A 28-GHz 20.4-dBm CMOS Power Amplifier with Adaptive Common-Gate Cross Feedback Linearization

A 28-GHz power amplifier (PA) with adaptive cross feedback (ACF) is presented. The ACF is employed by an adaptively controllable RC-feedback circuit from the source to the opposite drain nodes of the common-gate (CG) stages in a differential cascode amplifier. The proposed ACF makes the PA stable even with large power transistors. It also linearizes the PA by decreasing the feedback adaptively at high powers which improves amplitude distortion (AM-AM) and power-added efficiency (PAE) as well as the saturation power (P-Sat). The proposed PA is implemented with a 28-nm bulk CMOS process with a 0.144 um(2) core chip area. It is shown that the ACF increases P-Sat, peak PAE, and output 1-dB gain compression point (OP1dB) from 20.1 dBm to 20.4 dBm, 34% to 37.2%, and 17.4 dBm to 18.2 dBm, respectively at 28.5 GHz. The proposed PA shows a 28-dB peak gain at 28.6 GHz with 26.8 GHz to 30.8 GHz (14.0%) 3-dB gain bandwidth, which is the highest P-Sat and gain among the reported Ka-band bulk CMOS PAs.