基于多周期欠采样技术的生物电阻抗成像硬件系统∗

摘要

Biomediccal research has learned that the real and imaginary parts of the complex impedance of human tissue contain abundant information of physiology and pathology. While the imaginary part of the complex impedance information is so weak that it is difficult to obtain. However,it becomes easy to acquire imaginary part when the ex￣citation frequency reaches above 1 MHz. Aiming at this problem,this paper designed a bio￣electrical impedance tomo￣graphy system hardware based on CAN bus. The system hardware makes the excitation frequency extend to 10 MHz. Digital synthesizer-AD9852 is adopted to provide the clock signal of uniform for data acquisition boards. Every data acquisition board uses 16 bit,1MSPS differential ADC-AD7677 to acquire data,and high frequency waveforms are sampled by using multi￣cycle undersampling technology. At last,the real and imaginary parts of complex impedance are calculated by adapting digital phase sensitive demodulation technique.%生物医学研究表明，人体组织复阻抗的实部和虚部均包含着丰富的生理和病理信息，而复阻抗的虚部信息很微弱，不易提取，要求激励频率达到1 MHz以上，提取出虚部信息，从而提高诊断准确性。针对该问题，本文设计了一种基于CAN总线的生物电阻抗成像系统硬件电路，使激励信号的频率扩至10 MHz。电路中采用数字合成器AD9852为各数据采集单元提供统一的时钟信号，采用16位1MSPS的模数转换器AD7677以及多周期欠采样技术对高频段波形采集信号，最后利用数字相敏解调技术获取复阻抗的实部和虚部信息。