FPGA-based multi-frequency excitation and modulation technology in EIT system

In order to obtain more bioelectrical impedance information at different frequencies simultaneously, a multi-frequency excitation source and a multi-frequency demodulation module are developed using FPGA. The source can provide both sweep frequency and multi-frequency excitation signal. The range of frequency is 0~16.67 MHz, phase and amplitude of the generator can be changed conveniently. Result shows that the source has many advantages, such as high precision, good stability and convenient adjustment. Multi-frequency digital quadrature demodulation is also accomplished by FPGA, since the excitation signal and the reference signal are generated at the same time, error caused by the difference of frequency between the two signals is avoided effectively. It can meet the need for data acquisition system in multi-frequency electrical impedance tomography very well.