Design of Doherty Power Amplifiers for Handset Applications

In this paper, we analyze the power drive of a Doherty power amplifier (PA), and introduce a technique for proper input dividing without a coupler. For the proper Doherty operation, we place a phase compensation circuit at the input of the carrier amplifier. We also propose an output matching of Doherty PA to reduce the number of matching components, and to match the output impedances to enhance efficiency and linearity in consideration of the uneven input drive. The PA circuit is fabricated using a 2-μm InGaP/GaAs heterojunction bipolar transistor process and combined for Doherty operation using merged lumped components. For the IEEE 802.16e m-WiMAX signal, which has a 9.54-dB crest factor and 8.75-MHz bandwidth, the PA has an error vector magnitude of 3% and a power-added efficiency of 40.2% at an output power of 26 dBm.