Bandwidth Optimization of Doherty Power Amplifier Based on Source Converters for 5G Mobile Handsets

In this study, wideband Doherty power amplifiers (DPAs) based on converters comprising one transformer and two capacitors are investigated. Moreover, the parallel and series-type Doherty combiners are investigated. The series-type Doherty combiner is shown to have wider characteristics than the parallel-type converter-based Doherty combiner via numerical analysis. An approximate analysis was applied to the series-type combiner, and a quasi-optimum design parameter was derived for wideband matching. A quasi-optimum design parameter was compared with a true optimum solution derived by numerical analysis, and its certainty was verified. A combiner with parameters close to the true optimum solution was designed and evaluated. A DPA fabricated using this combiner was adequately small for a 5G mobile handset and could be operated in the frequency range of 2.2-2.7 GHz with efficiency exceeding 35% and a sufficiently low distortion under an amplifying wideband modulated signal [fractional bandwidth (FBW): 4% = 0.1/2.5 GHz]. The proposed combiner and its design techniques helped in designing a compact and long battery life of 5G mobile phones with high data throughput at a few gigahertz frequency ranges.