Broadband and asymmetrical Doherty based on circuit parameter solution space

Abstract

The input impedance of the post-matching network (PMN) is configured as a complex value. The parameter solution space is determined based on the fundamental principles of the Doherty power amplifier (DPA), enabling the DPA to achieve high efficiency at the output power back-off (OBO). The parameter solution space comprises three variables: the phase parameter of the output matching network for the carrier power amplifier (carrier PA), the phase parameter of the output matching network for the peaking power amplifier (peaking PA), and the input impedance of PMN. These parameters are optimized to enable the DPA to achieve high efficiency at the OBO. In this paper, a one-to-one mapping relationship is established between the frequency and the parameter solution space, allowing for a precise optimization of the DPA across a broad frequency range. Leveraging this mapping relationship, an asymmetric DPA designed to operate over the 1.8–2.6 GHz frequency band is designed and fabricated, demonstrating the feasibility and effectiveness of the proposed approach. Under continuous wave excitation, the test results show that the drain efficiency (DE) is 42.7%–56.4% at 9.5 dB OBO and the saturated DE is 45.8%–71.1%. The saturated output power of this DPA is 46.9–48.8 dBm with a gain of 5.5–8.0 dB at saturation. A 20-MHz long-term-evolution modulated signal with a peak-to-average power ratio of 8 dB is also applied to the fabricated DPA at 1.8, 2.1, and 2.6 GHz. Under these conditions, at 8 dB OBO, the DPA shows an adjacent channel power ratio always lower than 48 dBc after digital pre-distortion linearization.

Keywords

Doherty power amplifier / Output matching network / Parameter solution space

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2024 Zhejiang University Press