The Design Of Doherty Power Amplifier In Digital Repeater Based On WCDMA Standard

With the development of 3G technology,the WCDMA signal is characterized with a higher PAR,in which multi-carrier modulation is adopted.The power amplifiers,class A and AB,using power backoff scheme are difficult to meet the effiency requirement under the condiction of a high PAR,which cause a huge energy dissipation while producing a lot of heat.What's more,it degrades the system performance and raises the production cost.Therefore,enhancing the efficiency of power amplifier is one of the key poinst of 3G based station and repeater.In recent years,with the development of Digital Predistortion Technology(DPD),the linearity of power amplifier has been improved.Then the study and application of Doherty power amplifier in WCDMA digital repeater becomes a hot spot.This paper studies the structure characteristic and working principle of Doherty power amplifier then designs the Doherty power amplifier according to the model of MRF6S21140 LDMOS and adopts the ADS software developed by Agilent company to be the simulation software.Main work including:firstly,optimal designs for bias circuit design,matching network design,and the load modulation are given. Secondly,a design stratege with a comprehensive consideration of offset line network in output match is adopted.Meanwhile,a offset line with appropriate length is added, which offer a solution to the problem of power leakage and improve the performance of Doherty power amplifier.Thirdly,the simulation analysis is presented which is based on WCDMA 3GPP software test platform offered by ADS.Finally,hardware modules are developed to verify the system.The test result shows that,the output power added efficiency of Doherty power amplifier cover the basic needs,when the output power is 43dBm,the efficiency reaches to 22.3%,and when the output power is 47dBm,the efficiency reaches to 38%, at last,under full output power,the efficiency reaches a peak of%48.With the gain of power amplifier exceeds 10dBm,the system fully adapts the application requirement for high efficient power amplifier in WCDMA standard.