Research On Digital Down Conversion Techniques In Digital Signal Processor

With the continuous development of radar technology, digital radar and software-based radar will be the development trend of the future radar. As an important part in radar digital process, wideband digital receiver systems will directly affect the performance of radar signal processing. Therefore, applying the IF digital technology and accomplishing the radar signal processing of digital down conversion in radar signal processor have important theoretical significance and application value.GC5016, as one of the TI Company producing chips which is used for digital down conversion, has high-speed multi-channel and programmable features. This article attempts to apply it in the design of radar signal processor, and obtain a good application effects.In the basic theory of the digital down conversion processing, first of all, the bandpass sampling theorem is researched, and depending on the application conditions, the best sampling theorem without cepstral, general sampling theorem and zero IF sampling theorem are analyzed; secondly, multi-rate digital signal processing technology is studied, both CIC filters and FIR filters which are commonly used in the digital down-conversion process are emphasis in this study; at the same time, a multi-stage filter extraction coefficient distribution formula is presented; finally, the basic principles of signal quadrature demodulation technology is analyzed and the merits of quadrature demodulation technology are given, in the meanwhile, the IQ unbalance which appears in quadrature demodulation process is investigated. Based on results of the analysis, and combining with specific engineering design requirements, the entire digital down conversion system in radar signal processor is simulated with Simulink. The results confirm the theoretical conclusions and provide technical support for follow-up engineering practice.Based on theoretical analysis and simulation results, the digital down conversion system in signal processor is designed in this article, which includes signal ordination modules, IF sampling modules, digital down conversion module and baseband signal processing modules. Aiming at the requirements of the system, the key parameters of digital down conversion system are analyze, and the use method and configuration parameters of GC5016 in radar signal processor are given.Using the scheme, radar signal processor with digital down conversion system is completely designed. In order to verify system performance, the signal processor performance tests are carried out, including frequency test, synchronization test, amplitude, phase coherence test and signal to noise ratio analysis test. The results shows that the signal processors can preferably complete the signal processing of digital down conversion, and the IQ channels possess good amplitude and phase coherence, and have the higher SNR.