Abstract
Recognizing that the ratio of the peaking and main amplifier transconductances is a crucial parameter in the design of Doherty power amplifiers, we propose an analytical method to specify the optimum value of this ratio. The method is validated both through simulations based on circuit-level model of the Doherty power amplifier and the experiments using a 100 W dual driven symmetrical LDMOS Doherty power amplifier manufactured. According to the experiments, overdriven peaking amplifier is resulting in lower drain voltage at the main side, hence causing low power efficiency. Conversely, underdriven peaking amplifier is saturating the main amplifier, which in turn results in decreased linearity. Both simulation and experimental results clearly revealed that the amplifier efficiency and linearity strongly depend on the drive levels of the main and peaking amplifiers. The third-order intermodulation distortion of a 44 dBm and 2.655 GHz Doherty power amplifier which is measured as − 29.75 dBc in the overdriven case, is increased up to − 19.40 dBc in the underdriven case. However, the drain efficiency which is measured at 47.84% in the overdriven case is improved to 54.36% when the peaking amplifier is operated in the underdriven mode for 47 dBm and 2.655 GHz.
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