Electrical Impedance Tomography (ct) Imaging System Driver Circuit

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 obtain 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 other 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 driver circuit of EIT system, then the driver circuit which consists of constant current source and multichannel switch circuit is designed. The constant current source in the dissertation refers to current root mean square of amplitude of which is invariable in particular. The constant current source is composed of Direct Digital Synthesis(DDS), D/A converter, 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. The single frequency DDS and dual-frequency DDS are designed after analyzing DDS and VCCS of constant current source in detail.Then simulation and analysis of VCCS circuit are conducted, and finally the design of schematic and the production of PCB are completed. The constant current source realizes that frequency,amplitude and phase can be adjustable.MCU is chosed to control multichannel switch circuit. Control program is compiled after introducing the different drive patterns, then the design of schematic and the production of PCB for the multichannel switch system are finished.The constant current source reaches the requirements of EIT system according to the test, and multichannel switch circuit can realize the control for the circuit.