Oversampling And Its Application In Biomedical Signal Detecting

Analog to digital converter (ADC) which determines system accuracy is the requisite device in the modern signal detection. Especially, in the biomedical signal detecting with strong background noise, high precision ADC decreases the requirement to amplifier gain. Oversampling can increase ADC's detecting precision and simplify or wipe off anti aliasing filter, but it primarily has intensive study in∑-?ADC. In this paper, oversampling in N bits'ADC is investigated.Firstly, many open questions of oversampling in N bits'ADC are analyzed for the first time. A new method, adding shaped signal, is put forward to avoid invalidation of oversampling. Its feasibility is verified in theory. By simulation experiment, it holds an advantage when oversampling rate is less than 49, compared with old method, dithering. Simultaneously, the parameters of shaped signal with optimum oversampling efficiency are obtained by simulation. Moreover, hardware platform is rigged up to measure ECG, which confirms significance of shaped signal in oversampling.Secondly, low pass filter (LPF) in oversampling is researched. Filter's parameters which make oversampling achieve the goal are computed by theoretical analysis. And filters are designed, including averaging filter with low attenuation characteristic, Chebyshev filter with high attenuation characteristic and varying parameter LPF. Besides, for the purpose of improving efficiency, the method of combining LPF with downsampling is investigated. The simulation results show oversampling can't attain its optimum efficiency until oversampling rate matched the LPF's parameter.Finally, two applications about oversampling are expounded. Oversampling simplifies digital lock-in amplifier, raises precision and optimizes the detecting of bio-impedance spectroscopy. And an optimum arithmetic is proposed to solve the problem of operation and memory space brought in by oversampling. The sensor digitalization interface based on AD7674 and FPGA verifies the feasibility of software defined instrument and the rationality of varying parameter LPF.The systemic study about oversampling of N bits'ADC is carried out. Its results can be as a guide of oversampling's application and further the development of biomedical signal detecting.