Key Technologies On Analog Front-end Circuit For ECG Signal Acquisition

Advances in information technology have accelerated the growth of health care system.Recent advances in wireless body area network and wearable system chips promotes personalized care and effective treatment of various diseases.With the development of very large-scale integration and the implementation of on-chip systems,the goal of miniaturization of biological systems has been realized in the contemporary era.Bioelectrical signal acquisition analog front-end is one of the most essential blocks in portable medical applications and is a bridge connecting the front-end interface system to the data processor.Therefore,research on low-power,miniaturized,high-performance biosensor system has become important both in industry and application prospects.The low frequency and small amplitude characteristics of the ECG signal raise strict requirements for noise performance,energy and die area.In this thesis,the analog front-end circuit of ECG signal acquisition is mainly studied.Some key techniques of ECG signal acquisition and processing have been studied systematically.This thesis firstly describes the characteristics of electrodes and ECG signals,and according to the features of the analog front-end environment,the design requirements of the analog front-end circuits are obtained.Based on the analysis,a low-power and high performance analog front-end circuit is studied from the perspective of key circuits and technologies.Finally,a chopper-coupled current-reuse instrumentation amplifier,a low-pass filter and a successive approximation analog-to-digital converter are used to realize the system architecture,so the ECG signals are effectively acquired and processed.(1)The multi-channel current-reuse amplifier is used in the instrumentation amplifier to realize the sharing same current between two input stages and reduce the power consumption.The chopper modulation technology is used to eliminate the flicker noise and input offset voltage.The DC servo loop,ripple reduction loop and driven-right-leg circuit are used to reduce the electrode offset voltage,amplifier output ripple and power line interference of analog front-end circuit respectively.In addition,in order to improve the acquisition quality and reduce ECG signal attenuation amplitude,a new dynamic matching chopper coupling method is adopted to improve the input impedance.(2)In order to eliminate high-frequency noise and set effective signal bandwidth to avoid the aliasing of analog-to-digital converter,a third-order switched capacitor filter is proposed.(3)Considering the requirement of low power consumption,the dummy capacitor is used in the successive approximation analog-to-digital converter,and the total capacitance is halved at the same precision,which effectively reduces the power consumption and area of the chip.Based on SMIC 0.18μm CMOS technology,a low-power current-reused analog front-end circuit for ECG signal acquisition has been realized.Finally,the prototype of this analog front-end chip has been measured.The chip occupies 0.72mm~2 active area and consumes16.11μW from a 1.8V supply voltage.It achieves 39.6d B gain,93d B CMRR,85d B PSRR,8.62bit ENOB,input-referred noise lower than 1.4μVrms and input impedance higher than2.6GΩ.The proposed analog front-end circuit can meet the design requirements very well.