DESIGNING AN OCTAVE-BANDWIDTH DOHERTY AMPLIFIER USING A NOVEL POWER COMBINATION METHOD

In this paper, an octave bandwidth Doherty power amplifler (DPA) using a novel combiner is presented. The fundamental bandwidth limitation of the load modulation concept of a conventional Doherty structure is solved based on the proposed combination method. For veriflcation, an octave bandwidth asymmetric Doherty architecture is implemented by using gallium-nitride (GaN) HEMT Cree CGH40010 and CGH40025 devices in the carrier and peaking ampliflers, respectively. The carrier and peaking ampliflers are designed to achieve optimal operation with 25› load and source impedances. The reduced load and source impedances simplify the matching circuits for broadband operation. Key building blocks, including the proposed combiner, carrier and peaking ampliflers as well as the 50/25› input power divider, are outlined. The measurement results represent higher than 37% and 52% drain e-ciencies in 6dB load modulation region across the frequency range from 0.85 to 1.85GHz and 0.90 to 1.60GHz, respectively. The implemented Doherty amplifler represents acceptable linearity across the whole operation frequency range. In two-tone signal characterization, the implemented DPA performs with a drain e-ciency of 55% and an inter-modulation distortion (IMD) of i30dBc at an average output power of 41.2dBm at the center operation frequency of 1.35GHz. In order to observe wideband signal characterization, a single carrier wideband code-division multiple access (W-CDMA) signal with a peak-to-average power ratio (PAPR) of 6.5dB is applied and a drain e-ciency of 51% with an adjacent-channel leakage ratio (ACLR) of i31dBc is achieved at an average output power of 38.4dBm.