摘要
以FPGA芯片为核心的数字化生物电阻抗测量实验平台,主要完成直接数字频率合成(DDS)的电流源模块、V/I变换和数字解调模块的研究。采用DDS技术生成正弦信号发生器,由THS4021改进的Howland电路设计压控电流源,在不同负载条件下测量其输出电流幅值的频率响应,并在不同频率下测量电流源的输出阻抗,对恒流源性能的稳定性和精度进行测定。解调方法采用数字化解调,测试不同激励频率下的数字正交解调输出误差变化情况。最后采用盐水槽实验系统进行成像实验。结果表明,电流源可在6.1～390.6 kHz范围输出多频激励信号,在600 kHz前保持在190 kΩ的输出阻抗。当信号频率从200 kHz逐渐增加到1.6 MHz时,解调电路输出的I和Q路误差逐渐增加,对应的幅度误差从1.13%增加到7.19%,相位误差从1.03%增大到5.34%。采用相邻激励-相邻测量模式对环氧树脂棒进行盐水槽成像实验,成像结果表明系统能够对单个目标物体实现较准确的定位,验证了本研究平台的可行性。
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 voltage-controlled 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 multi-frequency 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.
出处
《中国生物医学工程学报》
CAS
CSCD
北大核心
2013年第3期266-272,共7页
Chinese Journal of Biomedical Engineering
基金
国家自然科学基金(31000449)
天津科技支撑计划重点项目(10ZCGYSF00100)
