Design Of Digital Noise Source Based On Direct Digital Frequency Synthesize Technology

With the development of the information technology and the application of microcomputer, the computer becomes the most widespread electronic installation in the field of information processing and transmission. Because of the special structure and the working way of the computer, it inevitably radiates electromagnetic wave, these electromagnetic emission signals often contain the useful information which make seriously threat to the information security. It's a simple and effective way to use cover interfere signal blocking other's theft.The digital noise source is specially designed for preventing the leak of the security information. The traditional noise source has much shortcoming like the sole disturbance style, the complex operation debugging and so on. This dissertation first puts forward a new realization method of total digital noise source which based on the analysis and discussion of the noise interference signal form and realization mode required by enveloped interference, and combines with the characteristics and advantages of direct digital frequency synthesis technology. This digital noise source takes direct digital frequency synthesis technology as the design of hardware basis and uses Monte Carlo method to produce random data sequence, to control the output amplitude, frequency and phase of DDS directly, which obtains the amplitude modulation, frequency modulation and phase modulation noise signal. This kind of noise source has many characters such as simple system structure, convenient producing debug, low cost and multi-style modulation mode realized with no hardware circuit change. It can also changes distributed performance of the noise.In the dissertation, put forward two kind of digital noise sources realization plan according to the topic request at first, and chose the plan of using micro-computer to control the DDS chip. Then introduce the principle and the characteristic analysis of the DDS in this system design, and examine the independent and the uniform of the pseudo-random number sequence produced by Monte Carlo method. Complete the design and debugging of the computer interfere system on this basis. Finally, introduce the hardware electric circuit and the software design of the interfering system in details. The hardware part includes the outside circle of micro-computer, the interface circle, the outside circle of the DDS the noise signal enlargement and the transmission part. The software part analyses the transmission relationship between pseudo-random number sequence and the frequency control word, then gives out the flow chart of the main program.This system has been detected by the experiments and the tests. The results show that it has evidently interface performance, suffices the requirement of the system. This system obtained the Grade B certificates from the Information Security Certification Center of People's Liberation Army.