| Due to the rapidly developed wireless communication technology, varies of wireless equipments have rushed into our lives, which make the spectrum become more and more crowded. Amplifier is a crucial element of the wireless communications, but due to its nonlinear effects and strong interference, it will seriously affect the quality of communication without any linearization processing. Besides the linearity, the power added efficiency(PAE) is another important factor of the amplifier. Generally speaking, the traditional high linearity amplifier with low PAE, in order to solve the paradox, this thesis will discuss and process the following.The linearization technology and efficiency enhancement technology are introduced firstly, and their advantages and disadvantages are compared, meanwhile the research status of high efficiency and low distortion technology are briefly described. Then the basic knowledge of amplifier is introduced, including operating modes, nonlinear characteristics, nonlinear index, etc. Eventually, based on theoretical study and scheme analysis, the out-of-band termination technique is combined with the dynamic bias technique to achieve the high efficiency and low distortion.The reason as to generating the third order intermodulation(IMD3) has been analyzed, and the expression of third order intermodulation has been studied to present the effect of parameters. In some cases, when the input power reaches to near the 1dB compress point, the IMD3 will appear a minimal point, which is called the IMD sweet spot. Since it appears at high input power, the PAE of amplifier will also be high. Based on this, the high efficiency and low distortion can be obtained by adjusting the bias under the given condition of linearity and input power.To verify this scheme, the NPN Silicon Germanium RF Transistor BFP620 of Infineon has been used, and the center frequency is 2.4GHz. The baseband shorted stub and 2nd harmonic shorted stub are added to the input and output terminations to obtain the IMD sweet spot. For a given value of IMD3 and base bias, the highest efficiency can be found by adjusting collector bias and input power, and the corresponding value can also be obtained. Lastly, the improvement of efficiency and linearization under all conditions are summarized.The result indicates that when the IMD3 is ?45dBc, the efficiency of amplifier can reach up to 40%, and it also indicates that if the amplifier has the high efficiency and low distortion, its return loss should be low at the center frequency. |
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