| Nowadays,wireless communication and semiconductor chip have been applied into every aspect of our life.Cellphone communication,Wi-Fi,Satellite Television,radar communication and giant server have changed our lifestyle.GaN power amplifier is one of the most important rendezvous points of wireless communication and semiconductor chip.On one hand,it can be used in the next generation of wireless communication mode,meeting the needs of high power,high efficiency and large bandwidth.On the other hand,it is outstanding among the third generation of compound semiconductor and contains excellent performance.In this paper,the material growth of AlGaN/GaN and the fabricating process of HEMT device are described,and the equivalent circuit model is established.Furthermore,the researches on high power,high efficiency and large bandwidth GaN power amplifiers are studied in detail.New theoretical methods are proposed,thus an X-band high power amplifier,an X-band high efficiency power amplifier and a C-band wideband power amplifier are realized.The main research results in this paper are listed:1,AlGaN/GaN HEMT fabricating process is presented and the equivalent circuit model is established.The working principle of AlGaN/GaN HEMT is introduced,the forming mechanism of 2DEG is analyzed,the growth process of AlGaN/GaN heterojunction material is illustrated,and the fabricating process of HEMT is described.The performances of HEMT,including DC,frequency and power properties,are characterized and analyzed.The equivalent circuit model is established,and the parameters are extracted by DC characteristics and S-parameters at different conditions.The model fits well with the device characteristics and provides the foundation for the following circuit design.2,An X-band 100W internally-matched power amplifier is developed.The optimal source and load impedances of 1.25mm gate width AlGaN/GaN HEMT are measured by Loadpull technology,and are expanded to large gate width device proportionally.Impedance matching is realized by T-type matching network and power divider,and the two-cell combined X-band internally-matched power amplifier is further implemented.An X-band test fixture with good transmission and reflection characteristics is designed and manufactured.The measurement results show that the power amplifier has 110W saturation output power and 53.1%maximum PAE at 8GHz.3,X-band 200W power combined amplifiers are manufactured.Two methods are proposed to realize 200W power combined amplifier.The first way is combining two 100W internally-matched power amplifiers by Wilkinson power divider outside the package.A cavity shielding box is fabricated to measure the performance.The power amplifier shows saturation power of 207W,maximum PAE of 53.0%and power gain of 10.0dB.The second way is using the 8-way internally-matched divider with good transmission,reflection and isolation characteristics,and T-type matching network to combine four chips inside the package.This method reduces the interference between chips,and decreases the size of the 200W power amplifier to 1/37 of the first method.4,A theoretical research on the third harmonic of high efficiency class-F power amplifier is carried out.We analyze some usual methods to improve PAE,and point out that class-F and inverse class-F(class-F-1)design methods are two effective ways at high frequencies.The results show that appropriate third harmonic voltage component can modulate the output waveform of class-F power amplifier and improve the fundamental harmonic power and efficiency.The effect of?I-V Knee effect?decreasing the power and efficiency of class-F power amplifier is discussed.The optimum third harmonic components with and without?I-V Knee effect?are compared.The conclusion is that the?I-V Knee effect?makes the optimum third harmonic impedance deviate from the ideal open point of class-F power amplifier.5,An X-band class-F-1 internally-matched power amplifier is realized.The influence of the parasitic parameters on class-F-1 harmonic impedance at different frequencies is analyzed.Output capacitance Cds affects the harmonic impedance at X-band seriously,thus HEMT die plane is not the best design reference plane any more.By the compensation design method,second harmonic open and third harmonic short are realized at current source plane,and the current and voltage waveform overlap and harmonic power decrease.Therefore the class-F-1 impedance condition,waveform condition and spectrum condition are realized.The measurement results show that,in continuous wave mode,the class-F-1power amplifier has the PAE of 61.7%which is 16.3%higher than class-AB amplifier realized by the same kind of HEMT at X-band.6,A novel graphical method for dual-frequency matching is presented.We point out that the key of the output matching of power amplifier is matching Loadline to system impedance.Dual-frequency matching is realized by two section microwave line structure.Two intersecting circles are used to describe the dual-frequency matching process at SmithChart,and the matching parameters are solved by geometrical method,where the 1/4wavelength matching at SmithChart is extended from single-frequency to dual-frequency effectively.Compared to the traditional algebra method,the proposed graphical method is simple,intuitive,and contains explicit physical meaning.Simulation and measurement results show that the proposed method can be used in dual-frequency matching and bandwidth extending.7,A C-band wideband 100W internally-matched power amplifier is implemented.The point-to-point Loadline theory is expanded to point-to-area.The theory method to draw the power contours at SmithChart is described,then the contours Popt-1dB are painted,and then the influence of the parasitic parameters on the power contours is analyzed.The system impedance of 50 Ohm is transformed into the Popt-1dB power contours in wideband by two section matching network and a tapered transmission line power divider.Therefore a 5GHz-8GHz wideband 100W power amplifier with the gain flatness less than 1d B is realized. |
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