Doherty Power Amplifier Based on Asymmetric Cells with Complex Combining Load

This article presents a Doherty power amplifier (DPA) based on asymmetric cells with a complex combining load (CCL). In this study, a new and intuitive design technique using the Smith chart is proposed for developing the load network of the CCL-DPA. The peaking amplifier consists of a larger cell size compared to that of the carrier amplifier in order to achieve higher power gain and peak output power in comparison with the conventional CCL-DPAs based on symmetric cells. For verification purposes, the proposed asymmetric CCL-DPA was designed and implemented using 6- and 10-W GaN-HEMTs for the carrier and peaking amplifiers, respectively. For the 1.68-GHz continuous-wave signal, the asymmetric CCL-DPA exhibited a power-added efficiency (PAE) of 68.0% and a drain efficiency (DE) of 73.9% at a peak output power of 43.5 dBm. When an output power back-off of 9.5 dB was used, a PAE of 52.0% and a DE of 54.7% were achieved. Using the long-term evolution signal with a peak-to-average power ratio of 9.6 dB and a signal bandwidth of 10 MHz, a PAE of 53.6%, a DE of 56.4%, and a power gain of 13.5 dB were obtained at a power level of 34.0 dBm. Using a digital predistortion technique, an adjacent channel leakage power ratio of -48 dBc was achieved at the same power level.