dBm, and 32.9%, respectively. The measured small signal gain was 24.1 dB. When 5G-NR modulation signals (64-QAM, 100-Msym/s, 9.7-dB PAPR) were used, under conditions where the EVM was less than -25 dB, the measured output power and ACLR were 13.3 dBm and -29.4 dBc, respectively.