Abstract：In this work the digital bioelectricity impedance measurement experiment platform with the core of FPGA was studied and completed the research of the DDS module, V/I conversion and digital demodulation. DDS technology was used to generate a sinusoidal signal generator. Howland circuit improved by THS4021 was used to design a voltagecontrolled current source, the amplitude of the output current of the frequency response was measured in different load conditions, and the output impedance of the current source was measured at different frequencies, which proved stability and accuracy of the constant current source. The digital demodulation was used in the study and tested digital quadrature demodulation output error under different excitation frequency. At last we used salt water tank experimental system for imaging experiments. The current source could produce multifrequency excitation signal in the range of 6.1~390.6 kHz. When the signal frequency gradually increased from 200 kHz to 1.6 MHz, the I and Q channel errors which produced from the demodulation circuit was increased gradually, corresponding to the amplitude error from 1.13% to 7.19%, the phase error increases from 1.03% to 5.34%. The salt water tank experiments was carried for epoxy stick with the adjacent driving–adjacent measurement, and the imaging results showed that the system could achieve a more accurate positioning on a single target object, and verified the feasibility of the present research platform.
［1］任超世. 生物电阻抗测量技术 ［J］. 中国医疗器械信息, 2004, 10(1): 21-25.
［2］Saulnier GJ, Blue RS, Newell JC, et al. Electrical Impedance Tomography ［J］. IEEE Signal Processing Magazine, 2001, 18(6): 31-43.
［3］Boone K, Barber D. Review: Imaging with electricity: Report of the European concerted action on impedance tomography ［J］. Journal of Medical Engineering & Technology, 1997, 21(6): 201-232.
［4］Halter RJ, Hartov A, Paulsen KD. A broadband high frequency electrical impedance tomography system for breast imaging ［J］. IEEE Trans Biomed Eng, 2008, 55(2): 650-659.［5］Ren Chaoshi, Li Zhangyong, Wang Wei. Noninvasive gastric motility measurement and evaluation by bioimpedance ［J］. Journal of Clinical Rehabilitative Tissue Engineering Research, 2010, 14(9): 1653-1657.
［6］Brown BH. Cardiac and respiratory related electrical impedance changes in the human thorax. IEEE Trans Biomed Eng, 1994, 41(8):729-733
［7］N. Liu, Saulnier GJ, Newell JC. A multichannel synthesizer and voltmeter for electrical impedance tomography. Proceedings of the 25Th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2003, 4: 3110-3113.
［8］刘延勇，董秀珍，尤富生，等. 两种基于直接数字合成技术的阻抗激励源的对比研究 ［J］. 第四军医大学学报, 2005, 26(17): 1618-1620.
［9］王 超,王化祥. 电阻抗断层图像重建算法研究-预迭代算法提出 ［J］. 信号处理, 2002, 18(6): 547-555.
［10］王 研，沙 洪，任超世. 电阻抗断层成像线电极的仿真研究 ［J］. 生物医学工程学杂志, 2007, 24 (5): 986-989.
［11］Wang Huaxiang, Cui Ziqiang. FPGA based signal generator in EIT system ［J］. Chinese Journal Of Electron Devices, 2007, 30(1): 90-96.
［12］Ho KC, Chan YT, Inkol R. A digital quatrature demodulation system ［J］. IEEE Transactions on Aerospace and Electronic Systems, 1996, 32(4): 1218-1227.
［13］Zhao Fei, Guo Wei. Two kinds of dds implementing with FPGA ［J］. Modern Electronics Technique, 2010, 29(1): 204-206.
［14］秦玲，张良，赖青贵，等. 基于功率运算放大器的恒流源技术研究 ［J］. 通信电源技术, 2007, 24(1): 43-46.
［15］杨彬，党瑞荣，杨灏. 一种高精度波形发生器的设计及实现 ［J］. 石油仪器, 2007, 21(1): 11-13.
［16］吴右，沙洪，任超世. 基于DSP Builder的EIT正交序列解调方法与电路设计 ［J］. 国际生物医学工程杂志, 2009, 32(5): 276-279.
［17］Tong IO, Eung JW, David H. Multifrequency EIT system with radially symmetric architecture ［J］. Phys Meas, 2007, 28(7): 183-196.
