Abstract
We have proposed advanced design methods of Doherty amplifier for high efficiency base station power amplifiers with wide bandwidth. First, we develop Doherty amplifier with uneven power drive which is provided more input power to the peaking cell than the carrier cell for full power operation and appropriate load modulation. Second, we optimize the matching circuits of the carrier and peaking cells individually to enhance the linearity and efficiency. Third, we optimize the bias circuit to solve an asymmetric ACLR (Adjacent Channel Leakage Ratio) characteristics for wideband signals such as WCDMA 4FA. The proposed design methods are applied to implement Doherty amplifier using a MRF5P21180. For a 2.14 GHz WCDMA 4FA signal, the amplifier is optimized at 25 W average output power. The drain efficiency and ACLR measured at the power are 33 % and -41 dBc, which represent about 1.3 % and 3 dB improvements, respectively, compared to the Doherty amplifier with even power drive. Additionally, the PEP of the amplifier is about 180 W, while that of the comparable Doherty amplifier is about 165 W. The difference of ACLR with the bias circuit optimization between lower and upper ACLR is reduced below 2 dB at whole average output power range.
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