The Thoretical Research Of Digital Frequency Conversion And Realization With Fpga

Along with the functions of communication system are getting more and more complicated, Software-Defined Radio (SDR) becomes the trend of the future communication, which aims to construct an open, standardization, modular general hardware platform. As one of the core technologies emploied by SDR receivers, digital frequency conversion is also widely used, which can directly convert the analog signal into digital processing. This paper focuses on the spectrum transform in the process of frequency conversion and its realization basing on FPGA.The main work and innovation points in this paper include:1) Study the process of spectral transformation in low-pass sampling. Throuth putting digital mixing into an equivalent of analog mixing, spectrum after sampling can be divided into three cases:all low pass sampling, low pass and band pass sampling and spectrum aliasing sampling. The results show that the most important kind of sampling structure, namely four times the intermediate frequency is a special case in the analysis and the uniqueness is proven.2) Considering the particularity of sine signal, the Brigham theorem which can ensure no spectrum leak after DFT is modified. The chapter four focuses on the causes of spectrum leak:limited numbers sampling and the possible spectrum distortion problem after DFT. A new constraint condition that the sampling number must be even is added and the validity of modified theorem is illustrated using MATLAB.3) In the hardware design of the digital frequency conversion, the relation between ADC’s quantization amplitude and PAPR is analyzed, which is based on the PCM mathematical model. The derived result can directly guide the chip selection of ADC and in the practical application ADC should be left three allowances.This paper results from the spectral analysis and the conclusion can be applied in platform design. In the end, the designed hardware platform is tested. Clock phase noise, signal carrier and five carrier wave frequency conversions are included in the design contents.