  In this article, we present a dual-band 28/38-GHz power amplifier (PA) with
inter-band suppression for millimeter-wave 5G communications. The dual-band
operation is achieved using a center-tapped transformer network with an extra
resonator which can provide optimum load impedance of the transistor in the two
bands and synthesize a short-circuit between the two bands. This feature
suppresses the PA signal emissions in the inter band, commonly allocated for
other applications. A design procedure is developed for the proposed matching
network including physical limits on the quality factor and the coupling
coefficient of the transformer. The PA is designed using a 22-nm fully-depleted
silicon-on-insulator (FD-SOI) CMOS process. The transistor stacking and a
four-path transformer parallel-series power combining techniques are used to
achieve high output power using the low-voltage process. The PA achieves
simulated performance of 22.6/22.0 dBm saturated output power, 19.8/20.0 dBm
output power at 1-dB gain compression, and 33/32 % maximum power-added
efficiency (PAE) at 28/38 GHz. The inter-band suppression is 6 dB at 33 GHz.
