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| A Bioelectricity Impedance Measurement System Research Based on FPGA |
| Institute of Biomedical Engineering, Chinese Academy of Medical Sciences, Tianjin 300192, China |
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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.
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