Digital Correlator Based On Programmable Logic Device FPGA

As more and more attention to particles in science and technology at home and abroad, the distribution of the size of particles and the measurement of particles concentration are also has been paid more attention, measurement of particle size become a major aids in research and production. In particle tests, dynamic light scattering technique is the most commonly measurement method applicable to sub-micron and nano-meter in domestic and foreign. It mainly uses Brownian motion caused by Doppler effect in liquid particles to measure. Over the years, Chinese scholars had an extensive and in-depth study of dynamic light scattering, but for the key component digital correlator of the instrument to be imported from abroad that the use of the technology has not been a breakthrough to nano-size instrument research. Digital correlation is an important section in nano-particle measurement technology, the response of digital correlator which has high-speed and real-time processing features will affect the final result directly. Therefore need to calculate the scattering intensity autocorrelation function accurately and provide accurate and reliable information on particle size distribution for the computer, to ensure the accuracy of nano-particle size measurement. The difficulty on study digital correlator lies in the higher channels which should be above 100 and speed of data processing.This paper systematically introduces the research background and progress on digital correlator and the relevant theory of dynamic light scattering, a typical device and data analysis methods of dynamic light scattering in detail. The main realization methods of digital correlation were described in detail, research on the basis of existing methods and the theoretical study on implementation of 256-channel digital correlation, the way that correlation before data collection has been proposed, and implement 256-channel digital correlator with programmable logic devices FPGA.256-channel digital correlation based on FPGA has been discussed systematically, using top-down design method and the digital correlator is divided into sampling counting module, autocorrelation control module, autocorrelation calculate module and output storage uint. Simulation of each module by simulation tools such as Quartus and Modelsim, the autocorrelation function in matlab and the simulation results will be compared, to obtain the feasibility and correctness of this method. Implement digital correlator by Cyclone III device and using SCM realizing pulse generator, simulation the movement times of particle size analyzer which into FPGA for the realized of hardware and lay a good foundation through the integral simulation.In order to further enhance the real-time performance of autocorrelation, presents a method that sampling and calculation in real-time, this method with high feasibility and real time when the channels is less than 64, but as the same time resources occupancy rate is high. It is considered from internal macro function LPM of FPGA or parallel computing to further improved.