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目的：本文研究了基于现场可编程门阵列（Field Programmable Gate Array，FPGA）超声成像系统中数字动态滤波器的实现方法和过程。方法：动态滤波器中FIR 滤波器采用分布式算法（Distributed Arithmetic, DA）实现结构，并在应用中对DA 算法进行了改进，包括数据并行处理结构的设计、对查找表（Look Up Table，LUT）输入字长N 大小的控制和具有对称系数的FIR 滤波器的采用。改进后的DA 实现在FPGA 资源占用和处理速度之间达到了平衡。同时，结合多级流水线结构，动态滤波器实现了数字超声信号并行处理。结果：采用常值滤波器（远场匹配参数）进行滤波后，超声回波图像远场分辨率达到了要求，但越靠近近场效果越差。相比之下，本文设计的基于FPGA 超声信号动态数字滤波器达到了很好的滤波效果，使回声图像近场和远场都有最佳分辨率。结论：利用FPGA 实现超声系统中动态滤波器是完全可行的，并且有助于提高系统的稳定性和可靠性，并大大减低系统成本。

英文摘要:

Objective: This paper talks about implementation methods and processes of digital dynamic filter based on Field Programmable Gate Array (FPGA) in the ultrasound imaging system. Methods: In this paper finite impulse response (FIR) filter using distributed arithmetic (DA) implementation structure and in the application of the DA algorithm we do some improvement including the structure of parallel data processing, controlling the size of the input word length N in the Look-Up Table (LUT) and using the FIR filter with symmetric coefficients. The structure improved can achieves balance between processing speed and occupation in the FPGA resources, at the same time, the FIR filter with pipeline structure can process digital ultrasonic signal in parallel way. Results: The resolution of ultrasonic echo image in the Far-field is satisfied using the constant coefficient filter (the parameters of filter in the far-field). However, as closer to the near field, worse the effect of the image is. In contrast, the digital dynamic filter based on FPGA can achieve a good filtering effect, so the images of the ultrasonic echo have the best resolution in the near-filed and the far-field. Conclusions: The implementation of digital dynamic filter based on FPGA in the ultrasonic systems is entirely feasible, and it's helpful for improving the system stability and reliability.

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