The Design Of Broadband High-Efficiency Power Amplifier Integrated With Filtering Characteristic

The new generation communication system has been developed towards highly efficient and miniaturization,however,the power amplifier and filter in the traditional radio frequency front end were separately designed and simply cascaded among the most design methods to amplify and filter the signal.These methods cause the large circuit size and additional energy dissipation at the same time.The filtering power amplifier can effectively improve the filter characteristics and linearity of the traditional power amplifier and greatly reduce the insertion loss and design complexity of the circuit system.Therefore,the broadband high efficiency power amplifier integrated with filtering characteristic has become one of research hotspot in recent years.This thesis starts from the design of broadband filter matching network and design two power amplifiers with wide bandwidth,high efficiency and excellent filtering characteristics,realizing the bandwidth expansion and efficiency improvement of filtering power amplifier.The main work and innovation points of this paper are as follows:(1)A novel broadband bandpass filtering impedance transformer was proposed,which consists of a terminated coupled line structure and impedance tuning network.This structure can match the fundamental and the second harmonic impedance of the transistor perfectly,and the working bandwidth and efficiency of the filter power amplifier are significantly improved.A broadband high efficiency filter power amplifier is designed according the proposed filter matching network.Measured results show the drain efficiencies are all above 69%in the working band of 2.0-2.4GHz with 400MHz bandwidth.At the 2.2GHz central frequency point with the best matching characteristics,the drain efficiency reaches 78.2%.In addition,the rejection level was larger than 52.8dB and 31dB for the lower and higher suppression band respectively,which shows an excellent filtering characteristic.(2)A design method of improving filtering broadband high-efficiency Doherty power amplifier(DPA)based on post-matching topology was proposed.The filtering characteristic of the proposed DPA is improved by a post-matching network and a wideband power divider network with filtering function.The proposed novel post-matching network is composed of one coupled line and two microstrip stubs.Simulated results show that the proposed post-matching network can improve the IMD2 about 20dB compared with a low-pass post-matching network.The measurement results show that drain efficiencies of the proposed DPA at the saturation power level and 6-dB output back-off(OBO)are 60.1%-65.5%and 48%-53%,respectively,in the 2.2-2.6GHz band.Meanwhile,a good filtering performance was obtained.For lower and higher rejection bands,the suppression levels are greater than 29.2dB and 41.1dB,respectively.The measured adjacent channel power ratios(ACPRs)of 20MHz-LTE signal are-51.8dBc and-51.2dBc after digital predistortion.The two power amplifiers designed and implemented in this thesis both have good performances,which are of great practical significance for the exploration and development of filtering power amplifiers,and they have large application value in the miniaturized and green mobile communication system.