Research On Power Amplifiers Based On Real Frequency Technique

Power amplifiers?PAs? is the key energy consumption cell in the wireless communication systems,so the power amplifier research is of particular importance.PA designers should have sufficient theoretical basis and engineering experience,which requires designers to invest a lot of time and effort,thereby increasing the development costs.To solve this problem,this thesis research a few high-performance power amplifier structures and matching network design methods.Through the study of these contents,the author wishes to provide a theoretical basis for the development of PA design software.Firstly,the techniques of performance improvement for PAs are studied: reducing the optimization variable number,improving the drain efficiency of PAs,suppressing the intermodulation component under concurrent mode and harmonics suppression.For this purpose,a semi-analytic matching network design method,a two-way dual-band architecture and a loss topology at the harmonics are proposed.Secondly,to solve the matching problem of broadband/dual-band PAs,a distributed parameter matching method is proposed via real frequency technique?RFT?.Finally,there is an issue to be solved that RFT is hard to obtain a required matching network for high order matching network.A set of extended Chebyshev function is proposed to solve this problem.A synthesis method is also proposed to ensure a successful synthesis of the high order impedance function.The main contents and innovation points of this dissertation are listed as followed:1.A semi-analytic matching network design method is proposed for PAs.The matching network is composed of commensurate transmission lines with this approach,which can reduce the number of optimization variables by half.Moreover,it can achieve the similar results as the circuit consisted of lumped elements.To further decrease the number of the variable for each matching network,this design method is divided into three steps.In this way,the target matching network can be found quickly.To verify the proposed method,a dual-band PA at 2.4/3.5GHz and an ultra wideband PA covering 0.9-2 GHz are designed.2.A two-way dual-band architecture which can suppress the harmonics and prevent useless intermodulation component is proposed to obtain an optimal performance at the two bands.This architecture is validated by two PAs,one of which is a 0.9/1.8 GHz dual-band PA and the other is a 1.8/2.5 GHz dual-band Doherty PA.A loss topology at the harmonics is also proposed in this thesis,which can suppress the harmonics and reduce the influence of harmonic impedance mismatch at the load.This structure is validated by a broadband PA of 1.6-2.6 GHz.3.A distributed parameter broadband matching method is proposed for power amplifier via RFT.A new cost function is adopted to describe the matching state better,and Richards transformation is applied to obtain a distributed matching network directly.A broadband PA from 0.9 to 2.8 GHz is designed to validate the proposed method.According to measurement results,the output power of about 39.5 d Bm,power added efficiency of 52.2%-85.1% and gain of 14.2-16.8 d B are achieved in the operation band.4.A sub-optimal dual-band matching method is proposed for power amplifier via RFT.This method extends the impedance design space,and it has a relation of region-to-region between the required fundamental and second harmonic impedances.Meanwhile,an enhanced cost function based on driving point function that could better describe harmonic impedance mismatching degree is also proposed for harmonic impedances control.A dual-band PA is designed to demonstrate the proposed matching method.The gain at the two bands are respectively 10.6 d B and 11.2 d B with the saturated output power of 40.6 d Bm and 41.2 d Bm,and the drain efficiency is respectively 70.3% and 71.4%.5.A new method named “Feldtkeller correction approach” is proposed to synthesize impedance function.With this method,the remaining impedance function?Zin?is corrected after each element is extracted from Zin,making it possible to ensure a successful synthesis.To demonstrate the robustness of this method,several randomly generated impedance functions are tested,and the average relative error of 100 35th-order impedance functions generated randomly is calculated to be 3.7567*10^-5.These results demonstrate that the proposed approach can be used to synthesize the impedance function lower than 36th-order successfully.6.A semi-analytical broadband matching approach is proposed based on the extended Chebyshev function and RFT.As for the extended Chebyshev function,there are still a set of impedance functions when the order and impedance ratio is fixed.The first element extracted from the functions is distributed in a wide range,and the one that can absorb the transistor's parasitic and package parameters will be chosen.In this way,the input impedance at current generator plane will be pure resistor at the fundamental frequency,and it will reach a good matching state.To achieve better performances,real frequency technique is applied to adjust the harmonic impedances preventing it from falling into the low-efficiency region.On the other hand,the proposed extended Chebyshev function can also be used in the design of filter or impedance transformer.To validate the effectiveness of the proposed matching approach,two PAs which respectively operate in the band of 1.7-2.4 GHz and 1.6-3.5 GHz are designed.