Design of a Tri-Band Doherty Amplifier Based on Generalized Impedance Inverter

摘要

This paper introduces a methodology for implementing multi-band Doherty power amplifiers. Traditionally, a 90 degrees impedance inverter line is required in Doherty architecture. In this contribution, a generalized impedance inverter line is utilized to construct multi-band Doherty power amplifiers. A tri-band Doherty power amplifier operating at 1.15, 1.85 and 2.55 GHz is designed to validate the proposed method. Measurement results show the fabricated Doherty power amplifier achieves 6 dB output back-off drain efficiencies of 62.3%, 49.3% and 50.5% at 1.15, 1.85 and 2.55 GHz, respectively. The peaking output power of the fabricated tri-band Doherty power amplifier is 43.2, 43.7 and 43.8 dBm with drain efficiencies of 64.5%, 62.2% and 64.5% at three working frequency points, respectively. Furthermore, when the designed Doherty power amplifier is driven by a 20 MHz wideband LTE signal with peak-to-average-power ratio of 6.4 dB, adjacent channel power ratios of -29.4 and -57.1 dBc are achieved before and after digital pre-distortion at 1.85 GHz.