Research And Design On 5G High Efficiency And High Back-off Doherty Power Amplifier

RF power amplifier plays an important role in wireless comnunication systems.The Doherty power amplifiers(DPAs)are widely regarded as an effective structure to achieve high efficiency of modulated signals in the output power back-off(OPBO)condition,and therefore have been widely used in base station communication systems.However,with the rapid advent of the 5G communication era,there is an increasing demand for high efficiency and wide OPBO range.Achieving high efficiency and wide OPBO range simultaneously is a significant challenge for DPA designs.In recent years,DPAs based on GaN high electron mobility transistors(HEMTs)have attracted great attention.This is largely due to their outstanding material properties,such as its high cutoff frequency and high power density,especially the excellent trade-off between output power and efficiency.However,the presence of parasitic effect,especially the parasitic capacitance at the output of GaN HEMT,has been a major issue limiting the performance of DPAs' drain efficiency and OPBO range.Therefore,it is of great importance to study the parasitic effects in DPA circuit designs.In this thesis,a high efficient and wide OPBO range DPA based on the parasitic capacitance of the CGH40010 GaN HEMT is proposed.A parallel shorted microstrip line is applied between the transistor output and the output matching network to resonate with the internal output capacitor of the transistor to achieve parasitic capacitance compensation.This achieves high saturation efficiency over a wide OPBO range of higher frequencies.The results of the test indicates that measured drain efficiency(DE)is 67.2?73.3%at saturation and 40.4?52.2%at 6 dB OPBO,over the frequency range from 2.7 to 3.6 GHz,which agrees well with the simulation results.High efficiency of the DPA is observed with saturation output power ranging from 43.9 to 44.7 dBm within the 900MHz bandwidth.Especially in the range of 2.9 GHz to 3.3 GHz,the efficiency after 10 dB power back-off is higher than 40%,and the saturation efficiency is 70.2?73.3%.When excited by a 20 MHz LTE signal with a 7.5 dB PAPR,the proposed DPA combined with digital predistortion(DPD)achieves an adjacent channel leakage ratio(ACLR)of less than-47.2 dBc.The measured results show that the design of DPA is innovative and feasible.