The Research And Realization Of AD Frequency Transformation Based On DSP

With the unceasing development of digital signal processing technique, AD converter device has been widely used in sampling of various analog signal and processing of digital signal, meanwhile, the ideal framework of modern wireless communication is to digitalize directly in radio frequency, that is to say, based on ultrahigh speed ADC and high performance digital signal processor, to achieve radio frequency sampling of analog signal, which is easy to realize because of the present technical reason, so that we could realize the down-sampling of intermediate frequency directly in virtue of high speed ADC and DSP relatively. Therefore, taking advantage of AD device and digital filtering technique to realize mixing and other frequency transformation function is a comparatively advanced, novel and practical method. In the paper, we advanced the method of mixing function by means of AD and DSP software programming, which is a typical application of frequency transformation with AD and digital filter.The design is based on the idea of realizing frequency transformation combining AD converter and DSP. In which deep research and discussion in the frequency transformation function with AD convert circuit are made, the theory of frequency transformation are Depicted systematically, and the band-pass sampling, decimation and the relative theory in multi-rate signal processing are discussed sufficiently. The design also realizes FIR digital filter with DSP, and with the help of software programming intermediate frequency band-pass sampling and filtering are implemented, that is, directly realizes down-sampling at the intermediate frequency as well as modulation and demodulation of AM signal taking advantage of digital method. The receive frequency range is 0~30MHz band-pass signal. The system consists of two parts: analog part and digital part. As for the analog part there are analog audio input, analog high-frequency input, and DA analog output. The digital part is responsible for combining digital signal processor DSP with ADC to realize frequency spectrum remove, which is to realize the function of modulation and demodulation. The whole hardware system is mainly composed of ADC, DAC, DSP, CPLD, etc. while DSP is the main controller;we expandthe external FLASH and SRAM. In addition, the system peripheral interface contains USB, serial port, which is used to realize data communication with computer. I have accomplished the system schematic design and layout;in this case, I finish the prospect task of the paper with the help of ready made DSK, and complete the software for frequency transformation. Seen from the experiment waveform, the ADC and DSP based system could realize the digital frequency transformation very well, which will be a good way to simplify frequency transformation circuit, which has a significant meaning in the usability of ADC and DSP in communication signal processing.