Compact design of linear Doherty power amplifier with harmonic control for handset applications

A highly linear and efficient Doherty power amplifier (PA) for handset applications is presented. To improve the performances, we analyze the Doherty operation with respect to harmonic load conditions. The fundamental and harmonic loads are implemented using the output capacitor of the device and a lumped quarter-wave transformer. By using elaborate matching techniques, the size issue of a Doherty amplifier is overcome. The Doherty PA is implemented using an InGaP/GaAs heterojunction bipolar transistor and is tested at 1.9 GHz using a long-term evolution signal with 16-quadrature amplitude modulation, 7.5-dB peak-to-average power ratio, and 10-MHz bandwidth. The PA with a 3.4 V supply voltage delivers a power-added efficiency of 45.8% and an evolved universal terrestrial radio access adjacent channel leakage ratio (E - UTRAACLR) of -35 dBc at an average output power of 27.5 dBm.