Acquisition Of Multi-Channel Biomedical Signal Based On Bipolar Square Wave Modulation

Multi-channel physiological potential signals can reflect many physiological and pathological characteristics of human body.Typical multi-channel physiological potential signals,such as multi lead ECG and EEG,are of great significance in clinical diagnosis and health care.In this paper,a two frequency double polarity square wave modulation and demodulation technique is proposed,which can be used for multichannel synchronous acquisition of physiological potential signals.In this method,the original signal is modulated by square wave carrier signal with two frequency doubling relation,and the modulated signal is obtained.The multi-channel modulated signal is added to a mixed signal.After collecting by analog to digital converter,the signal is demodulated and restored to obtain each channel signal.Compared with the traditional frequency division multiplexing technology,the carrier signal is square wave signal,which is easy to generate.The demodulation algorithm only includes addition and subtraction operations,and omits a large number of multiplication operations,which is suitable for low-cost microprocessor application scenarios.Compared with the traditional time division multiplexing technology,the sampling rate does not decrease with increasing number of channels,acquisition SNR of each channel can be improved significantly compared to time division multiplexing method.The modulation and demodulation algorithm combined with the oversampling technology can improve the accuracy,so it can reduce the gain requirement of amplifying circuit and simplify the circuit design.The modulation and demodulation process,easy to implement sampling rate of each channel is not increased with the increase of channel number decreased,so the channel acquisition precision compared with the time division multiplexing method has obvious enhancement.The principle and implementation of two frequency polarity square wave modulation and demodulation technology at the beginning of this article.Then starting from the principle of digital phase locking technique,discussed adjacent crosstalk rejection problem,carrier frequency and filter selection problem when using this modulation demodulation algorithm in the acquisition of multi-channel biomedical signal,designed a MATLAB based simulation experiment to verify the correctness of the proposed algorithm and signal-to-noise ratio(SNR)upgrading function compared with the traditional time-division multiplexing technology,analyzed the level of adjacent channel crosstalk in terms of different carrier frequencies and word length of different filters.Based on the double frequency bipolar square wave modulation and demodulation technology,a set of eight lead ECG acquisition device is designed and implemented to verify the effectiveness and practicability of the method,the related hardware circuit design and the corresponding LabVIEW based PC acquisition software are completed.The experiment shows that the new modulation demodulation method can simplify the design of hardware circuit while ensuring the accuracy of multichannel signal acquisition.This method has great potential in the field of portable lowcost physiological signal acquisition,and also provides a reference for weak signal acquisition in other fields.