Electronically Tunable Doherty Power Amplifier for Multi-Mode Multi-Band Base Stations

This paper proposes an electronically reconfigurable Doherty amplifier capable of efficiently amplifying multi-standard multi-band wireless signals centered at widely spaced frequencies. The paper outlines closed form equations for an effective design methodology of frequency agile Doherty amplifiers driven with multi-mode signals using a small number of electronically tunable devices. As a proof of concept, a reconfigurable Doherty prototype is designed and fabricated to operate at 1.9, 2.14, and 2.6 GHz meant to efficiently amplify signals with peak-to-average power ratio equal to 6, 9 and 12 dB. The measurement results obtained using continuous wave signals reveal drain efficiencies of about 67% and 42% at the peak power and 12 dB output back off power respectively for the three operating frequencies. In addition, the reconfigurable Doherty amplifier is successfully linearized when driven with 20 MHz wideband code-division multiple access and 20 MHz long term evolution signals, using a Volterra based digital predistrtion algorithm which exploits a pruned Volterra series.