Design And Implementation Of A Multi-band RF Front-End On Software Defined Radio

The concept of software radio(Software Defined Radio)was first proposed in the United States in the 1990 s.Compared with the traditional receiver using analog circuit to realize the signal receiving function,the new concept is more willing to implement various functions in the digital domain.The ideal structure of software radio is that ADC or DAC should be close to the antenna end as much as possible,and FPGA and other digital devices should be used to complete the data processing.However,due to the limitation of ADC/DAC conversion rate and FPGA/DSP data processing speed by the device technology level,the existing software radio equipment can not completely abandon the RF front-end module.With the development of the times,the front-end circuit not only needs to be able to complete the reception and transmission of various frequency band signals,but also needs to have miniaturization,low power consumption,high reliability and many other characteristics,using a single ADC to complete the reception of multiple frequency band signals,or receiving as many functional frequency band signals as possible on a single circuit board,all of which work on the transmission of software radio The exhibition has certain promotion significance.First of all,the research background and significance of the subject are described,and the main work of this paper is introduced.Based on the research of the software radio platform architecture proposed by the predecessors,the superheterodyne architecture,zero if architecture,low if architecture and broadband digital direct sampling architecture are compared,the advantages and disadvantages of each common architecture are analyzed,and some main parameters of the RF receiving link are explained,such as sensitivity,noise coefficient,etc.This paper hopes to receive signals in three frequency bands,1258.29-1278.75 MHz,2400-2440 MHz and 8250-8450 MHz.In the design,1258.29-1278.75 MHz and 2400-2440 MHz frequency band signals are received on the same link through RF direct band-pass sampling;8250-8450 MHz frequency band frequency hopping signals are received through two analog down conversion links through more traditional heterodyne structure.Secondly,according to the requirements of the project,the relevant chips are selected,including low-noise amplifier,filter,power divider,etc.,and the gain,noise coefficient and other parameters of the designed RF front-end link are calculatedtheoretically.Through ADS software,the RF front-end link scheme is tested in terms of frequency selectivity,link gain and link noise coefficient It is proved that the verification results are almost consistent with the theoretical calculation results and meet the project index requirements.Then,it introduces the design of some key devices in the link,such as the cascade design of low-noise amplifier,which avoids the cascade self excitation between multiple low-noise amplifiers.For example,the design of frequency synthesizer module,which uses two PLL chips to generate the local vibration signals needed by the link.For example,the design of automatic gain module,which uses the cascade of two voltage control gain chips to complete the automatic gain module with the maximum gain of71 d B The schematic diagram and PCB board are designed by Cadence software.Finally,the hardware of the components and the whole of the multi band RF front-end link is tested,which verifies that the designed link can meet the system requirements.