The Design Of Dual-Band Doherty Power Amplifier And Digital Pre-Distortion

At the moment that everything is interconnected and the rate of communication is increasing,the RF front end presents the characteristic of multi-mode work.The performance of communication systems is directly affected by the RF power amplifiers,which is the key component when the base station works in the downlink.The Doherty RF power amplifier has attracted wide attention since it was proposed,which can maintain the feature of high efficiency at power back-off point.Thus,it’s with the development of good vision when we combine the Doherty circuit and the multi-mode characteristic.Besides,it’s a good solution of introducing digital pre-distortion into Doherty circuit at the present stage in order to further improve the linearity of power amplifier.The main works of the thesis as follow:(1)A Doherty power amplifier operating at 2.14GHz is designed and realized,which is based on the NPTB00004.The circuit is simulated with ADS and then fabricated and tested.It achieves efficiencies of up to 55%at peak power(39dBm,8W)point and 41%at back-off power(33dBm,8W)point.(2)A dual-band Doherty power amplifier operating at 957MHz and 2300MHz is designed and realized,which is based on the CREE CGH40010F.Taking the Pi-type micro-strip line as the basic structure,dual-band matching is realized in the input matching circuit,output matching circuit and combining circuit.The power divider circuit adopts the broadband design.The dual-band Doherty circuit is simulated and the optimum structure parameters are obtained.The power amplifier is fabricated and tested.And the measured results are analyzed.(3)To further improve the adjacent channel leakage ratio of power amplifier,a co-simulation of ADS Ptolemy and MATLAB is adopted.Digital pre-distortion is performed at the simulation level.The baseband data is extracted from the input and output of the Doherty amplifier in the ADS Ptolemy,and then imported into the MATLAB.The behavior model of Doherty power amplifier is established in the MATLAB,which is based on the generalized memory polynomial model.The DPD model is established in the inverse process of behavior model in the same order and then the pre-distortion data is passed back to the ADS Ptolemy.The improved spectrum and the better ACLR are obtained from the simulation.And the simulated results are analyzed.