The Hardware Design Of Optional Spectrum Signal Generator

The real-time property of optional spectrum signal generator in signalreconstruction, the high precision characteristic of digital quadrature modulatormust be carried out by high-powered digital signal processing system. Based onthe analysis of different architectures and real-time properties of distributedparallel signal processing system, two kinds of distributed high-speed paralleldigital quadrature modulation system based on PC and multiple digital signalprocessors (DSP) are presented in this paper, of which the digital quadraturemodulators based on digital signal processing algorithm or direct digitalfrequency synthesizer (DDS) both possess higher ratio of signal to noise incontrast to the method of conventional linear digital quadrature modulation.AD9857 is the core of the digital quadrature modulator based on DDS. Theinternal structure and operating principle of the up-converter (AD9857) areanalyzed in this paper. In order to realize interpolation and low-pass filter highefficiently, the method of digital quadrature modulation based on cascadeintegral comb (CIC) filter used by AD9857 is analyzed by computer simulation.The hardware achieving principle and method of the digital quadraturemodulator is presented in this paper, and then the eight-channel parallel digitalquadrature modulation system based on DDS is developed. At the same time, inorder to realize high-speed data exchange between PC and the eight-channeldigital quadrature modulators, the USB2.0 data transfer system based onEZ-USB FX2 is developed in this paper, which reduces the electromagneticinterference between PC and digital signal processing system maximum,improves the reliability of the hardware system and the speed of data transfer inthe signal processing system. At last, the hardware design of the eight-channeldigital quadrature modulation system is achieved on the whole. The hardwaresystem of three-channel digital quadrature modulators based on DSP, universalserial bus (USB) and digital-analog convertor (DAC) is also designed andanalyzed in this paper, besides, the functions of the hardware system (DSPsystem, DAC system and data passage) are tested, eventually, the performanceof the hardware system is tested, and the actual signal reconstruction accuracy(SNR) is over 65dB, which reachs the domestic advanced level.