Design And Implementation Of A Digital Transmitter With Flexible Frequency Conversion Based On FPGA

With the development of wireless communication technology,integrated military combat platforms generally use radio frequency transmitters as the radio frequency front end.However,traditional analog radio frequency transmitters have complex structures,poor flexibility,and single function.FPGAs(Field Programmable Gate Array)based highly integrated and miniaturized digital transmitters have become the focus of research.Combining the actual needs of the military integrated combat platform,in order to optimize the complex architecture and the inability to flexible frequency conversion of current digital transmitter system,the main work of this article is to design and implement a reconfigurable,low-complexity,flexible frequency conversion all-digital transmitter.The all-digital transmitter architecture described in this article is mainly composed of a baseband signal module,a PC peak clipping module,an oversampling module,a digital upconversion module,a quantization modulation module,and a phase calibration module.In a variety of communication scenarios,the performance of digital transmitters is reflected in that the transmitted signal can meet multiple carrier frequencies(1-3 GHz,stepping 40 MHz),multimode modulation(16QAM,QPSK,OFDM),multiple bandwidth(1-40MHz)and multi-channel(4 channels)phase-aligned transmission requirements at a sampling rate of 30.4Gsps.At the same time it has better than-36 d Bc ACPR(adjacent channel power leakage ratio)and-15 d Bm output power,and can also be filtered by an ESC filter Far-end noise.Compared with the existing public digital transmitter structure,the features of this paper are as follows: the first is to use the look-up table mapping method to achieve quantization modulation,which can generate different pulse sequence look-up tables by changing the frequency characteristic values,thereby outputting different carrier frequencies,which reflects the characteristics of highly flexible frequency conversion,also the structure of the look-up table is very simple,which avoids complex real-time calculations and reduces the complexity of the system implementation;the second is to add a PC peak clipping module not only reduces the peak-to-average ratio of the OFDM signal,but also improves the ACPR of the OFDM radio frequency signal.The third is for some scenarios where ACPR needs to be improved,adding constraints on the basis of the original quantized modulation,and regenerating a new pulse sequence look-up table,which can effectively improve the ACPR of the output signal.The fourth is to add a phase calibration module to achieve phase alignment of the output signal of the Multi-Gigabit Transceiver,so that the multi-channel signal after phase calibration can reduce the distortion of subsequent multi-channel signal transmission.It can meet the communication needs of multi-channel massive MIMO,and provide a good foundation for the research and development of diversified and complex new digital transmitters in the future.