Research On High Efficiency Power Amplifier Based On Doherty Technique For LTE

The3G/4G communication system commonly adopts technologies which havehigh data transmission rate, high frequency spectrum utilization of multi-carriertechnology, such as OFDM. The modulation envelope of the signal has a high PAPR.Non-constant envelope signal amplified by nonlinear amplifier will produce in-bandsignal distortion and spectral leakage. This increases difficulty in the design of theamplifier. Therefore, the research in a high peak-to-average ratio signal, high-efficiencypower amplifier is a hot issue of the moment. Doherty structure is a more modernamplifier technology, which is more mature and easily integrated with technologieswhich improve the power amplifier efficiency and linearity etc. the Doherty architectureis widely deployed in modern communication systems.On the base of Doherty principle, an adaptive power divider structure is proposed.The structure can flexibly adjust the input power distribution ratio to improve theefficiency of the Doherty structure within a wider power range. By researching Dohertystructure’s power allocation ratio and the theoretical analysis, circuit simulation resultsshow that the proposed adaptive power divider structure can improve the power addedefficiency linear with only poorly degree linearity. This paper also studied thepower-added efficiency and linearity on different working conditions of the carrier andpeak amplifiers in Doherty structure.In order to achieve the design specifications, the entire LTE amplifier systemincludes a driver amplifier and a final stage amplifier. The driver amplifier is added inorder to archive enough link gain. The final amplifier circuit introduced the adaptivepower divider Doherty structure. Then a detailed description of the driver amplifier andthe final amplifier design process are shown. Using ADS software to simulate thepower-added efficiency and third-order intermediation characteristics of Dohertystructure which contains the adaptive power divider simulation. Compared withtraditional Doherty structure which had normal power divider, the proposed adaptivestructure can improve the power added efficiency in a wider power range and only asmall deterioration in linearity. Finally, the overall amplifier system are produced and tested. The test results andsimulation results are very close, proved that the proposed adaptive power dividerstructure is indeed to improve the Doherty structure’s power added efficiency. There issome practical value in communication applications.