| Power amplifier is an important device in the wireless communication base station. Located at the end of the transmitter, it connects to the antenna and transmits power signal. PA produces most of the nonlinear distortion in the base station, so the linearity of PA will affect the emission performance of base station and communicating quality. PA is also the device that consume most power and produce most heat, and its working efficiency will affect the power consumption,stability and temperature. So the linearization and efficiency enhancement are two key techniques in the base station. But there are many problems in present-day technological developments of PA. Based on the practice applications of PA system, this dissertation is focused on the linearity and efficiency of three types PA.First of all, general analysis methods of PA, including linearity and efficiency, are presented and summarized. The relationship of optimal impedance and electrical characteristics of transistors at maximum output power, is analyzed based on the power match, which is the key difference between PA and small signal amplifier. Then the loadpull contours obtained from the nonoptimal impedance, and the math model for nonlinearity, are analyzed.In this dissertation, chapter three, four and five are focused on three types PA in two categories techniques of efficiency enhancement, which is LINC, Doherty and ET, respectively:1,LINC PA belongs to the first category that is called load modulation. The key design of LINC efficiency is its combiner. Among various kinds of combiner for LINC, Chireix can bring higher efficiency since there is no isolation resistor and the related power consumption, so it will be discussed and designed in this dissertation. Then the phase loadpull in Chireix combiner is analyzed in details. The input impedance of Chireix combiner is obtained based on the loadpull contours. Based on the characteristic of impedance, a novel impedance match method between PA and combiner is proposed, to improve the saturate power and the efficiency in the backoff region of output power. The validity to improve performance and the convenience to circuit tuning of this method are proved by implementation and measurement.2,Doherty PA also belongs to the category of load modulation. Being different from LINC, the loadpull type in Doherty is power pull. Although Doherty is the mainstream PA in modern wireless base station, there are many problems to be solved. In this dissertation, the threshold voltage of transistor drain that caused Doherty can not achieve ideal power backoff, is analyzed. Based on this, a novel improvement method to reach the desired power back-off, is presented by increasing the impedance seen by main power amplifier in the power back-off region. The validity of this method to improve output power backoff and efficiency is proved by simulation results.3,ET PA belongs to the second category that is called power supply modulation. This kind PA can improve efficiency by modifying the drain supply according to the amplitude of input signal. The linearity of ETPA is deteriorated because of the dynamic supply, so the performance of DPD linearization with traditional memory polynomial model of PA has some difficulties. In this dissertation, the impact to the circuit parameter caused by the time-varied supply is discussed. Especially the drain-source parasitical capacitor at the pin of transistor is varied with the power supply, and the match is also changed. Based on the analysis, the improvement of traditional memory polynomial model is presented, by adding cross term of current and memory signals. The validation of this new model to improve performance of DPD in ETPA is proved by simulation results, for both high and low power output with single carrier and multiple carriers.
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