The Design Of The Scanning Electron Microscope Image Data Acquisition And Transmission System

The development of science and technology promotes product to higher accuracy and more convenience,which can also lead the inspection equipments,such as SEM,change to the same direction.However,few domestic companies and institutes can manufacture the SEM.Furthermore,the performance of obsolete SEM in China cannot catch up with the development of the information technology.Therefore,the domestic SEM market has been monopolized by some foreign companies.It has significance for our country to research and design the brand new SEM for breaking the monopoly of foreign companies and creating our own SEM.We mainly design a brand new image data acquisition and transmission system of SEM,which can provide higher accuracy and multi-resolution switch.This thesis mainly involves two aspects.One is design of hardware of system.This part introduces design of circuits of the image data acquisition,which contains the design of circuit of image data acquisition,the output circuit of contrast,the improvement design of row scanning circuit based on FPGA on the layer of RTL,the design of USB communication interface circuit,etc.The another is the design of software algorithm of system,which contains the design of FPGA Ping-Pong operation algorithm regarding image data transmission and storage in higher speed,the design of comprehensive control programming based on the core of Cortex-M3,the generic module design based on MFC in PC,and the improvement of protocol data unit,etc.The system designed in this thesis mainly supports for the sampling and transmission control based on 640*480 resolution digital images.It has been considered to acquire a higher-resolution digital image data,such as 1280*960 resolution in the future.Therefore,the system can realize both high and low resolution switch freely and the subsequent extension and implementation of autofocus function.The main research works and innovation in this thesis are as follows:(1)Design the image grayscale output circuit with the two-stage amplifier,and realize the design of image contrast output circuit with the method of D/A converter.(2)Implement high-speed USB data transfer with the CH374 by using ARM as the master micro-chip,it is convenient that laptop computers and other portable devices are used as an upper computer.(3)Design the transmitting method of anti-collision by separating the image data and command data.Specifically,we adopt the multi-endpoints in USB chip to transmit image data and command data on the physical layer,respectively.As well as we adopt the series algorithm to ensure orderly reading different types of data on the software application layer.Based on the software and hardware layer,fluent transmission can be ensured.All of these works make the system with a good performance for preventing data block,and improving transmission efficiency.(4)Use the two pieces of FPGA chip to transmit SEM control parameters,and handle the image data,respectively.It makes the circuit structure clear and easy to design PCB layout,and provides convenience for the follow-up function extension of the two modules.