A 5-GHz Quadrature Switched-Capacitor Power Amplifier With IQ-Cell-Sharing and Serial Transformer Combiner in 28-nm CMOS

This letter presents a 5-GHz quadrature digital power amplifier (DPA) with serial transformer power combiner and in-phase and quadrature (IQ)-cell-sharing, which overcomes the 3-dB power loss in the conventional quadrature counterpart. A four-way differential serial-combining transformer (SCT) power combiner is adopted for output power close to the watt level. Implemented in 28-nm CMOS technology, the DPA is powered by 1.1-/2.2-V power supplies and only occupies
$0.98\times 0.58$
mm2 core area. It achieves 28.6-dBm peak output power with power added efficiency (PAE) of 24.4% at 5 GHz. With 20-MHz 64-quadraticamplitude modulation (QAM) 802.11ac signal, the DPA achieves Pavg of 18.6 dBm and average PAE of 10.7% with −25.0 dB error vector magnitude (EVM) at 5 GHz with digital predistortion (DPD).