Journal
IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES
Volume 64, Issue 7, Pages 2014-2024Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TMTT.2016.2574861
Keywords
Broadband; digital linearization; Doherty; high efficiency; integrated compensating reactance (CR); power amplifiers (PAs)
Categories
Funding
- Science Foundation Ireland [13/RC/2077, 12/IA/1267]
- Science Foundation Ireland (SFI) [12/IA/1267] Funding Source: Science Foundation Ireland (SFI)
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This paper presents a high-efficiency gallium nitride Doherty power amplifier (DPA) using an integrated compensating reactance (CR) for broadband operation. With an additional quarter-wavelength transmission line integrated in the peaking amplifier output, a CR is generated to compensate the load impedance of the carrier amplifier in the low-power region and thus enhance the back-off efficiency over a wide frequency range without affecting the Doherty load modulation at saturation. For this purpose, a peaking output matching network (OMN) is employed to convert the output impedance of the peaking device into quasi-short circuit when it is off and achieve proper impedance matching when it is on. A two-point matching technique using the transmission (ABCD) matrix is employed to design such desired OMN. Measurement results show that the DPA has a 6-dB back-off efficiency of 50%-55% and a saturated efficiency of 57%-71% over the frequency band of 1.7-2.8 GHz (49% fractional bandwidth). When driven by a 20-MHz long term evolution modulated signal at 6.5-dB backoff power, the DPA can achieve an average efficiency of more than 50% with high linearity after linearization over the design frequency band.
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