电阻抗断层成像技术（Electrical Impedance Tomography，EIT）是最近三十年发展起来的一种新型成像技术。该技术通过在人体表面放置电极阵列，注入电流信号，测量电压信号，进而提取和人体生理、病理状态相关的组织或器官的电特性信息，不但能够反映解剖学结构，而且能够得到功能性图像，这是目前多数临床成像技术难以做到的，因而电阻抗断层成像技术越来越受到人们的重视。64794

    论文分析了EIT系统的结构，重点研究了EIT中的驱动电路，并对驱动电路进行了设计。驱动电路是由恒流源和多路开关选择电路两个部分组成。恒流源是由直接数字频率合成（Direct Digital Synthesis，DDS）、D/A转换电路、放大电路、滤波电路和电压控制电流源（Voltage Controlled Current Source，VCCS）几个部分组成，其中DDS为恒流源的主要部分。DDS主要是由相位累加器、相位调制器、ROM查找表和DAC组成，其核心组成部分是相位累加器。在驱动模式方面，重点研究了注入式驱动模式，对比分析了邻近驱动和对向驱动两种方法，并进一步根据强制等势点的观念，分析了电极对敏感场的分布影响。

毕业论文关键词：EIT，驱动电路，DDS，恒流源

毕业设计说明书（论文）外文摘要

Title     The study of the patterns of EIT system driver                                  

Abstract

Electrical Impedance Tomography (EIT) is a new imaging technology growing in recent thirty years. The currents are injected into human body using electrodes attached to the skin, and the voltages that obtains on the electrodes are measured to produce images by computing electrical properties within the human body. EIT can give not only anatomy structure, but also functional image, and imaging technologies are difficult to do this. Therefore, more and more attention has been paid on EIT.

This dissertation analyzes the structure of EIT system, and focuses on researching the drive circuit which constant current source and multichannel switch circuit is designed. The constant current source is composed of Direct Digital Synthesis (DDS), D/A convert, amplifier, filter and Voltage Controlled Current Source (VCCS), wherein the DDS is a major component of the constant current source. DDS is mainly composed of the phase accumulator, phase modulator, ROM lookup table and DAC. The core part of DDS is the phase accumulator. At the driver pattern，the injected driver pattern is studied，the two methods of the adjacent driver and the subtend driver are contrastively analyzed，and based on the concept of the equipotential node, the distributing of the sensitivity field through the electrodes is analyzed．

Keywords: EIT, driver circuit, DDS, constant current source

目   次

1  绪论 1

1.1  EIT的发展背景和历史 1

1.2  EIT特点 2

1.3  EIT研究中存在的问题 3

1.4  本文主要研究工作 4

2  EIT系统的构成 5

2.1  EIT系统的基本工作原理 5

2.2  EIT系统的总体结构 7

2.3  EIT系统的驱动模式 8

3  恒流源软件设计 9

3.1  DDS原理及结构 9

3.2  DDS的优点