| The scaning generator is the key component of the scanning electron microscope,which is mainly responsible for generating scanning waveform to control the electron beam to scan the sample,and digitizing the sample signal output by detector into image and uploading it to the host computer for display.Its performance directly affects the imaging quality of scanning electron microscope.At present,there are few researches on scan generators in China.Most of the existing scan generators have low resolution and slow scanning speed,and the functions of waveform scanning and data acquisition are also weak,which are only suitable for low-end scanning electron microscopes.The domestic urgent need of research and development of high-level scanning generators,so that China can achieve breakthroughs in key technologies in the field of mid-to-high-end electron microscopy,and narrow the gap with Western countries in the field of scanning electron microscopy technology.In this paper,a scanning generator system with high speed,high resolution and low noise is developed.The system is composed of power supply,scanning generator lower computer and host computer software.Firstly,by studying low-noise power supply technology,and aiming at the noise characteristics during debugging,a low-noise linear power supply constructed by discrete components is designed to supply power to the scaning generator system,which reduces power fluctuations and stabilizes the waveform of the scan generator.Secondly,by analyzing the needs of mid-to-high-end electron microscopes for scanning generators,the multi-core heterogeneous chip ZYNQ7020 with strong performance is adopted as the main controller,which has both high-speed application interfaces and powerful control capabilities.According to the function division of the main controller,two channels of waveform scanning circuits and four channels of data acquisition circuits are designed on the FPGA side of the main controller.The high-speed DDR3 memory.chip is designed on the ARM side to store data,and the UDP protocol is used to transmit data through gigabit Ethernet.At the same time,in order to improve the resolution of the system,the hardware scanning rotation and scanning translation circuits are integrated on the waveform scanning circuit.By studying the characteristics of multi-core systems and the interaction between multi-cores,a dual-core AMP asymmetric architecture is used on the ARM side,so that two ARM cores can handle different tasks respectively to improve system efficiency;The interaction between ARM and FPGA use AMBA AXI protocol to adapt to different interactive tasks.According to the requirements of the vector scanning task,the Bresenham linear and circular algorithm are used to generate the scanning waveform,which avoids floating-point calculation and meets the real-time requirements of the lower computer.Finally,the hostcomputer software developed based on C#and WPF is designed,and the software functions of PC controlling the lower computer through instructions and processing and displaying the image signal input from the lower computer is realized.After testing,the ripple of power supply system is only about 550uV when the output current is full load of 1.5A,which meets the power supply requirements of the system.The measured bandwidth of the designed Gigabit Ethernet reaches 973Mbps,and the lower computer does not lose packets under the extreme transmission test.In regular scanning tasks,the lower computer can generate corresponding waveforms according to instructions,and the resolution can be set from 256x256 to 16384x16384.At the same time,in the vector scan mode,the lower computer can also generate the corresponding scanning waveform according to the instruction.In summary,the scaning generator designed in this paper can meet the development needs of mid-to-high-end scanning electron microscopes. |
