Design of Doherty RFPA for Mobile WiMAX Base Stations.
RF power amplifiers in mobile WiMAX transceivers operate in an inherently nonlinear manner. It is possible to amplify the signal in the linear region, and avoid distortion, using output power back-off; however, this approach may suffer significant reduction in efficiency and power output. This paper investigates the use of Doherty techniques instead of back-off, to simultaneously achieve good efficiency and acceptable linearity. A 3.5 GHz Doherty RFPA has been designed and optimized using a large signal model simulation of the active device, and performance analysis under different drive levels. However, the Doherty EVM is generally poor for mobile WiMAX. Linearity may be improved by further digital pre-distortion, and a simple pre-distortion method using forward and reverse AM-AM and AM-PM modeling. Measurements on the realized amplifier show that this approach satisfies the EVM requirements for WiMAX base stations. It exhibits a PAE over 60%, and increases the maximum linear output power to 43 dBm, whilst improving the EVM.
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ABSTRACT: The road towards the reduction in the carbon footprint associated with power-hungry wireless communication devices will require a holistic design approach to ensure that energy saving can be achieved throughout the entire system. The information and communication technology today accounted for 3 and 2% global power consumption and global CO2 emissions, respectively, where a significant portion is a result of the power consumption in the radio frequency (RF) power amplifier device. Moreover, tomorrow amplifiers will need to be reconfigurable and host a plethora of modulated signals to support effective signal processing. Therefore performance metrics such as linearity, power efficiency and their trade-off should be at the forefront of the RF power amplifier design. This study proposes an energy-efficient power amplifier design based on the Doherty configuration as part of a green RF front end for mobile WiMAX. The authors extend the classical Doherty to incorporate a three-stage load modulation design with a proposed new output power combiner. The performance of the three-stage load modulation RF power amplifier is compared with the legacy two-stage load modulation technique. The experimental results show that 30 dBm output power can be achieved with 67 power-added efficiency, which represents a 14 improvement over the current state-of-the-art system while meeting the power output requirements for mobile WiMAX.IET Science Measurement ? Technology 05/2012; 6(3-3):117-124. DOI:10.1049/iet-smt.2011.0127 · 0.95 Impact Factor
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