Study Of Key Circuits Design In High Precision Low Power ΣΔADC For Bio-potential Detection

Bioelectricity signal is a kind of special signal,which can reflect the health status and vital signs of human body in some degree.Bioelectricity signal plays a great important role in many applications related to medicine such as detection and treatment.Direct at the series of characteristics of bioelectricity signal,for instance,low amplitude low frequency,Sigma Delta ADC’s outstanding advantages make it be an excellent choice.Sigma Delta ADCs acquire high precision by using oversampling,noise shaping and down-sampling digital decimation filtering.Utilizing undemanding analog circuits to process low precision signal in analog area can reduce the design difficulty of analog circuits;meanwhile making the best of digital signal process’ s strong power.In this paper,summary of Sigma-Delta ADC is present first,then the comparison of characteristics and performance between Nyquist ADC and Sigma-Delta ADC is made,so as to definitize the outstanding advantages of Sigma-Delta ADC in high precision filed.After that we analyze the basic principle of Sigma-Delta modulator,and summarize the relations between the modulator’s performance and its order,oversampling ratio,quantizer.We verify the feasibility of selected modulator structure,and use Simulink tools in the MATLAB to model.The influence of various non-ideal factors on modulator is analyzed,such as clock jitter,switched capacitance thermal noise,amplifier thermal noise,amplifier limited DC gain,limited GBW and limited slew rate and so on.To provide reliable evidences for circuit design follow-up,the parameters of circuit design is calculated,such as the value of sampling capacitor,amplifier DC gain,GBW,slew rate.The circuit modules mainly include the design of two phase non-overlapping clock,switched capacitor integrator,the dynamic latch comparator.Based on TSMC 65 nm technology,this paper design a low power single loop second order single bit Sigma-Delta modulator,which voltage supply,sampling frequency,ENOB is 0.9 V,250 k Hz,16 bit respectively.The performance of each sub-circuit module and whole modulator circuit is simulated by the Spectre tools in Cadence simulation platform,the simulation output data of modulator is imported into MATLAB and conducted FFT spectrum analysis.The simulation results indicate that the SNR,SNDR,SFDR,THD,ENOB is 96.6 d B,96.4d B,102.8 d B,-98.5 d B,15.73 bit respectively,and meet design requirement basically.