Research On Doherty Power Amplier For Wireless Communication

After the emergence of mobile phone in the 1980 s,the wireless communication technology has been experiencing ever-increasing development.Now,it has dominated people's life and communication.With the rapid development of wireless communication industry,our demand for large capacity information is also increasing.The requirement of wireless communication technology is becoming more and more stringent.Power amplifier(PA)is the most energy-intensive component of a wireless communication system.Its efficiency is crucial to the energy consumption of the whole system.we should be committed to improving its efficiency to ensure saving and environmental protection.Because of the increasing demand for large information capacity transmission,a variety of complex modulation schemes have been widely used.As a result,signals often have high peak-to-average ratios(PAPRs).When dealing with these signals,traditional PA is difficult to guarantee efficient both in back-off region and saturated region.Therefore,sophisticated PA structures represented by Doherty power amplifier has become the mainstream configuration.This structure is usually composed of two different-biased sub-amplifiers,i.e peak PA and carrier PAs.The carrier PA is class-AB mode and the peak PA is class-C mode.So,when dealing with signals,two sub amplifiers conduct in turn with the increase of input power.The peak PA is conducted when the carrier PA reaches saturation.This operating principle can ensure that the PA is able to efficiently amplify the signal both in the back-off region and saturation region.This thesis mainly presents some research on the Doherty PA(DPA).The traditional Doherty structure has obvious shortage in terms of large bandwidth because the load modulation network(LMN)is composed of two quarter-wave transmission lines,whose impedances are sensitive to frequency.So the impedance is difficult to remain stable in a wide frequency range.As a result,it is difficult to broaden the bandwidth of the DPA.The noble LMN in this thesis can greatly limit the drift with the frequency and keep impedance stable.Furthermore,with the increasing demand for large-capacity information,the signals in the wireless communication system become more and more complex and the PAPRs is higher than ever before.In response to this situation,we should make the DPA efficient in a greater power range.Compared to the traditional two-way DPA,the three-way DPA can efficiently process the signals with higher PAPRs.The impedance drift also exists in the three-way DPA.So,we must also optimize the LMN.In this thesis,a new load modulation network with a shunt quarter-wave short stub isintroduced for bandwidth extension.Then author designed a three-way Doherty power amplifier to demonstrate the effectiveness.The test results show that it is readily observed that drain efficiency??%53 is experimentally achieved in a 600-MHz bandwidth ranging from 2.0 GHz to 2.6 GHz.The highest value reaches 76% at 2.6 GHz.Besides,at least 43.6 d Bm output power is maintained,with a peak value of 45.4 d Bm at 2.2 GHz.